片段被销毁后停止处理程序

Question

我有一个Fragment，它设置一个ListView 并创建一个Handler 以定期更新Listview。但是，看起来Handler 在Fragment 被销毁后仍在运行。

以下是代码。

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    //boilerplate code

    final Handler handler = new Handler();
    handler.post(new Runnable() {
        @Override
        public void run() {
            assignAdapter();
            handler.postDelayed(this, 15000);
        }
    });

    return v;
}

在Fragment 销毁后更新ListView 会导致应用程序崩溃。当Fragment 被破坏时，如何使Handler 停止？我也想知道如果应用暂停对Handler 有什么影响。

Answer 1

你需要像这样实现处理程序

private Handler myHandler;
private Runnable myRunnable = new Runnable() {
    @Override
    public void run() {
        //Do Something
    }
};

@Override
public void onDestroy () {

    mHandler.removeCallbacks(myRunnable);
    super.onDestroy ();

}

Answer 2

您需要在片段中存储对您的处理程序和可运行的引用，然后当片段被销毁时，您需要从可运行的处理程序中删除回调。

private Handler mHandler;
private Runnable mRunnable;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    //boilerplate code

    mRunnable = new Runnable() {
        @Override
        public void run() {
            assignAdapter();
            handler.postDelayed(this, 15000);
        }
    };

    mHandler = new Handler(mRunnable);
    mHandler.post();

    return v;
}

@Override
public void onDestroy() {
    mHandler.removeCallbacks(mRunnable);
    super.onDestroy();
}

Answer 3

另一种停止处理程序的方法是使用WeakReference 到片段：

static final class UpdateUIRunnable implements Runnable {

        final WeakReference<RouteGuideFragment> weakRefToParent;
        final Handler handler;

        public UpdateUIRunnable(RouteGuideFragment fragment, Handler handler) {
            weakRefToParent = new WeakReference<RouteGuideFragment>(fragment);
            this.handler = handler;
        }

        public void scheduleNextRun() {
            handler.postDelayed(this, INTERVAL_TO_REDRAW_UI);
        }

        @Override
        public void run() {
            RouteGuideFragment fragment = weakRefToParent.get();

            if (fragment == null || fragment.hasBeenDestroyed()) {
                Log.d("UIUpdateRunnable", "Killing updater -> fragment has been destroyed.");
                return;
            }

            if (fragment.adapter != null) {
                try {
                    fragment.adapter.forceUpdate();
                } finally {
                    // schedule again
                    this.scheduleNextRun();
                }
            }
        }
    }

其中fragment.hasBeenDestroyed() 只是片段的mDestroyed 属性的getter：

@Override
public void onDestroy() {
    super.onDestroy();
    mDestroyed = true;
}

Answer 4

有人发布了另一个类似的问题，问题是由于ChildFragmentManager 中的错误引起的。基本上，当ChildFragmentManager 与Activity 分离时，它的内部状态会中断。看看original answer here

Answer 5

使用Rxjava，更好

subscription = Observable.timer(1000, TimeUnit.MILLISECONDS)
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(aLong -> whatToDo());

private void whatToDo() {
   System.out.println("Called after 1 second");
}

然后在ondestroy()方法调用

RxUtils.unsubscribe(subscription);