1.點選back 鍵後，彈出對話方塊

@Override
 public boolean onKeyDown(int keyCode, KeyEvent event) {
  if(keyCode==KeyEvent.KEYCODE_BACK){
   final AlertDialog exit=new AlertDialog.Builder(this).create();
   exit.setTitle("系統提示");
  OnClickListener listener=new OnClickListener() {   
   @Override
   public void onClick(DialogInterface dialog, int which) {
    switch(which){
    case AlertDialog.BUTTON1: 
     finish();
     break;
    case AlertDialog.BUTTON2:  
     exit.cancel();       
     break;
    default:
           break;
    }
   }
  };
  exit.setButton("確定", listener);
  exit.setButton2("取消", listener);
  exit.show();
  }
  return super.onKeyDown(keyCode, event);
 }
 

2.如果是想要點選返回鍵，點選兩次才返回時，為了防止意外點選情況

@Override
 public boolean onKeyDown(int keyCode, KeyEvent event) {
  // TODO Auto-generated method stub
  if(keyCode==event.KEYCODE_BACK){
   if(System.currentTimeMillis()-time>2000){
    time=System.currentTimeMillis();
   }else{
    finish();
   }
   return true;
  }
  return super.onKeyDown(keyCode, event);
 }
 

3. 當用戶點選自定義的退出按鈕或返回鍵時，在onDestroy()裡強制退出應用，或直接殺死程序

@Override
 public boolean onKeyDown(int keyCode, KeyEvent event) {
  // TODO Auto-generated method stub
   if(keyCode==event.KEYCODE_BACK){
    new AlertDialog.Builder(this).
    setIcon(R.drawable.aa4)
    .setTitle(R.string.add_user)
    .setMessage(R.string.action_settings)
    .setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() { 
                 @Override 
                 public void onClick(DialogInterface dialog, int which) { 
                 } 
             })
    .setPositiveButton(R.string.address, new DialogInterface.OnClickListener() { 
      public void onClick(DialogInterface dialog, int whichButton) {
     finish();
      }
     }
    ).show();
              return true;
   }
  return super.onKeyDown(keyCode, event);
 }
  
  @Override
 protected void onDestroy() {
  // TODO Auto-generated method stub
  android.os.Process.killProcess(android.os.Process.myPid());
  super.onDestroy();
 }
 

public boolean onKeyDown(int keyCode, android.view.KeyEvent event) {
		if(keyCode==KeyEvent.KEYCODE_BACK){
			return true;
		}else{
			return  super.onKeyDown(keyCode, event);
		}
}