Hay una parte en mis aplicaciones que muestra la ruta del archivo cargado por el usuario a través de OpenFileDialog. Está ocupando demasiado espacio para mostrar la ruta completa, pero no quiero mostrar solo el nombre del archivo, ya que puede ser ambiguo. Así que preferiría mostrar la ruta del archivo en relación con el directorio ensamblado / exe.

Por ejemplo, el ensamblaje reside en C:\Program Files\Dummy Folder\MyProgramy el archivo en C:\Program Files\Dummy Folder\MyProgram\Data\datafile1.datese momento me gustaría que se muestre .\Data\datafile1.dat. Si el archivo está dentro C:\Program Files\Dummy Folder\datafile1.dat, entonces me gustaría ..\datafile1.dat. Pero si el archivo está en el directorio raíz o 1 directorio debajo de la raíz, entonces muestre la ruta completa.

¿Qué solución recomendarías? Regex?

Básicamente quiero mostrar información útil de la ruta del archivo sin ocupar demasiado espacio en la pantalla.

EDITAR: Solo para aclarar un poco más. El propósito de esta solución es ayudar al usuario o a mí mismo a saber qué archivo cargué por última vez y aproximadamente de qué directorio provenía. Estoy usando un cuadro de texto de solo lectura para mostrar la ruta. La mayoría de las veces, la ruta del archivo es mucho más larga que el espacio de visualización del cuadro de texto. Se supone que la ruta es informativa pero no lo suficientemente importante como para ocupar más espacio en la pantalla.

El comentario de Alex Brault fue bueno, al igual que Jonathan Leffler. La función Win32 proporcionada por DavidK solo ayuda con parte del problema, no con todo, pero gracias de todos modos. En cuanto a la solución de James Newton-King, lo intentaré más tarde cuando esté libre.

.NET Core 2.0 tiene Path.GetRelativePath, de lo contrario, usar esto.

/// <summary>
/// Creates a relative path from one file or folder to another.
/// </summary>
/// <param name="fromPath">Contains the directory that defines the start of the relative path.</param>
/// <param name="toPath">Contains the path that defines the endpoint of the relative path.</param>
/// <returns>The relative path from the start directory to the end path or <c>toPath</c> if the paths are not related.</returns>
/// <exception cref="ArgumentNullException"></exception>
/// <exception cref="UriFormatException"></exception>
/// <exception cref="InvalidOperationException"></exception>
public static String MakeRelativePath(String fromPath, String toPath)
{
    if (String.IsNullOrEmpty(fromPath)) throw new ArgumentNullException("fromPath");
    if (String.IsNullOrEmpty(toPath))   throw new ArgumentNullException("toPath");

    Uri fromUri = new Uri(fromPath);
    Uri toUri = new Uri(toPath);

    if (fromUri.Scheme != toUri.Scheme) { return toPath; } // path can't be made relative.

    Uri relativeUri = fromUri.MakeRelativeUri(toUri);
    String relativePath = Uri.UnescapeDataString(relativeUri.ToString());

    if (toUri.Scheme.Equals("file", StringComparison.InvariantCultureIgnoreCase))
    {
        relativePath = relativePath.Replace(Path.AltDirectorySeparatorChar, Path.DirectorySeparatorChar);
    }

    return relativePath;
}

Un poco tarde para la pregunta, pero también necesitaba esta función también. Estoy de acuerdo con DavidK en que, dado que hay una función de API incorporada que proporciona esto, debe usarla. Aquí hay un contenedor administrado para ello:

public static string GetRelativePath(string fromPath, string toPath)
{
    int fromAttr = GetPathAttribute(fromPath);
    int toAttr = GetPathAttribute(toPath);

    StringBuilder path = new StringBuilder(260); // MAX_PATH
    if(PathRelativePathTo(
        path,
        fromPath,
        fromAttr,
        toPath,
        toAttr) == 0)
    {
        throw new ArgumentException("Paths must have a common prefix");
    }
    return path.ToString();
}

private static int GetPathAttribute(string path)
{
    DirectoryInfo di = new DirectoryInfo(path);
    if (di.Exists)
    {
        return FILE_ATTRIBUTE_DIRECTORY;
    }

    FileInfo fi = new FileInfo(path);
    if(fi.Exists)
    {
        return FILE_ATTRIBUTE_NORMAL;
    }

    throw new FileNotFoundException();
}

private const int FILE_ATTRIBUTE_DIRECTORY = 0x10;
private const int FILE_ATTRIBUTE_NORMAL = 0x80;

[DllImport("shlwapi.dll", SetLastError = true)]
private static extern int PathRelativePathTo(StringBuilder pszPath, 
    string pszFrom, int dwAttrFrom, string pszTo, int dwAttrTo);

Respuesta de .NET Core 2.0

.NET Core 2.0 tiene Path.GetRelativePath que se puede usar así:

var relativePath = Path.GetRelativePath(
    @"C:\Program Files\Dummy Folder\MyProgram",
    @"C:\Program Files\Dummy Folder\MyProgram\Data\datafile1.dat");

En el ejemplo anterior, la relativePathvariable es igual aData\datafile1.dat .

Respuesta alternativa .NET

La solución de @ Dave no funciona cuando las rutas de los archivos no terminan con un carácter de barra diagonal ( /) que puede suceder si la ruta es una ruta de directorio. Mi solución soluciona ese problema y también utiliza la Uri.UriSchemeFileconstante en lugar de la codificación rígida "FILE".

