How to determine correct device orientation in Android N multi-window mode?

Question

From Multi-Window documentation:

Disabled features in multi-window mode

Certain features are disabled or ignored when a device is in multi-window mode, because they don’t make sense for an activity which may be sharing the device screen with other activities or apps. Such features include:

• Some System UI customization options are disabled; for example, apps cannot hide the status bar if they are not running in full-screen mode.
• The system ignores changes to the android:screenOrientation attribute.

I get that for most apps it doesn't make sense to distinct between portrait and landscape modes, however I am working on SDK which contains camera view which user can put on any activity they wish - including activity that supports multi-window mode. The problem is that camera view contains SurfaceView/TextureView which displays the camera preview and in order to display preview correctly in all activity orientations, knowledge about correct activity orientation is required so that camera preview can be correctly rotated.

The problem is that my code which calculates correct activity orientation by examining current configuration orientation (portrait or landscape) and current screen rotation. The problem is that in multi-window mode current configuration orientation does not reflect the real activity orientation. This then results with camera preview being rotated by 90 degrees because Android reports different configuration than orientation.

My current workaround is to check for requested activity orientation and use that as a basis, but there are two problems with that:

1. the requested activity orientation does not have to reflect actual activity orientation (i.e. request may still not be fulfilled)
2. the requested activity orientation can be 'behind', 'sensor', 'user', etc. which does not reveal any information about current activity orientation.
3. According to documentation, screen orientation is actually ignored in multi-window mode, so 1. and 2. just won't work

Is there any way to robustly calculate correct activity orientation even in multi-window configuration?

Here is my code that I currently use (see comments for problematic parts):

protected int calculateHostScreenOrientation() {
    int hostScreenOrientation = ActivityInfo.SCREEN_ORIENTATION_UNSPECIFIED;
    WindowManager wm = (WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE);
    int rotation = getDisplayOrientation(wm);

    boolean activityInPortrait;
    if ( !isInMultiWindowMode() ) {
        activityInPortrait = (mConfigurationOrientation == Configuration.ORIENTATION_PORTRAIT);
    } else {
        // in multi-window mode configuration orientation can be landscape even if activity is actually in portrait and vice versa
        // Try determining from requested orientation (not entirely correct, because the requested orientation does not have to
        // be the same as actual orientation (when they differ, this means that OS will soon rotate activity into requested orientation)
        // Also not correct because, according to https://developer.android.com/guide/topics/ui/multi-window.html#running this orientation
        // is actually ignored.
        int requestedOrientation = getHostActivity().getRequestedOrientation();
        if ( requestedOrientation == ActivityInfo.SCREEN_ORIENTATION_PORTRAIT ||
                requestedOrientation == ActivityInfo.SCREEN_ORIENTATION_REVERSE_PORTRAIT ||
                requestedOrientation == ActivityInfo.SCREEN_ORIENTATION_SENSOR_PORTRAIT ||
                requestedOrientation == ActivityInfo.SCREEN_ORIENTATION_USER_PORTRAIT ) {
            activityInPortrait = true;
        } else if ( requestedOrientation == ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE ||
                requestedOrientation == ActivityInfo.SCREEN_ORIENTATION_REVERSE_LANDSCAPE ||
                requestedOrientation == ActivityInfo.SCREEN_ORIENTATION_SENSOR_LANDSCAPE ||
                requestedOrientation == ActivityInfo.SCREEN_ORIENTATION_USER_LANDSCAPE ) {
            activityInPortrait = false;
        } else {
            // what to do when requested orientation is 'behind', 'sensor', 'user', etc. ?!?
            activityInPortrait = true; // just guess
        }
    }

    if ( activityInPortrait ) {
        Log.d(this, "Activity is in portrait");
        if (rotation == Surface.ROTATION_0) {
            Log.d(this, "Screen orientation is 0");
            hostScreenOrientation = ActivityInfo.SCREEN_ORIENTATION_PORTRAIT;
        } else if (rotation == Surface.ROTATION_180) {
            Log.d(this, "Screen orientation is 180");
            hostScreenOrientation = ActivityInfo.SCREEN_ORIENTATION_REVERSE_PORTRAIT;
        } else if (rotation == Surface.ROTATION_270) {
            Log.d(this, "Screen orientation is 270");
            // natural display rotation is landscape (tablet)
            hostScreenOrientation = ActivityInfo.SCREEN_ORIENTATION_PORTRAIT;
        } else {
            Log.d(this, "Screen orientation is 90");
            // natural display rotation is landscape (tablet)
            hostScreenOrientation = ActivityInfo.SCREEN_ORIENTATION_REVERSE_PORTRAIT;
        }
    } else {
        Log.d(this, "Activity is in landscape");
        if (rotation == Surface.ROTATION_90) {
            Log.d(this, "Screen orientation is 90");
            hostScreenOrientation = ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE;
        } else if (rotation == Surface.ROTATION_270) {
            Log.d(this, "Screen orientation is 270");
            hostScreenOrientation = ActivityInfo.SCREEN_ORIENTATION_REVERSE_LANDSCAPE;
        } else if (rotation == Surface.ROTATION_0) {
            Log.d(this, "Screen orientation is 0");
            // natural display rotation is landscape (tablet)
            hostScreenOrientation = ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE;
        } else {
            Log.d(this, "Screen orientation is 180");
            // natural display rotation is landscape (tablet)
            hostScreenOrientation = ActivityInfo.SCREEN_ORIENTATION_REVERSE_LANDSCAPE;
        }
    }
    return hostScreenOrientation;
}

