Android - 更改视图背景图像onclick

我正在尝试更改视图的背景图片onclick，这是代码：

Hi,
I am trying to change the background image of a view onclick, here is the code:

public class ScreenChanger extends Activity{
	
	private ImageButton imagebutton;
	private ImageButton imagebuttonRED;
	private ImageButton imagebuttonBLUE;
	private ImageButton imagebuttonYELW;
	private ImageButton imagebuttonGRN;
	private View layout;
	
	
	@Override
	public void onCreate(Bundle savedInstanceState) {
	    super.onCreate(savedInstanceState);
	    setContentView(R.layout.screenview);
	    imagebutton = (ImageButton) findViewById(R.id.imageButton1);
	    
	    imagebuttonRED = (ImageButton) findViewById(R.id.ImageButton04);
	    imagebuttonBLUE = (ImageButton) findViewById(R.id.ImageButton02);
	    imagebuttonYELW = (ImageButton) findViewById(R.id.ImageButton03);
	    imagebuttonGRN = (ImageButton) findViewById(R.id.ImageButton01);
	    
	    layout = (View) findViewById(R.layout.screenview);
	
	    imagebutton.setOnClickListener(new OnClickListener() {

	        public void onClick(View v) {
	            setContentView(R.layout.main);
	            Intent myIntent = new Intent(ScreenChanger.this, FlashLightActivity.class);
	            ScreenChanger.this.startActivity(myIntent);
	        }
	    });
	
	    imagebuttonRED.setOnClickListener(new OnClickListener() {

	        public void onClick(View v) {
	        	setContentView(layout);
	            layout.setBackgroundColor(drawable.red);
	        }
	    });
	    imagebuttonBLUE.setOnClickListener(new OnClickListener() {

	        public void onClick(View v) {
	        	setContentView(layout);
	            layout.setBackgroundColor(drawable.blue);
	        }
	    });
	    imagebuttonYELW.setOnClickListener(new OnClickListener() {

	        public void onClick(View v) {
	        	setContentView(layout);
	            layout.setBackgroundColor(drawable.yellow);
	        }
	    });
	    imagebuttonGRN.setOnClickListener(new OnClickListener() {

	        public void onClick(View v) {
	        	setContentView(layout);
	            layout.setBackgroundColor(drawable.green);
	        }
	    });
	    
}
}

我遇到的问题是当我点击按钮关闭我的按钮时app

The problem i have is when i click the button it closes my app