/// <summary>
/// Creates a relative path from one file or folder to another.
/// </summary>
/// <param name="fromPath">Contains the directory that defines the start of the relative path.</param>
/// <param name="toPath">Contains the path that defines the endpoint of the relative path.</param>
/// <returns>The relative path from the start directory to the end path.</returns>
/// <exception cref="ArgumentNullException"><paramref name="fromPath"/> or <paramref name="toPath"/> is <c>null</c>.</exception>
/// <exception cref="UriFormatException"></exception>
/// <exception cref="InvalidOperationException"></exception>
public static string GetRelativePath(string fromPath, string toPath)
{
    if (string.IsNullOrEmpty(fromPath))
    {
        throw new ArgumentNullException("fromPath");
    }

    if (string.IsNullOrEmpty(toPath))
    {
        throw new ArgumentNullException("toPath");
    }

    Uri fromUri = new Uri(AppendDirectorySeparatorChar(fromPath));
    Uri toUri = new Uri(AppendDirectorySeparatorChar(toPath));

    if (fromUri.Scheme != toUri.Scheme)
    {
        return toPath;
    }

    Uri relativeUri = fromUri.MakeRelativeUri(toUri);
    string relativePath = Uri.UnescapeDataString(relativeUri.ToString());

    if (string.Equals(toUri.Scheme, Uri.UriSchemeFile, StringComparison.OrdinalIgnoreCase))
    {
        relativePath = relativePath.Replace(Path.AltDirectorySeparatorChar, Path.DirectorySeparatorChar);
    }

    return relativePath;
}

private static string AppendDirectorySeparatorChar(string path)
{
    // Append a slash only if the path is a directory and does not have a slash.
    if (!Path.HasExtension(path) &&
        !path.EndsWith(Path.DirectorySeparatorChar.ToString()))
    {
        return path + Path.DirectorySeparatorChar;
    }

    return path;
}

Respuesta de interoperabilidad de Windows

Hay una API de Windows llamada PathRelativePathToA que se puede usar para encontrar una ruta relativa. Tenga en cuenta que las rutas de archivo o directorio que pasa a la función deben existir para que funcione.

var relativePath = PathExtended.GetRelativePath(
    @"C:\Program Files\Dummy Folder\MyProgram",
    @"C:\Program Files\Dummy Folder\MyProgram\Data\datafile1.dat");

public static class PathExtended
{
    private const int FILE_ATTRIBUTE_DIRECTORY = 0x10;
    private const int FILE_ATTRIBUTE_NORMAL = 0x80;
    private const int MaximumPath = 260;

    public static string GetRelativePath(string fromPath, string toPath)
    {
        var fromAttribute = GetPathAttribute(fromPath);
        var toAttribute = GetPathAttribute(toPath);

        var stringBuilder = new StringBuilder(MaximumPath);
        if (PathRelativePathTo(
            stringBuilder,
            fromPath,
            fromAttribute,
            toPath,
            toAttribute) == 0)
        {
            throw new ArgumentException("Paths must have a common prefix.");
        }

        return stringBuilder.ToString();
    }

    private static int GetPathAttribute(string path)
    {
        var directory = new DirectoryInfo(path);
        if (directory.Exists)
        {
            return FILE_ATTRIBUTE_DIRECTORY;
        }

        var file = new FileInfo(path);
        if (file.Exists)
        {
            return FILE_ATTRIBUTE_NORMAL;
        }

        throw new FileNotFoundException(
            "A file or directory with the specified path was not found.",
            path);
    }

    [DllImport("shlwapi.dll", SetLastError = true)]
    private static extern int PathRelativePathTo(
        StringBuilder pszPath,
        string pszFrom,
        int dwAttrFrom,
        string pszTo,
        int dwAttrTo);
}

Hay una función Win32 (C ++) en shlwapi.dll que hace exactamente lo que desea: PathRelativePathTo()

Sin embargo, no conozco ninguna forma de acceder a esto desde .NET que no sea P / Invocarlo.

Si está utilizando .NET Core 2.0,Path.GetRelativePath() está disponible proporcionando esta funcionalidad específica:

        var relativeTo = @"C:\Program Files\Dummy Folder\MyProgram";
        var path = @"C:\Program Files\Dummy Folder\MyProgram\Data\datafile1.dat";

        string relativePath = System.IO.Path.GetRelativePath(relativeTo, path);

        System.Console.WriteLine(relativePath);
        // output --> Data\datafile1.dat 

De lo contrario, para .NET full framework (a partir de v4.7) recomendamos usar una de las otras respuestas sugeridas.

He usado esto en el pasado.

/// <summary>
/// Creates a relative path from one file
/// or folder to another.
/// </summary>
/// <param name="fromDirectory">
/// Contains the directory that defines the
/// start of the relative path.
/// </param>
/// <param name="toPath">
/// Contains the path that defines the
/// endpoint of the relative path.
/// </param>
/// <returns>
/// The relative path from the start
/// directory to the end path.
/// </returns>
/// <exception cref="ArgumentNullException"></exception>
public static string MakeRelative(string fromDirectory, string toPath)
{
  if (fromDirectory == null)
    throw new ArgumentNullException("fromDirectory");

  if (toPath == null)
    throw new ArgumentNullException("toPath");

  bool isRooted = (Path.IsPathRooted(fromDirectory) && Path.IsPathRooted(toPath));

  if (isRooted)
  {
    bool isDifferentRoot = (string.Compare(Path.GetPathRoot(fromDirectory), Path.GetPathRoot(toPath), true) != 0);

    if (isDifferentRoot)
      return toPath;
  }

  List<string> relativePath = new List<string>();
  string[] fromDirectories = fromDirectory.Split(Path.DirectorySeparatorChar);

  string[] toDirectories = toPath.Split(Path.DirectorySeparatorChar);

  int length = Math.Min(fromDirectories.Length, toDirectories.Length);

  int lastCommonRoot = -1;

