Question

I have a simple program which is able to change the background color after clicking a button, but it does not work

public class ChangeBackgroundActivity extends Activity {
/** Called when the activity is first created. */
    Button blueButton;
    LinearLayout myLO;
    @Override
   public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        myLO=(LinearLayout)findViewById(R.layout.main);
        blueButton=(Button)findViewById(R.id.button1);
        blueButton.setOnClickListener(new OnClickListener() {

            public void onClick(View arg0) {
            // TODO Auto-generated method stub
            myLO.setBackgroundColor(0x0000FF); //blue color code #0000FF    
        }
    });
    }
}

Answer 1

Try With this,

main.xml

   <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/myLayout"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" >

        <Button
            android:id="@+id/button1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentLeft="true"
            android:layout_alignParentTop="true"
            android:layout_marginLeft="64dp"
            android:layout_marginTop="71dp"
            android:text="changeColor" />

    </LinearLayout>

ChangeBackgroundActivity.java

public class ChangeBackgroundActivity extends Activity {
/** Called when the activity is first created. */
    Button blueButton;
    LinearLayout myLO;
    @Override
   public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        myLO=(LinearLayout)findViewById(R.id.myLayout);
        blueButton=(Button)findViewById(R.id.button1);
        blueButton.setOnClickListener(new OnClickListener() {

            public void onClick(View arg0) {
            // TODO Auto-generated method stub
            myLO.setBackgroundColor(Color.BLUE);

        }
    });
    }
}