双击Back退出应用 android中弹出吐司

第一种方法：

public void onBackPressed() {

		if (isState) { //isState初始值为true
			isState = false;
			Toast.makeText(this, "请双击back退出程序", Toast.LENGTH_SHORT).show();
			new Timer().schedule(new TimerTask() {

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

第二种方法：

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);
        }
    }
}