在android棉花糖上获得realPath返回null？

Question

我使用这个函数从URI获得的图像路径：

private static String getRealPathFromURI(Context context, Uri contentUri) { 
     Cursor cursor = null; 
     try { 
      String[] proj = {MediaStore.Images.Media.DATA}; 
      cursor = context.getContentResolver().query(contentUri, proj, null, null, null); 
      int column_index = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA); 
      cursor.moveToFirst(); 
      return cursor.getString(column_index); 
     } finally { 
      if (cursor != null) { 
       cursor.close(); 
      } 
     } 
    } 

上述功能正常工作与< 23版本。但它与android棉花糖返回null？

I am using emulator nexus 4 with android 6.0 x86_64 

模拟器具有存储权限。

可能是什么问题？

Answer 1

/** 
* Get a file path from a Uri. This will get the the path for Storage Access 
* Framework Documents, as well as the _data field for the MediaStore and 
* other file-based ContentProviders. 
* 
* @param context The context. 
* @param uri The Uri to query. 
* @author paulburke 
*/ 
public static String getPath(final Context context, final Uri uri) { 

    final boolean isKitKat = Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT; 

    // DocumentProvider 
    if (isKitKat && DocumentsContract.isDocumentUri(context, uri)) { 
     // ExternalStorageProvider 
     if (isExternalStorageDocument(uri)) { 
      final String docId = DocumentsContract.getDocumentId(uri); 
      final String[] split = docId.split(":"); 
      final String type = split[0]; 

      if ("primary".equalsIgnoreCase(type)) { 
       return Environment.getExternalStorageDirectory() + "/" + split[1]; 
      } 

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

      final String id = DocumentsContract.getDocumentId(uri); 
      final Uri contentUri = ContentUris.withAppendedId(
        Uri.parse("content://downloads/public_downloads"), Long.valueOf(id)); 

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

      Uri contentUri = null; 
      if ("image".equals(type)) { 
       contentUri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI; 
      } else if ("video".equals(type)) { 
       contentUri = MediaStore.Video.Media.EXTERNAL_CONTENT_URI; 
      } else if ("audio".equals(type)) { 
       contentUri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI; 
      } 

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

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

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

     return getDataColumn(context, uri, null, null); 
    } 
    // File 
    else if ("file".equalsIgnoreCase(uri.getScheme())) { 
     return uri.getPath(); 
    } 

    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, Uri uri, String selection, 
     String[] selectionArgs) { 

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

    try { 
     cursor = context.getContentResolver().query(uri, projection, selection, selectionArgs, 
       null); 
     if (cursor != null && cursor.moveToFirst()) { 
      final 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 boolean isExternalStorageDocument(Uri uri) { 
    return "com.android.externalstorage.documents".equals(uri.getAuthority()); 
} 

/** 
* @param uri The Uri to check. 
* @return Whether the Uri authority is DownloadsProvider. 
*/ 
public static boolean isDownloadsDocument(Uri uri) { 
    return "com.android.providers.downloads.documents".equals(uri.getAuthority()); 
} 

/** 
* @param uri The Uri to check. 
* @return Whether the Uri authority is MediaProvider. 
*/ 
public static boolean isMediaDocument(Uri uri) { 
    return "com.android.providers.media.documents".equals(uri.getAuthority()); 
} 

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

从here从这个answer拍摄。这是一个丑陋的黑客，不能保证在所有设备上都能正常工作，但根据我的经验，它可以在99％的设备上运行。根据CommonsWare，你不应该假设你通过ContentResolver获得的流可以转换为文件。相反，您应该使用context.getContentResolver().openInputStream(fileUri)方法从该Uri打开inputstream。请参阅他的commonsBlog post了解更多信息，以及如何处理Uris