文档建议反馈控制台
首页
学习
活动
专区
圈层
工具
MCP广场
文章/答案/技术大牛
发布
社区首页 >问答首页 >片段中的网络调用

问片段中的网络调用
EN

Stack Overflow用户
提问于 2017-09-13 19:51:08
回答 5查看 1.6K关注 0票数 0

我正在制作一个新闻应用程序，其中我有3个标签，这是趋势，最新和流行。我已经实现了选项卡布局。现在，当每个片段被选中时，我必须在每个片段中显示列表。我正在使用下面的google新闻API

https://newsapi.org/v1/articles?source=google-news&sortBy=top

现在我想根据选择的选项卡过滤API中的数据，比如如果选择了选项卡popular，那么URL应该是https://newsapi.org/v1/articles?source=google-news&sortBy=popular，它将显示在相应的片段中。

我已经在第一个选项卡中进行了网络调用，并且它可以很好地工作。但当我切换标签时，它就崩溃了。因此，我感到困惑的是，如何才能根据所选的选项卡进行网络呼叫。

这是我的mainActivity：

代码语言：javascript
复制
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initializeViews();


        setSupportActionBar(toolbar);
        getSupportActionBar().setDisplayShowHomeEnabled(true);
        getSupportActionBar().setDisplayUseLogoEnabled(true);
        setupViewPager(viewPager);
        tabLayout.setupWithViewPager(viewPager);
    }

    private void setupViewPager(ViewPager viewPager) {

        ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
        adapter.addFragment(new TopStories(), "top stories");
        adapter.addFragment(new Trending(), "trending");
        adapter.addFragment(new Latest(), "latest");
        adapter.addFragment(new Popular(), "popular");
        viewPager.setAdapter(adapter);
    }

    private void initializeViews() {
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        viewPager = (ViewPager) findViewById(R.id.viewpager);
        tabLayout = (TabLayout) findViewById(R.id.tabs);
    }


     class ViewPagerAdapter extends FragmentPagerAdapter {

         private final List<Fragment> mFragmentList = new ArrayList<>();
         private final List<String> mFragmentTitleList = new ArrayList<>();

         public ViewPagerAdapter(FragmentManager manager) {
             super(manager);
         }

         @Override
         public Fragment getItem(int position) {
             return mFragmentList.get(position);
         }

         @Override
         public int getCount() {
             return mFragmentList.size();
         }

         public void addFragment(Fragment fragment, String title) {
             mFragmentList.add(fragment);
             mFragmentTitleList.add(title);
         }

         @Override
         public CharSequence getPageTitle(int position) {
             return mFragmentTitleList.get(position);
         }
     }

Fragment1：

代码语言：javascript
复制
 public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.top_stories,container,false);
        if (ParamConstants.API_KEY.isEmpty()) {
            Toast.makeText(getContext(), "Please obtain your API KEY first from themoviedb.org", Toast.LENGTH_LONG).show();

        }

        recyclerView = (RecyclerView)rootView.findViewById(R.id.news_recycle);
        recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));

        fetchNews(recyclerView);

        return rootView;
    }

    private void fetchNews(final RecyclerView rv) {
        ApiInterface apiService = ApiClient.getClient().create(ApiInterface.class);
        Call<JsonElement> call = apiService.getNews("google-news", "top", ParamConstants.API_KEY);
        call.enqueue(new Callback<JsonElement>() {
            @Override
            public void onResponse(Call<JsonElement> call, Response<JsonElement> response) {
                Log.d("resonse", response.toString());
                JsonElement object = response.body();
                Type listType = new TypeToken<List<News>>() {
                }.getType();
                news = new Gson().fromJson(object.getAsJsonObject().getAsJsonArray("articles"), listType);
                rv.setAdapter(new NewsAdapter(news, R.layout.news_list_item, getContext()));
                recyclerView.addItemDecoration(new DividerItemDecoration(getContext(),DividerItemDecoration.VERTICAL_LIST));
            }

            @Override
            public void onFailure(Call<JsonElement> call, Throwable t) {
                Log.e(TAG, t.toString());
            }
        });


        Call<JsonElement> source = apiService.getSources("", "", "");
        source.enqueue(new Callback<JsonElement>() {
            @Override
            public void onResponse(Call<JsonElement> call, Response<JsonElement> response) {
                Log.d("sources", response.body().toString());

                Type listType = new TypeToken<List<NewsResponse>>() {
                }.getType();
                newsResponse = new Gson().fromJson(response.body().getAsJsonObject().getAsJsonArray("sources"), listType);
                newsResponse.get(0).getCategory().toString();
            }

            @Override
            public void onFailure(Call<JsonElement> call, Throwable t) {
                Log.e("sourcesfailure", t.toString());
            }
        });
    }

Fragment2：

代码语言：javascript
复制
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.trending_fragment,container,false);


        if (ParamConstants.API_KEY.isEmpty()) {
            Toast.makeText(getContext(), "Please obtain your API KEY first from themoviedb.org", Toast.LENGTH_LONG).show();

        }

        recyclerView = (RecyclerView)rootView.findViewById(R.id.news_recycle);
        recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));

        fetchTrendingNews(recyclerView);

return rootView;

