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获取图片

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Uri格式有下面三种：

  1. file:////storage/emulated/0/123/绑定手环/绑定手环_其他用户绑定.png
  2. content://media/external/images/media/75342
  3. content://com.android.providers.media.documents/document/image:75342

Uri处理

InputStream is = getActivity().getContentResolver().openInputStream(uri);

上面代码可以打开1和2格式的Uri,3格式的Uri打开会抛异常：

java.lang.SecurityException: Permission Denial: reading com.android.providers.media.MediaDocumentsProvider uri content://com.android.providers.media.documents/document/image:75343 from pid=24763, uid=10209 requires android.permission.MANAGE_DOCUMENTS, or grantUriPermission()

Uri获取 

if (Build.VERSION.SDK_INT < SystemInfo.ANDROID_VERSION_CODE.KITKAT){
             intent = new Intent();
             intent.setAction(Intent.ACTION_GET_CONTENT);
             intent.setType("image/*");
             getActivity().startActivityForResult(intent, REQ_PHOTO);
         } else {
             intent = new Intent(Intent.ACTION_OPEN_DOCUMENT);
             intent.addCategory(Intent.CATEGORY_OPENABLE);
             intent.setType("image/*");
             getActivity().startActivityForResult(intent, REQ_PHOTO_KITKAT);
         }

Intent.ACTION_GET_CONTENT 4.4以前选择图片:

  • file:////storage/emulated/0/123/绑定手环/绑定手环_其他用户绑定.png
  • content://media/external/images/media/75342

Intent.ACTION_GET_CONTENT 4.4以后选择相册中图片：

  • file:////storage/emulated/0/123/绑定手环/绑定手环_其他用户绑定.png
  • content://media/external/images/media/75342

Intent.ACTION_GET_CONTENT 4.4以后选择最近中图片，或者文件管理器中图片：

  • content://com.android.providers.media.documents/document/image:75342

Intent.ACTION_OPEN_DOCUMENT 4.4以后以这种方式选择图片都返回：

  • content://com.android.providers.media.documents/document/image:75342

4.4以前Android会打开注册了监听Intent.ACTION_GET_CONTENT的App,但4.4以后Android会打开一个documentsui 的内置程序，根据其中选择图片的位置不同，返回不同格式的Uri。

即4.4以前使用Intent.ACTION_GET_CONTENT选择图片方式和返回是固定的：

  • file:////storage/emulated/0/123/绑定手环/绑定手环_其他用户绑定.png
  • content://media/external/images/media/75342

但4.4以后使用Intent.ACTION_GET_CONTENT选择图片时，会根据选择的位置（最近，相册和文件管理器等）返回不同格式的Uri。

所以4.4以后使用Intent.ACTION_OPEN_DOUCMENT来选择图片返回固定格式的Uri。

Storage access framework中的Uri使用

@TargetApi(Build.VERSION_CODES.KITKAT)
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());
}

官方解析方法见：http://developer.android.com/intl/zh-cn/guide/topics/providers/document-provider.html

参考资料：http://stackoverflow.com/questions/19834842/android-gallery-on-kitkat-returns-different-uri-for-intent-action-get-content#

4.4中新增特性：Storage Access Framework
作用目的：The SAF makes it simple for users to browse and open documents, images, and other files across all of their their preferred document storage providers. A standard, easy-to-use UI lets users browse files and access recents in a consistent way across apps and providers

让用户通过一个storage providers访问所有资源，并且提供一个统一的UI浏览访问图片，文件等。

什么是时候返回的Uri是Provider中提供的？什么时候是直接“file:////绝对路径”的格式？

Uri和URI是两个不同的东西：
URI格式：http://username:password@host:8080/directory/file?query#fragment