  // find common root
  for (int x = 0; x < length; x++)
  {
    if (string.Compare(fromDirectories[x], toDirectories[x], true) != 0)
      break;

    lastCommonRoot = x;
  }

  if (lastCommonRoot == -1)
    return toPath;

  // add relative folders in from path
  for (int x = lastCommonRoot + 1; x < fromDirectories.Length; x++)
  {
    if (fromDirectories[x].Length > 0)
      relativePath.Add("..");
  }

  // add to folders to path
  for (int x = lastCommonRoot + 1; x < toDirectories.Length; x++)
  {
    relativePath.Add(toDirectories[x]);
  }

  // create relative path
  string[] relativeParts = new string[relativePath.Count];
  relativePath.CopyTo(relativeParts, 0);

  string newPath = string.Join(Path.DirectorySeparatorChar.ToString(), relativeParts);

  return newPath;
}

Como señala Alex Brault, especialmente en Windows, la ruta absoluta (con letra de unidad y todo) es inequívoca y, a menudo, mejor.

¿No debería su OpenFileDialog utilizar una estructura de árbol de navegador normal?

Para establecer alguna nomenclatura, RefDir es el directorio relativo al que desea especificar la ruta; la AbsName es el nombre de ruta absoluta que desea asignar; y RelPath es la ruta relativa resultante.

Tome la primera de estas opciones que coincida:

• Si tiene letras de unidad diferentes, no hay una ruta relativa de RefDir a AbsName; debes usar AbsName.
• Si AbsName está en un subdirectorio de RefDir o es un archivo dentro de RefDir, simplemente elimine RefDir del inicio de AbsName para crear RelPath; opcionalmente anteponga "./" (o ". \" ya que está en Windows).
• Encuentre el prefijo común más largo de RefDir y AbsName (donde D: \ Abc \ Def y D: \ Abc \ Default comparten D: \ Abc como el prefijo común más largo; tiene que ser una asignación de componentes de nombre, no un simple común más largo subcadena); llámalo LCP. Eliminar LCP de AbsName y RefDir. Para cada componente de ruta restante en (RefDir - LCP), anteponga ".. \" a (AbsName - LCP) para obtener RelPath.

Para ilustrar la última regla (que es, por supuesto, con mucho la más compleja), comience con:

RefDir = D:\Abc\Def\Ghi
AbsName = D:\Abc\Default\Karma\Crucible

Luego

LCP = D:\Abc
(RefDir - LCP) = Def\Ghi
(Absname - LCP) = Default\Karma\Crucible
RelPath = ..\..\Default\Karma\Crucible

Mientras escribía, DavidK produjo una respuesta que sugiere que no eres el primero en necesitar esta función y que hay una función estándar para hacer este trabajo. Úsalo. Pero tampoco hay daño en poder pensar desde los primeros principios.

Excepto que los sistemas Unix no admiten letras de unidad (por lo que todo está siempre ubicado en el mismo directorio raíz y, por lo tanto, la primera viñeta es irrelevante), la misma técnica podría usarse en Unix.

Es un largo camino, pero la clase System.Uri tiene un método llamado MakeRelativeUri. Tal vez podrías usar eso. Es una lástima que System.IO.Path no tenga esto.

Como se señaló anteriormente .NET Core 2.x tiene implementación de Path.GetRelativePath.

El siguiente código está adaptado de las fuentes y funciona bien con .NET 4.7.1 Framework.

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

//Adapted from https://github.com/dotnet/corefx/blob/master/src/Common/src/CoreLib/System/IO/Path.cs#L697
// by Anton Krouglov

using System.Runtime.CompilerServices;
using System.Diagnostics;
using System.Text;
using Xunit;

namespace System.IO {
    // Provides methods for processing file system strings in a cross-platform manner.
    // Most of the methods don't do a complete parsing (such as examining a UNC hostname), 
    // but they will handle most string operations.
    public static class PathNetCore {

        /// <summary>
        /// Create a relative path from one path to another. Paths will be resolved before calculating the difference.
        /// Default path comparison for the active platform will be used (OrdinalIgnoreCase for Windows or Mac, Ordinal for Unix).
        /// </summary>
        /// <param name="relativeTo">The source path the output should be relative to. This path is always considered to be a directory.</param>
        /// <param name="path">The destination path.</param>
        /// <returns>The relative path or <paramref name="path"/> if the paths don't share the same root.</returns>
        /// <exception cref="ArgumentNullException">Thrown if <paramref name="relativeTo"/> or <paramref name="path"/> is <c>null</c> or an empty string.</exception>
        public static string GetRelativePath(string relativeTo, string path) {
            return GetRelativePath(relativeTo, path, StringComparison);
        }

        private static string GetRelativePath(string relativeTo, string path, StringComparison comparisonType) {
            if (string.IsNullOrEmpty(relativeTo)) throw new ArgumentNullException(nameof(relativeTo));
            if (string.IsNullOrEmpty(path)) throw new ArgumentNullException(nameof(path));
            Debug.Assert(comparisonType == StringComparison.Ordinal ||
                         comparisonType == StringComparison.OrdinalIgnoreCase);

            relativeTo = Path.GetFullPath(relativeTo);
            path = Path.GetFullPath(path);

            // Need to check if the roots are different- if they are we need to return the "to" path.
            if (!PathInternalNetCore.AreRootsEqual(relativeTo, path, comparisonType))
                return path;

            int commonLength = PathInternalNetCore.GetCommonPathLength(relativeTo, path,
                ignoreCase: comparisonType == StringComparison.OrdinalIgnoreCase);

