He estado luchando para cargar archivos desde WebView desde los últimos días y no hay progreso. Busqué en Google e implementé todas las soluciones sugeridas, pero ninguna funciona, como: soluciones sugeridas aquí , y así sucesivamente.

Problema: Tengo una página HTML con el siguiente código para cargar un archivo. Funciona bien en un navegador de escritorio como Firefox y en el navegador integrado de emulador / AVD, es decir, cuando hago clic en el botón "Examinar ..." representado por elemento, el navegador abre un cuadro de diálogo donde puedo elegir un archivo para cargar.

Sin embargo, en el emulador de Android 3.0 / AVD, cuando hago clic en "Elegir archivo", ¡no pasa nada, no se abre ningún diálogo de archivo!

<form method="POST" enctype="multipart/form-data">
File to upload: <input type="file" name="uploadfile">&nbsp;&nbsp;
<input type="submit" value="Press to Upload..."> to upload the file!
</form>

¿Podría alguien sugerir una posible solución lo antes posible?

Esta es una solución completa para todas las versiones de Android, también tuve dificultades con esto.

public class MyWb extends Activity {
/** Called when the activity is first created. */

WebView web;
ProgressBar progressBar;

private ValueCallback<Uri> mUploadMessage;  
 private final static int FILECHOOSER_RESULTCODE=1;  

 @Override  
 protected void onActivityResult(int requestCode, int resultCode,  
                                    Intent intent) {  
  if(requestCode==FILECHOOSER_RESULTCODE)  
  {  
   if (null == mUploadMessage) return;  
            Uri result = intent == null || resultCode != RESULT_OK ? null  
                    : intent.getData();  
            mUploadMessage.onReceiveValue(result);  
            mUploadMessage = null;  
  }
  }  

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    web = (WebView) findViewById(R.id.webview01);
    progressBar = (ProgressBar) findViewById(R.id.progressBar1);

    web = new WebView(this);  
    web.getSettings().setJavaScriptEnabled(true);
    web.loadUrl("http://www.script-tutorials.com/demos/199/index.html");
    web.setWebViewClient(new myWebClient());
    web.setWebChromeClient(new WebChromeClient()  
    {  
           //The undocumented magic method override  
           //Eclipse will swear at you if you try to put @Override here  
        // For Android 3.0+
        public void openFileChooser(ValueCallback<Uri> uploadMsg) {  

            mUploadMessage = uploadMsg;  
            Intent i = new Intent(Intent.ACTION_GET_CONTENT);  
            i.addCategory(Intent.CATEGORY_OPENABLE);  
            i.setType("image/*");  
            MyWb.this.startActivityForResult(Intent.createChooser(i,"File Chooser"), FILECHOOSER_RESULTCODE);  

           }

        // For Android 3.0+
           public void openFileChooser( ValueCallback uploadMsg, String acceptType ) {
           mUploadMessage = uploadMsg;
           Intent i = new Intent(Intent.ACTION_GET_CONTENT);
           i.addCategory(Intent.CATEGORY_OPENABLE);
           i.setType("*/*");
           MyWb.this.startActivityForResult(
           Intent.createChooser(i, "File Browser"),
           FILECHOOSER_RESULTCODE);
           }

        //For Android 4.1
           public void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType, String capture){
               mUploadMessage = uploadMsg;  
               Intent i = new Intent(Intent.ACTION_GET_CONTENT);  
               i.addCategory(Intent.CATEGORY_OPENABLE);  
               i.setType("image/*");  
               MyWb.this.startActivityForResult( Intent.createChooser( i, "File Chooser" ), MyWb.FILECHOOSER_RESULTCODE );

           }

    });  


    setContentView(web);  


}

public class myWebClient extends WebViewClient
{
    @Override
    public void onPageStarted(WebView view, String url, Bitmap favicon) {
        // TODO Auto-generated method stub
        super.onPageStarted(view, url, favicon);
    }

    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        // TODO Auto-generated method stub

        view.loadUrl(url);
        return true;

    }

    @Override
    public void onPageFinished(WebView view, String url) {
        // TODO Auto-generated method stub
        super.onPageFinished(view, url);

        progressBar.setVisibility(View.GONE);
    }
}

//flipscreen not loading again
@Override
public void onConfigurationChanged(Configuration newConfig){        
    super.onConfigurationChanged(newConfig);
}

// To handle "Back" key press event for WebView to go back to previous screen.
/*@Override
public boolean onKeyDown(int keyCode, KeyEvent event) 
{
    if ((keyCode == KeyEvent.KEYCODE_BACK) && web.canGoBack()) {
        web.goBack();
        return true;
    }
    return super.onKeyDown(keyCode, event);
}*/
}

También quiero agregar que la "página de carga" como la de este ejemplo, no funcionará en <4 versiones, ya que tiene una función de vista previa de imagen, si desea que funcione use una carga PHP simple sin vista previa.

Actualización :

Encuentre la solución para dispositivos lollipop aquí y gracias por gauntface

Actualización 2 :

Solución completa para todos los dispositivos Android hasta oreo aquí y esta es una versión más avanzada , deberías buscarla, tal vez pueda ayudar.

