Write to external storage on Android 7

问题

I want to write to the external storage in my Android app, but I don't seem to get the permissions right. The App runs on Android 7, so I request the permissions on runtime like this:

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
permission = ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE);

if (permission != PackageManager.PERMISSION_GRANTED) {
    // We don't have permission so prompt the user
    int ACCESS_EXTERNAL_STORAGE_STATE = 1;
    ActivityCompat.requestPermissions(this,
            new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
            ACCESS_EXTERNAL_STORAGE_STATE);
}

permission = ActivityCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE);

if (permission != PackageManager.PERMISSION_GRANTED) {
    // We don't have permission so prompt the user
    int ACCESS_EXTERNAL_STORAGE_STATE = 1;
    ActivityCompat.requestPermissions(this,
            new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
            ACCESS_EXTERNAL_STORAGE_STATE);
}
...
    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        switch (requestCode)
        {
            case 1: {
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED)
                {
                    //reload my activity with permission granted or use the features what required the permission
                } else
                {
                    Toast.makeText(this, "The app was not allowed to write to your storage. Hence, it cannot function properly. Please consider granting it this permission", Toast.LENGTH_LONG).show();
                }
            }
        }
    }

One observation I made is that onRequestPermissionsResult seems to return that the permission was not granted, but I was also never prompted when starting the app to permit writing to external storage.

I set these permissions in the Manifest:

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

The code to write to the storage is here:

public static void appendByteBuffer(byte[] data)
{
    String filename = Environment.getExternalStorageDirectory().getAbsolutePath()+"/test.raw";
    //filename value is "/storage/emulated/0/test.raw"
    File rawAudioFile = new File(filename);
    if (!rawAudioFile.exists())
    {
        try
        {
            rawAudioFile.createNewFile();
        }
        catch (IOException e)
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    try (FileOutputStream output = new FileOutputStream(filename, true)) {
        output.write(data);
    } catch (IOException e) {}
}

03-16 14:50:49.988 19145-19306/? W/System.err: java.io.IOException: Permission denied 03-16 14:50:49.988 19145-19306/? W/System.err:
at java.io.UnixFileSystem.createFileExclusively0(Native Method) 03-16 14:50:49.988 19145-19306/? W/System.err: at java.io.UnixFileSystem.createFileExclusively(UnixFileSystem.java:280) 03-16 14:50:49.989 19145-19306/? W/System.err: at java.io.File.createNewFile(File.java:948) 03-16 14:50:49.989 19145-19306/? W/System.err: at com.meeter.study.AppUtils.appendByteBuffer(AppUtils.java:76) 03-16 14:50:49.989 19145-19306/? W/System.err: at

回答1:

Use ContextCompat instead of ActivityCompat for checkSelfPermission:

Replace:

permission = ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE);
permission = ActivityCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE);

With:

permission = ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE);
permission = ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE);

Then, Add onRequestPermissionsResult method to handle ALLOW, DENY selection. Hope this helps.

@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        switch (requestCode) {
            case ACCESS_EXTERNAL_STORAGE_STATE: {
                // If request is cancelled, the result arrays are empty.
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                   // Write to the storage (ex: call appendByteBuffer(byte[] data) here)

                } else {
                    Toast.makeText(getApplicationContext(), "Please grant permission.", Toast.LENGTH_LONG).show();
                }
                break;
            }
}

来源：https://stackoverflow.com/questions/42842648/write-to-external-storage-on-android-7