How to Set Background Color of an Activity to White Programmatically

How to set background color of an Activity to white programmatically?

Get a handle to the root layout used, then set the background color on that. The root layout is whatever you called setContentView with.

 setContentView(R.layout.main);

  // Now get a handle to any View contained 
  // within the main layout you are using
  View someView = findViewById(R.id.randomViewInMainLayout);

  // Find the root view
  View root = someView.getRootView();

  // Set the color
  root.setBackgroundColor(getResources().getColor(android.R.color.red));

Changing background color in a activity.

In your styles.xml set the android:windowBackground attribute for whatever theme you are using for application or activity. You can find the theme you are using in your AndroidManifest.xml.

<resources xmlns:tools="http://schemas.android.com/tools">

   <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.NoActionBar">
        <!-- Customize your theme here. -->
        <item name="android:windowBackground">@color/somecolor</item>
    </style>

</resources>

Note: If you have views in your layout that aren't transparent, it will block you from seeing the color you set here.

Android: Changing Background-Color of the Activity (Main View)

Try creating a method in your Activity something like...

public void setActivityBackgroundColor(int color) {
    View view = this.getWindow().getDecorView();
    view.setBackgroundColor(color);
}

Then call it from your OnClickListener passing in whatever colour you want.

How to change background color in android app

You need to use the android:background property , eg

android:background="@color/white"

Also you need to add a value for white in the strings.xml

<color name="white">#FFFFFF</color>

Edit : 18th Nov 2012

The first two letters of an 8 letter color code provide the alpha value, if you are using the html 6 letter color notation the color is opaque.

Eg :

Android Studio, Change the color of the background by pressing a switch button

Ok, did find on an Indian video.
the short solution, add activity main XML the line of code with //JUST THIS

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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"
    android:id="@+id/rView" // JUST THIS
    tools:context=".MainActivity">

and in the mainactivity.java

final Switch BackgroundColorButton = (Switch) findViewById(R.id.BackgroundColorButton);
            BackgroundColorButton.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    if(BackgroundColorButton.isChecked())
                    {
                        BackgroundColorButton.setText("White Mode");
                        screenView.setBackgroundColor(Color.BLACK);//JUST THIS

                    }
                    else
                    {
                        BackgroundColorButton.setText("Dark Mode");
                        screenView.setBackgroundColor(Color.WHITE);//JUST THIS
                    }
                }
            });

Trying to change main activity background color on button click

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

    Button btn = (Button) findViewById(R.id.newgame_button);

    btn.setOnClickListener(new View.OnClickListener() 
    {
        @Override
        public void onClick(View v) {
            changeBackground(v);
        }
    }); 
}

Change this to

   Activity activity;
@Override
protected void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main_menu);
    actvity = this;
    Button btn = (Button) findViewById(R.id.newgame_button);

    btn.setOnClickListener(new View.OnClickListener() 
    {
        @Override
        public void onClick(View v) {

           actvity.findViewById(android.R.id.content).setBackgroundColor(Color.BLACK);
        }
    }); 
}

Change background color of the screen

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    int id = item.getItemId();

    if (id == R.id.colourred) {
        //toolBar.setBackgroundColor(Color.RED);
        getWindow().getDecorView().setBackgroundColor(Color.RED);
        getWindow().getDecorView().setBackgroundColor(Color.parseColor("#FFCC33"));
        //or like below with color code
        //toolBar.setBackgroundColor(Color.parseColor("#FFCC33"));
        return true;
    }else if(id==R.id.color_green){
        getWindow().getDecorView().setBackgroundColor(Color.parseColor("#green_color_code"));
    }else if(id==R.id.other_id){
        getWindow().getDecorView().setBackgroundColor(Color.parseColor("#other_color_code"));
    }
}

And if you wish to change activity background color then visit this How to set background color of Activity to white programmatically?

getWindow().getDecorView().setBackgroundColor(Color.WHITE);//change activity bg color

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