Método de trabajo de HONEYCOMB (API 11) a Oreo (API 27)
[No probado en Pie 9.0]

static WebView mWebView;
private ValueCallback<Uri> mUploadMessage;
public ValueCallback<Uri[]> uploadMessage;
public static final int REQUEST_SELECT_FILE = 100;
private final static int FILECHOOSER_RESULTCODE = 1;

Modificado onActivityResult()

@Override
public void onActivityResult(int requestCode, int resultCode, Intent intent)
{
    if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP)
    {
        if (requestCode == REQUEST_SELECT_FILE)
        {
            if (uploadMessage == null)
                return;
            uploadMessage.onReceiveValue(WebChromeClient.FileChooserParams.parseResult(resultCode, intent));
            uploadMessage = null;
        }
    }
    else if (requestCode == FILECHOOSER_RESULTCODE)
    {
        if (null == mUploadMessage)
            return;
    // Use MainActivity.RESULT_OK if you're implementing WebView inside Fragment
    // Use RESULT_OK only if you're implementing WebView inside an Activity
        Uri result = intent == null || resultCode != MainActivity.RESULT_OK ? null : intent.getData();
        mUploadMessage.onReceiveValue(result);
        mUploadMessage = null;
    }
    else
        Toast.makeText(getActivity().getApplicationContext(), "Failed to Upload Image", Toast.LENGTH_LONG).show();
}

Ahora en onCreate()o onCreateView()pegue el siguiente código

    WebSettings mWebSettings = mWebView.getSettings();
    mWebSettings.setJavaScriptEnabled(true);
    mWebSettings.setSupportZoom(false);
    mWebSettings.setAllowFileAccess(true);
    mWebSettings.setAllowFileAccess(true);
    mWebSettings.setAllowContentAccess(true);

mWebView.setWebChromeClient(new WebChromeClient()
{
    // For 3.0+ Devices (Start)
    // onActivityResult attached before constructor
    protected void openFileChooser(ValueCallback uploadMsg, String acceptType)
    {
        mUploadMessage = uploadMsg;
        Intent i = new Intent(Intent.ACTION_GET_CONTENT);
        i.addCategory(Intent.CATEGORY_OPENABLE);
        i.setType("image/*");
        startActivityForResult(Intent.createChooser(i, "File Browser"), FILECHOOSER_RESULTCODE);
    }


    // For Lollipop 5.0+ Devices
    public boolean onShowFileChooser(WebView mWebView, ValueCallback<Uri[]> filePathCallback, WebChromeClient.FileChooserParams fileChooserParams)
    {
        if (uploadMessage != null) {
            uploadMessage.onReceiveValue(null);
            uploadMessage = null;
        }

        uploadMessage = filePathCallback;

        Intent intent = fileChooserParams.createIntent();
        try
        {
            startActivityForResult(intent, REQUEST_SELECT_FILE);
        } catch (ActivityNotFoundException e)
        {
            uploadMessage = null;
            Toast.makeText(getActivity().getApplicationContext(), "Cannot Open File Chooser", Toast.LENGTH_LONG).show();
            return false;
        }
        return true;
    }

    //For Android 4.1 only
    protected void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType, String capture)
    {
        mUploadMessage = uploadMsg;
        Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
        intent.addCategory(Intent.CATEGORY_OPENABLE);
        intent.setType("image/*");
        startActivityForResult(Intent.createChooser(intent, "File Browser"), FILECHOOSER_RESULTCODE);
    }

    protected void openFileChooser(ValueCallback<Uri> uploadMsg)
    {
        mUploadMessage = uploadMsg;
        Intent i = new Intent(Intent.ACTION_GET_CONTENT);
        i.addCategory(Intent.CATEGORY_OPENABLE);
        i.setType("image/*");
        startActivityForResult(Intent.createChooser(i, "File Chooser"), FILECHOOSER_RESULTCODE);
    }
});

¡Esta es la única solución que encontré que funciona!

WebView webview;

private ValueCallback<Uri> mUploadMessage;
private final static int FILECHOOSER_RESULTCODE = 1;

@Override
protected void onActivityResult(int requestCode, int resultCode,
        Intent intent) {
    if (requestCode == FILECHOOSER_RESULTCODE) {
        if (null == mUploadMessage)
            return;
        Uri result = intent == null || resultCode != RESULT_OK ? null
                : intent.getData();
        mUploadMessage.onReceiveValue(result);
        mUploadMessage = null;

    }
}

// Next part 

class MyWebChromeClient extends WebChromeClient {
    // The undocumented magic method override
    // Eclipse will swear at you if you try to put @Override here
    public void openFileChooser(ValueCallback<Uri> uploadMsg) {

        mUploadMessage = uploadMsg;
        Intent i = new Intent(Intent.ACTION_GET_CONTENT);
        i.addCategory(Intent.CATEGORY_OPENABLE);
        i.setType("image/*");
        Cv5appActivity.this.startActivityForResult(
                Intent.createChooser(i, "Image Browser"),
                FILECHOOSER_RESULTCODE);
    }
}

En 5.0 Lollipop, Google agregó un método oficial, WebChromeClient.onShowFileChooser . Incluso proporcionan una manera de generar automáticamente la intención del selector de archivos para que use la entrada de aceptar tipos mime.

public class MyWebChromeClient extends WebChromeClient {
        // reference to activity instance. May be unnecessary if your web chrome client is member class.
    private MyActivity activity;

    public boolean onShowFileChooser(WebView webView, ValueCallback<Uri[]> filePathCallback, FileChooserParams fileChooserParams) {
        // make sure there is no existing message
        if (myActivity.uploadMessage != null) {
            myActivity.uploadMessage.onReceiveValue(null);
            myActivity.uploadMessage = null;
        }

        myActivity.uploadMessage = filePathCallback;

        Intent intent = fileChooserParams.createIntent();
        try {
            myActivity.startActivityForResult(intent, MyActivity.REQUEST_SELECT_FILE);
        } catch (ActivityNotFoundException e) {
            myActivity.uploadMessage = null;
            Toast.makeText(myActivity, "Cannot open file chooser", Toast.LENGTH_LONG).show();
            return false;
        }

        return true;
    }
}


public class MyActivity extends ... {
    public static final int REQUEST_SELECT_FILE = 100;
    public ValueCallback<Uri[]> uploadMessage;

    protected void onActivityResult(int requestCode, int resultCode, Intent data){
        if (requestCode == REQUEST_SELECT_FILE) {
                if (uploadMessage == null) return;
                uploadMessage.onReceiveValue(WebChromeClient.FileChooserParams.parseResult(resultCode, data));
                uploadMessage = null;
            }
        }
    }
}

Para las versiones de Android anteriores a KitKat, los métodos privados mencionados en las otras respuestas funcionan. No he encontrado una buena solución para KitKat (4.4).

