Question

我已授予编写外部和可移动存储的权限。但我仍然无法在Android 7上的SD卡上随处写。

Intent intent = storageVolume.createAccessIntent(null);
startActivityForResult(intent, 989);

RxPermissions.getInstance(getActivity())
                .request(Manifest.permission.WRITE_EXTERNAL_STORAGE)
                .subscribe(granted -> {
                    if (!granted) return;
                    showAlternativeDirectoryChooser();//success
                }, throwable -> {
                });

以下是文件夹创建的代码：

DocumentFile documentFile = DocumentFile.fromFile(dir);
DocumentFile test = documentFile.createDirectory("test_folder");

test == null

Answer 1

Android提供您需要在SWAP中使用的Uri。 Uri根本不一定与您尝试访问的路径相关。你不能猜到它。你必须实际使用你给予的Uri。

如果您致电onActivityResult或DocumentFile.fromFile，那么您错了。

Answer 2

您不能使用：

DocumentFile documentFile = DocumentFile.fromFile(dir);

因为它不是SAF有效的Uri。

如果您不想使用ACTION_OPEN_DOCUMENT_TREE或ACTION_OPEN_DOCUMENT来获取Uri ，则可以使用以下方法将FILE转换为Uri（SAF）：从API19（Android4.4-Kitkat）到API28（ Android8-Oreo）。如果您要访问应用程序外部的外部可移动存储，则返回的Uri与返回对话框及其对API 28安全限制（SAF权限）的有效性相同。

    /**
 * Ing.N.Nyerges 2019 V2.0
 *
 * Storage Access Framework(SAF) Uri's creator from File (java.IO),
 * for removable external storages
 *
 * @param context Application Context
 * @param file File path + file name
 * @return Uri[]:
 *   uri[0] = SAF TREE Uri
 *   uri[1] = SAF DOCUMENT Uri
 */
@RequiresApi(api = Build.VERSION_CODES.KITKAT)
public static Uri[] getSafUris (Context context, File file) {

    Uri[] uri = new Uri[2];
    String scheme = "content";
    String authority = "com.android.externalstorage.documents";

    // Separate each element of the File path
    // File format: "/storage/XXXX-XXXX/sub-folder1/sub-folder2..../filename"
    // (XXXX-XXXX is external removable number
    String[] ele = file.getPath().split(File.separator);
    //  ele[0] = not used (empty)
    //  ele[1] = not used (storage name)
    //  ele[2] = storage number
    //  ele[3 to (n-1)] = folders
    //  ele[n] = file name

    // Construct folders strings using SAF format
    StringBuilder folders = new StringBuilder();
    if (ele.length > 4) {
        folders.append(ele[3]);
        for (int i = 4; i < ele.length - 1; ++i) folders.append("%2F").append(ele[i]);
    }

    String common = ele[2] + "%3A" + folders.toString();

    // Construct TREE Uri
    Uri.Builder builder = new Uri.Builder();
    builder.scheme(scheme);
    builder.authority(authority);
    builder.encodedPath("/tree/" + common);
    uri[0] = builder.build();

    // Construct DOCUMENT Uri
    builder = new Uri.Builder();
    builder.scheme(scheme);
    builder.authority(authority);
    if (ele.length > 4) common = common + "%2F";
    builder.encodedPath("/document/" + common + file.getName());
    uri[1] = builder.build();

    return uri;
}

然后，您可以使用以下方式调用权限：

    context.grantUriPermission(context.getPackageName(), uri, Intent
            .FLAG_GRANT_READ_URI_PERMISSION | Intent
            .FLAG_GRANT_WRITE_URI_PERMISSION);
    context.getContentResolver().takePersistableUriPermission(uri, Intent
            .FLAG_GRANT_READ_URI_PERMISSION | Intent
            .FLAG_GRANT_WRITE_URI_PERMISSION);

无法在Android 7上使用DocumentFile.createDirectory（）创建目录

2 个答案: