Android Recyclerview GridLayoutManager espaciado de columnas

¿Cómo se configura el espaciado de columna con un RecyclerView usando un GridLayoutManager? Establecer el margen / relleno dentro de mi diseño no tiene ningún efecto.

RecyclerViews admite el concepto de ItemDecoration : compensaciones especiales y dibujo alrededor de cada elemento. Como se ve en esta respuesta , puede usar

public class SpacesItemDecoration extends RecyclerView.ItemDecoration {
  private int space;

  public SpacesItemDecoration(int space) {
    this.space = space;
  }

  @Override
  public void getItemOffsets(Rect outRect, View view, 
      RecyclerView parent, RecyclerView.State state) {
    outRect.left = space;
    outRect.right = space;
    outRect.bottom = space;

    // Add top margin only for the first item to avoid double space between items
    if (parent.getChildLayoutPosition(view) == 0) {
        outRect.top = space;
    } else {
        outRect.top = 0;
    }
  }
}

Luego agréguelo a través de

mRecyclerView = (RecyclerView) rootView.findViewById(R.id.my_recycler_view);
int spacingInPixels = getResources().getDimensionPixelSize(R.dimen.spacing);
mRecyclerView.addItemDecoration(new SpacesItemDecoration(spacingInPixels));

El siguiente código funciona bien y cada columna tiene el mismo ancho:

public class GridSpacingItemDecoration extends RecyclerView.ItemDecoration {

    private int spanCount;
    private int spacing;
    private boolean includeEdge;

    public GridSpacingItemDecoration(int spanCount, int spacing, boolean includeEdge) {
        this.spanCount = spanCount;
        this.spacing = spacing;
        this.includeEdge = includeEdge;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        int position = parent.getChildAdapterPosition(view); // item position
        int column = position % spanCount; // item column

        if (includeEdge) {
            outRect.left = spacing - column * spacing / spanCount; // spacing - column * ((1f / spanCount) * spacing)
            outRect.right = (column + 1) * spacing / spanCount; // (column + 1) * ((1f / spanCount) * spacing)

            if (position < spanCount) { // top edge
                outRect.top = spacing;
            }
            outRect.bottom = spacing; // item bottom
        } else {
            outRect.left = column * spacing / spanCount; // column * ((1f / spanCount) * spacing)
            outRect.right = spacing - (column + 1) * spacing / spanCount; // spacing - (column + 1) * ((1f /    spanCount) * spacing)
            if (position >= spanCount) {
                outRect.top = spacing; // item top
            }
        }
    }
}

Uso

1. sin filo

int spanCount = 3; // 3 columns
int spacing = 50; // 50px
boolean includeEdge = false;
recyclerView.addItemDecoration(new GridSpacingItemDecoration(spanCount, spacing, includeEdge));

2. con borde

int spanCount = 3; // 3 columns
int spacing = 50; // 50px
boolean includeEdge = true;
recyclerView.addItemDecoration(new GridSpacingItemDecoration(spanCount, spacing, includeEdge));

La siguiente es la solución simple paso a paso si desea un espacio igual alrededor de los elementos y tamaños de elementos iguales.

ItemOffsetDecoration

public class ItemOffsetDecoration extends RecyclerView.ItemDecoration {

    private int mItemOffset;

    public ItemOffsetDecoration(int itemOffset) {
        mItemOffset = itemOffset;
    }

    public ItemOffsetDecoration(@NonNull Context context, @DimenRes int itemOffsetId) {
        this(context.getResources().getDimensionPixelSize(itemOffsetId));
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent,
            RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        outRect.set(mItemOffset, mItemOffset, mItemOffset, mItemOffset);
    }
}

Implementación

En su código fuente, ItemOffsetDecorationel RecyclerView. valor de compensación de su elemento debe ser la mitad del valor real que desea agregar como espacio entre los elementos.

mRecyclerView.setLayoutManager(new GridLayoutManager(context, NUM_COLUMNS);
ItemOffsetDecoration itemDecoration = new ItemOffsetDecoration(context, R.dimen.item_offset);
mRecyclerView.addItemDecoration(itemDecoration);

Además, establezca el valor de desplazamiento del elemento como relleno para su RecyclerView, y especifique android:clipToPadding=false.

<android.support.v7.widget.RecyclerView
    android:id="@+id/recyclerview_grid"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:clipToPadding="false"
    android:padding="@dimen/item_offset"/>

Prueba esto. Se encargará de un espacio igual alrededor. Funciona tanto con List, Grid y StaggeredGrid.

Editado

El código actualizado debe manejar la mayoría de los casos de esquina con tramos, orientación, etc. Tenga en cuenta que si usa setSpanSizeLookup () con GridLayoutManager, se recomienda establecer setSpanIndexCacheEnabled () por razones de rendimiento.