Descubrí que necesitaba 3 definiciones de interfaz para manejar varias versiones de Android.

public void openFileChooser(ValueCallback < Uri > uploadMsg) {
  mUploadMessage = uploadMsg;
  Intent i = new Intent(Intent.ACTION_GET_CONTENT);
  i.addCategory(Intent.CATEGORY_OPENABLE);
  i.setType("image/*");
  FreeHealthTrack.this.startActivityForResult(Intent.createChooser(i, "Image Chooser"), FILECHOOSER_RESULTCODE);
}

public void openFileChooser(ValueCallback < Uri > uploadMsg, String acceptType) {
  openFileChooser(uploadMsg);
}

public void openFileChooser(ValueCallback < Uri > uploadMsg, String acceptType, String capture) {
  openFileChooser(uploadMsg);
}

Esta solución también funciona para Honeycomb y Ice Cream Sandwich. Parece que Google introdujo una nueva característica genial (aceptar atributo) y olvidó implementar una sobrecarga para la compatibilidad con versiones anteriores.

protected class CustomWebChromeClient extends WebChromeClient
{
    // For Android 3.0+
    public void openFileChooser( ValueCallback<Uri> uploadMsg, String acceptType ) 
    {  
        context.mUploadMessage = uploadMsg;  
        Intent i = new Intent(Intent.ACTION_GET_CONTENT);  
        i.addCategory(Intent.CATEGORY_OPENABLE);  
        i.setType("image/*");  
        context.startActivityForResult( Intent.createChooser( i, "File Chooser" ), MainActivity.FILECHOOSER_RESULTCODE );  
    }

    // For Android < 3.0
    public void openFileChooser( ValueCallback<Uri> uploadMsg ) 
    {
        openFileChooser( uploadMsg, "" );
    }
}

La solución completa de hifarrer es muy útil para mí.

pero encontré muchos otros problemas: admitir otro tipo de mime, enumerar dispositivos de captura (cámara, video, grabadora de audio), abrir el dispositivo de captura de inmediato (por ejemplo, <input accept = "image / *; capture">) ...

Entonces, hice una solución que funciona exactamente igual que la aplicación de navegador web predeterminada.

Usé android-4.4.3_r1 / src / com / android / browser / UploadHandler.java. (gracias a Rupert Rawnsley)

package org.mospi.agatenativewebview;

import java.io.File;
import java.lang.reflect.Method;
import java.net.URL;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.ActivityNotFoundException;
import android.content.DialogInterface;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.provider.MediaStore;
import android.view.View;
import android.webkit.JsResult;
import android.webkit.ValueCallback;
import android.webkit.WebChromeClient;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebSettings.PluginState;
import android.widget.Toast;

public class MainActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        WebView webView = (WebView) findViewById(R.id.webView1);

        initWebView(webView);
        webView.loadUrl("http://google.com"); // TODO input your url

    }

    private final static Object methodInvoke(Object obj, String method, Class<?>[] parameterTypes, Object[] args) {
        try {
            Method m = obj.getClass().getMethod(method, new Class[] { boolean.class });
            m.invoke(obj, args);
        } catch (Exception e) {
            e.printStackTrace();
        }

        return null;
    }

    private void initWebView(WebView webView) {

        WebSettings settings = webView.getSettings();

        settings.setJavaScriptEnabled(true);
        settings.setAllowFileAccess(true);
        settings.setDomStorageEnabled(true);
        settings.setCacheMode(WebSettings.LOAD_NO_CACHE);
        settings.setLoadWithOverviewMode(true);
        settings.setUseWideViewPort(true);
        settings.setSupportZoom(true);
        // settings.setPluginsEnabled(true);
        methodInvoke(settings, "setPluginsEnabled", new Class[] { boolean.class }, new Object[] { true });
        // settings.setPluginState(PluginState.ON);
        methodInvoke(settings, "setPluginState", new Class[] { PluginState.class }, new Object[] { PluginState.ON });
        // settings.setPluginsEnabled(true);
        methodInvoke(settings, "setPluginsEnabled", new Class[] { boolean.class }, new Object[] { true });
        // settings.setAllowUniversalAccessFromFileURLs(true);
        methodInvoke(settings, "setAllowUniversalAccessFromFileURLs", new Class[] { boolean.class }, new Object[] { true });
        // settings.setAllowFileAccessFromFileURLs(true);
        methodInvoke(settings, "setAllowFileAccessFromFileURLs", new Class[] { boolean.class }, new Object[] { true });

        webView.setScrollBarStyle(View.SCROLLBARS_INSIDE_OVERLAY);
        webView.clearHistory();
        webView.clearFormData();
        webView.clearCache(true);

        webView.setWebChromeClient(new MyWebChromeClient());
        // webView.setDownloadListener(downloadListener);
    }

    UploadHandler mUploadHandler;

