android-fragments 更改配置后从后台线程更新recyclerview项

gstyhher  于 2022-11-14  发布在  Android
关注(0)|答案(3)|浏览(151)

我在Fragment中有一个RecyclerView。我也有一个AsyncTask,它从后台线程更新RecyclerView的项目。问题是当我旋转设备(或导致任何其他配置更改)时,AsyncTask无法更新视图。
在这里你可以看到简化的代码:
HomeFragment

public class HomeFragment extends Fragment {

    public HomeFragment() {
    }

    public static HomeFragment newInstance() {
        return new HomeFragment();
    }

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

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_home, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        RecyclerView mRecyclerView = requireView().findViewById(R.id.recyclerview);
        Activity activity = requireActivity();
        ArrayList<String> items = new ArrayList<>(Arrays.asList("Item1", "Item2", "Item3"));
        ListAdapter adapter = new ListAdapter(activity, items);
        mRecyclerView.setAdapter(adapter);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(activity));
    }
}

RecyclerView及其内部AsyncTask类的适配器:

public class ListAdapter extends RecyclerView.Adapter<ListAdapter.ViewHolder> {

    private final ArrayList<String> items;
    private final LayoutInflater mInflater;
    private RecyclerView mRecyclerView;

    public ListAdapter(Context context, ArrayList<String> items) {
        mInflater = LayoutInflater.from(context);
        this.items = items;
    }

    @Override
    public void onAttachedToRecyclerView(@NonNull RecyclerView recyclerView) {
        super.onAttachedToRecyclerView(recyclerView);
        mRecyclerView = recyclerView;
    }

    @NonNull
    @Override
    public ListAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View mItemView = mInflater.inflate(R.layout.item, parent, false);
        return new ViewHolder(mItemView, this);
    }

    @Override
    public void onBindViewHolder(@NonNull ListAdapter.ViewHolder holder, int position) {
        holder.name.setText(items.get(position));
    }

    @Override
    public int getItemCount() {
        return items.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        final ListAdapter mAdapter;
        final TextView name;

        public ViewHolder(@NonNull View itemView, ListAdapter mAdapter) {
            super(itemView);
            this.mAdapter = mAdapter;
            this.name = itemView.findViewById(R.id.file_name);
            itemView.setOnClickListener(v -> {
                Task task = new Task();
                task.execute();
            });
        }
    }

    class Task extends AsyncTask<Void, Integer, Void> {

        @Override
        protected void onProgressUpdate(Integer... values) {
            mRecyclerView.post(() ->
                    ((ViewHolder) Objects.requireNonNull(mRecyclerView.findViewHolderForLayoutPosition(0))).
                            name.setText(String.valueOf(values[0])));
            mRecyclerView.invalidate();
        }

        @Override
        protected Void doInBackground(Void... voids) {
            for (int i = 0; i <= 30; i++) {
                publishProgress(i);
                SystemClock.sleep(500);
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void unused) {
            ((ViewHolder) Objects.requireNonNull(mRecyclerView.findViewHolderForLayoutPosition(0))).name.setText("task is finished");
        }
    }
}

正如你所看到的,我使用了mRecyclerView.post()方法来避免接触非UI线程的视图。我如何在旋转设备后更新项目?
我之前尝试过的:

  • 更改适配器数据集并调用notifyDataSetChanged()
  • 在Fragment中创建一个用于更新项的方法,并从AsyncTask调用它
  • 正在重置RecyclerView的适配器
  • ...
nr9pn0ug

nr9pn0ug1#

AsyncTask自API级别30起已弃用。它存在一些问题,尤其是对于配置更改per documentation:
AsyncTask旨在使UI线程的使用变得正确和简单。但是,最常见的用例是集成到UI中,而这会导致上下文泄漏、错过回调或在配置更改时崩溃。
由于这些问题,它不应该用于长时间运行的任务。
AsyncTasks最好用于短时间的操作(最多几秒)。如果您需要长时间保持线程运行,强烈建议您使用java.util.concurrent包提供的各种API,如Executor、ThreadPoolExecutor和FutureTask。

问题:

当您在doInBackground中运行任务时,当配置发生变化时,将重新创建Activity(即,销毁旧Activity,并创建新Activity);但是附加到旧Activity的AsyncTask继续运行(导致内存泄漏);稍后当onPostExecute()准备好将结果发布到UI线程时也是如此;则将它们释放到被销毁的Activity而不是屏幕上显示的当前Activity;因此用户不会看到它们。因此,在您的情况下,结果被忽略。
因此,建议使用其他后台线程替代方案,如Executors,通过回调更新UI,或通过ViewModel(配置更改后仍有效)和LiveData将结果发布到UI。