Tenga en cuenta que parece que con StaggeredGrid, parece haber un error en el que el índice de los niños se vuelve extraño y difícil de rastrear, por lo que el código a continuación podría no funcionar muy bien con StaggeredGridLayoutManager.

public class ListSpacingDecoration extends RecyclerView.ItemDecoration {

  private static final int VERTICAL = OrientationHelper.VERTICAL;

  private int orientation = -1;
  private int spanCount = -1;
  private int spacing;
  private int halfSpacing;


  public ListSpacingDecoration(Context context, @DimenRes int spacingDimen) {

    spacing = context.getResources().getDimensionPixelSize(spacingDimen);
    halfSpacing = spacing / 2;
  }

  public ListSpacingDecoration(int spacingPx) {

    spacing = spacingPx;
    halfSpacing = spacing / 2;
  }

  @Override
  public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {

    super.getItemOffsets(outRect, view, parent, state);

    if (orientation == -1) {
        orientation = getOrientation(parent);
    }

    if (spanCount == -1) {
        spanCount = getTotalSpan(parent);
    }

    int childCount = parent.getLayoutManager().getItemCount();
    int childIndex = parent.getChildAdapterPosition(view);

    int itemSpanSize = getItemSpanSize(parent, childIndex);
    int spanIndex = getItemSpanIndex(parent, childIndex);

    /* INVALID SPAN */
    if (spanCount < 1) return;

    setSpacings(outRect, parent, childCount, childIndex, itemSpanSize, spanIndex);
  }

  protected void setSpacings(Rect outRect, RecyclerView parent, int childCount, int childIndex, int itemSpanSize, int spanIndex) {

    outRect.top = halfSpacing;
    outRect.bottom = halfSpacing;
    outRect.left = halfSpacing;
    outRect.right = halfSpacing;

    if (isTopEdge(parent, childCount, childIndex, itemSpanSize, spanIndex)) {
        outRect.top = spacing;
    }

    if (isLeftEdge(parent, childCount, childIndex, itemSpanSize, spanIndex)) {
        outRect.left = spacing;
    }

    if (isRightEdge(parent, childCount, childIndex, itemSpanSize, spanIndex)) {
        outRect.right = spacing;
    }

    if (isBottomEdge(parent, childCount, childIndex, itemSpanSize, spanIndex)) {
        outRect.bottom = spacing;
    }
  }

  @SuppressWarnings("all")
  protected int getTotalSpan(RecyclerView parent) {

    RecyclerView.LayoutManager mgr = parent.getLayoutManager();
    if (mgr instanceof GridLayoutManager) {
        return ((GridLayoutManager) mgr).getSpanCount();
    } else if (mgr instanceof StaggeredGridLayoutManager) {
        return ((StaggeredGridLayoutManager) mgr).getSpanCount();
    } else if (mgr instanceof LinearLayoutManager) {
        return 1;
    }

    return -1;
  }

  @SuppressWarnings("all")
  protected int getItemSpanSize(RecyclerView parent, int childIndex) {

    RecyclerView.LayoutManager mgr = parent.getLayoutManager();
    if (mgr instanceof GridLayoutManager) {
        return ((GridLayoutManager) mgr).getSpanSizeLookup().getSpanSize(childIndex);
    } else if (mgr instanceof StaggeredGridLayoutManager) {
        return 1;
    } else if (mgr instanceof LinearLayoutManager) {
        return 1;
    }

    return -1;
  }

  @SuppressWarnings("all")
  protected int getItemSpanIndex(RecyclerView parent, int childIndex) {

    RecyclerView.LayoutManager mgr = parent.getLayoutManager();
    if (mgr instanceof GridLayoutManager) {
        return ((GridLayoutManager) mgr).getSpanSizeLookup().getSpanIndex(childIndex, spanCount);
    } else if (mgr instanceof StaggeredGridLayoutManager) {
        return childIndex % spanCount;
    } else if (mgr instanceof LinearLayoutManager) {
        return 0;
    }

    return -1;
  }

  @SuppressWarnings("all")
  protected int getOrientation(RecyclerView parent) {

    RecyclerView.LayoutManager mgr = parent.getLayoutManager();
    if (mgr instanceof LinearLayoutManager) {
        return ((LinearLayoutManager) mgr).getOrientation();
    } else if (mgr instanceof GridLayoutManager) {
        return ((GridLayoutManager) mgr).getOrientation();
    } else if (mgr instanceof StaggeredGridLayoutManager) {
        return ((StaggeredGridLayoutManager) mgr).getOrientation();
    }

    return VERTICAL;
  }

  protected boolean isLeftEdge(RecyclerView parent, int childCount, int childIndex, int itemSpanSize, int spanIndex) {

    if (orientation == VERTICAL) {

        return spanIndex == 0;

    } else {

        return (childIndex == 0) || isFirstItemEdgeValid((childIndex < spanCount), parent, childIndex);
    }
  }

  protected boolean isRightEdge(RecyclerView parent, int childCount, int childIndex, int itemSpanSize, int spanIndex) {

    if (orientation == VERTICAL) {

        return (spanIndex + itemSpanSize) == spanCount;

    } else {

        return isLastItemEdgeValid((childIndex >= childCount - spanCount), parent, childCount, childIndex, spanIndex);
    }
  }

  protected boolean isTopEdge(RecyclerView parent, int childCount, int childIndex, int itemSpanSize, int spanIndex) {

    if (orientation == VERTICAL) {

        return (childIndex == 0) || isFirstItemEdgeValid((childIndex < spanCount), parent, childIndex);

    } else {

        return spanIndex == 0;
    }
  }

  protected boolean isBottomEdge(RecyclerView parent, int childCount, int childIndex, int itemSpanSize, int spanIndex) {

    if (orientation == VERTICAL) {

        return isLastItemEdgeValid((childIndex >= childCount - spanCount), parent, childCount, childIndex, spanIndex);

    } else {

        return (spanIndex + itemSpanSize) == spanCount;
    }
  }

  protected boolean isFirstItemEdgeValid(boolean isOneOfFirstItems, RecyclerView parent, int childIndex) {

    int totalSpanArea = 0;
    if (isOneOfFirstItems) {
        for (int i = childIndex; i >= 0; i--) {
            totalSpanArea = totalSpanArea + getItemSpanSize(parent, i);
        }
    }

    return isOneOfFirstItems && totalSpanArea <= spanCount;
  }

  protected boolean isLastItemEdgeValid(boolean isOneOfLastItems, RecyclerView parent, int childCount, int childIndex, int spanIndex) {

    int totalSpanRemaining = 0;
    if (isOneOfLastItems) {
        for (int i = childIndex; i < childCount; i++) {
            totalSpanRemaining = totalSpanRemaining + getItemSpanSize(parent, i);
        }
    }

    return isOneOfLastItems && (totalSpanRemaining <= spanCount - spanIndex);
  }
}

Espero eso ayude.

El siguiente código manejará StaggeredGridLayoutManager, GridLayoutManager y LinearLayoutManager.

public class SpacesItemDecoration extends RecyclerView.ItemDecoration {

    private int halfSpace;

    public SpacesItemDecoration(int space) {
        this.halfSpace = space / 2;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {

        if (parent.getPaddingLeft() != halfSpace) {
            parent.setPadding(halfSpace, halfSpace, halfSpace, halfSpace);
            parent.setClipToPadding(false);
        }

        outRect.top = halfSpace;
        outRect.bottom = halfSpace;
        outRect.left = halfSpace;
        outRect.right = halfSpace;
    }
}

Entonces úsalo

mRecyclerView.addItemDecoration(new SpacesItemDecoration(mMargin));

Aquí hay una solución que no requiere "spanCount" (número de columnas). Lo uso porque uso GridAutofitLayoutManager (calcula el número de columnas de acuerdo con el tamaño de celda requerido)

(tenga en cuenta que esto solo funcionará en GridLayoutManager )

public class GridSpacesItemDecoration extends RecyclerView.ItemDecoration {
    private final boolean includeEdge;
    private int spacing;


    public GridSpacesItemDecoration(int spacing, boolean includeEdge) {
        this.spacing = spacing;
        this.includeEdge = includeEdge;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        if (parent.getLayoutManager() instanceof GridLayoutManager) {
            GridLayoutManager layoutManager = (GridLayoutManager)parent.getLayoutManager();
            int spanCount = layoutManager.getSpanCount();
            int position = parent.getChildAdapterPosition(view); // item position
            int column = position % spanCount; // item column

            if (includeEdge) {
                outRect.left = spacing - column * spacing / spanCount; // spacing - column * ((1f / spanCount) * spacing)
                outRect.right = (column + 1) * spacing / spanCount; // (column + 1) * ((1f / spanCount) * spacing)

                if (position < spanCount) { // top edge
                    outRect.top = spacing;
                }
                outRect.bottom = spacing; // item bottom
            } else {
                outRect.left = column * spacing / spanCount; // column * ((1f / spanCount) * spacing)
                outRect.right = spacing - (column + 1) * spacing / spanCount; // spacing - (column + 1) * ((1f /    spanCount) * spacing)
                if (position >= spanCount) {
                    outRect.top = spacing; // item top
                }
            }

        }

    }
}

Aquí está el GridAutofitLayoutManager si alguien está interesado:

public class GridAutofitLayoutManager extends GridLayoutManager {
    private int mColumnWidth;
    private boolean mColumnWidthChanged = true;

    public GridAutofitLayoutManager(Context context, int columnWidth)
    {
        /* Initially set spanCount to 1, will be changed automatically later. */
        super(context, 1);
        setColumnWidth(checkedColumnWidth(context, columnWidth));
    }

    public GridAutofitLayoutManager(Context context,int unit, int columnWidth)
    {
        /* Initially set spanCount to 1, will be changed automatically later. */
        super(context, 1);
        int pixColumnWidth = (int) TypedValue.applyDimension(unit, columnWidth, context.getResources().getDisplayMetrics());
        setColumnWidth(checkedColumnWidth(context, pixColumnWidth));
    }

    public GridAutofitLayoutManager(Context context, int columnWidth, int orientation, boolean reverseLayout)
    {
        /* Initially set spanCount to 1, will be changed automatically later. */
        super(context, 1, orientation, reverseLayout);
        setColumnWidth(checkedColumnWidth(context, columnWidth));
    }

    private int checkedColumnWidth(Context context, int columnWidth)
    {
        if (columnWidth <= 0)
        {
            /* Set default columnWidth value (48dp here). It is better to move this constant
            to static constant on top, but we need context to convert it to dp, so can't really
            do so. */
            columnWidth = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 48,
                    context.getResources().getDisplayMetrics());
        }
        return columnWidth;
    }

    public void setColumnWidth(int newColumnWidth)
    {
        if (newColumnWidth > 0 && newColumnWidth != mColumnWidth)
        {
            mColumnWidth = newColumnWidth;
            mColumnWidthChanged = true;
        }
    }

    @Override
    public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state)
    {
        int width = getWidth();
        int height = getHeight();
        if (mColumnWidthChanged && mColumnWidth > 0 && width > 0 && height > 0)
        {
            int totalSpace;
            if (getOrientation() == VERTICAL)
            {
                totalSpace = width - getPaddingRight() - getPaddingLeft();
            }
            else
            {
                totalSpace = height - getPaddingTop() - getPaddingBottom();
            }
            int spanCount = Math.max(1, totalSpace / mColumnWidth);
            setSpanCount(spanCount);

            mColumnWidthChanged = false;
        }
        super.onLayoutChildren(recycler, state);
    }
}

Finalmente:

mDevicePhotosView.setLayoutManager(new GridAutofitLayoutManager(getContext(), getResources().getDimensionPixelSize(R.dimen.item_size)));
mDevicePhotosView.addItemDecoration(new GridSpacesItemDecoration(Util.dpToPx(getContext(), 2),true));

Solo hay una solución fácil, que puede recordar e implementar donde sea necesario. Sin errores, sin cálculos locos. Ponga margen en el diseño de la tarjeta / elemento y ponga el mismo tamaño que el relleno en RecyclerView:

item_layout.xml

<CardView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:margin="10dp">

activity_layout.xml

<RecyclerView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="10dp"/>

ACTUALIZAR:

Si desea FIJAR el tamaño de su RecyclerViewartículo en todos los dispositivos. Puedes hacer asi

public class GridSpacingItemDecoration extends RecyclerView.ItemDecoration {

    private int mSpanCount;
    private float mItemSize;

    public GridSpacingItemDecoration(int spanCount, int itemSize) {
        this.mSpanCount = spanCount;
        mItemSize = itemSize;
    }

    @Override
    public void getItemOffsets(final Rect outRect, final View view, RecyclerView parent,
            RecyclerView.State state) {
        final int position = parent.getChildLayoutPosition(view);
        final int column = position % mSpanCount;
        final int parentWidth = parent.getWidth();
        int spacing = (int) (parentWidth - (mItemSize * mSpanCount)) / (mSpanCount + 1);
        outRect.left = spacing - column * spacing / mSpanCount;
        outRect.right = (column + 1) * spacing / mSpanCount;

        if (position < mSpanCount) {
            outRect.top = spacing;
        }
        outRect.bottom = spacing;
    }
}

recyclerview_item.xml

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="@dimen/recycler_view_item_width" 
    ...
    >
    ...
</LinearLayout>

dimens.xml

 <dimen name="recycler_view_item_width">60dp</dimen>

Actividad

int numberOfColumns = 3;
mRecyclerView.setLayoutManager(new GridLayoutManager(this, numberOfColumns));
mRecyclerView.setAdapter(...);
mRecyclerView.addItemDecoration(new GridSpacingItemDecoration(3,
        getResources().getDimensionPixelSize(R.dimen.recycler_view_item_width)));

La respuesta seleccionada es casi perfecta, pero dependiendo del espacio, el ancho de los elementos puede no ser igual. (En mi caso fue crítico). Así que terminé con este código que aumenta un poco el espacio, por lo que todos los elementos tienen el mismo ancho.

   class GridSpacingItemDecoration(private val columnCount: Int, @Px preferredSpace: Int, private val includeEdge: Boolean): RecyclerView.ItemDecoration() {