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent intent) {

        if (requestCode == Controller.FILE_SELECTED) {
            // Chose a file from the file picker.
            if (mUploadHandler != null) {
                mUploadHandler.onResult(resultCode, intent);
            }
        }

        super.onActivityResult(requestCode, resultCode, intent);
    }

    class MyWebChromeClient extends WebChromeClient {
        public MyWebChromeClient() {

        }

        private String getTitleFromUrl(String url) {
            String title = url;
            try {
                URL urlObj = new URL(url);
                String host = urlObj.getHost();
                if (host != null && !host.isEmpty()) {
                    return urlObj.getProtocol() + "://" + host;
                }
                if (url.startsWith("file:")) {
                    String fileName = urlObj.getFile();
                    if (fileName != null && !fileName.isEmpty()) {
                        return fileName;
                    }
                }
            } catch (Exception e) {
                // ignore
            }

            return title;
        }

        @Override
        public boolean onJsAlert(WebView view, String url, String message, final JsResult result) {
            String newTitle = getTitleFromUrl(url);

            new AlertDialog.Builder(MainActivity.this).setTitle(newTitle).setMessage(message).setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {

                @Override
                public void onClick(DialogInterface dialog, int which) {
                    result.confirm();
                }
            }).setCancelable(false).create().show();
            return true;
            // return super.onJsAlert(view, url, message, result);
        }

        @Override
        public boolean onJsConfirm(WebView view, String url, String message, final JsResult result) {

            String newTitle = getTitleFromUrl(url);

            new AlertDialog.Builder(MainActivity.this).setTitle(newTitle).setMessage(message).setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {

                @Override
                public void onClick(DialogInterface dialog, int which) {
                    result.confirm();
                }
            }).setNegativeButton(android.R.string.cancel, new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {
                    result.cancel();
                }
            }).setCancelable(false).create().show();
            return true;

            // return super.onJsConfirm(view, url, message, result);
        }

        // Android 2.x
        public void openFileChooser(ValueCallback<Uri> uploadMsg) {
            openFileChooser(uploadMsg, "");
        }

        // Android 3.0
        public void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType) {
            openFileChooser(uploadMsg, "", "filesystem");
        }

        // Android 4.1
        public void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType, String capture) {
            mUploadHandler = new UploadHandler(new Controller());
            mUploadHandler.openFileChooser(uploadMsg, acceptType, capture);
        }

        // Android 4.4, 4.4.1, 4.4.2
        // openFileChooser function is not called on Android 4.4, 4.4.1, 4.4.2,
        // you may use your own java script interface or other hybrid framework.          

        // Android 5.0.1
        public boolean onShowFileChooser(
                WebView webView, ValueCallback<Uri[]> filePathCallback,
                FileChooserParams fileChooserParams) {

            String acceptTypes[] = fileChooserParams.getAcceptTypes();

            String acceptType = "";
            for (int i = 0; i < acceptTypes.length; ++ i) {
                if (acceptTypes[i] != null && acceptTypes[i].length() != 0)
                    acceptType += acceptTypes[i] + ";";
            }
            if (acceptType.length() == 0)
                acceptType = "*/*";

            final ValueCallback<Uri[]> finalFilePathCallback = filePathCallback;

            ValueCallback<Uri> vc = new ValueCallback<Uri>() {

                @Override
                public void onReceiveValue(Uri value) {

                    Uri[] result;
                    if (value != null)
                        result = new Uri[]{value};
                    else
                        result = null;

                    finalFilePathCallback.onReceiveValue(result);

                }
            };

            openFileChooser(vc, acceptType, "filesystem");


            return true;
       }
    };

    class Controller {
        final static int FILE_SELECTED = 4;

        Activity getActivity() {
            return MainActivity.this;
        }
    }

    // copied from android-4.4.3_r1/src/com/android/browser/UploadHandler.java
    //////////////////////////////////////////////////////////////////////

    /*
     * Copyright (C) 2010 The Android Open Source Project
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *      http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

    // package com.android.browser;
    //
    // import android.app.Activity;
    // import android.content.ActivityNotFoundException;
    // import android.content.Intent;
    // import android.net.Uri;
    // import android.os.Environment;
    // import android.provider.MediaStore;
    // import android.webkit.ValueCallback;
    // import android.widget.Toast;
    //
    // import java.io.File;
    // import java.util.Vector;
    //
    // /**
    // * Handle the file upload callbacks from WebView here
    // */
    // public class UploadHandler {

