輕按兩下Back退出應用 android中彈出吐司

第一種方法：      

public void onBackPressed() {      

if (isState) { //isState初始值為true
      isState = false;
      Toast.makeText(this, "請輕按兩下back退出程式", Toast.LENGTH_SHORT).show();
      new Timer().schedule(new TimerTask() {

        @Override
        public void run() {
          // TODO Auto-generated method stub
          isState = true;
        }
      }, 2000);
    } else {
      finish();
    }
  }      

第二種方法：

public class MainActivity extends Activity {


    private Toast toast;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        toast = Toast.makeText(getApplicationContext(), "确定退出？", 0);

    }
    public void onBackPressed() {
        quitToast();
    }
    /*
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        System.out.println(keyCode + "...." + event.getKeyCode());
        if(keyCode == KeyEvent.KEYCODE_BACK){
            quitToast();
        }
        return super.onKeyDown(keyCode, event);
    }
    */
    private void quitToast() {
        if(null == toast.getView().getParent()){
            toast.show();
        }else{
            System.exit(0);
        }
    }
}
public class MainActivity extends Activity {


    private Toast toast;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        toast = Toast.makeText(getApplicationContext(), "确定退出？", 0);

    }
    public void onBackPressed() {
        quitToast();
    }
    /*
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        System.out.println(keyCode + "...." + event.getKeyCode());
        if(keyCode == KeyEvent.KEYCODE_BACK){
            quitToast();
        }
        return super.onKeyDown(keyCode, event);
    }
    */
    private void quitToast() {
        if(null == toast.getView().getParent()){
            toast.show();
        }else{
            System.exit(0);
        }
    }
}