Get rid of unnecessary root layouts for fullscreen activities

Question

How to get rid of unnecessary root layouts for fullscreen activities?

I have a simple fullscreen activity. The layout inspector shows a large hierarchy of root layouts provided by Android, that I don't need in fullscreen.

Can I get rid of them?

• If YES, how?
• If NO, why not?

The testing setup

Open Android Studio. Create a new project. Accept the default settings. Choose "Empty Activity". You get this manifest:

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

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

You get this layout/activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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"
    tools:context="com.blcknx.myapplication.MainActivity">

    <TextView
        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" />

</android.support.constraint.ConstraintLayout>

Call Tools > Android > Layout Inspector to see the generated root templates.

To make it fullscreen, just add an id HelloWorld to the TextView in the layout and update MainActivity.java:

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView layout = findViewById(R.id.HelloWorld);
        layout.setSystemUiVisibility(
                View.SYSTEM_UI_FLAG_LOW_PROFILE
                        | View.SYSTEM_UI_FLAG_FULLSCREEN
                        | View.SYSTEM_UI_FLAG_LAYOUT_STABLE
                        | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY
                        | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
                        | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
        );
    }
}

The flags are hiding the navigation, but they don't remove the unused layouts.

Your answer

Use a simple TextView. Show it fullscreen. Check by Tools > Android > Layout Inspector how far you removed the root layouts. Show a screenshot. Show your code.

Answer 1

You can get rid of action_bar_container having changed your activity's theme from DarkActionBar to NoActionBar:

<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
    ...
</style>

Then you'll get following tree:

If you want to go even more and get rid of ContentFrameLayout, than you can do this:

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        val contentView = findViewById(android.R.id.content)
        val parent = contentView.parent as ViewGroup
        parent.removeView(contentView)
        LayoutInflater.from(this).inflate(R.layout.activity_main, parent)
    }

This will be the view hierarchy tree:

Not sure whether you should remove android.R.id.content view, maybe some libraries are assuming that there should exist such a view.

As to action_mode_bar_stubs: you should not be concerned about them, as long as those are ViewStubs, which do not affect overall performance, because they are lazily inflated into view hierarchy.

Answer 2

Activity Code

import android.app.Activity;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.view.Window;
import android.view.WindowManager;

public class ThirdActivity extends Activity {

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {

    requestWindowFeature(Window.FEATURE_NO_TITLE);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN);

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_third);
}
}

R.layout.third_activity

<?xml version="1.0" encoding="utf-8"?>
 <TextView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
tools:context=".ThirdActivity"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="Hello World"
android:gravity="center">
 </TextView>

styles.xml

<style name="AppTheme2" parent="@android:style/Theme"/>

AndroidManifest.xml

<activity android:name=".ThirdActivity" android:theme="@style/AppTheme2">

Please don't mind the indentation.

Thanks,

Answer 3

Yes, you are probably looking for ConstraintLayout. It's similar to a RelativeLayout, but with more possibilities and easier to use. Because you can position views everywhere in the ConstraintLayout you can get rid of all those unnecessary layouts, thus flatten the hierarchy.