java - Android 存储 - 即使设置了权限，也无法读取应用程序目录之外的目录文件

Question

尝试获取外部存储目录下的文件列表会导致没有文件，即使它们存在并且已设置读取该目录的权限。

给出以下示例:

MainActivity.java

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        File ed = Environment.getExternalStorageDirectory();

        File[] fs = ed.listFiles();
        Log.i(ed.getAbsolutePath(), (fs != null ? fs.length : "no") + " files found");

    }
}

AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.test">

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

app/build.gradle

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.3"

    defaultConfig {
        applicationId "com.test"
        minSdkVersion 11
        targetSdkVersion 23
...

在物理设备(Nexus 5，Android 6.0.1)上测试，这是 logcat:

06-15 11:42:17.309 16732-16732/com.test I//storage/emulated/0: no files found

没有其他警告或错误。

通过adb shell工具我可以看到以下子目录及其权限

$ cd /storage/emulated/
$ ls -l 
drwxrwx--x root     sdcard_rw          1970-03-05 14:05 Alarms
drwxrwx--x root     sdcard_rw          2015-09-10 23:44 Android
drwxrwx--x root     sdcard_rw          2015-08-11 18:40 BDArenaConnector
drwxrwx--x root     sdcard_rw          2015-02-03 14:14 DCIM
drwxrwx--x root     sdcard_rw          2016-06-14 10:59 Download
drwxrwx--x root     sdcard_rw          2015-09-15 11:48 MOGO_AUDIANCE
drwxrwx--x root     sdcard_rw          2015-06-19 11:49 Manga Mobile
drwxrwx--x root     sdcard_rw          2015-10-19 21:02 Memes
drwxrwx--x root     sdcard_rw          1970-03-05 14:05 Movies
drwxrwx--x root     sdcard_rw          2016-05-24 11:01 Music
drwxrwx--x root     sdcard_rw          2015-01-12 20:43 Notifications
drwxrwx--x root     sdcard_rw          2015-11-24 19:19 PerfectViewer
drwxrwx--x root     sdcard_rw          2016-06-01 16:58 Pictures
drwxrwx--x root     sdcard_rw          1970-03-05 14:05 Podcasts
drwxrwx--x root     sdcard_rw          2015-04-30 10:16 ROMs
drwxrwx--x root     sdcard_rw          2015-01-12 20:36 Ringtones
drwxrwx--x root     sdcard_rw          2015-08-10 18:57 SKMaps
drwxrwx--x root     sdcard_rw          2015-09-15 11:48 ShareSDK
drwxrwx--x root     sdcard_rw          2015-08-16 10:40 Telegram
drwxrwx--x root     sdcard_rw          2015-05-29 21:36 TuneIn Radio
drwxrwx--x root     sdcard_rw          2016-05-27 00:08 WhatsApp
drwxrwx--x root     sdcard_rw          2015-05-20 09:21 airdroid
drwxrwx--x root     sdcard_rw          2016-05-31 16:59 backups
drwxrwx--x root     sdcard_rw          2015-11-10 14:42 bluetooth
drwxrwx--x root     sdcard_rw          2015-11-15 19:43 com.facebook.katana
drwxrwx--x root     sdcard_rw          2015-08-10 18:44 > com.facebook.orca
drwxrwx--x root     sdcard_rw          2015-09-15 11:51 ktplay
drwxrwx--x root     sdcard_rw          2015-04-23 20:30 media
drwxrwx--x root     sdcard_rw          1970-03-05 14:04 obb
drwxrwx--x root     sdcard_rw          2015-02-07 19:11 panoramas
drwxrwx--x root     sdcard_rw          2015-06-19 11:53 smart-tools
drwxrwx--x root     sdcard_rw          2015-09-28 12:56 wp

我知道这个目录应该可供应用程序读取，因为其他一些应用程序可以毫无问题地执行此操作(例如 Astro 文件管理器或 PerfectViewer)。

Answer 1

再次针对 6.0 进行编译时需要运行时权限

    public class MainActivity extends AppCompatActivity {

        private static final int REQUEST_RUNTIME_PERMISSION = 1;

        @Override
        protected void onCreate(Bundle savedInstanceState) {

            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);

             checkPremission();
            }


         void checkPremission() {
                //select which permission you want
                final String permission = Manifest.permission.WRITE_EXTERNAL_STORAGE;
                    // if in fragment use getActivity()
                if (ContextCompat.checkSelfPermission(ActivityName.this, permission)
                        != PackageManager.PERMISSION_GRANTED) {
                    if (ActivityCompat.shouldShowRequestPermissionRationale(ActivityName.this, permission)) {

                    } else {
                        ActivityCompat.requestPermissions(ActivityName.this, new String[]{permission}, REQUEST_CAMERA_PERMISSION);
                    }
                } else {
                    // you have permission go ahead
                    File ed = Environment.getExternalStorageDirectory();
                    File[] fs = ed.listFiles();
                    Log.i(ed.getAbsolutePath(), (fs != null ? fs.length : "no") + " files found");
                }
            }

            @Override
            public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
                switch (requestCode) {
                    case REQUEST_RUNTIME_PERMISSION:
                        final int numOfRequest = grantResults.length;
                        final boolean isGranted = numOfRequest == 1
                                && PackageManager.PERMISSION_GRANTED == grantResults[numOfRequest - 1];
                        if (isGranted) {
                            // you have permission go ahead
                           File ed = Environment.getExternalStorageDirectory();

                           File[] fs = ed.listFiles();
                           Log.i(ed.getAbsolutePath(), (fs != null ? fs.length : "no") + " files found");
                        }else{
                            // you dont have permission show toast
                        }
                        break;
                    default:
                        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
                }
            }
}