    class UploadHandler {
        /*
         * The Object used to inform the WebView of the file to upload.
         */
        private ValueCallback<Uri> mUploadMessage;
        private String mCameraFilePath;
        private boolean mHandled;
        private boolean mCaughtActivityNotFoundException;
        private Controller mController;
        public UploadHandler(Controller controller) {
            mController = controller;
        }
        String getFilePath() {
            return mCameraFilePath;
        }
        boolean handled() {
            return mHandled;
        }
        void onResult(int resultCode, Intent intent) {
            if (resultCode == Activity.RESULT_CANCELED && mCaughtActivityNotFoundException) {
                // Couldn't resolve an activity, we are going to try again so skip
                // this result.
                mCaughtActivityNotFoundException = false;
                return;
            }
            Uri result = intent == null || resultCode != Activity.RESULT_OK ? null
                    : intent.getData();
            // As we ask the camera to save the result of the user taking
            // a picture, the camera application does not return anything other
            // than RESULT_OK. So we need to check whether the file we expected
            // was written to disk in the in the case that we
            // did not get an intent returned but did get a RESULT_OK. If it was,
            // we assume that this result has came back from the camera.
            if (result == null && intent == null && resultCode == Activity.RESULT_OK) {
                File cameraFile = new File(mCameraFilePath);
                if (cameraFile.exists()) {
                    result = Uri.fromFile(cameraFile);
                    // Broadcast to the media scanner that we have a new photo
                    // so it will be added into the gallery for the user.
                    mController.getActivity().sendBroadcast(
                            new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, result));
                }
            }
            mUploadMessage.onReceiveValue(result);
            mHandled = true;
            mCaughtActivityNotFoundException = false;
        }
        void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType, String capture) {
            final String imageMimeType = "image/*";
            final String videoMimeType = "video/*";
            final String audioMimeType = "audio/*";
            final String mediaSourceKey = "capture";
            final String mediaSourceValueCamera = "camera";
            final String mediaSourceValueFileSystem = "filesystem";
            final String mediaSourceValueCamcorder = "camcorder";
            final String mediaSourceValueMicrophone = "microphone";
            // According to the spec, media source can be 'filesystem' or 'camera' or 'camcorder'
            // or 'microphone' and the default value should be 'filesystem'.
            String mediaSource = mediaSourceValueFileSystem;
            if (mUploadMessage != null) {
                // Already a file picker operation in progress.
                return;
            }
            mUploadMessage = uploadMsg;
            // Parse the accept type.
            String params[] = acceptType.split(";");
            String mimeType = params[0];
            if (capture.length() > 0) {
                mediaSource = capture;
            }
            if (capture.equals(mediaSourceValueFileSystem)) {
                // To maintain backwards compatibility with the previous implementation
                // of the media capture API, if the value of the 'capture' attribute is
                // "filesystem", we should examine the accept-type for a MIME type that
                // may specify a different capture value.
                for (String p : params) {
                    String[] keyValue = p.split("=");
                    if (keyValue.length == 2) {
                        // Process key=value parameters.
                        if (mediaSourceKey.equals(keyValue[0])) {
                            mediaSource = keyValue[1];
                        }
                    }
                }
            }
            //Ensure it is not still set from a previous upload.
            mCameraFilePath = null;
            if (mimeType.equals(imageMimeType)) {
                if (mediaSource.equals(mediaSourceValueCamera)) {
                    // Specified 'image/*' and requested the camera, so go ahead and launch the
                    // camera directly.
                    startActivity(createCameraIntent());
                    return;
                } else {
                    // Specified just 'image/*', capture=filesystem, or an invalid capture parameter.
                    // In all these cases we show a traditional picker filetered on accept type
                    // so launch an intent for both the Camera and image/* OPENABLE.
                    Intent chooser = createChooserIntent(createCameraIntent());
                    chooser.putExtra(Intent.EXTRA_INTENT, createOpenableIntent(imageMimeType));
                    startActivity(chooser);
                    return;
                }
            } else if (mimeType.equals(videoMimeType)) {
                if (mediaSource.equals(mediaSourceValueCamcorder)) {
                    // Specified 'video/*' and requested the camcorder, so go ahead and launch the
                    // camcorder directly.
                    startActivity(createCamcorderIntent());
                    return;
               } else {
                    // Specified just 'video/*', capture=filesystem or an invalid capture parameter.
                    // In all these cases we show an intent for the traditional file picker, filtered
                    // on accept type so launch an intent for both camcorder and video/* OPENABLE.
                    Intent chooser = createChooserIntent(createCamcorderIntent());
                    chooser.putExtra(Intent.EXTRA_INTENT, createOpenableIntent(videoMimeType));
                    startActivity(chooser);
                    return;
                }
            } else if (mimeType.equals(audioMimeType)) {
                if (mediaSource.equals(mediaSourceValueMicrophone)) {
                    // Specified 'audio/*' and requested microphone, so go ahead and launch the sound
                    // recorder.
                    startActivity(createSoundRecorderIntent());
                    return;
                } else {
                    // Specified just 'audio/*',  capture=filesystem of an invalid capture parameter.
                    // In all these cases so go ahead and launch an intent for both the sound
                    // recorder and audio/* OPENABLE.
                    Intent chooser = createChooserIntent(createSoundRecorderIntent());
                    chooser.putExtra(Intent.EXTRA_INTENT, createOpenableIntent(audioMimeType));
                    startActivity(chooser);
                    return;
                }
            }
            // No special handling based on the accept type was necessary, so trigger the default
            // file upload chooser.
            startActivity(createDefaultOpenableIntent());
        }
        private void startActivity(Intent intent) {
            try {
                mController.getActivity().startActivityForResult(intent, Controller.FILE_SELECTED);
            } catch (ActivityNotFoundException e) {
                // No installed app was able to handle the intent that
                // we sent, so fallback to the default file upload control.
                try {
                    mCaughtActivityNotFoundException = true;
                    mController.getActivity().startActivityForResult(createDefaultOpenableIntent(),
                            Controller.FILE_SELECTED);
                } catch (ActivityNotFoundException e2) {
                    // Nothing can return us a file, so file upload is effectively disabled.
                    Toast.makeText(mController.getActivity(), R.string.uploads_disabled,
                            Toast.LENGTH_LONG).show();
                }
            }
        }
        private Intent createDefaultOpenableIntent() {
            // Create and return a chooser with the default OPENABLE
            // actions including the camera, camcorder and sound
            // recorder where available.
            Intent i = new Intent(Intent.ACTION_GET_CONTENT);
            i.addCategory(Intent.CATEGORY_OPENABLE);
            i.setType("*/*");
            Intent chooser = createChooserIntent(createCameraIntent(), createCamcorderIntent(),
                    createSoundRecorderIntent());
            chooser.putExtra(Intent.EXTRA_INTENT, i);
            return chooser;
        }
        private Intent createChooserIntent(Intent... intents) {
            Intent chooser = new Intent(Intent.ACTION_CHOOSER);
            chooser.putExtra(Intent.EXTRA_INITIAL_INTENTS, intents);
            chooser.putExtra(Intent.EXTRA_TITLE,
                    mController.getActivity().getResources()
                            .getString(R.string.choose_upload));
            return chooser;
        }
        private Intent createOpenableIntent(String type) {
            Intent i = new Intent(Intent.ACTION_GET_CONTENT);
            i.addCategory(Intent.CATEGORY_OPENABLE);
            i.setType(type);
            return i;
        }
        private Intent createCameraIntent() {
            Intent cameraIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
            File externalDataDir = Environment.getExternalStoragePublicDirectory(
                    Environment.DIRECTORY_DCIM);
            File cameraDataDir = new File(externalDataDir.getAbsolutePath() +
                    File.separator + "browser-photos");
            cameraDataDir.mkdirs();
            mCameraFilePath = cameraDataDir.getAbsolutePath() + File.separator +
                    System.currentTimeMillis() + ".jpg";
            cameraIntent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(new File(mCameraFilePath)));
            return cameraIntent;
        }
        private Intent createCamcorderIntent() {
            return new Intent(MediaStore.ACTION_VIDEO_CAPTURE);
        }
        private Intent createSoundRecorderIntent() {
            return new Intent(MediaStore.Audio.Media.RECORD_SOUND_ACTION);
        }
    }
}

cadena adicional resoruce de res / values ​​/ string.xml:

<string name="uploads_disabled">File uploads are disabled.</string>
<string name="choose_upload">Choose file for upload</string>

Si está utilizando proguard, es posible que necesite la siguiente opción en proguard-project.txt:

-keepclassmembers class * extends android.webkit.WebChromeClient {
   public void openFileChooser(...);
}

ACTUALIZACIÓN # 1 (2015.09.09)

agrega código para la compatibilidad de Android 5.0.1.

Esto es trabajo para mi. También trabajo para turrón y malvavisco [ [

import android.Manifest;
import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.content.res.Configuration;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.provider.MediaStore;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.KeyEvent;
import android.view.View;
import android.webkit.ValueCallback;
import android.webkit.WebChromeClient;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Toast;

import java.io.File;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class MainActivity extends AppCompatActivity {
    private static final String TAG = MainActivity.class.getSimpleName();
    private final static int FCR = 1;
    WebView webView;
    private String mCM;
    private ValueCallback<Uri> mUM;
    private ValueCallback<Uri[]> mUMA;

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent intent) {
        super.onActivityResult(requestCode, resultCode, intent);

        if (Build.VERSION.SDK_INT >= 21) {
            Uri[] results = null;

            //Check if response is positive
            if (resultCode == Activity.RESULT_OK) {
                if (requestCode == FCR) {

                    if (null == mUMA) {
                        return;
                    }
                    if (intent == null) {
                        //Capture Photo if no image available
                        if (mCM != null) {
                            results = new Uri[]{Uri.parse(mCM)};
                        }
                    } else {
                        String dataString = intent.getDataString();
                        if (dataString != null) {
                            results = new Uri[]{Uri.parse(dataString)};
                        }
                    }
                }
            }
            mUMA.onReceiveValue(results);
            mUMA = null;
        } else {

            if (requestCode == FCR) {
                if (null == mUM) return;
                Uri result = intent == null || resultCode != RESULT_OK ? null : intent.getData();
                mUM.onReceiveValue(result);
                mUM = null;
            }
        }
    }

    @SuppressLint({"SetJavaScriptEnabled", "WrongViewCast"})
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if (Build.VERSION.SDK_INT >= 23 && (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED || ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED)) {
            ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE, Manifest.permission.CAMERA}, 1);
        }

        webView = (WebView) findViewById(R.id.ifView);
        assert webView != null;

        WebSettings webSettings = webView.getSettings();
        webSettings.setJavaScriptEnabled(true);
        webSettings.setAllowFileAccess(true);

        if (Build.VERSION.SDK_INT >= 21) {
            webSettings.setMixedContentMode(0);
            webView.setLayerType(View.LAYER_TYPE_HARDWARE, null);
        } else if (Build.VERSION.SDK_INT >= 19) {
            webView.setLayerType(View.LAYER_TYPE_HARDWARE, null);
        } else if (Build.VERSION.SDK_INT < 19) {
            webView.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
        }

        webView.setWebViewClient(new Callback());
        webView.loadUrl("https://infeeds.com/");
        webView.setWebChromeClient(new WebChromeClient() {

            //For Android 3.0+
            public void openFileChooser(ValueCallback<Uri> uploadMsg) {

                mUM = uploadMsg;
                Intent i = new Intent(Intent.ACTION_GET_CONTENT);
                i.addCategory(Intent.CATEGORY_OPENABLE);
                i.setType("*/*");
                MainActivity.this.startActivityForResult(Intent.createChooser(i, "File Chooser"), FCR);
            }

            // For Android 3.0+, above method not supported in some android 3+ versions, in such case we use this
            public void openFileChooser(ValueCallback uploadMsg, String acceptType) {

                mUM = uploadMsg;
                Intent i = new Intent(Intent.ACTION_GET_CONTENT);
                i.addCategory(Intent.CATEGORY_OPENABLE);
                i.setType("*/*");
                MainActivity.this.startActivityForResult(
                        Intent.createChooser(i, "File Browser"),
                        FCR);
            }

            //For Android 4.1+
            public void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType, String capture) {

                mUM = uploadMsg;
                Intent i = new Intent(Intent.ACTION_GET_CONTENT);
                i.addCategory(Intent.CATEGORY_OPENABLE);
                i.setType("*/*");
                MainActivity.this.startActivityForResult(Intent.createChooser(i, "File Chooser"), MainActivity.FCR);
            }