    /**
     * In this algorithm space should divide by 3 without remnant or width of items can have a difference
     * and we want them to be exactly the same
     */
    private val space = if (preferredSpace % 3 == 0) preferredSpace else (preferredSpace + (3 - preferredSpace % 3))

    override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State?) {
        val position = parent.getChildAdapterPosition(view)

        if (includeEdge) {

            when {
                position % columnCount == 0 -> {
                    outRect.left = space
                    outRect.right = space / 3
                }
                position % columnCount == columnCount - 1 -> {
                    outRect.right = space
                    outRect.left = space / 3
                }
                else -> {
                    outRect.left = space * 2 / 3
                    outRect.right = space * 2 / 3
                }
            }

            if (position < columnCount) {
                outRect.top = space
            }

            outRect.bottom = space

        } else {

            when {
                position % columnCount == 0 -> outRect.right = space * 2 / 3
                position % columnCount == columnCount - 1 -> outRect.left = space * 2 / 3
                else -> {
                    outRect.left = space / 3
                    outRect.right = space / 3
                }
            }

            if (position >= columnCount) {
                outRect.top = space
            }
        }
    }

}

Copié el código proporcionado por @edwardaa y lo hago perfecto para admitir RTL:

public class GridSpacingItemDecoration extends RecyclerView.ItemDecoration {
    private int spanCount;
    private int spacing;
    private boolean includeEdge;
    private int headerNum;
    private boolean isRtl = TextUtilsCompat.getLayoutDirectionFromLocale(Locale.getDefault()) == ViewCompat.LAYOUT_DIRECTION_RTL;

    public GridSpacingItemDecoration(int spanCount, int spacing, boolean includeEdge, int headerNum) {
        this.spanCount = spanCount;
        this.spacing = spacing;
        this.includeEdge = includeEdge;
        this.headerNum = headerNum;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        int position = parent.getChildAdapterPosition(view) - headerNum; // item position
        if (position >= 0) {
            int column = position % spanCount; // item column
            if(isRtl) {
                column = spanCount - 1 - column;
            }
            if (includeEdge) {
                outRect.left = spacing - column * spacing / spanCount; // spacing - column * ((1f / spanCount) * spacing)
                outRect.right = (column + 1) * spacing / spanCount; // (column + 1) * ((1f / spanCount) * spacing)

                if (position < spanCount) { // top edge
                    outRect.top = spacing;
                }
                outRect.bottom = spacing; // item bottom
            } else {
                outRect.left = column * spacing / spanCount; // column * ((1f / spanCount) * spacing)
                outRect.right = spacing - (column + 1) * spacing / spanCount; // spacing - (column + 1) * ((1f /    spanCount) * spacing)
                if (position >= spanCount) {
                    outRect.top = spacing; // item top
                }
            }
        } else {
            outRect.left = 0;
            outRect.right = 0;
            outRect.top = 0;
            outRect.bottom = 0;
        }
    }
}

Las respuestas anteriores han aclarado formas de establecer el manejo de márgenes GridLayoutManager y LinearLayoutManager.

Pero para StaggeredGridLayoutManager, la respuesta de Pirdad Sakhizada dice: "Puede que no funcione muy bien con StaggeredGridLayoutManager". Debería ser el problema sobre IndexOfSpan.

Puede obtenerlo de esta manera:

private static class MyItemDecoration extends RecyclerView.ItemDecoration {
    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        int index = ((StaggeredGridLayoutManager.LayoutParams) view.getLayoutParams()).getSpanIndex();
    }
}

public class GridSpacingItemDecoration extends RecyclerView.ItemDecoration {

    private int spanCount;
    private int spacing;
    private boolean includeEdge;

    public GridSpacingItemDecoration(int spanCount, int spacing, boolean includeEdge) {
        this.spanCount = spanCount;
        this.spacing = spacing;
        this.includeEdge = includeEdge;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        StaggeredGridLayoutManager.LayoutParams params = (StaggeredGridLayoutManager.LayoutParams) view.getLayoutParams();
        int column = params.getSpanIndex();

        if (includeEdge) {
            outRect.left = spacing - column * spacing / spanCount; // spacing - column * ((1f / spanCount) * spacing)
            outRect.right = (column + 1) * spacing / spanCount; // (column + 1) * ((1f / spanCount) * spacing)

            if (position < spanCount) { // top edge
                outRect.top = spacing;
            }
            outRect.bottom = spacing; // item bottom
        } else {
            outRect.left = column * spacing / spanCount; // column * ((1f / spanCount) * spacing)
            outRect.right = spacing - (column + 1) * spacing / spanCount; // spacing - (column + 1) * ((1f /    spanCount) * spacing)
            if (position >= spanCount) {
                outRect.top = spacing; // item top
            }
        }
    }
}

