Android 廣播接收器在 ViewPager 中使用時注冊多個偵聽器

Question

我有一個 ViewPager，它使用 Fragments 構建一個選項卡式視圖。 在片段中，我正在為該片段數據集注冊一個廣播接收器（數據從 RESTApi 更新。）

有 4 個選項卡，但每次用戶將選項卡帶入視圖時，它似乎都在注冊一個新的偵聽器，這不是很好。

我在 OnViewCreated() 方法中注冊它

它應該在 create() 中嗎？

我的片段 Class

public class DynamicFragment extends Fragment {

private static final String ARG_SECTION_NUMBER = "section_number";
private static final String ARG_TITLE = "title";
//.......
//.......

private Context context;
RecyclerView cardRecyclerView;
View view;
PresentationAdapter presentationAdapter;

public DynamicFragment() {
    // Required empty public constructor
    SyncApplication.getContext().registerReceiver(mReceiver, new IntentFilter(Sync.BROADCAST_FILTER));
}

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    this.context = context;

}

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    sectionNumber = getArguments() != null ? getArguments().getInt(ARG_SECTION_NUMBER) : 1;
    title = getArguments() != null ? getArguments().getString(ARG_TITLE) : "Search";
}

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

    if (title.equals("Search")){
        Search search = new Search(inflater, container, savedInstanceState);
        return search.setView();
    }
    else{
        view = inflater.inflate(R.layout.fragment_dynamic, container, false);
        cardRecyclerView = view.findViewById(R.id.presentation_cards_recycler);
        presentationAdapter = new PresentationAdapter(context, getPresentationListByCategory());
        cardRecyclerView.setLayoutManager(new GridLayoutManager(context, 2));
        cardRecyclerView.setItemAnimator(new DefaultItemAnimator());
        cardRecyclerView.setAdapter(presentationAdapter);

        // Inflate the layout for this fragment
    }
    return view;
}

public void updateCardView() {
    if (presentationList != null && presentationList.size() > 0) {
        if (presentationAdapter != null) {
            presentationAdapter.setPresentationList(getPresentationListByCategory());
            presentationAdapter.notifyDataSetChanged();
        }
    }
}

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    if (context != null) {
        context.registerReceiver(mReceiver, new IntentFilter(Sync.BROADCAST_FILTER));
    }
}

public ArrayList<Presentation> getPresentationListByCategory() {
    dbManager = new DbManager(context);
    presentationList = dbManager.getAllPresentations();
    ArrayList<Presentation> presentationsByCategory = new ArrayList();

    for (Presentation presentation : presentationList) {
        if (presentation.getCategory_name().equals(title)) {
            presentationsByCategory.add(presentation);
        }
    }
    return presentationsByCategory;
}

public static DynamicFragment newInstance(String val) {
    DynamicFragment fragment = new DynamicFragment();
    Bundle args = new Bundle();
    args.putString("title", val);
    fragment.setArguments(args);
    return fragment;
}

BroadcastReceiver mReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        // Do what you need in here
        String message = intent.getStringExtra("syncMessage");
        Log.d("Fragment Reciever", message);
        if (message.equals("DownloadComplete")) {
            updateCardView();
        }
    }
};

}

Answer 1

您在Fragment有兩個地方注冊BroadcastReceiver ：

public DynamicFragment() {
    // Required empty public constructor
    SyncApplication.getContext().registerReceiver(mReceiver, new IntentFilter(Sync.BROADCAST_FILTER));
}

和

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    if (context != null) {
        context.registerReceiver(mReceiver, new IntentFilter(Sync.BROADCAST_FILTER));
    }
}

由於他們都使用相同的IntentFilter ，這已經是太多了。 除此之外，您不會取消注冊任何已注冊的BroadcastReceiver ，因此它們仍然處於活動狀態。

您應該在onResume()中注冊一個BroadcastReceiver並在onPause()中取消注冊。 另請參閱廣播概述

Answer 2

您可以在活動中而不是在片段中注冊接收器。

在活動中接收到廣播后，您可以獲取在視圖尋呼機中顯示的片段的當前實例，然后為該片段調用 updateCardView() 方法。

這樣，您只需在活動中注冊一次接收器。