Android开发之点击两次Back键退出App

Back按键的方法是onKeyDown()方法，重写该方法就可以改变back按键的作用。

实现点击两次Back按键退出app，有两种方法：

方法1.

     private static boolean isAppExit=false;  //定义一个变量，标示是否退出
     private static Handler mHandler = new Handler() {
         @Override
         public void handleMessage(Message msg) {
             super.handleMessage(msg);
             isAppExit = false;
         }
     };

     @Override
     public boolean onKeyDown(int keyCode, KeyEvent event) {      //重写onKeyDown()方法
         // TODO Auto-generated method stub
         if (keyCode==KeyEvent.KEYCODE_BACK&&event.getRepeatCount()==0) {
             exit();
             return true;
         }
         return super.onKeyDown(keyCode, event);
     }

     private void exit() {
         if (!isAppExit) {
         isAppExit = true;
         Toast.makeText(getApplicationContext(), "再按一次后退键退出程序",
                 Toast.LENGTH_SHORT).show();
         // 利用handler延迟发送更改状态信息
         mHandler.sendEmptyMessageDelayed(0, 2000);
         } else {
         this.finish();
         }
     }

方法2.

     private long clickTime = 0; //记录第一次点击的时间
     @Override
     public boolean onKeyDown(int keyCode, KeyEvent event) {
         if (keyCode == KeyEvent.KEYCODE_BACK) {
             exit();
             return true;
         }
         return super.onKeyDown(keyCode, event);
     } 

     private void exit() {
         if ((System.currentTimeMillis() - clickTime) > 2000) {
             Toast.makeText(getApplicationContext(), "再按一次后退键退出程序",
                     Toast.LENGTH_SHORT).show();
             clickTime = System.currentTimeMillis();
         } else {
             Log.e(TAG, "exit application");
             this.finish();
         }
     }