Android: Unable to add window. Permission denied for this window type

if you use apiLevel >= 19, don't use

WindowManager.LayoutParams.type = WindowManager.LayoutParams.TYPE_SYSTEM_ALERT 

which gets the following error:

android.view.WindowManager$BadTokenException: Unable to add window android.view.ViewRootImpl$W@40ec8528 -- permission denied for this window type

Use this instead:

LayoutParams.TYPE_TOAST or TYPE_APPLICATION_PANEL

I tried my best to try all the examples available for this issue. Finally I got the answer for this I don know how much is it reliable but my app is not crashing now.

windowManager = (WindowManager)getSystemService(WINDOW_SERVICE);
    //here is all the science of params
    final LayoutParams myParams = new LayoutParams(
            WindowManager.LayoutParams.WRAP_CONTENT,
            WindowManager.LayoutParams.WRAP_CONTENT,
            LayoutParams.TYPE_SYSTEM_ERROR,
            WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED
                    | WindowManager.LayoutParams.FLAG_TURN_SCREEN_ON
                    | WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON,
            PixelFormat.TRANSLUCENT
    );

In your manifest file just give the permission

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

Addition to this you can also check for the API level if its >=23 then

 if(Build.VERSION.SDK_INT >= 23) {
    if (!Settings.canDrawOverlays(Activity.this)) {
        Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION,
                Uri.parse("package:" + getPackageName()));
        startActivityForResult(intent, 1234);
    }
}
            else
{
    Intent intent = new Intent(Activity.this, Service.class);
    startService(intent);
}

I hope it helps someone somewhere. Full example https://anam-android-codes.blogspot.in/?m=1

I guess you should differentiate the target (before and after Oreo)

int LAYOUT_FLAG;
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
    LAYOUT_FLAG = WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY;
} else {
    LAYOUT_FLAG = WindowManager.LayoutParams.TYPE_PHONE;
}

params = new WindowManager.LayoutParams(
    WindowManager.LayoutParams.WRAP_CONTENT,
    WindowManager.LayoutParams.WRAP_CONTENT,
    LAYOUT_FLAG,
    WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE | WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
    PixelFormat.TRANSLUCENT);

For what should be completely obvious reasons, ordinary Apps are not allowed to create arbitrary windows on top of the lock screen. What do you think I could do if I created a window on your lockscreen that could perfectly imitate the real lockscreen so you couldn't tell the difference?

The technical reason for your error is the use of the TYPE_KEYGUARD_DIALOG flag - it requires android.permission.INTERNAL_SYSTEM_WINDOW which is a signature-level permission. This means that only Apps signed with the same certificate as the creator of the permission can use it.

The creator of android.permission.INTERNAL_SYSTEM_WINDOW is the Android system itself, so unless your App is part of the OS, you don't stand a chance.

There are well defined and well documented ways of notifying the user of information from the lockscreen. You can create customised notifications which show on the lockscreen and the user can interact with them.