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);

Answer 2

You can find your answer in the doc, here: https://developer.android.com/reference/android/support/v4/app/NotificationCompat.html

Edit:: Well, the answer is in the doc. However, after a good bit of research and digging, it seems as though the consensus amongst the community is that this is not possible for just any application. Only specific icons can be placed on the right side of the status bar (i.e. Clock, Weather, System info, etc...).

I'm sorry there isn't a more exciting answer, but at least you can stop stressing out about why you can't figure it out.

Edit 2:: Apparently, pre-lollipop devices had access to private apis that allowed you to work with system icons (again, think about the alarm icon). Afterward, the apis were removed. This stackoverflow post goes over the whole situation pretty extensively.

Edit 3:: If you can live with placing you icon on the left side of the status bar you can convert text to bitmap like this:

 TextView textView = new TextView(activity.getContext());
 textView.setText("Hello World");
 textView.setDrawingCacheEnabled(true);
 textView.destroyDrawingCache();
 textView.buildDrawingCache();
 Bitmap bitmap = getTransparentBitmapCopy(textView.getDrawingCache());
 private Bitmap getTransparentBitmapCopy(Bitmap source) { 
    int width = source.getWidth(); 
    int height = source.getHeight(); 
    Bitmap copy = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
    int[] pixels = new int[width * height];
    source.getPixels(pixels, 0, width, 0, 0, width, height);
    copy.setPixels(pixels, 0, width, 0, 0, width, height);
    return copy;
 }