            // If there is nothing in common they can't share the same root, return the "to" path as is.
            if (commonLength == 0)
                return path;

            // Trailing separators aren't significant for comparison
            int relativeToLength = relativeTo.Length;
            if (PathInternalNetCore.EndsInDirectorySeparator(relativeTo))
                relativeToLength--;

            bool pathEndsInSeparator = PathInternalNetCore.EndsInDirectorySeparator(path);
            int pathLength = path.Length;
            if (pathEndsInSeparator)
                pathLength--;

            // If we have effectively the same path, return "."
            if (relativeToLength == pathLength && commonLength >= relativeToLength) return ".";

            // We have the same root, we need to calculate the difference now using the
            // common Length and Segment count past the length.
            //
            // Some examples:
            //
            //  C:\Foo C:\Bar L3, S1 -> ..\Bar
            //  C:\Foo C:\Foo\Bar L6, S0 -> Bar
            //  C:\Foo\Bar C:\Bar\Bar L3, S2 -> ..\..\Bar\Bar
            //  C:\Foo\Foo C:\Foo\Bar L7, S1 -> ..\Bar

            StringBuilder
                sb = new StringBuilder(); //StringBuilderCache.Acquire(Math.Max(relativeTo.Length, path.Length));

            // Add parent segments for segments past the common on the "from" path
            if (commonLength < relativeToLength) {
                sb.Append("..");

                for (int i = commonLength + 1; i < relativeToLength; i++) {
                    if (PathInternalNetCore.IsDirectorySeparator(relativeTo[i])) {
                        sb.Append(DirectorySeparatorChar);
                        sb.Append("..");
                    }
                }
            }
            else if (PathInternalNetCore.IsDirectorySeparator(path[commonLength])) {
                // No parent segments and we need to eat the initial separator
                //  (C:\Foo C:\Foo\Bar case)
                commonLength++;
            }

            // Now add the rest of the "to" path, adding back the trailing separator
            int differenceLength = pathLength - commonLength;
            if (pathEndsInSeparator)
                differenceLength++;

            if (differenceLength > 0) {
                if (sb.Length > 0) {
                    sb.Append(DirectorySeparatorChar);
                }

                sb.Append(path, commonLength, differenceLength);
            }

            return sb.ToString(); //StringBuilderCache.GetStringAndRelease(sb);
        }

        // Public static readonly variant of the separators. The Path implementation itself is using
        // internal const variant of the separators for better performance.
        public static readonly char DirectorySeparatorChar = PathInternalNetCore.DirectorySeparatorChar;
        public static readonly char AltDirectorySeparatorChar = PathInternalNetCore.AltDirectorySeparatorChar;
        public static readonly char VolumeSeparatorChar = PathInternalNetCore.VolumeSeparatorChar;
        public static readonly char PathSeparator = PathInternalNetCore.PathSeparator;

        /// <summary>Returns a comparison that can be used to compare file and directory names for equality.</summary>
        internal static StringComparison StringComparison => StringComparison.OrdinalIgnoreCase;
    }

    /// <summary>Contains internal path helpers that are shared between many projects.</summary>
    internal static class PathInternalNetCore {
        internal const char DirectorySeparatorChar = '\\';
        internal const char AltDirectorySeparatorChar = '/';
        internal const char VolumeSeparatorChar = ':';
        internal const char PathSeparator = ';';

        internal const string ExtendedDevicePathPrefix = @"\\?\";
        internal const string UncPathPrefix = @"\\";
        internal const string UncDevicePrefixToInsert = @"?\UNC\";
        internal const string UncExtendedPathPrefix = @"\\?\UNC\";
        internal const string DevicePathPrefix = @"\\.\";

        //internal const int MaxShortPath = 260;

        // \\?\, \\.\, \??\
        internal const int DevicePrefixLength = 4;

        /// <summary>
        /// Returns true if the two paths have the same root
        /// </summary>
        internal static bool AreRootsEqual(string first, string second, StringComparison comparisonType) {
            int firstRootLength = GetRootLength(first);
            int secondRootLength = GetRootLength(second);

            return firstRootLength == secondRootLength
                   && string.Compare(
                       strA: first,
                       indexA: 0,
                       strB: second,
                       indexB: 0,
                       length: firstRootLength,
                       comparisonType: comparisonType) == 0;
        }

        /// <summary>
        /// Gets the length of the root of the path (drive, share, etc.).
        /// </summary>
        internal static int GetRootLength(string path) {
            int i = 0;
            int volumeSeparatorLength = 2; // Length to the colon "C:"
            int uncRootLength = 2; // Length to the start of the server name "\\"

            bool extendedSyntax = path.StartsWith(ExtendedDevicePathPrefix);
            bool extendedUncSyntax = path.StartsWith(UncExtendedPathPrefix);
            if (extendedSyntax) {
                // Shift the position we look for the root from to account for the extended prefix
                if (extendedUncSyntax) {
                    // "\\" -> "\\?\UNC\"
                    uncRootLength = UncExtendedPathPrefix.Length;
                }
                else {
                    // "C:" -> "\\?\C:"
                    volumeSeparatorLength += ExtendedDevicePathPrefix.Length;
                }
            }

            if ((!extendedSyntax || extendedUncSyntax) && path.Length > 0 && IsDirectorySeparator(path[0])) {
                // UNC or simple rooted path (e.g. "\foo", NOT "\\?\C:\foo")

