[On Top Of Other Application] #tags:Android

ChatHeadService.java

public class ChatHeadService extends Service {

  private WindowManager windowManager;
  private ImageView chatHead;

  @Override public IBinder onBind(Intent intent) {
    // Not used
    return null;
  }

  @Override public void onCreate() {
    super.onCreate();

    windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);

    chatHead = new ImageView(this);
    chatHead.setImageResource(R.drawable.android_head);

    WindowManager.LayoutParams params = new WindowManager.LayoutParams(
        WindowManager.LayoutParams.WRAP_CONTENT,
        WindowManager.LayoutParams.WRAP_CONTENT,
        WindowManager.LayoutParams.TYPE_PHONE,
        WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
        PixelFormat.TRANSLUCENT);

    params.gravity = Gravity.TOP | Gravity.LEFT;
    params.x = 0;
    params.y = 100;

    windowManager.addView(chatHead, params);
  }

  @Override
  public void onDestroy() {
    super.onDestroy();
    if (chatHead != null) windowManager.removeView(chatHead);
  }
}

SYSTEM_ALERT_WINDOW.java

> It is a new behaviour introduced in Marshmallow 6.0.1
> Every app that requests the SYSTEM_ALERT_WINDOW permission and that is installed through the Play Store (version 6.0.5 or higher is required), will have granted the permission automatically.
> If instead the app is sideloaded, the permission is not automatically granted.

 
 Screen-overlay-detected-blocks-android-permissions
 ======================================================\
This popup is caused by the manifest.PERMISSION.SYSTEM_ALERT_WINDOW permission declared by the manifest. The are 3 categories of permissions, that developer must be aware of.:

A. Normal permission - do nothing with them, just declare in the Manifest
B. Vulnerable permissions - declare in Manifest and ask for permission at first time. They can be changed through system settings
C. Above dangerous permissions: SYSTEM_ALERT_WINDOW and WRITE_SETTINGS belong to this category. They must be granted, but are not visible in system settings. To request for it you don't use a standard way (int checkSelfPermission (String permission)) but you have to check Settings.canDrawOverlays() or Settings.System.canWrite() appropriately
  
 
You will need <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />
   
public class MainActivity extends AppCompatActivity {

    public final static int REQUEST_CODE = 10101;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        if (checkDrawOverlayPermission()) {
            startService(new Intent(this, PowerButtonService.class));
        }
    }

    public boolean checkDrawOverlayPermission() {
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) {
            return true;
        }
        if (!Settings.canDrawOverlays(this)) {
            Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION,
                Uri.parse("package:" + getPackageName()));
            startActivityForResult(intent, REQUEST_CODE);
            return false;
        } else {
            return true;
        }
    }

    @Override
    @TargetApi(Build.VERSION_CODES.M)
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == REQUEST_CODE) {
            if (Settings.canDrawOverlays(this)) {
                startService(new Intent(this, PowerButtonService.class));
            }
        }
    }
}