/** 
 * 退出 
 */ 
@Override 
public boolean dispatchKeyEvent(KeyEvent event) { 
  if (event.getKeyCode() == KeyEvent.KEYCODE_BACK 
      && event.getAction() == KeyEvent.ACTION_DOWN 
      && event.getRepeatCount() == 0) {       
    //具体的操作代码 
  } 
  return super.dispatchKeyEvent(event); 
} 

@Override 
public void onBackPressed() { 
  super.onBackPressed(); 
} 

/** 
 * Called when the activity has detected the user's press of the back 
 * key. The default implementation simply finishes the current activity, 
 * but you can override this to do whatever you want. 
 */ 
public void onBackPressed() { 
  finish(); 
}