                i = 1; //  Drive rooted (\foo) is one character
                if (extendedUncSyntax || (path.Length > 1 && IsDirectorySeparator(path[1]))) {
                    // UNC (\\?\UNC\ or \\), scan past the next two directory separators at most
                    // (e.g. to \\?\UNC\Server\Share or \\Server\Share\)
                    i = uncRootLength;
                    int n = 2; // Maximum separators to skip
                    while (i < path.Length && (!IsDirectorySeparator(path[i]) || --n > 0)) i++;
                }
            }
            else if (path.Length >= volumeSeparatorLength &&
                     path[volumeSeparatorLength - 1] == PathNetCore.VolumeSeparatorChar) {
                // Path is at least longer than where we expect a colon, and has a colon (\\?\A:, A:)
                // If the colon is followed by a directory separator, move past it
                i = volumeSeparatorLength;
                if (path.Length >= volumeSeparatorLength + 1 && IsDirectorySeparator(path[volumeSeparatorLength])) i++;
            }

            return i;
        }

        /// <summary>
        /// True if the given character is a directory separator.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal static bool IsDirectorySeparator(char c) {
            return c == PathNetCore.DirectorySeparatorChar || c == PathNetCore.AltDirectorySeparatorChar;
        }

        /// <summary>
        /// Get the common path length from the start of the string.
        /// </summary>
        internal static int GetCommonPathLength(string first, string second, bool ignoreCase) {
            int commonChars = EqualStartingCharacterCount(first, second, ignoreCase: ignoreCase);

            // If nothing matches
            if (commonChars == 0)
                return commonChars;

            // Or we're a full string and equal length or match to a separator
            if (commonChars == first.Length
                && (commonChars == second.Length || IsDirectorySeparator(second[commonChars])))
                return commonChars;

            if (commonChars == second.Length && IsDirectorySeparator(first[commonChars]))
                return commonChars;

            // It's possible we matched somewhere in the middle of a segment e.g. C:\Foodie and C:\Foobar.
            while (commonChars > 0 && !IsDirectorySeparator(first[commonChars - 1]))
                commonChars--;

            return commonChars;
        }

        /// <summary>
        /// Gets the count of common characters from the left optionally ignoring case
        /// </summary>
        internal static unsafe int EqualStartingCharacterCount(string first, string second, bool ignoreCase) {
            if (string.IsNullOrEmpty(first) || string.IsNullOrEmpty(second)) return 0;

            int commonChars = 0;

            fixed (char* f = first)
            fixed (char* s = second) {
                char* l = f;
                char* r = s;
                char* leftEnd = l + first.Length;
                char* rightEnd = r + second.Length;

                while (l != leftEnd && r != rightEnd
                                    && (*l == *r || (ignoreCase &&
                                                     char.ToUpperInvariant((*l)) == char.ToUpperInvariant((*r))))) {
                    commonChars++;
                    l++;
                    r++;
                }
            }

            return commonChars;
        }

        /// <summary>
        /// Returns true if the path ends in a directory separator.
        /// </summary>
        internal static bool EndsInDirectorySeparator(string path)
            => path.Length > 0 && IsDirectorySeparator(path[path.Length - 1]);
    }

    /// <summary> Tests for PathNetCore.GetRelativePath </summary>
    public static class GetRelativePathTests {
        [Theory]
        [InlineData(@"C:\", @"C:\", @".")]
        [InlineData(@"C:\a", @"C:\a\", @".")]
        [InlineData(@"C:\A", @"C:\a\", @".")]
        [InlineData(@"C:\a\", @"C:\a", @".")]
        [InlineData(@"C:\", @"C:\b", @"b")]
        [InlineData(@"C:\a", @"C:\b", @"..\b")]
        [InlineData(@"C:\a", @"C:\b\", @"..\b\")]
        [InlineData(@"C:\a\b", @"C:\a", @"..")]
        [InlineData(@"C:\a\b", @"C:\a\", @"..")]
        [InlineData(@"C:\a\b\", @"C:\a", @"..")]
        [InlineData(@"C:\a\b\", @"C:\a\", @"..")]
        [InlineData(@"C:\a\b\c", @"C:\a\b", @"..")]
        [InlineData(@"C:\a\b\c", @"C:\a\b\", @"..")]
        [InlineData(@"C:\a\b\c", @"C:\a", @"..\..")]
        [InlineData(@"C:\a\b\c", @"C:\a\", @"..\..")]
        [InlineData(@"C:\a\b\c\", @"C:\a\b", @"..")]
        [InlineData(@"C:\a\b\c\", @"C:\a\b\", @"..")]
        [InlineData(@"C:\a\b\c\", @"C:\a", @"..\..")]
        [InlineData(@"C:\a\b\c\", @"C:\a\", @"..\..")]
        [InlineData(@"C:\a\", @"C:\b", @"..\b")]
        [InlineData(@"C:\a", @"C:\a\b", @"b")]
        [InlineData(@"C:\a", @"C:\A\b", @"b")]
        [InlineData(@"C:\a", @"C:\b\c", @"..\b\c")]
        [InlineData(@"C:\a\", @"C:\a\b", @"b")]
        [InlineData(@"C:\", @"D:\", @"D:\")]
        [InlineData(@"C:\", @"D:\b", @"D:\b")]
        [InlineData(@"C:\", @"D:\b\", @"D:\b\")]
        [InlineData(@"C:\a", @"D:\b", @"D:\b")]
        [InlineData(@"C:\a\", @"D:\b", @"D:\b")]
        [InlineData(@"C:\ab", @"C:\a", @"..\a")]
        [InlineData(@"C:\a", @"C:\ab", @"..\ab")]
        [InlineData(@"C:\", @"\\LOCALHOST\Share\b", @"\\LOCALHOST\Share\b")]
        [InlineData(@"\\LOCALHOST\Share\a", @"\\LOCALHOST\Share\b", @"..\b")]
        //[PlatformSpecific(TestPlatforms.Windows)]  // Tests Windows-specific paths
        public static void GetRelativePath_Windows(string relativeTo, string path, string expected) {
            string result = PathNetCore.GetRelativePath(relativeTo, path);
            Assert.Equal(expected, result);