            //For Android 5.0+
            public boolean onShowFileChooser(
                    WebView webView, ValueCallback<Uri[]> filePathCallback,
                    WebChromeClient.FileChooserParams fileChooserParams) {

                if (mUMA != null) {
                    mUMA.onReceiveValue(null);
                }

                mUMA = filePathCallback;
                Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
                if (takePictureIntent.resolveActivity(MainActivity.this.getPackageManager()) != null) {

                    File photoFile = null;

                    try {
                        photoFile = createImageFile();
                        takePictureIntent.putExtra("PhotoPath", mCM);
                    } catch (IOException ex) {
                        Log.e(TAG, "Image file creation failed", ex);
                    }
                    if (photoFile != null) {
                        mCM = "file:" + photoFile.getAbsolutePath();
                        takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(photoFile));
                    } else {
                        takePictureIntent = null;
                    }
                }

                Intent contentSelectionIntent = new Intent(Intent.ACTION_GET_CONTENT);
                contentSelectionIntent.addCategory(Intent.CATEGORY_OPENABLE);
                contentSelectionIntent.setType("*/*");
                Intent[] intentArray;

                if (takePictureIntent != null) {
                    intentArray = new Intent[]{takePictureIntent};
                } else {
                    intentArray = new Intent[0];
                }

                Intent chooserIntent = new Intent(Intent.ACTION_CHOOSER);
                chooserIntent.putExtra(Intent.EXTRA_INTENT, contentSelectionIntent);
                chooserIntent.putExtra(Intent.EXTRA_TITLE, "Image Chooser");
                chooserIntent.putExtra(Intent.EXTRA_INITIAL_INTENTS, intentArray);
                startActivityForResult(chooserIntent, FCR);

                return true;
            }
        });
    }

    // Create an image file
    private File createImageFile() throws IOException {

        @SuppressLint("SimpleDateFormat") String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
        String imageFileName = "img_" + timeStamp + "_";
        File storageDir = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES);
        return File.createTempFile(imageFileName, ".jpg", storageDir);
    }

    @Override
    public boolean onKeyDown(int keyCode, @NonNull KeyEvent event) {

        if (event.getAction() == KeyEvent.ACTION_DOWN) {

            switch (keyCode) {
                case KeyEvent.KEYCODE_BACK:

                    if (webView.canGoBack()) {
                        webView.goBack();
                    } else {
                        finish();
                    }

                    return true;
            }
        }

        return super.onKeyDown(keyCode, event);
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
    }

    public class Callback extends WebViewClient {
        public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
            Toast.makeText(getApplicationContext(), "Failed loading app!", Toast.LENGTH_SHORT).show();
        }
    }
}

Me pareció necesario definir public void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType, String capture), en Android 4.1. Luego seguí la solución de Michel Olivier.

De hecho, he logrado que el selector de archivos aparezca en Kitkat, para seleccionar una imagen y obtener la ruta del archivo en el resultado de la actividad, pero lo único que no puedo "arreglar" (causa esta solución) es hacer que la entrada archivada se llene fuera con los datos del archivo.

¿Alguien sabe de alguna manera cómo acceder al campo de entrada desde una actividad? Estoy usando este comentario de ejemplo . Es solo esta última pieza, el último ladrillo en la pared que solo tengo que colocar en el lugar correcto (aunque podría activar la carga del archivo de imagen directamente desde el código.

ACTUALIZACIÓN # 1

No soy un desarrollador de Android hardcore, así que mostraré el código en el nivel de novato. Estoy creando una nueva actividad en una actividad ya existente

Parte manifestada

<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<application android:label="TestApp">
 <activity android:name=".BrowseActivity"></activity>
</application>

Estoy creando mi clase BrowseActivity a partir de esta respuesta de ejemplo . La instancia de WebChromeClient () se ve básicamente igual, excepto la última pieza, que activa la parte de la interfaz de usuario del selector ...

private final static int FILECHOOSER_RESULTCODE=1;  
private final static int KITKAT_RESULTCODE = 2;

...

// The new WebChromeClient() looks pretty much the same, except one piece...

WebChromeClient chromeClient = new WebChromeClient(){  
    // For Android 3.0+
    public void openFileChooser(ValueCallback<Uri> uploadMsg) { /* Default code */ }  

    // For Android 3.0+
    public void openFileChooser( ValueCallback uploadMsg, String acceptType ) { /* Default code */ }  

    //For Android 4.1, also default but it'll be as example
    public void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType, String capture){
        mUploadMessage = uploadMsg;
        Intent i = new Intent(Intent.ACTION_GET_CONTENT);
        i.addCategory(Intent.CATEGORY_OPENABLE);
        i.setType("*/*");
        BrowseActivity.this.startActivityForResult(Intent.createChooser(i, "File Chooser"), BrowseActivity.FILECHOOSER_RESULTCODE);

    }  

    // The new code
    public void showPicker( ValueCallback<Uri> uploadMsg ){  
        // Here is part of the issue, the uploadMsg is null since it is not triggered from Android
        mUploadMessage = uploadMsg; 
        Intent i = new Intent(Intent.ACTION_GET_CONTENT);
        i.addCategory(Intent.CATEGORY_OPENABLE);
        i.setType("*/*");
        BrowseActivity.this.startActivityForResult(Intent.createChooser(i, "File Chooser"), BrowseActivity.KITKAT_RESULTCODE);
    }}