Un poco diferente de la respuesta de edwardaa, la diferencia es cómo se determina la columna, porque en casos como elementos con varias alturas, la columna no se puede determinar simplemente por% spanCount

class VerticalGridSpacingDecoration(private val spacing: Int) : RecyclerView.ItemDecoration() {

  override fun getItemOffsets(
    outRect: Rect,
    view: View,
    parent: RecyclerView,
    state: State
  ) {
    val layoutManager = parent.layoutManager as? GridLayoutManager
    if (layoutManager == null || layoutManager.orientation != VERTICAL) {
      return super.getItemOffsets(outRect, view, parent, state)
    }

    val spanCount = layoutManager.spanCount
    val position = parent.getChildAdapterPosition(view)
    val column = position % spanCount
    with(outRect) {
      left = if (column == 0) 0 else spacing / 2
      right = if (column == spanCount.dec()) 0 else spacing / 2
      top = if (position < spanCount) 0 else spacing
    }
  }
}

Aquí está mi modificación de SpacesItemDecorationque puede tomar numOfColums y espacio igualmente en la parte superior, inferior, izquierda y derecha .

public class SpacesItemDecoration extends RecyclerView.ItemDecoration {
    private int space;
    private int mNumCol;

    public SpacesItemDecoration(int space, int numCol) {
        this.space = space;
        this.mNumCol=numCol;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view,
                               RecyclerView parent, RecyclerView.State state) {

        //outRect.right = space;
        outRect.bottom = space;
        //outRect.left = space;

        //Log.d("ttt", "item position" + parent.getChildLayoutPosition(view));
        int position=parent.getChildLayoutPosition(view);

        if(mNumCol<=2) {
            if (position == 0) {
                outRect.left = space;
                outRect.right = space / 2;
            } else {
                if ((position % mNumCol) != 0) {
                    outRect.left = space / 2;
                    outRect.right = space;
                } else {
                    outRect.left = space;
                    outRect.right = space / 2;
                }
            }
        }else{
            if (position == 0) {
                outRect.left = space;
                outRect.right = space / 2;
            } else {
                if ((position % mNumCol) == 0) {
                    outRect.left = space;
                    outRect.right = space/2;
                } else if((position % mNumCol) == (mNumCol-1)){
                    outRect.left = space/2;
                    outRect.right = space;
                }else{
                    outRect.left=space/2;
                    outRect.right=space/2;
                }
            }

        }

        if(position<mNumCol){
            outRect.top=space;
        }else{
            outRect.top=0;
        }
        // Add top margin only for the first item to avoid double space between items
        /*
        if (parent.getChildLayoutPosition(view) == 0 ) {

        } else {
            outRect.top = 0;
        }*/
    }
}

y use el siguiente código en su lógica.

recyclerView.addItemDecoration(new SpacesItemDecoration(spacingInPixels, numCol));

Hay una solución muy simple pero flexible para este problema usando solo XML que funciona en cada LayoutManager.

Suponga que desea un espaciado igual de X (8dp por ejemplo).

1. Envuelva su elemento CardView en otro diseño

2. Dele al diseño exterior un relleno de X / 2 (4dp)

3. Haga que el fondo del diseño exterior sea transparente

...

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="200dp"
    android:layout_height="200dp"
    android:background="@android:color/transparent"
    android:padding="4dip">

    <android.support.v7.widget.CardView
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </android.support.v7.widget.CardView>

</LinearLayout>

4. Dele a su RecyclerView un relleno de X / 2 (4dp)

...

<android.support.v7.widget.RecyclerView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="4dp" />

y eso es. Tienes un espaciado perfecto de X (8dp).

Para aquellos que tienen problemas con staggeredLayoutManager (como https://imgur.com/XVutH5u )

Los métodos de recyclerView:

getChildAdapterPosition(view)
getChildLayoutPosition(view)

a veces devuelve -1 como índice, por lo que podríamos tener problemas para configurar itemDecor. Mi solución es anular el método obsoleto de ItemDecoration:

public void getItemOffsets(Rect outRect, int itemPosition, RecyclerView parent)

en lugar del novato:

public void getItemOffsets(Rect outRect, View view, RecyclerView parent, State state)

Me gusta esto:

recyclerView.addItemDecoration(new RecyclerView.ItemDecoration() {
            @Override
            public void getItemOffsets(Rect outRect, int itemPosition, RecyclerView parent) {
                TheAdapter.VH vh = (TheAdapter.VH) recyclerView.findViewHolderForAdapterPosition(itemPosition);
                View itemView = vh.itemView;    //itemView is the base view of viewHolder
                //or instead of the 2 lines above maybe it's possible to use  View itemView = layoutManager.findViewByPosition(itemPosition)  ... NOT TESTED

                StaggeredGridLayoutManager.LayoutParams itemLayoutParams = (StaggeredGridLayoutManager.LayoutParams) itemView.getLayoutParams();

                int spanIndex = itemLayoutParams.getSpanIndex();

                if (spanIndex == 0)
                    ...
                else
                    ...
            }
        });

Parece que funciona para mí hasta ahora :)

Las respuestas a esta pregunta parecen más complejas de lo que deberían ser. Aquí está mi opinión sobre esto.

