android - 从 Activity 解析到 fragment 的数据不会出现在第一次加载时

Question

我有一个 fragment ，我在其中加载回收器 View ，并从一个从 JSON 加载数据的 Activity 中为其加载数据。但是，当 fragment 第一次打开时，它不会加载数据，只有在再次单击 fragment 时才会加载。下面列出了我的 Activity 和 fragment 的代码。

Activity

public class MainActivity extends AppCompatActivity {
ActionBar actionbar;
TextView textview;
ActionBar.LayoutParams layoutparams;
public static final int NUMBER_OF_ADS = 2;

private RequestQueue mRequestQueue;
private AdLoader adLoader;
private List<Object> mTrollList = new ArrayList<>();
private List<UnifiedNativeAd> mNativeAds = new ArrayList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    MobileAds.initialize(this, getString(R.string.admob_app_id));
    BottomNavigationView bottomnav = findViewById(R.id.bottom_navigation);
    BottomNavigationViewHelper.removeShiftMode(bottomnav);
    bottomnav.setOnNavigationItemSelectedListener(navListener);

    mRequestQueue = Volley.newRequestQueue(this);


    getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container ,new VideoFragment()).commit();
    bottomnav.setSelectedItemId(R.id.navigation_videos);
    getSupportActionBar().setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM);
    getSupportActionBar().setCustomView(R.layout.actionbar_new);
    bottomnav.setItemIconTintList(null);
    if (savedInstanceState == null) {
        // Update the RecyclerView item's list with menu items.
        addMenuItemsFromJson();
        // Update the RecyclerView item's list with native ads.
        loadNativeAds();

    }
}

private void insertAdsInMenuItems() {
    if (mNativeAds.size() <= 0) {
        return;
    }
    if(mTrollList.size()<1){
        return;
    }
    int offset = (mTrollList.size() / mNativeAds.size()) + 1;
    int index = 2;
    for (UnifiedNativeAd ad : mNativeAds) {
        mTrollList.add(index, ad);
        index = index + offset;
    }

}

private void loadNativeAds() {

    AdLoader.Builder builder = new AdLoader.Builder(Objects.requireNonNull(this), getString(R.string.ad_unit_id));
    adLoader = builder.forUnifiedNativeAd(
            new UnifiedNativeAd.OnUnifiedNativeAdLoadedListener() {
                @Override
                public void onUnifiedNativeAdLoaded(UnifiedNativeAd unifiedNativeAd) {
                    // A native ad loaded successfully, check if the ad loader has finished loading
                    // and if so, insert the ads into the list.
                    mNativeAds.add(unifiedNativeAd);
                    if (!adLoader.isLoading()) {
                        insertAdsInMenuItems();
                    }
                }
            }).withAdListener(
            new AdListener() {
                @Override
                public void onAdFailedToLoad(int errorCode) {
                    // A native ad failed to load, check if the ad loader has finished loading
                    // and if so, insert the ads into the list.
                    Log.e("MainActivity", "The previous native ad failed to load. Attempting to"
                            + " load another.");
                    if (!adLoader.isLoading()) {
                        insertAdsInMenuItems();
                    }
                }
            }).build();

    //Do something after 100ms
    adLoader.loadAds(new AdRequest.Builder().build(), NUMBER_OF_ADS);
}


public List<Object> getRecyclerViewItems() {
    return mTrollList;
}

private void addMenuItemsFromJson(){
    String url =getString(R.string.server_link);
    JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, url, null,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    try {
                        JSONArray jsonArray = response.getJSONArray("server_response");
                        for(int i = 0; i < jsonArray.length(); i++){
                            JSONObject ser =jsonArray.getJSONObject(i);

                            String troll_image = ser.getString("troll_image");
                            String troll_caption =  ser.getString("troll_caption");
                            TrollItem trollItem = new TrollItem(troll_image,troll_caption);
                            mTrollList.add(trollItem);

                        }

                    } catch (JSONException e) {
                        e.printStackTrace();

                    }
                }
            }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            error.printStackTrace();
        }

    });

    mRequestQueue.add(request);
}



public void setActionBarTitle(String title) {
    actionbar = getSupportActionBar();

    textview = new TextView(getApplicationContext());

    layoutparams = new ActionBar.LayoutParams(ActionBar.LayoutParams.MATCH_PARENT, ActionBar.LayoutParams.WRAP_CONTENT);

    textview.setLayoutParams(layoutparams);

    textview.setText(title);

    textview.setTextColor(Color.BLACK);

    textview.setGravity(Gravity.CENTER);
    textview.setTypeface(null, Typeface.BOLD);

    textview.setTextSize(20);

    actionbar.setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM);

    actionbar.setCustomView(textview);
}

private BottomNavigationView.OnNavigationItemSelectedListener navListener
        = new BottomNavigationView.OnNavigationItemSelectedListener() {

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {

        switch (item.getItemId()) {
            case R.id.navigation_videos:
                Fragment videoFragment = new VideoFragment();
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                        videoFragment).commit();
                break;
            case R.id.navigation_photos:
                Fragment photoFragment = new PhotoFragment();
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                        photoFragment).commit();
                break;
            case R.id.navigation_dvd:
                Fragment dvdFragment = new DvdFragment();
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                        dvdFragment).commit();
                break;
            case R.id.navigation_news:
                Fragment newsFargment = new NewsFragment();
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                        newsFargment).commit();
                break;
            case R.id.navigation_troll:
                Log.e("datafirst", String.valueOf(mTrollList.size()+"activity"));
                Fragment trollFragment = new TrollFragment();
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                        trollFragment).commit();
                break;
        }return true;}};}

fragment

public class TrollFragment extends Fragment {
private RecyclerView mRecyclerView;
private TrollAdapter mTrollAdapter;
private List<Object> mTrollList;



public TrollFragment() {
    // Required empty public constructor
}
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // retain this fragment
    setRetainInstance(true);
    MainActivity activity = (MainActivity) getActivity();
    mTrollList = activity.getRecyclerViewItems();

    Log.e("datafirst", String.valueOf(mTrollList.size()));
   getContext();

}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment

    ((MainActivity) Objects.requireNonNull(getActivity())).setActionBarTitle("Trolls");
    View rootView = inflater.inflate(R.layout.fragment_troll, container, false);
    mRecyclerView = rootView.findViewById(R.id.recycler_view_troll);
    mRecyclerView.setHasFixedSize(true);


    SnapHelper snapHelper = new PagerSnapHelper();
    snapHelper.attachToRecyclerView(mRecyclerView);
    mRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity(), LinearLayoutManager.VERTICAL, false));
    mTrollAdapter = new TrollAdapter(getActivity(), mTrollList);
    mRecyclerView.setAdapter(mTrollAdapter);

    return rootView;
}}

Answer 1

而不是从 fragment 中调用 getRecyclerViewItems。使用

将数据传递给您的 fragment

fragmentObject.setArguments(bundle);

然后在你的 fragment 中使用

getArguments(); 

获取数据。

这样您也可以在第一次运行时获取数据，并且您的 fragment 对 MainActivity 的依赖性将被删除( fragment 的使用方式)