Y algunas cosas mas

web = new WebView(this);
// Notice this part, setting chromeClient as js interface is just lazy
web.getSettings().setJavaScriptEnabled(true);
web.addJavascriptInterface(chromeClient, "jsi" );
web.getSettings().setAllowFileAccess(true);
web.getSettings().setAllowContentAccess(true);
web.clearCache(true);
web.loadUrl( "http://as3breeze.com/upload.html" );
web.setWebViewClient(new myWebClient());
web.setWebChromeClient(chromeClient);


@Override protected void onActivityResult(int requestCode, int resultCode, Intent intent) {  
  Log.d("Result", "("+requestCode+ ") - (" +resultCode  + ") - (" + intent + ") - " + mUploadMessage);  
    if (null == intent) return;  
    Uri result = null;  
    if(requestCode==FILECHOOSER_RESULTCODE)  
    {  
        Log.d("Result","Old android");  
        if (null == mUploadMessage) return;  
        result = intent == null || resultCode != RESULT_OK ? null  : intent.getData();  
        mUploadMessage.onReceiveValue(result);  
        mUploadMessage = null;  
    } else if (requestCode == KITKAT_RESULTCODE) {  
        Log.d("Result","Kitkat android");  
        result = intent.getData();  
        final int takeFlags = intent.getFlags() & (Intent.FLAG_GRANT_READ_URI_PERMISSION  | Intent.FLAG_GRANT_WRITE_URI_PERMISSION);  
        String path = getPath( this, result);  
        File selectedFile = new File(path); 
//I used you example with a bit of editing so thought i would share, here i added a method to upload the file to the webserver
File selectedFile = new File(path);  
            UploadFile(selectedFile);


        //mUploadMessage.onReceiveValue( Uri.parse(selectedFile.toString()) );  
        // Now we have the file but since mUploadMessage was null, it gets errors
    }  
}

 public void UploadFile(File selectedFile)
{
    Random rnd = new Random();
    String sName = "File" + rnd.nextInt(999999) + selectedFile.getAbsolutePath().substring(selectedFile.getAbsolutePath().lastIndexOf("."));
    UploadedFileName = sName;
    uploadFile = selectedFile;
    if (progressBar != null && progressBar.isShowing())
    {
        progressBar.dismiss();
    }
 // prepare for a progress bar dialog
    progressBar = new ProgressDialog(mContext);
    progressBar.setCancelable(true);
    progressBar.setMessage("Uploading File");
    progressBar.setProgressStyle(ProgressDialog.STYLE_SPINNER);            
    progressBar.show();
    new Thread() {

        public void run() 
        {
            int serverResponseCode;
            String serverResponseMessage;
            HttpURLConnection connection = null;
            DataOutputStream outputStream = null;
            DataInputStream inputStream = null;
            String pathToOurFile = uploadFile.getAbsolutePath();
            String urlServer = "http://serveraddress/Scripts/UploadHandler.php?name" + UploadedFileName;
            String lineEnd = "\r\n";
            String twoHyphens = "--";
            String boundary =  "*****";

            int bytesRead, bytesAvailable, bufferSize;
            byte[] buffer;
            int maxBufferSize = 1*1024*1024;

            try
            {
                FileInputStream fileInputStream = new FileInputStream(uploadFile);

                URL url = new URL(urlServer);
                connection = (HttpURLConnection) url.openConnection();
                Log.i("File", urlServer);

                // Allow Inputs & Outputs.
                connection.setDoInput(true);
                connection.setDoOutput(true);
                connection.setUseCaches(false);

                // Set HTTP method to POST.
                connection.setRequestMethod("POST");

                connection.setRequestProperty("Connection", "Keep-Alive");
                connection.setRequestProperty("Content-Type", "multipart/form-data;boundary="+boundary);
                Log.i("File", "Open conn");

                outputStream = new DataOutputStream( connection.getOutputStream() );

                outputStream.writeBytes(twoHyphens + boundary + lineEnd);
                outputStream.writeBytes("Content-Disposition: form-data; name=\"uploadedfile\";filename=\"" + pathToOurFile +"\"" + lineEnd);
                outputStream.writeBytes(lineEnd);
                Log.i("File", "write bytes");

                bytesAvailable = fileInputStream.available();
                bufferSize = Math.min(bytesAvailable, maxBufferSize);
                buffer = new byte[bufferSize];
                Log.i("File", "available: " + fileInputStream.available());

                // Read file
                bytesRead = fileInputStream.read(buffer, 0, bufferSize);

                Log.i("file", "Bytes Read: " + bytesRead);
                while (bytesRead > 0)
                {
                    outputStream.write(buffer, 0, bufferSize);
                    bytesAvailable = fileInputStream.available();
                    bufferSize = Math.min(bytesAvailable, maxBufferSize);
                    bytesRead = fileInputStream.read(buffer, 0, bufferSize);
                }

                outputStream.writeBytes(lineEnd);
                outputStream.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd);

                // Responses from the server (code and message)
                serverResponseCode = connection.getResponseCode();
                serverResponseMessage = connection.getResponseMessage();
                Log.i("file repsonse", serverResponseMessage);

//once the file is uploaded call a javascript function to verify the user wants to save the image
                progressBar.dismiss();
                runOnUiThread(new Runnable() 
                {

                    @Override
                    public void run() 
                    {
                        Log.i("start", "File name: " + UploadedFileName);
                        WebView myWebView = (WebView) findViewById(R.id.webview);
                        myWebView.loadUrl("javascript:CheckImage('" + UploadedFileName + "')");
                    }
                });


                fileInputStream.close();
                outputStream.flush();
                outputStream.close();
            }
            catch (Exception ex)
            {
                Log.i("exception", "Error: " + ex.toString());
            }               
        }
    }.start();