Digamos que desea un espacio de 1dp entre los elementos de la cuadrícula. Haz lo siguiente:

1. Agregue un relleno de 0.5dp a cada elemento
2. Agregue un relleno de -0.5dp a RecycleView
3. ¡Eso es! :)

Esto también funcionará RecyclerViewcon el encabezado.

public class GridSpacingItemDecoration extends RecyclerView.ItemDecoration {

    private int spanCount;
    private int spacing;
    private boolean includeEdge;
    private int headerNum;

    public GridSpacingItemDecoration(int spanCount, int spacing, boolean includeEdge, int headerNum) {
        this.spanCount = spanCount;
        this.spacing = spacing;
        this.includeEdge = includeEdge;
        this.headerNum = headerNum;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        int position = parent.getChildAdapterPosition(view) - headerNum; // item position

        if (position >= 0) {
            int column = position % spanCount; // item column

            if (includeEdge) {
                outRect.left = spacing - column * spacing / spanCount; // spacing - column * ((1f / spanCount) * spacing)
                outRect.right = (column + 1) * spacing / spanCount; // (column + 1) * ((1f / spanCount) * spacing)

                if (position < spanCount) { // top edge
                    outRect.top = spacing;
                }
                outRect.bottom = spacing; // item bottom
            } else {
                outRect.left = column * spacing / spanCount; // column * ((1f / spanCount) * spacing)
                outRect.right = spacing - (column + 1) * spacing / spanCount; // spacing - (column + 1) * ((1f /    spanCount) * spacing)
                if (position >= spanCount) {
                    outRect.top = spacing; // item top
                }
            }
        } else {
            outRect.left = 0;
            outRect.right = 0;
            outRect.top = 0;
            outRect.bottom = 0;
        }
    }
    }
}

La respuesta de yqritc funcionó perfectamente para mí. Sin embargo, estaba usando Kotlin, así que aquí está el equivalente de eso.

class ItemOffsetDecoration : RecyclerView.ItemDecoration  {

    // amount to add to padding
    private val _itemOffset: Int

    constructor(itemOffset: Int) {
        _itemOffset = itemOffset
    }

    constructor(@NonNull context: Context, @DimenRes itemOffsetId: Int){
       _itemOffset = context.resources.getDimensionPixelSize(itemOffsetId)
    }

    /**
     * Applies padding to all sides of the [Rect], which is the container for the view
     */
    override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView,state: RecyclerView.State) {
        super.getItemOffsets(outRect, view, parent, state)
        outRect.set(_itemOffset, _itemOffset, _itemOffset, _itemOffset)
    }
}

Todo lo demás es lo mismo.

Para los usuarios de StaggeredGridLayoutManager , tenga cuidado, muchas respuestas aquí, incluida la más votada, calcula la columna del elemento con el siguiente código:

int column = position % spanCount

que supone que los elementos 1º / 3º / 5º / .. siempre se encuentran en el lado izquierdo y los elementos 2º / 4º / 6º / .. siempre se encuentran en el lado derecho. ¿Es esta suposición siempre cierta? No.

Digamos que su primer elemento tiene 100dp de alto y el segundo solo tiene 50dp, adivine dónde está ubicado su tercer elemento, ¿izquierda o derecha?

Terminé haciéndolo así para mi RecyclerView con GridLayoutManager y HeaderView .

En el siguiente código, configuro un espacio de 4dp entre cada elemento (2dp alrededor de cada elemento individual y un relleno de 2dp alrededor de toda la vista del reciclador).

layout.xml

<android.support.v7.widget.RecyclerView
    android:id="@+id/recycleview"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="2dp" />

fragmento / actividad

GridLayoutManager manager = new GridLayoutManager(getContext(), 3);
recyclerView.setLayoutManager(manager);
int spacingInPixels = Utils.dpToPx(2);
recyclerView.addItemDecoration(new SpacesItemDecoration(spacingInPixels));

SpaceItemDecoration.java

public class SpacesItemDecoration extends RecyclerView.ItemDecoration {

    private int mSpacing;

    public SpacesItemDecoration(int spacing) {
        mSpacing = spacing;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView recyclerView, RecyclerView.State state) {
        outRect.left = mSpacing;
        outRect.top = mSpacing;
        outRect.right = mSpacing;
        outRect.bottom = mSpacing;
    }
}

Utils.java

public static int dpToPx(final float dp) {
    return Math.round(dp * (Resources.getSystem().getDisplayMetrics().xdpi / DisplayMetrics.DENSITY_DEFAULT));
}

Para que la solución https://stackoverflow.com/a/29905000/1649371 (arriba) funcionara, tuve que modificar los siguientes métodos (y todas las llamadas posteriores)

@SuppressWarnings("all")
protected int getItemSpanSize(RecyclerView parent, View view, int childIndex) {