    }

    private void fetchTrendingNews(final RecyclerView recyclerView) {

        ApiInterface apiService = ApiClient.getClient().create(ApiInterface.class);
        Call<JsonElement> call = apiService.getNews("BBC News", "popular", ParamConstants.API_KEY);
        call.enqueue(new Callback<JsonElement>() {
            @Override
            public void onResponse(Call<JsonElement> call, Response<JsonElement> response) {
                Log.d("resonse", response.toString());
                JsonElement object = response.body();
                Type listType = new TypeToken<List<News>>() {
                }.getType();
                news = new Gson().fromJson(object.getAsJsonObject().getAsJsonArray("articles"), listType);
                recyclerView.setAdapter(new NewsAdapter(news, R.layout.news_list_item, getContext()));
                recyclerView.addItemDecoration(new DividerItemDecoration(getContext(),DividerItemDecoration.VERTICAL_LIST));
            }

            @Override
            public void onFailure(Call<JsonElement> call, Throwable t) {
                Log.e(TAG, t.toString());
            }
        });
    }

错误日志：

代码语言：javascript
复制
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
                                                                             at com.kotlin.whatshappening.activity.fragment.Trending.onCreateView(Trending.java:65)
                                                                             at android.support.v4.app.Fragment.performCreateView(Fragment.java:2184)
                                                                             at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1298)
                                                                             at android.support.v4.app.FragmentManagerImpl.moveFragmentsToInvisible(FragmentManager.java:2323)
                                                                             at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2136)
                                                                             at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2092)
                                                                             at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:1969)
                                                                             at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:620)
                                                                             at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:143)
                                                                             at android.support.v4.view.ViewPager.populate(ViewPager.java:1268)
                                                                             at android.support.v4.view.ViewPager.populate(ViewPager.java:1116)
                                                                             at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1642)
                                                                             at android.view.View.measure(View.java:18809)
                                                                             at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954)
                                                                             at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
                                                                             at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
                                                                             at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
                                                                             at android.view.View.measure(View.java:18809)
                                                                             at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954)
                                                                             at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
                                                                             at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
                                                                             at android.view.View.measure(View.java:18809)
                                                                             at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954)
                                                                             at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
                                                                             at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
                                                                             at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
                                                                             at android.view.View.measure(View.java:18809)
                                                                             at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954)
                                                                             at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
                                                                             at android.view.View.measure(View.java:18809)
                                                                             at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954)
                                                                             at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
                                                                             at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
                                                                             at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
                                                                             at android.view.View.measure(View.java:18809)
                                                                             at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5954)
                                                                             at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
                                                                             at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
                                                                             at android.view.View.measure(View.java:18809)
                                                                             at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2112)
                                                                             at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1228)
                                                                             at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1464)
                                                                             at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1119)
                                                                             at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6060)
                                                                             at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
                                                                             at android.view.Choreographer.doCallbacks(Choreographer.java:670)
                                                                             at android.view.Choreographer.doFrame(Choreographer.java:606)
                                                                             at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
                                                                             at android.os.Handler.handleCallback(Handler.java:746)
                                                                             at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                             at android.os.Looper.loop(Looper.java:148)
                                                                             at android.app.ActivityThread.main(ActivityThread.java:5443)
                                                                             at java.lang.reflect.Method.invoke(Native Method)
                                                                            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.

如何根据所选的每个选项卡进行网络调用。

android
android-fragments
tabs
EN

回答 5

Stack Overflow用户

发布于 2017-09-13 20:02:54

1.)在setUpViewPager方法中创建一个片段，添加三次。

2.)并将参数设置为具有某个屏幕可区分数字的片段对象。

3.)在该片段中，从getArguments方法获取屏幕编号。

4.)现在，根据这个数字，在单个片段中调用您的apis。

您不需要创建三个不同的片段就可以在RecyclerView中显示数据。

票数 0
EN

Stack Overflow用户

发布于 2017-09-13 20:05:19

试试这个。我希望这对你有帮助。

代码语言：javascript
复制
Context mContext = rootView.getContext();

LinearLayoutManager  mLinearLayoutManager = new LinearLayoutManager(mContext, LinearLayoutManager.VERTICAL, false);

recyclerView.setLayoutManager(mLinearLayoutManager)

如果您想要获取当前选项卡标题，那么，使用此命令，您可以获得当前当前选项卡标题：

代码语言：javascript
复制
adapter.getPageTitle(viewpager.getCurrentItem());
票数 0
EN

Stack Overflow用户

发布于 2017-09-13 20:06:06

您的片段可能会在收到来自服务器的响应之前调用onDestroyView()方法，在这种情况下，如果您在UI元素(视图)上做任何工作，它将提供NullPointerException，因此请始终检查它：

代码语言：javascript
复制
@Override
            public void onResponse(Call<JsonElement> call, Response<JsonElement> response) {
                if(getActivity==null){
                return;
                }
                //do your UI code here
            }

            @Override
            public void onFailure(Call<JsonElement> call, Throwable t) {
                Log.e(TAG, t.toString());
                if(getActivity==null){
                return;
                }
                //do your UI code here
            }
票数 0
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：

https://stackoverflow.com/questions/46196819

复制
相关文章

相似问题

领券

腾讯云开发者

扫码关注腾讯云开发者

扫码关注腾讯云开发者

领取腾讯云代金券

热门产品

热门推荐

更多推荐

Copyright © 2013 - 2026 Tencent Cloud. All Rights Reserved. 腾讯云 版权所有 

深圳市腾讯计算机系统有限公司 ICP备案/许可证号：粤B2-20090059 粤公网安备44030502008569号

腾讯云计算（北京）有限责任公司 京ICP证150476号 |  京ICP备11018762号

问题归档专栏文章快讯文章归档关键词归档开发者手册归档开发者手册 Section 归档