Android 存储访问框架的使用

介绍

存储访问框架，简称：SAF， 就是系统文件选择器 + 文件操作 API。先选择文件，在用文件操作 API 处理文件。系统文件选择器，就和 Windows 的文件选择框一样。

其实绝大多数 app, 都不会使用这个东西，因为太不方便了。图片，视频，普通文件，需要用户去翻文件夹找，这样的用户体验实在太差了。所以大家都是用第三方的或者自己写一个文件选择器。

之所以讲 SAF，一，是因为 Android11 以后，使用 MediaStore 无法访问到非多媒体文件了，需要依赖 SAF 了。二，外卡和 SD 卡的操作依赖于存储访问框架授权。

打开系统文件选择器与文件过滤

        Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT);
        intent.addCategory(Intent.CATEGORY_OPENABLE);
        intent.setType("application/*");

        startActivityForResult(intent, REQUEST_CODE)

setType 的值是 mime type, 可以是 "image/“, “/“, 其中是通配符。“image/“代码所有类型的图片。“/*“代表所有类型的文件。

当只需要打开几种文件类型时，可以用 Intent.EXTRA_MIME_TYPES。同时 setType 设成“/”。

         Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT);
        intent.addCategory(Intent.CATEGORY_OPENABLE);
        intent.setType("*/*");
        intent.putExtra(Intent.EXTRA_MIME_TYPES, new String[] {
                "application/pdf", // .pdf
                "application/vnd.oasis.opendocument.text", // .odt
                "text/plain" // .txt
        });


        startActivityForResult(intent, REQUEST_CODE)

Intent.ACTION_PICK 和 ACTION_GET_CONTENT，也可以打开文件选择框。ACTION_GET_CONTENT 更加宽泛，除了文件其他类型的内容还可以取。