    RecyclerView.LayoutManager mgr = parent.getLayoutManager();
    if (mgr instanceof GridLayoutManager) {
        return ((GridLayoutManager) mgr).getSpanSizeLookup().getSpanSize(childIndex);
    } else if (mgr instanceof StaggeredGridLayoutManager) {
        return ((StaggeredGridLayoutManager.LayoutParams) view.getLayoutParams()).isFullSpan() ? spanCount : 1;
    } else if (mgr instanceof LinearLayoutManager) {
        return 1;
    }

    return -1;
}

@SuppressWarnings("all")
protected int getItemSpanIndex(RecyclerView parent, View view, int childIndex) {

    RecyclerView.LayoutManager mgr = parent.getLayoutManager();
    if (mgr instanceof GridLayoutManager) {
        return ((GridLayoutManager) mgr).getSpanSizeLookup().getSpanIndex(childIndex, spanCount);
    } else if (mgr instanceof StaggeredGridLayoutManager) {
        return ((StaggeredGridLayoutManager.LayoutParams) view.getLayoutParams()).getSpanIndex();
    } else if (mgr instanceof LinearLayoutManager) {
        return 0;
    }

    return -1;
}

Este enlace funcionó para mí en todas las situaciones, puede intentar esto.

Si tiene un interruptor de alternancia que alterna entre la lista y la cuadrícula, no olvide llamar recyclerView.removeItemDecoration()antes de configurar cualquier decoración de elemento nueva. De lo contrario, los nuevos cálculos para el espaciado serían incorrectos.

Algo como esto.

        recyclerView.removeItemDecoration(gridItemDecorator)
        recyclerView.removeItemDecoration(listItemDecorator)
        if (showAsList){
            recyclerView.layoutManager = LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false)
            recyclerView.addItemDecoration(listItemDecorator)
        }
        else{
            recyclerView.layoutManager = GridLayoutManager(this, spanCount)
            recyclerView.addItemDecoration(gridItemDecorator)
        }

Si está utilizando Encabezado con GridLayoutManager, use este código escrito en kotlin para espaciar entre las cuadrículas:

inner class SpacesItemDecoration(itemSpace: Int) : RecyclerView.ItemDecoration() {
    var space: Int = itemSpace

    override fun getItemOffsets(outRect: Rect?, view: View?, parent: RecyclerView?, state: RecyclerView.State?) {
        super.getItemOffsets(outRect, view, parent, state)
        val position = parent!!.getChildAdapterPosition(view)
        val viewType = parent.adapter.getItemViewType(position)
       //check to not to set any margin to header item 
        if (viewType == GridViewAdapter.TYPE_HEADER) {
            outRect!!.top = 0
            outRect.left = 0
            outRect.right = 0
            outRect.bottom = 0
        } else {
            outRect!!.left = space
            outRect.right = space
            outRect.bottom = space

            if (parent.getChildLayoutPosition(view) == 0) {
                outRect.top = space
            } else {
                outRect.top = 0
            }
        }
    }
    }

Y pasar ItemDecorationa recyclerviewcomo

mIssueGridView.addItemDecoration(SpacesItemDecoration(10))

Al usar CardView para niños, el problema con los espacios entre los elementos se puede resolver configurando app: cardUseCompatPadding en true.

Para márgenes más grandes, aumente la elevación del elemento. CardElevation es opcional (use el valor predeterminado).

<androidx.cardview.widget.CardView
    xmlns:app="http://schemas.android.com/apk/res-auto"
    app:cardUseCompatPadding="true"
    app:cardElevation="2dp">

gracias respuesta de edwardaa https://stackoverflow.com/a/30701422/2227031

Otro punto a tener en cuenta es que:

Si el espaciado total y el ancho total del elemento no son iguales al ancho de la pantalla, también debe ajustar el ancho del elemento, por ejemplo, en el método del adaptador onBindViewHolder

Utils.init(_mActivity);
int width = 0;
if (includeEdge) {
    width = ScreenUtils.getScreenWidth() - spacing * (spanCount + 1);
} else {
    width = ScreenUtils.getScreenWidth() - spacing * (spanCount - 1);
}
int itemWidth = width / spanCount;

ConstraintLayout.LayoutParams layoutParams = (ConstraintLayout.LayoutParams) holder.imageViewAvatar.getLayoutParams();
// suppose the width and height are the same
layoutParams.width = itemWidth;
layoutParams.height = itemWidth;
holder.imageViewAvatar.setLayoutParams(layoutParams);

Una versión de Kotlin que hice basada en la gran respuesta de edwardaa

class RecyclerItemDecoration(private val spanCount: Int, private val spacing: Int) : RecyclerView.ItemDecoration() {

  override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State) {

    val spacing = Math.round(spacing * parent.context.resources.displayMetrics.density)
    val position = parent.getChildAdapterPosition(view)
    val column = position % spanCount

    outRect.left = spacing - column * spacing / spanCount
    outRect.right = (column + 1) * spacing / spanCount

    outRect.top = if (position < spanCount) spacing else 0
    outRect.bottom = spacing
  }

}