            // Check that we get the equivalent path when the result is combined with the sources
            Assert.Equal(
                Path.GetFullPath(path).TrimEnd(Path.DirectorySeparatorChar),
                Path.GetFullPath(Path.Combine(Path.GetFullPath(relativeTo), result))
                    .TrimEnd(Path.DirectorySeparatorChar),
                ignoreCase: true,
                ignoreLineEndingDifferences: false,
                ignoreWhiteSpaceDifferences: false);
        }
    }
}

Estoy usando esto:

public static class StringExtensions
{
  /// <summary>
  /// Creates a relative path from one file or folder to another.
  /// </summary>
  /// <param name="absPath">Absolute path.</param>
  /// <param name="relTo">Directory that defines the start of the relative path.</param> 
  /// <returns>The relative path from the start directory to the end path.</returns>
  public static string MakeRelativePath(this string absPath, string relTo)
  {
      string[] absParts = absPath.Split(Path.DirectorySeparatorChar);
      string[] relParts = relTo.Split(Path.DirectorySeparatorChar);

      // Get the shortest of the two paths
      int len = absParts.Length < relParts.Length
          ? absParts.Length : relParts.Length;

      // Use to determine where in the loop we exited
      int lastCommonRoot = -1;
      int index;

      // Find common root
      for (index = 0; index < len; index++)
      {
          if (absParts[index].Equals(relParts[index], StringComparison.OrdinalIgnoreCase))
              lastCommonRoot = index;
          else 
            break;
      }

      // If we didn't find a common prefix then throw
      if (lastCommonRoot == -1)
          throw new ArgumentException("The path of the two files doesn't have any common base.");

      // Build up the relative path
      var relativePath = new StringBuilder();

      // Add on the ..
      for (index = lastCommonRoot + 1; index < relParts.Length; index++)
      {
        relativePath.Append("..");
        relativePath.Append(Path.DirectorySeparatorChar);
      }

      // Add on the folders
      for (index = lastCommonRoot + 1; index < absParts.Length - 1; index++)
      {
        relativePath.Append(absParts[index]);
        relativePath.Append(Path.DirectorySeparatorChar);
      }
      relativePath.Append(absParts[absParts.Length - 1]);

      return relativePath.ToString();
  }
}

Utilizar:

RelPath = AbsPath.Replace(ApplicationPath, ".")

Si está seguro de que su ruta absoluta 2 siempre es relativa a la ruta absoluta, simplemente elimine los primeros N caracteres de la ruta2, donde N es la longitud de la ruta1.

Desea usar el CommonPathmétodo de esta RelativePathclase. Una vez que tenga la ruta común, simplemente quítela de la ruta que desea mostrar.

Namespace IO.Path

    Public NotInheritable Class RelativePath

        Private Declare Function PathRelativePathTo Lib "shlwapi" Alias "PathRelativePathToA" ( _
            ByVal pszPath As String, _
            ByVal pszFrom As String, _
            ByVal dwAttrFrom As Integer, _
            ByVal pszTo As String, _
            ByVal dwAttrTo As Integer) As Integer

        Private Declare Function PathCanonicalize Lib "shlwapi" Alias "PathCanonicalizeA" ( _
            ByVal pszBuf As String, _
            ByVal pszPath As String) As Integer

        Private Const FILE_ATTRIBUTE_DIRECTORY As Short = &H10S

        Private Const MAX_PATH As Short = 260

        Private _path As String
        Private _isDirectory As Boolean

#Region " Constructors "

        Public Sub New()

        End Sub

        Public Sub New(ByVal path As String)
            _path = path
        End Sub

        Public Sub New(ByVal path As String, ByVal isDirectory As Boolean)
            _path = path
            _isDirectory = isDirectory
        End Sub

#End Region

        Private Shared Function StripNulls(ByVal value As String) As String
            StripNulls = value
            If (InStr(value, vbNullChar) > 0) Then
                StripNulls = Left(value, InStr(value, vbNullChar) - 1)
            End If
        End Function

        Private Shared Function TrimCurrentDirectory(ByVal path As String) As String
            TrimCurrentDirectory = path
            If Len(path) >= 2 And Left(path, 2) = ".\" Then
                TrimCurrentDirectory = Mid(path, 3)
            End If
        End Function

        ''' <summary>
        ''' 3. conforming to general principles: conforming to accepted principles or standard practice
        ''' </summary>
        Public Shared Function Canonicalize(ByVal path As String) As String
            Dim sPath As String

            sPath = New String(Chr(0), MAX_PATH)

            If PathCanonicalize(sPath, path) = 0 Then
                Canonicalize = vbNullString
            Else
                Canonicalize = StripNulls(sPath)
            End If

        End Function

        ''' <summary>
        ''' Returns the most common path between two paths.
        ''' </summary>
        ''' <remarks>
        ''' <para>returns the path that is common between two paths</para>
        ''' <para>c:\FolderA\FolderB\FolderC</para>
        '''   c:\FolderA\FolderD\FolderE\File.Ext
        ''' 
        '''   results in:
        '''       c:\FolderA\
        ''' </remarks>
        Public Shared Function CommonPath(ByVal path1 As String, ByVal path2 As String) As String
            'returns the path that is common between two paths
            '
            '   c:\FolderA\FolderB\FolderC
            '   c:\FolderA\FolderD\FolderE\File.Ext
            '
            '   results in:
            '       c:\FolderA\

