Android 返回键返回上一级Activity

实现功能: 有两个Activity，一个为MainMenu，一个为PictureScribble，MainMenu进入PictureScribble后，在PictureScribble中单击返回键返回MainMenus.

public boolean OnKeyDown(int keyCode,KeyEvent event){    
        if (keyCode==KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {    
            Intent myIntent; 
            myIntent = new Intent(PictureScribble.this, MainMenu.class); 
            startActivity(myIntent); 
            this.finish();    
        }       
        return false;    
     }