    Intent intent = new Intent(Intent.ACTION_PICK,  
                    android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
    intent.setType("image/*");

```java
    Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
    intent.setType("image/*");

下面列举了所有的 mime type:

    private static final String[][] MIME_TYPES = new String[][]{
            {"3gp", "video/3gpp"},
            {"apk", "application/vnd.android.package-archive"},
            {"asf", "video/x-ms-asf"},
            {"avi", "video/x-msvideo"},
            {"bin", "application/octet-stream"},
            {"bmp", "image/bmp"},
            {"c", "text/plain"},
            {"class", "application/octet-stream"},
            {"conf", "text/plain"},
            {"cpp", "text/plain"},
            {"doc", "application/msword"},
            {"docx", "application/vnd.openxmlformats-officedocument.wordprocessingml.document"},
            {"xls", "application/vnd.ms-excel"},
            {"xlsx", "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"},
            {"exe", "application/octet-stream"},
            {"gif", "image/gif"},
            {"gtar", "application/x-gtar"},
            {"gz", "application/x-gzip"},
            {"h", "text/plain"},
            {"htm", "text/html"},
            {"html", "text/html"},
            {"jar", "application/java-archive"},
            {"java", "text/plain"},
            {"jpeg", "image/jpeg"},
            {"jpg", "image/jpeg"},
            {"js", "application/x-JavaScript"},
            {"log", "text/plain"},
            {"m3u", "audio/x-mpegurl"},
            {"m4a", "audio/mp4a-latm"},
            {"m4b", "audio/mp4a-latm"},
            {"m4p", "audio/mp4a-latm"},
            {"ape", "audio/ape"},
            {"flac", "audio/flac"},
            {"m4u", "video/vnd.mpegurl"},
            {"m4v", "video/x-m4v"},
            {"mov", "video/quicktime"},
            {"mp2", "audio/x-mpeg"},
            {"mp3", "audio/x-mpeg"},
            {"mp4", "video/mp4"},
            {"mkv", "video/x-matroska"},
            {"flv", "video/x-flv"},
            {"divx", "video/x-divx"},
            {"mpa", "video/mpeg"},
            {"mpc", "application/vnd.mpohun.certificate"},
            {"mpe", "video/mpeg"},
            {"mpeg", "video/mpeg"},
            {"mpg", "video/mpeg"},
            {"mpg4", "video/mp4"},
            {"mpga", "audio/mpeg"},
            {"msg", "application/vnd.ms-outlook"},
            {"ogg", "audio/ogg"},
            {"pdf", "application/pdf"},
            {"png", "image/png"},
            {"pps", "application/vnd.ms-powerpoint"},
            {"ppt", "application/vnd.ms-powerpoint"},
            {"pptx", "application/vnd.openxmlformats-officedocument.presentationml.presentation"},
            {"prop", "text/plain"},
            {"rc", "text/plain"},
            {"rmvb", "audio/x-pn-realaudio"},
            {"rtf", "application/rtf"},
            {"sh", "text/plain"},
            {"tar", "application/x-tar"},
            {"tgz", "application/x-compressed"},
            {"txt", "text/plain"},
            {"wav", "audio/x-wav"},
            {"wma", "audio/x-ms-wma"},
            {"wmv", "audio/x-ms-wmv"},
            {"wps", "application/vnd.ms-works"},
            {"xml", "text/plain"},
            {"z", "application/x-compress"},
            {"zip", "application/x-zip-compressed"},
            {"rar", "application/x-rar"},
            {"", "*/*"}
    };

打开指定文件夹

利用 DocumentsContract.EXTRA_INITIAL_URI，在打开文件选择器的时候，跳转到指定文件夹。只有 android 8 以上才行。

Uri uri = Uri.parse("content://com.android.externalstorage.documents/document/primary:Download");
Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT);
intent.addCategory(Intent.CATEGORY_OPENABLE);
intent.setType("*/*");
intent.putExtra(DocumentsContract.EXTRA_INITIAL_URI, uri);
startActivityForResult(intent, 1);

文件夹权限申请

当需要读取非公共文件夹里面的文件时，可以申请授权，授权后保存 Uri，之后可以拼接这个 Uri 操作文件夹里的所有文件。

尤其是 SD 卡，从 Android 5 开始文件的修改删除必须先授权，且必须通过 SVF 框架接口才能操作。

可以使用 EXTRA_INITIAL_URI，打开指定文件夹，让用户授权

        Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
       Uri uri = Uri.parse("content://com.android.externalstorage.documents/document/primary:Download");

       intent.putExtra(DocumentsContract.EXTRA_INITIAL_URI, uri);

        startActivityForResult(intent) 

需要注意的是，Android 11 以后，无法授权访问存储根目录，以及 Download/，Android/, 这两个文件夹也无法授权。

创建文件夹

创建文件夹有两个情况，一个是在已授权的文件夹下，可以使用 SVF 框架 API。

DocumentsContract.createDocument()

还有一种是在无授权的文件夹下创建，那么可以直接指定类型和名字，通过跳系统选择框创建。

        Intent intent = new Intent(Intent.ACTION_CREATE_DOCUMENT);
        intent.addCategory(Intent.CATEGORY_OPENABLE);
        intent.setType("application/txt");
        intent.putExtra(Intent.EXTRA_TITLE, "testfile.txt");

        startActivityForResult(intent)

存储访问框架 API

存储访问框架 API，都在 DocumentsContract 里面，典型的有：

  public static @Nullable Uri renameDocument(@NonNull ContentResolver content,
            @NonNull Uri documentUri, @NonNull String displayName) throws FileNotFoundException {

    }

    /**
     * Delete the given document.
     *
     * @param documentUri document with {@link Document#FLAG_SUPPORTS_DELETE}
     * @return if the document was deleted successfully.
     */
    public static boolean deleteDocument(@NonNull ContentResolver content, @NonNull Uri documentUri)
            throws FileNotFoundException {

    }

    /**
     * Copies the given document.