            Dim sResult As String = String.Empty
            Dim iPos1, iPos2 As Integer
            path1 = Canonicalize(path1)
            path2 = Canonicalize(path2)
            Do
                If Left(path1, iPos1) = Left(path2, iPos2) Then
                    sResult = Left(path1, iPos1)
                End If
                iPos1 = InStr(iPos1 + 1, path1, "\")
                iPos2 = InStr(iPos2 + 1, path1, "\")
            Loop While Left(path1, iPos1) = Left(path2, iPos2)

            Return sResult

        End Function

        Public Function CommonPath(ByVal path As String) As String
            Return CommonPath(_path, path)
        End Function

        Public Shared Function RelativePathTo(ByVal source As String, ByVal isSourceDirectory As Boolean, ByVal target As String, ByVal isTargetDirectory As Boolean) As String
            'DEVLIB
            '   05/23/05  1:47PM - Fixed call to PathRelativePathTo, iTargetAttribute is now passed to dwAttrTo instead of IsTargetDirectory.
            '       For Visual Basic 6.0, the fix does not change testing results,
            '           because when the Boolean IsTargetDirectory is converted to the Long dwAttrTo it happens to contain FILE_ATTRIBUTE_DIRECTORY,
            '
            Dim sRelativePath As String
            Dim iSourceAttribute, iTargetAttribute As Integer

            sRelativePath = New String(Chr(0), MAX_PATH)
            source = Canonicalize(source)
            target = Canonicalize(target)

            If isSourceDirectory Then
                iSourceAttribute = FILE_ATTRIBUTE_DIRECTORY
            End If

            If isTargetDirectory Then
                iTargetAttribute = FILE_ATTRIBUTE_DIRECTORY
            End If

            If PathRelativePathTo(sRelativePath, source, iSourceAttribute, target, iTargetAttribute) = 0 Then
                RelativePathTo = vbNullString
            Else
                RelativePathTo = TrimCurrentDirectory(StripNulls(sRelativePath))
            End If

        End Function

        Public Function RelativePath(ByVal target As String) As String
            Return RelativePathTo(_path, _isDirectory, target, False)
        End Function

    End Class

End Namespace

Dividiría ambas rutas en el nivel de directorio. A partir de ahí, encuentre el punto de divergencia y vuelva a la carpeta de ensamblaje, anteponiendo un '../' cada vez que pase un directorio.

Sin embargo, tenga en cuenta que una ruta absoluta funciona en todas partes y generalmente es más fácil de leer que una ruta relativa. Yo personalmente no le mostraría a un usuario una ruta relativa a menos que fuera absolutamente necesario.

Si sabe que toPath está contenido en fromPath, puede mantenerlo simple. Dejaré de lado las afirmaciones por brevedad.

public static string MakeRelativePath(string fromPath, string toPath)
{
    // use Path.GetFullPath to canonicalise the paths (deal with multiple directory seperators, etc)
    return Path.GetFullPath(toPath).Substring(Path.GetFullPath(fromPath).Length + 1);
}

La función que usa URI devolvió una ruta "casi" relativa. Incluyó el directorio que contiene directamente el archivo que ruta relativa quería obtener.

Hace algún tiempo escribí una función simple que devuelve la ruta relativa de la carpeta o archivo, e incluso si está en otra unidad, también incluye la letra de la unidad.

Por favor echa un vistazo:

    public static string GetRelativePath(string BasePath, string AbsolutePath)
    {
        char Separator = Path.DirectorySeparatorChar;
        if (string.IsNullOrWhiteSpace(BasePath)) BasePath = Directory.GetCurrentDirectory();
        var ReturnPath = "";
        var CommonPart = "";
        var BasePathFolders = BasePath.Split(Separator);
        var AbsolutePathFolders = AbsolutePath.Split(Separator);
        var i = 0;
        while (i < BasePathFolders.Length & i < AbsolutePathFolders.Length)
        {
            if (BasePathFolders[i].ToLower() == AbsolutePathFolders[i].ToLower())
            {
                CommonPart += BasePathFolders[i] + Separator;
            }
            else
            {
                break;
            }
            i += 1;
        }
        if (CommonPart.Length > 0)
        {
            var parents = BasePath.Substring(CommonPart.Length - 1).Split(Separator);
            foreach (var ParentDir in parents)
            {
                if (!string.IsNullOrEmpty(ParentDir))
                    ReturnPath += ".." + Separator;
            }
        }
        ReturnPath += AbsolutePath.Substring(CommonPart.Length);
        return ReturnPath;
    }

Si tiene un cuadro de texto de solo lectura, ¿no podría no convertirlo en una etiqueta y establecer AutoEllipsis = true?

alternativamente, hay publicaciones con código para generar la autoelipsis usted mismo: (esto lo hace para una cuadrícula, en su lugar, necesitaría pasar el ancho del cuadro de texto. No es del todo correcto, ya que corta un poco más de lo necesario , y no he podido encontrar dónde el cálculo es incorrecto. Sería bastante fácil modificarlo para eliminar la primera parte del directorio en lugar de la última si lo desea.

Private Function AddEllipsisPath(ByVal text As String, ByVal colIndex As Integer, ByVal grid As DataGridView) As String
    'Get the size with the column's width 
    Dim colWidth As Integer = grid.Columns(colIndex).Width

    'Calculate the dimensions of the text with the current font
    Dim textSize As SizeF = MeasureString(text, grid.Font)

    Dim rawText As String = text
    Dim FileNameLen As Integer = text.Length - text.LastIndexOf("\")
    Dim ReplaceWith As String = "\..."

