Android:当Fragments视图准备好时，如何通知Activity? [英] Android: how to notify Activity when Fragments views are ready?

问题描述

我在一个活动中使用Google Maps API V2，该活动具有下拉导航，其中地图位于第二位置.

I'm using Google Maps API V2 in an activity wih drop down navigation where the map is on the second position.

我正在按实际的方式添加地图:

I'm adding the map pragmatically like:

mMapFragment = supportMapFragment.newInstance();
getSupportFragmentManager()
        .beginTransaction()
        .replace(R.id.placeHolder, mMapFragment, TAG_MAP)
        .commit(); 

我想获得GoogleMap ovject，作为文档 https://developers.google .com/maps/documentation/android/map 表示应使用mMapFragment.getMap()完成，但返回null.

I want to get the GoogleMap ovject, as the documentation https://developers.google.com/maps/documentation/android/map say it should be done with mMapFragment.getMap(), but it returns null.

根据 http://developer.android. com/reference/com/google/android/gms/maps/SupportMapFragment.html 如果Fragment尚未经历onCreateView生命周期事件，则返回null.

according to http://developer.android.com/reference/com/google/android/gms/maps/SupportMapFragment.html it returns null if the Fragment hasn't gone through the onCreateView lifecycle event.

我怎么知道片段准备好了?

how can I know whenever the fragment is ready ?

我发现此重写onActivityCreated似乎是一个解决方案，但是随后我将不得不通过构造函数而不是newInstance()实例化片段，这有什么区别吗?

Overriding onActivityCreated seems like a solution, but then I'll have to instantiate the fragment through a constructor and not with newInstance(), does it make any difference ?

推荐答案

我的首选方法是使用回调从Fragment获取信号.此外，这是Android在与活动进行通信中建议的推荐方法.

My preferred method is to use a callback to get a signal from a Fragment. Also, this is the recommended method proposed by Android at Communicating with the Activity

例如，在您的Fragment中，添加一个接口并进行注册.

For your example, in your Fragment, add an interface and register it.

public static interface OnCompleteListener {
    public abstract void onComplete();
}

private OnCompleteListener mListener;

public void onAttach(Context context) {
    super.onAttach(context);
    try {
        this.mListener = (OnCompleteListener)context;
    }
    catch (final ClassCastException e) {
        throw new ClassCastException(context.toString() + " must implement OnCompleteListener");
    }
}

现在在Activity

public class MyActivity extends FragmentActivity implements MyFragment.OnCompleteListener {
    //...

    public void onComplete() {
        // After the fragment completes, it calls this callback.
        // setup the rest of your layout now
        mMapFragment.getMap()
    }
}

现在，无论您的Fragment中的任何内容表示已加载，请通知您的Activity它已准备就绪.

Now, whatever in your Fragment signifies that it's loaded, notify your Activity that it's ready.

@Override
protected void onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    // create your fragment
    //...

    // signal that you're done and tell the Actvity to call getMap()
    mListener.onComplete();
}

编辑2017-12-05 onAttach(活动活动)为

EDIT 2017-12-05 onAttach(Activity activity) is deprecated, use onAttach(Context context) instead. Code above adjusted.

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