Goto your res folder as shown in image below add a background image.

After adding a background image, goto the main.xml and add the below text:

<ImageView
android:layout_height=”wrap_content”
android:layout_width=”wrap_content”
android:src=”@drawable/background” />

Note: Do not add the extn to the image name, it wont recognize the file and give an error.

Next goto your main class and add the following:

super(context);
// Set the background
this.setBackgroundDrawable(this.getResources().getDrawable(R.drawable.background));

Another way to do this would be:

Resources res = getResources();
Drawable drawable = res.getDrawable(R.drawable.background);