     *
     * @param sourceDocumentUri document with {@link Document#FLAG_SUPPORTS_COPY}
     * @param targetParentDocumentUri document which will become a parent of the source
     *         document's copy.
     * @return the copied document, or {@code null} if failed.
     */
    public static @Nullable Uri copyDocument(@NonNull ContentResolver content,
            @NonNull Uri sourceDocumentUri, @NonNull Uri targetParentDocumentUri)
            throws FileNotFoundException {

    }

    /**
     * Moves the given document under a new parent.
     *
     * @param sourceDocumentUri document with {@link Document#FLAG_SUPPORTS_MOVE}
     * @param sourceParentDocumentUri parent document of the document to move.
     * @param targetParentDocumentUri document which will become a new parent of the source
     *         document.
     * @return the moved document, or {@code null} if failed.
     */
    public static @Nullable Uri moveDocument(@NonNull ContentResolver content,
            @NonNull Uri sourceDocumentUri, @NonNull Uri sourceParentDocumentUri,
            @NonNull Uri targetParentDocumentUri) throws FileNotFoundException {

    }

    /**
     * Removes the given document from a parent directory.
     *
     * <p>In contrast to {@link #deleteDocument} it requires specifying the parent.
     * This method is especially useful if the document can be in multiple parents.
     *
     * @param documentUri document with {@link Document#FLAG_SUPPORTS_REMOVE}
     * @param parentDocumentUri parent document of the document to remove.
     * @return true if the document was removed successfully.
     */
    public static boolean removeDocument(@NonNull ContentResolver content, @NonNull Uri documentUri,
            @NonNull Uri parentDocumentUri) throws FileNotFoundException {

    }

获取文件夹文件

使用 DocumentFile 类获取文件夹里文件列表。

    private ActivityResultLauncher<Object> openFile() {
        Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
        Uri uri = Uri.parse("content://com.android.externalstorage.documents/document/primary:AuthSDK");
        intent.putExtra(DocumentsContract.EXTRA_INITIAL_URI, uri);


        return startActivityForResult(intent, new ActivityResultCallback<Intent>() {
            @Override
            public void onActivityResult(Intent result) {

                for (DocumentFile documentFile : DocumentFile.fromTreeUri(BaseApplication.getInstance().getApplicationContext(), Uri.parse(result.getData().toString())).listFiles()) {

                     Log.i("", documentFile.getUri());
                }
            }
        });
    }

下面的代码演示了，使用 SVF 读取文件内容，写内容，通过 MediaStore 查询文件属性。

    private ActivityResultLauncher<Object> openFile() {
        Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
        Uri uri = Uri.parse("content://com.android.externalstorage.documents/document/primary:AuthSDK");
        intent.putExtra(DocumentsContract.EXTRA_INITIAL_URI, uri);


        return startActivityForResult(intent, new ActivityResultCallback<Intent>() {
            @Override
            public void onActivityResult(Intent result) {

                for (DocumentFile documentFile : DocumentFile.fromTreeUri(BaseApplication.getInstance().getApplicationContext(), Uri.parse(result.getData().toString())).listFiles()) {
                    try {
                        InputStream inputStream = BaseApplication.getInstance().getContentResolver().openInputStream(documentFile.getUri());
                        byte[] readData = new byte[1024];
                        inputStream.read(readData);

                        OutputStream outputStream = BaseApplication.getInstance().getContentResolver().openOutputStream(documentFile.getUri());
                        byte[] writeData = "alan gong".getBytes(StandardCharsets.UTF_8);
                        outputStream.write(writeData, 0, 9);
                        outputStream.close();
                        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
                            Uri mediaUri = MediaStore.getMediaUri(BaseApplication.getInstance().getApplicationContext(), documentFile.getUri());
                            long fileId = ContentUris.parseId(mediaUri);
                            Cursor query = BaseApplication.getInstance().getContentResolver().query(documentFile.getUri(), null, MediaStore.MediaColumns._ID + "=" + fileId, null, null);
                            int columnIndex = query.getColumnIndexOrThrow(MediaStore.MediaColumns.MIME_TYPE);
                            String mimeType = query.getString(columnIndex);
                            Log.i("", "");
                        }

                    } catch (FileNotFoundException e) {
                        e.printStackTrace();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        });
    }

使用 MediaStore.getMediaUri(documentUri) 可以转换，MediaStore Uri 和 Document Uri。通过 MediaStore Uri 中的数据库 id，就可以查询文件的所有属性了。

MediaStore Uri：content://media/external_primary/file/101750

Document Uri: content://com.android.externalstorage.documents/tree/primary%3AAuthSDK

另外，

非公共目录下不能用 File API 操作的，即使通过 SVF 授权了，READ_EXTRNAL_PERMISSION 的权限也给了。还是会抛出 FileNotFoundException， 并且显示 permission deny。

和 MediaStore API 的不同

存储访问框架 API 和 MediaStore API 的差异，在于存储访问框架 API，是基于系统文件选择框的，用户选择了文件，那么相当于授权了， 可以访问所有类型的文件。而 MediaStore 的特点是可以查询出所有文件，但是开启分区存储后，只能查处多媒体文件，其他类型文件是不可以的。