xamarin.android之 Android 4.4+ 获取图片真实路径

Android 4.4以下 选择图片是可以获取到图片路径的.高于Android 4.4获取图片路径只是获取到一个图片编号. 所以需要针对Android版本进行路径解析：

        #region 高于 v4.4 版本 解析真实路径

        public static String GetPath(Context context,Android.Net.Uri uri)
        {

            bool isKitKat = Build.VERSION.SdkInt >= BuildVersionCodes.Kitkat;

            // DocumentProvider  
            if (isKitKat && DocumentsContract.IsDocumentUri(context, uri))
            {
                // ExternalStorageProvider  
                if (isExternalStorageDocument(uri))
                {
                    String docId = DocumentsContract.GetDocumentId(uri);
                    String[] split = docId.Split(':');
                    String type = split[0];

                    if ("primary".Equals(type.ToLower()))
                    {
                        return Android.OS.Environment.ExternalStorageDirectory + "/" + split[1];
                    }

                    // TODO handle non-primary volumes  
                }
                // DownloadsProvider  
                else if (isDownloadsDocument(uri))
                {

                    String id = DocumentsContract.GetDocumentId(uri);
                    Android.Net.Uri contentUri = ContentUris.WithAppendedId(
                            Android.Net.Uri.Parse("content://downloads/public_downloads"),long.Parse(id));

                    return getDataColumn(context, contentUri, null, null);
                }
                // MediaProvider  
                else if (isMediaDocument(uri))
                {
                    String docId = DocumentsContract.GetDocumentId(uri);
                    String[] split = docId.Split(':');
                    String type = split[0];

                    Android.Net.Uri contentUri = null;
                    if ("image".Equals(type))
                    {
                        contentUri = MediaStore.Images.Media.ExternalContentUri;
                    }
                    else if ("video".Equals(type))
                    {
                        contentUri = MediaStore.Video.Media.ExternalContentUri;
                    }
                    else if ("audio".Equals(type))
                    {
                        contentUri = MediaStore.Audio.Media.ExternalContentUri;
                    }

                    String selection = "_id=?";
                    String[] selectionArgs = new String[] {
                    split[1]
            };

                    return getDataColumn(context, contentUri, selection, selectionArgs);
                }
            }
            // MediaStore (and general)  
            else if ("content".Equals(uri.Scheme.ToLower()))
            {

                // Return the remote address  
                if (isGooglePhotosUri(uri))
                    return uri.LastPathSegment;

                return getDataColumn(context, uri, null, null);
            }
            // File  
            else if ("file".Equals(uri.Scheme.ToLower()))
            {
                return uri.Path;
            }

            return null;
        }

        /** 
         * Get the value of the data column for this Uri. This is useful for 
         * MediaStore Uris, and other file-based ContentProviders. 
         * 
         * @param context The context. 
         * @param uri The Uri to query. 
         * @param selection (Optional) Filter used in the query. 
         * @param selectionArgs (Optional) Selection arguments used in the query. 
         * @return The value of the _data column, which is typically a file path. 
         */
        public static String getDataColumn(Context context,Android.Net.Uri uri, String selection,
                String[] selectionArgs)
        {

            ICursor cursor = null;
            String column = "_data";
            String[] projection = {
                column
            };

            try
            {
                cursor = context.ContentResolver.Query(uri, projection, selection, selectionArgs,
                        null);
                if (cursor != null && cursor.MoveToFirst())
                {
                    int index = cursor.GetColumnIndexOrThrow(column);
                    return cursor.GetString(index);
                }
            }
            finally
            {
                if (cursor != null)
                    cursor.Close();
            }
            return null;
        }


        /** 
         * @param uri The Uri to check. 
         * @return Whether the Uri authority is ExternalStorageProvider. 
         */
        public static bool isExternalStorageDocument(Android.Net.Uri uri)
        {
            return "com.android.externalstorage.documents".Equals(uri.Authority);
        }

        /** 
         * @param uri The Uri to check. 
         * @return Whether the Uri authority is DownloadsProvider. 
         */
        public static bool isDownloadsDocument(Android.Net.Uri uri)
        {
            return "com.android.providers.downloads.documents".Equals(uri.Authority);
        }

        /** 
         * @param uri The Uri to check. 
         * @return Whether the Uri authority is MediaProvider. 
         */
        public static bool isMediaDocument(Android.Net.Uri uri)
        {
            return "com.android.providers.media.documents".Equals(uri.Authority);
        }

        /** 
         * @param uri The Uri to check. 
         * @return Whether the Uri authority is Google Photos. 
         */
        public static bool isGooglePhotosUri(Android.Net.Uri uri)
        {
            return "com.google.android.apps.photos.content".Equals(uri.Authority);
        }

        #endregion