带有执行器的解决方案

  • 此处提供Executor

监听程序:

interface ProgressListener {
    void onPostExecute();

    void onProgressUpdate(int value);
}

片段:

ListAdapter adapter = new ListAdapter(activity, items, new ProgressListener() {
            @Override
            public void onPostExecute() {
                ((ListAdapter.ViewHolder) Objects.requireNonNull(recyclerView.
                        findViewHolderForLayoutPosition(0))).name.setText("task is finished");
            }

            @Override
            public void onProgressUpdate(int value) {
                recyclerView.post(() ->
                        ((ListAdapter.ViewHolder) Objects.requireNonNull(recyclerView.findViewHolderForLayoutPosition(0))).
                                name.setText(String.valueOf(value)));
                recyclerView.invalidate();
            }
        });

        mRecyclerView.setAdapter(adapter);

适配器:只使用单线程执行器:

public class ListAdapter extends RecyclerView.Adapter<ListAdapter.ViewHolder> {

    ProgressListener progressListener;

    public ListAdapter(Context context, ArrayList<String> items, ProgressListener listener) {
        mInflater = LayoutInflater.from(context);
        this.items = items;
        progressListener = listener;
    }
    
    
    // ........... CODE IS OMITTED
    
    
    // ViewHolder constructor
    
        public ViewHolder(@NonNull View itemView, ListAdapter mAdapter) {
            super(itemView);
            this.mAdapter = mAdapter;
            this.name = itemView.findViewById(R.id.file_name);
            itemView.setOnClickListener(v -> {
                Executors.newSingleThreadExecutor().execute(() -> {
                    for (int i = 0; i <= 30; i++) {
                        progressListener.onProgressUpdate(i);
                        SystemClock.sleep(500);
                    }
                    progressListener.onPostExecute();
                });
            });
        }
    

}

使用异步任务

  • 如果您仍需要使用AsyncTask解决此问题,如前所述,不建议使用AsyncTask。您需要某种方法来保留适配器& AsnyncTask示例;这里使用ViewModel:

创建ViewModel以保存适配器& AsnyncTask示例

public class MainViewModel extends AndroidViewModel {

    AsyncTask<Void, Integer, Void> myTask;
    ListAdapter adapter;

    public MainViewModel(@NonNull Application application) {
        super(application);
    }

}

在片段中:仅在适配器为null时示例化适配器,并将AsynkTask的示例传递给适配器:

if (viewModel.adapter == null)
        viewModel.adapter = new ListAdapter(activity, items, viewModel);
    recyclerView.setAdapter(viewModel.adapter);

最后使用适配器中的ViewModel AsynkTask示例:

public class ListAdapter extends RecyclerView.Adapter<ListAdapter.ViewHolder> {

    // ......... code is omitted

    private AsyncTask<Void, Integer, Void> task;

    public ListAdapter(Context context, ArrayList<String> items, AsyncTask<Void, Integer, Void> myTask) {
        mInflater = LayoutInflater.from(context);
        this.items = items;
        this.task = myTask;
    }
    
    // ......... code is omitted
    
    
    public class ViewHolder extends RecyclerView.ViewHolder {
        final ListAdapter mAdapter;
        final TextView name;

        public ViewHolder(@NonNull View itemView, ListAdapter mAdapter) {
            super(itemView);
            this.mAdapter = mAdapter;
            this.name = itemView.findViewById(R.id.file_name);
            itemView.setOnClickListener(v -> {
                task = new Task();
                task.execute();
            });
        }
    }
    
    
}
kqqjbcuj

kqqjbcuj2#

您可以使用下面的代码更新屏幕旋转中的回收程序视图。

@Override
public void onConfigurationChanged(@NonNull Configuration newConfig) {

    super.onConfigurationChanged(newConfig);

    if(adapter!=null){
        adapter.notifyDataSetChanged();
    }
}

onCreate()onCreateView()onActivityCreated()方法中呼叫setRetainInstance(true)

b09cbbtk

b09cbbtk3#

默认情况下,异步任务在后台线程上工作,我们无法从后台线程更新我们的用户界面,它用于密集的工作,如网络调用等。请尝试运行

runOnUiThread(new Runnable() {
        @Override
        public void run() {
            // WORK on UI thread here
        }
    });

语句,因为它指示后台处理已完成。请将更新视图的代码放在此run()方法中

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