private int getDisplayOrientation(WindowManager wm) {
    if (DeviceManager.getSdkVersion() < 8) {
        return wm.getDefaultDisplay().getOrientation();
    }

    return wm.getDefaultDisplay().getRotation();
}

private boolean isInMultiWindowMode() {
    return Build.VERSION.SDK_INT >= 24 && getHostActivity().isInMultiWindowMode();
}

protected Activity getHostActivity() {
    Context context = getContext();
    while (context instanceof ContextWrapper) {
        if (context instanceof Activity) {
            return (Activity) context;
        }
        context = ((ContextWrapper) context).getBaseContext();
    }
    return null;
}

EDIT: I've reported this also to Android issue tracker.

Answer 1

I don’t know if this should be considered a solution or just a workaround.

As you say, your problems come with Android N and its multi-window mode. When the app is in multi window, your Activity is not tied to the full display dimensions. This redefines the concept of Activity orientation. Quoting Ian Lake:

Turns out: “portrait” really just means the height is greater than the width and “landscape” means the width is greater than the height. So it certainly makes sense, with that definition in mind, that your app could transition from one to the other while being resized.

So there is no link anymore between Activity orientation changing and device physically being rotated. (I think the only reasonable use of Activity orientation changes now is to update your resources.)

Since you are interested in device dimensions, just get its DisplayMetrics. Quoting docs,

If requested from non-Activity context metrics will report the size of the entire display based on current rotation and with subtracted system decoration areas.

So the solution is:

final Context app = context.getApplicationContext();
WindowManager manager = (WindowManager) app.getSystemService(Context.WINDOW_SERVICE);
Display display = manager.getDefaultDisplay();
DisplayMetrics metrics = new DisplayMetrics();
display.getMetrics(metrics);
int width = metrics.widthPixels;
int height = metrics.heightPixels;
boolean portrait = height >= width;

Width and height values will be swapped (more or less) when the device is tilted.

If this works, I would personally run it every time, deleting the isInMultiWindowMode() branch, because

• it’s not expensive
• our assumptions stand also in the non-multi-window mode
• it will presumably work well with any other future kinds of modes
• you avoid the race condition of isInMultiWindowMode() described by CommonsWare

Answer 2

I thought you could utilise the accelerometer to detect where's "down" - and thus the orientation of the phone. The Engineer Guy explains that that's the way the phone itself does it.

I searched here on SO for a way to do that and found this answer. Basically you need to check which of the 3 accelerometers detect the most significant component of the gravitational pull, which you know is roughly 9.8m/s² near the ground of the earth. Here's the code snippet from it:

private boolean isLandscape;

mSensorManager = (SensorManager)getSystemService(SENSOR_SERVICE);
mSensorManager.registerListener(mSensorListener,     mSensorManager.getDefaultSensor(
                                      Sensor.TYPE_ACCELEROMETER),1000000);
private final SensorEventListener mSensorListener = new SensorEventListener() { 
    @Override 
    public void onSensorChanged(SensorEvent mSensorEvent) {   
        float X_Axis = mSensorEvent.values[0]; 
        float Y_Axis = mSensorEvent.values[1]; 

        if((X_Axis <= 6 && X_Axis >= -6) && Y_Axis > 5){
        isLandscape = false; 
        }
        else if(X_Axis >= 6 || X_Axis <= -6){
        isLandscape = true;
        }

    }

    public void onAccuracyChanged(Sensor sensor, int accuracy) {
    }
};  

Be careful as this code might not work in every situation, as you need to take into account scenarios like being on a stopping/accelerating train or moving the phone fast in a game - here's the orders of magnitude page on wiki to get you started. It looks like you're safe with the values Khalil put in his code (in his answer), but I would take extra caution and research into what values might be generated in the different scenarios.

It's not a flawless idea, but I think as long as the API is built the way it is - whithout allowing you to get their calculated orientation - I think it's a beneficial workaround.