notifications - How do I show text in android system status bar

Question

I'm trying to develop an app for Android Nougat and I want to show some info/text in the status bar generating from a android service routine. So my problem is, I don't know how to show the text in the status bar.

I added a sample image to show what exactly do I mean (red circle). I know it is possible, because I saw it in a battery monitor app from play store.

I already tried NotificationCombat.Builder, but I think this is not the right way. Maybe an overlay is, but after searching I didn't find something.

Can someone show me how to do it or give me a hint, please?

Edit: Here my test code for NotificationCompat.Builder

MainActivity.java

import android.app.Notification;
import android.app.NotificationManager;
import android.os.Bundle;
import android.support.v4.app.NotificationCompat;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;

public class MainActivity extends AppCompatActivity
{
    private final int NOTIFICATION_ID = 10;

    @Override
    protected void onCreate (Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(this);
        mBuilder.setContentTitle("Value");
        mBuilder.setContentText("123");
        mBuilder.setSmallIcon(R.mipmap.ic_launcher);
        mBuilder.setOngoing(true);
        mBuilder.setAutoCancel(false);

        //Intent resultIntent = new Intent(this, MainActivity.class);
        //PendingIntent resultPendingIntent = PendingIntent.getActivity(this, 0, resultIntent, PendingIntent.FLAG_UPDATE_CURRENT);
        //mBuilder.setContentIntent(resultPendingIntent);

        Notification notification = mBuilder.build();
        notification.flags |= Notification.FLAG_NO_CLEAR | Notification.FLAG_ONGOING_EVENT;

        NotificationManager mNotifyMgr = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
        mNotifyMgr.notify(NOTIFICATION_ID, notification);
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".MainActivity">

    <android.support.design.widget.CoordinatorLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <android.support.design.widget.AppBarLayout android:layout_height="wrap_content"
                                                    android:layout_width="match_parent"
                                                    android:theme="@style/AppTheme.AppBarOverlay">

            <android.support.v7.widget.Toolbar android:id="@+id/toolbar"
                                               android:layout_width="match_parent"
                                               android:layout_height="wrap_content"
                                               android:background="#000000"
                                               app:popupTheme="@style/AppTheme.PopupOverlay" />

        </android.support.design.widget.AppBarLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_alignParentLeft="true"
            android:layout_alignParentTop="true"
            android:orientation="vertical"
            app:layout_behavior="@string/appbar_scrolling_view_behavior"
            android:weightSum="100" >

            <TextView
                android:id="@+id/tv_value"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Hello World!"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintLeft_toLeftOf="parent"
                app:layout_constraintRight_toRightOf="parent"
                app:layout_constraintTop_toTopOf="parent"/>

        </LinearLayout>

    </android.support.design.widget.CoordinatorLayout>

</RelativeLayout>

Result:

Answer 1

I do found a solution, the keyword is overlay with a floating window.

int statusBarHeight = 0;
int resourceId = getResources().getIdentifier("status_bar_height", "dimen", "android");
if (resourceId > 0) statusBarHeight = getResources().getDimensionPixelSize(resourceId);

final WindowManager.LayoutParams parameters = new WindowManager.LayoutParams(
        WindowManager.LayoutParams.WRAP_CONTENT,
        statusBarHeight,
        WindowManager.LayoutParams.TYPE_SYSTEM_ERROR,   // Allows the view to be on top of the StatusBar
        WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN,    // Keeps the button presses from going to the background window and Draws over status bar
        PixelFormat.TRANSLUCENT);
parameters.gravity = Gravity.TOP | Gravity.CENTER;

LinearLayout ll = new LinearLayout(this);
ll.setBackgroundColor(Color.TRANSPARENT);
LinearLayout.LayoutParams layoutParameteres = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.MATCH_PARENT);
ll.setLayoutParams(layoutParameteres);

TextView tv = new TextView(this);
ViewGroup.LayoutParams tvParameters = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.MATCH_PARENT);
tv.setLayoutParams(tvParameters);
tv.setTextColor(Color.WHITE);
tv.setGravity(Gravity.CENTER);
tv.setText("123");
ll.addView(tv);

WindowManager windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
windowManager.addView(ll, parameters);