    Do While textSize.Width > colWidth
        ' Trim to make room for the ellipsis
        Dim LastFolder As Integer = rawText.LastIndexOf("\", rawText.Length - FileNameLen - 1)

        If LastFolder < 0 Then
            Exit Do
        End If

        rawText = rawText.Substring(0, LastFolder) + ReplaceWith + rawText.Substring(rawText.Length - FileNameLen)

        If ReplaceWith.Length > 0 Then
            FileNameLen += 4
            ReplaceWith = ""
        End If
        textSize = MeasureString(rawText, grid.Font)
    Loop

    Return rawText
End Function

Private Function MeasureString(ByVal text As String, ByVal fontInfo As Font) As SizeF
    Dim size As SizeF
    Dim emSize As Single = fontInfo.Size
    If emSize = 0 Then emSize = 12

    Dim stringFont As New Font(fontInfo.Name, emSize)

    Dim bmp As New Bitmap(1000, 100)
    Dim g As Graphics = Graphics.FromImage(bmp)

    size = g.MeasureString(text, stringFont)
    g.Dispose()
    Return size
End Function

    public static string ToRelativePath(string filePath, string refPath)
    {
        var pathNormalized = Path.GetFullPath(filePath);

        var refNormalized = Path.GetFullPath(refPath);
        refNormalized = refNormalized.TrimEnd('\\', '/');

        if (!pathNormalized.StartsWith(refNormalized))
            throw new ArgumentException();
        var res = pathNormalized.Substring(refNormalized.Length + 1);
        return res;
    }

Esto debería funcionar:

private string rel(string path) {
  string[] cwd  = new Regex(@"[\\]").Split(Directory.GetCurrentDirectory());
  string[] fp   = new Regex(@"[\\]").Split(path);

  int common = 0;

  for (int n = 0; n < fp.Length; n++) {
    if (n < cwd.Length && n < fp.Length && cwd[n] == fp[n]) {
      common++;
    }
  }

  if (common > 0) {
    List<string> rp = new List<string>();

    for (int n = 0; n < (cwd.Length - common); n++) {
      rp.Add("..");
    }

    for (int n = common; n < fp.Length; n++) {
      rp.Add(fp[n]);
    }

    return String.Join("/", rp.ToArray());
  } else {
    return String.Join("/", fp);
  }
}

Manera con Uri no funcionó en sistemas linux / macOS. La ruta '/ var / www / root' no se puede convertir a Uri. De manera más universal, hazlo todo con las manos.

public static string MakeRelativePath(string fromPath, string toPath, string sep = "/")
{
    var fromParts = fromPath.Split(new[] { '/', '\\'},
        StringSplitOptions.RemoveEmptyEntries);
    var toParts = toPath.Split(new[] { '/', '\\'},
        StringSplitOptions.RemoveEmptyEntries);

    var matchedParts = fromParts
        .Zip(toParts, (x, y) => string.Compare(x, y, true) == 0)
        .TakeWhile(x => x).Count();

    return string.Join("", Enumerable.Range(0, fromParts.Length - matchedParts)
        .Select(x => ".." + sep)) +
            string.Join(sep, toParts.Skip(matchedParts));
}        

PD: uso "/" como valor predeterminado de separador en lugar de Path.DirectorySeparatorChar, porque el resultado de este método se utiliza como uri en mi aplicación.

Aquí está el mío:

public static string RelativePathTo(this System.IO.DirectoryInfo @this, string to)
{
    var rgFrom = @this.FullName.Split(new[] { Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar }, StringSplitOptions.RemoveEmptyEntries);
    var rgTo = to.Split(new[] { Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar }, StringSplitOptions.RemoveEmptyEntries);
    var cSame = rgFrom.TakeWhile((p, i) => i < rgTo.Length && string.Equals(p, rgTo[i])).Count();

    return Path.Combine(
        Enumerable.Range(0, rgFrom.Length - cSame)
        .Select(_ => "..")
        .Concat(rgTo.Skip(cSame))
        .ToArray()
    );
}

Juega con algo como:

private String GetRelativePath(Int32 level, String directory, out String errorMessage) {
        if (level < 0 || level > 5) {
            errorMessage = "Find some more smart input data";
            return String.Empty;
        }
        // ==========================
        while (level != 0) {
            directory = Path.GetDirectoryName(directory);
            level -= 1;
        }
        // ==========================
        errorMessage = String.Empty;
        return directory;
    }

Y probarlo

[Test]
    public void RelativeDirectoryPathTest() {
        var relativePath =
            GetRelativePath(3, AppDomain.CurrentDomain.BaseDirectory, out var errorMessage);
        Console.WriteLine(relativePath);
        if (String.IsNullOrEmpty(errorMessage) == false) {
            Console.WriteLine(errorMessage);
            Assert.Fail("Can not find relative path");
        }
    }

En ASP.NET Core 2, si desea la ruta relativa a bin\Debug\netcoreapp2.2usted, puede usar la siguiente combinación:

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
public class RenderingService : IRenderingService
{

    private readonly IHostingEnvironment _hostingEnvironment;
    public RenderingService(IHostingEnvironment hostingEnvironment)
    {
    _hostingEnvironment = hostingEnvironment;
    }

    public string RelativeAssemblyDirectory()
    {
        var contentRootPath = _hostingEnvironment.ContentRootPath;
        string executingAssemblyDirectoryAbsolutePath = System.IO.Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location);
        string executingAssemblyDirectoryRelativePath = System.IO.Path.GetRelativePath(contentRootPath, executingAssemblyDirectoryAbsolutePath);
        return executingAssemblyDirectoryRelativePath;
    }
}