Android: Overlay TextView on LockScreen

Question

Im trying to overlay a TextView on top of the LockScreen (Similar to how Android Overlays the time).

Note: I dont want to by-pass the lockscreen, but just draw

Answer 1

Starting with Android Lollipop (5.0), support for lockscreen widgets has been removed (see the very bottom). Instead, you should be using Notifications, which can now appear on the lockscreen.

Answer 2

Since you want to display things out of your app activity, you can use a Service and WindowManager for that, the same way how Facebook Messenger and other floating windows apps works ;)

LockScreenTextService.class

import android.app.Service;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.graphics.PixelFormat;
import android.os.IBinder;
import android.support.v4.content.ContextCompat;
import android.view.Gravity;
import android.view.WindowManager;
import android.widget.TextView;

/**
 * Created on 2/20/2016.
 */
public class LockScreenTextService extends Service {

    private BroadcastReceiver mReceiver;
    private boolean isShowing = false;

    @Override
    public IBinder onBind(Intent intent) {
        // TODO Auto-generated method stub
        return null;
    }

    private WindowManager windowManager;
    private TextView textview;
    WindowManager.LayoutParams params;

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

        windowManager = (WindowManager)getSystemService(WINDOW_SERVICE);

        //add textview and its properties
        textview = new TextView(this);
        textview.setText("Hello There!");
        textview.setTextColor(ContextCompat.getColor(this, android.R.color.white));
        textview.setTextSize(32f);

        //set parameters for the textview
        params = new WindowManager.LayoutParams(
                WindowManager.LayoutParams.WRAP_CONTENT,
                WindowManager.LayoutParams.WRAP_CONTENT,
                WindowManager.LayoutParams.TYPE_SYSTEM_OVERLAY,
                WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
                        | WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL
                        | WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED
                        | WindowManager.LayoutParams.FLAG_WATCH_OUTSIDE_TOUCH,
                PixelFormat.TRANSLUCENT);
        params.gravity = Gravity.BOTTOM;

        //Register receiver for determining screen off and if user is present
        mReceiver = new LockScreenStateReceiver();
        IntentFilter filter = new IntentFilter(Intent.ACTION_SCREEN_OFF);
        filter.addAction(Intent.ACTION_USER_PRESENT);

        registerReceiver(mReceiver, filter);
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        return START_STICKY;
    }

    public class LockScreenStateReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(Context context, Intent intent) {
            if (intent.getAction().equals(Intent.ACTION_SCREEN_OFF)) {
                //if screen is turn off show the textview
                if (!isShowing) {
                    windowManager.addView(textview, params);
                    isShowing = true;
                }
            }

            else if(intent.getAction().equals(Intent.ACTION_USER_PRESENT)) {
                //Handle resuming events if user is present/screen is unlocked remove the textview immediately
                if (isShowing) {
                    windowManager.removeViewImmediate(textview);
                    isShowing = false;
                }
            }
        }
    }

    @Override
    public void onDestroy() {
        //unregister receiver when the service is destroy
        if (mReceiver != null) {
            unregisterReceiver(mReceiver);
        }

        //remove view if it is showing and the service is destroy
        if (isShowing) {
            windowManager.removeViewImmediate(textview);
            isShowing = false;
        }
        super.onDestroy();
    }

}

and add the necessary permission on AndroidManifest.xml and add the service

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.textonlockscreenusingservice">

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

    <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"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

        <service android:name=".LockScreenTextService" /> //this

    </application>

</manifest>

Don't forget to start the service on onCreate() of your activity

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    Intent intent = new Intent(this, LockScreenTextService.class);
    startService(intent);

}

TextView showing on lockscreen

TextView removed when unlocked