Question

我目前正在开发一款具有多个CountDownTimer的Android应用。在一天的特定时间段内，只会激活其中一个CountDownTimer（例如，在上午9点到上午10点，对象myCountDownTimer [0]将被激活并从上午9点到上午10点倒计时，但在上午10点到11点，myCountDownTimer [0 ]将被停用，myCountDownTimer [1]将工作并倒计时直到上午11点）。但现在我遇到了一个问题。为了在myCountDownTimer [0]完成倒计时之后激活myCountDownTimer [1]，我必须在MyCountDownTimer类之外调用myCountDownTimer [1]的构造函数。我试图在MyCountDownTimer类的onFinish（）方法中初始化对象myCountDownTimer [1]，但我的应用程序一直在崩溃。在做了一些研究之后，我想我必须使用回调来在不同的类之间进行通信。我尝试通过在线阅读和观看教程来理解回调方法，但我失败了。我还是很困惑。你能看一下我的代码并告诉我如何在我的代码中实现回调吗？非常感谢你，祝你有个美好的一天。

public class MainActivity extends Activity{
//...

private final int TIMER_SUM = 10;
MyCountDownTimer [] myCountDownTimer;
private int timerIndex;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    myCountDownTimer = new MyCountDownTimer[TIMER_SUM];
    timerIndex = 0;
    myCountDownTimer[timerIndex] = new MyCountDownTimer(getRemainingTime(), 100);
    myCountDownTimer[timerIndex].start();
}

private long getRemainingTime()
{
    //The method that returns the remaining milliseconds until next specified time.
}

private class MyCountDownTimer extends CountDownTimer
{   
    public MyCountDownTimer(long millisInFuture,
            long countDownInterval) {
        super(millisInFuture, countDownInterval);

        timerIndex++;
    }

    @Override
    public void onTick(long millisUntilFinished) {

        //This method display the remaining time.

    }

    @Override
    public void onFinish() {
        this.cancel();

        //I want to add a callback here to tell the MainActivity to create a new MyCountDownTimer object.
    }

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

}

如何在我的代码中使用回调？ --- Android应用程序开发

0 个答案: