片段未附加到上下文

Question

在工具栏的活动中,我得到了一个按钮,需要从该片段中的片段和更新列表中调用方法.现在是一个错误.打电话给活动

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()){
        case  R.id.menu_sort:
            ListFragment listFragment = new ListFragment();
            listFragment.sortByPopularity();
            break;
    }
    return super.onOptionsItemSelected(item);
}

片段代码.我没有附加活动时发现错误.但没有任何背景

public class ListFragment extends Fragment implements ListAdapter.ItemClickListener {

    /**
     * Needed
     */
    RecyclerView recyclerView;
    View view;
    List<BasePojo.Result> list;
    ListAdapter listAdapter;

    public ListFragment() {
    }

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

        /**
         * Main Initialization
         */
        view = inflater.inflate(R.layout.fragment_list, container, false);
        recyclerView = view.findViewById(R.id.recycler_list_detailed);
        recyclerView.setLayoutManager(new GridLayoutManager(getActivity(), 2));
        list = new ArrayList<>();
        listAdapter = new ListAdapter(list, setOnItemClickCallback());
        recyclerView.setAdapter(listAdapter);

        RetrofitClient.getApiService().getPhotosList(getString(R.string.api_key)).enqueue(new Callback<BasePojo>() {
            @Override
            public void onResponse(Call<BasePojo> call, Response<BasePojo> response) {
                BasePojo basePojo = response.body();
                list.addAll(basePojo.getResults());
                recyclerView.getAdapter().notifyDataSetChanged();
            }

            @Override
            public void onFailure(Call<BasePojo> call, Throwable t) {
                Log.d("tag", "Response failed" + t.toString());

            }
        });


        return view;
    }

    @Override
    public void onItemClick(View view, int position) {
        Log.v("in on click", "value " + position);

    }

    private OnItemClickListener.OnItemClickCallback setOnItemClickCallback() {
        OnItemClickListener.OnItemClickCallback onItemClickCallback = new OnItemClickListener.OnItemClickCallback() {
            @Override
            public void onItemClicked(View view, int position) {
                BasePojo.Result itemClicked = list.get(position);
                Bundle bundle = new Bundle();
                bundle.putString("title", itemClicked.getOriginalTitle());
                bundle.putString("overview", itemClicked.getOverview());
                bundle.putString("release_date", itemClicked.getReleaseDate());
                bundle.putString("vote_average", itemClicked.getVoteAverage().toString());
                bundle.putString("poster_path", itemClicked.getPosterPath());
                DetailedFragment detailedFragment = new DetailedFragment();
                detailedFragment.setArguments(bundle);
                FragmentManager manager = getActivity().getSupportFragmentManager();
                FragmentTransaction transaction = manager.beginTransaction();
                transaction.replace(R.id.main_frame_list, detailedFragment);
                Log.d("tag", "title is 111 " + bundle.get("title"));

                transaction.commit();
            }

        };
        return onItemClickCallback;
    }

    @Override
    public void onAttachFragment(Fragment childFragment) {
        super.onAttachFragment(childFragment);

    }

    public void sortByPopularity() {
        RetrofitClient.getApiService().getPopularList(getString(R.string.api_key)).enqueue(new Callback<BasePojo>() {
            @Override
            public void onResponse(Call<BasePojo> call, Response<BasePojo> response) {
                BasePojo basePojo = response.body();
                list.addAll(basePojo.getResults());
                recyclerView.getAdapter().notifyDataSetChanged();
            }

            @Override
            public void onFailure(Call<BasePojo> call, Throwable t) {
                Log.d("tag", "Response failed" + t.toString());

            }
        }); }

}

这是一个错误

05-09 12:48:26.915 5775-5775/com.borisruzanov.popularmovies E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.borisruzanov.popularmovies, PID: 5775
java.lang.IllegalStateException: Fragment ListFragment{6dbd6de} not attached to a context.
    at android.support.v4.app.Fragment.requireContext(Fragment.java:614)
    at android.support.v4.app.Fragment.getResources(Fragment.java:678)
    at android.support.v4.app.Fragment.getString(Fragment.java:700)
    at com.borisruzanov.popularmovies.ListFragment.sortByPopularity(ListFragment.java:110)
    at com.borisruzanov.popularmovies.MainActivity.onOptionsItemSelected(MainActivity.java:47)
    at android.app.Activity.onMenuItemSelected(Activity.java:3204)
    at android.support.v4.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:407)
    at android.support.v7.app.AppCompatActivity.onMenuItemSelected(AppCompatActivity.java:195)
    at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:108)
    at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:108)
    at android.support.v7.app.ToolbarActionBar$2.onMenuItemClick(ToolbarActionBar.java:63)
    at android.support.v7.widget.Toolbar$1.onMenuItemClick(Toolbar.java:203)
    at android.support.v7.widget.ActionMenuView$MenuBuilderCallback.onMenuItemSelected(ActionMenuView.java:780)
    at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:822)
    at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:171)
    at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:973)
    at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:963)
    at android.support.v7.widget.ActionMenuView.invokeItem(ActionMenuView.java:624)
    at android.support.v7.view.menu.ActionMenuItemView.onClick(ActionMenuItemView.java:150)
    at android.view.View.performClick(View.java:5610)
    at android.view.View$PerformClick.run(View.java:22265)
    at android.os.Handler.handleCallback(Handler.java:751)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6077)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)

非常感谢您的时间和帮助.如果我的问题看起来不太好请注意,我将教会如何更好地提问

Answer 1

就我而言，这个问题发生在我打电话时 getString()

更改此调用以getActivity().getString()解决问题。

Answer 2

使用commit()不能解决问题，我们应该尝试在Fragment的源代码中寻找解决方案。

因此，从您提供的错误堆栈中考虑，requireContext()在 Fragment 中是：

    public final Context requireContext() {
        Context context = getContext();
        if (context == null) {
            throw new IllegalStateException("Fragment " + this + " not attached to a context.");
        }
        return context;
    }

这意味着系统将检查Contextfrom getContext()，如果它为空，则会抛出异常。

所以，为了避免这个问题，我们可以getContext()在做我们的业务之前检查结果。

Answer 3

如果您使用CountDownTimer，您可能会收到在完成计时器之前分离片段的错误原因。如果您在onFinish回调中执行 ui 更改，则应检查上下文是否为 null 或不如下所示；

    timer = object : CountDownTimer(startTimeInMillis, 1000) {
        override fun onTick(millisUntilFinished: Long) {

        }

        override fun onFinish() {
            context?.let {
              //perform ui changes here 
            }
        }
    }
    timer?.start()

或者您应该在分离片段之前取消计时器，如下所示；

override fun onDestroy() {
    super.onDestroy()
    timer?.cancel()
}

Answer 4

科特林：

我的问题发生在 getString()

改变它来context.getString()解决它

Answer 5

如果某个片段未显示（未添加）或被删除，则它是context == null. 在这种情况下获取资源将导致此异常。getString(R.string.some_string)需要context并崩溃。

您可以检查片段是否存在，如下所示：

if (isAdded) {
    // Print getString(R.string.some_string).
}

但是，即使片段已释放，您也可能需要打印字符串，例如在 LogCat、分析或向服务器发送请求时。在这种情况下，您需要应用程序上下文来获取字符串资源。

class MyApplication : Application() {

    override fun onCreate() {
        super.onCreate()

        instance = this
    }


    companion object {
        lateinit var instance: MyApplication private set
    }
}

object Strings {
    fun get(@StringRes stringRes: Int, vararg formatArgs: Any = emptyArray()): String {
        return instance.getString(stringRes, *formatArgs)
    }
}

然后MyApplication在AndroidManifest中设置并使用：Strings.get(R.string.some_string)。

Answer 6

创建片段实例是不够的。
它需要通过事务附加到活动：

getFragmentManager()
    .beginTransaction()
    .replace(R.id.container_layout, fragment)
    .commit();

成功提交后，onAttach将调用片段中的方法，创建视图，然后可以与其视图进行交互。

根据您的情况，创建片段实例并将其附加到activity onCreate，然后sortByPopularity稍后在click事件中调用。

阅读有关片段生命周期的更多信息：https : //developer.android.com/guide/components/fragments