如何使 AsyncTask 是静态的并与 activity 分开？

Question

我正在使用从 AsyncTask 下载的列表。

一切都很好，只有当我退出应用程序并重新启动它时，列表增加了 2 倍 = AsyncTask 在我启动时工作了两次 Activity。我能以某种方式运行它 1 次并通常将其设为静态以便它不附加到 Activity 吗？

public class SpecialtyListActivity extends AppCompatActivity {
private static final String URL = "URL..";
public static ArrayList<Specialty> specialtyList = new ArrayList<>();
public static ArrayList<Worker> workerList = new ArrayList<>();
ListView listView;
EmployeesListFragment employeesListFragment;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.specialty_list);
listView = findViewById(R.id.spec_list);
employeesListFragment = new EmployeesListFragment();
if (Utils.isNetworkAvailable(this)) {
    new DataLoader(this).execute(URL);
} else {
    Toast.makeText(this, "No Network Connection", Toast.LENGTH_LONG).show();
}
}

@SuppressLint("StaticFieldLeak")
class DataLoader extends AsyncTask<String, Void, Void> {

@SuppressLint("StaticFieldLeak")
private Context mContext;
private ProgressDialog pdialog;
private final String TAG = getClass().getSimpleName();

DataLoader(Context context) {
    mContext = context;
}

@Override
protected void onPreExecute() {
    super.onPreExecute();
    pdialog = ProgressDialog.show(mContext, "__", "___");
}

@Override
protected void onPostExecute(Void result) {
    super.onPostExecute(result);
    if (mContext != null) {
        SpecialtyListAdapter adapter = new SpecialtyListAdapter(this.mContext, R.layout.specialty_list, specialtyList);
        listView.setAdapter(adapter);
        adapter.notifyDataSetChanged();
        pdialog.dismiss();
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

            }
        });
    }
}

@Override
protected Void doInBackground(String... params) {
    try {
        HttpHandler sh = new HttpHandler();
        String jsonStr = sh.makeServiceCall(params[0]);
        try {
            JSONObject reader = new JSONObject(jsonStr);
            JSONArray response = reader.getJSONArray("response");

            for (int i = 0; i < response.length(); i++) {
                String workerFName = response.getJSONObject(i).getString("f_name");
                String workerLName = response.getJSONObject(i).getString("l_name");
                String workerBithday = response.getJSONObject(i).getString("birthday");
                String workerAvatarUrl = response.getJSONObject(i).getString("avatr_url");
                int workerSpecialtyId = response.getJSONObject(i)
                        .getJSONArray("specialty")
                        .getJSONObject(0)
                        .getInt("specialty_id");
                String specialtyName = response.getJSONObject(i)
                        .getJSONArray("specialty")
                        .getJSONObject(0)
                        .getString("name");
                Specialty specialty = new Specialty(workerSpecialtyId, specialtyName);
                if (!specialtyList.contains(specialty)) {
                    specialtyList.add(specialty);
                }
                Worker worker = new Worker(workerFName, workerLName);
                worker.setBithday(workerBithday);
                worker.setAvatarLink(workerAvatarUrl);
                worker.setSpecialty(workerSpecialtyId);
                workerList.add(worker);
            }
        } catch (final JSONException e) {
            Log.e(TAG, "Json parsing error: " + e.getMessage());
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}
}

我还读到 AsyncTask 应该是静态的，该怎么做？

Answer 1

当activity 进入onDestroy() 时退出应用程序时应取消AsyncTask。在 asynctask 的 doInBackground() 中，你应该检查 isCancelled() 并在情况下停止它。通过这种方式，您将始终只有 1 个 asyncTask 运行.

Answer 2

I also read that AsyncTask should be static, how to do that?

没有任何地方说 AsyncTask 应该是静态的。但确实如此，因为您已将 DataLoader class 设为 SpecialtyListActivity 的内部 class，您可以通过将内部 DataLoader [=] 设为 slight performance edge 43=] 静态 class。只需添加静态修饰符：

static class DataLoader extends AsyncTask<String, Void, Void>

像这样对 class 定义使其静态。

您似乎认为 DataLoader AsyncTask 触发两次的原因是因为它以某种方式 "attached" 到您的 activity。您可以参考 Activity lifecycle 了解更多信息。

Can I somehow run it 1 time and generally make it static so that it is not attached to Activity?

您可以将 AsyncTask 设为单独的 class 而不是内部 class 或 activity。（但这并不能解决它触发两次的问题，因为它触发两次的原因不是因为它是 "attached to the activity"）。使用以下模式使您的 AsyncTask 与 activity.

松耦合

从你的 AsyncTask 中创建你想要的类型的第三个通用类型的 DataLoader，在你的情况下是 ArrayList<Worker>

//Third generic type is ArrayList<Worker>, this is what you want 
//to return to your activity once your AsyncTask completes.
class DataLoader extends AsyncTask<String, Void, ArrayList<Worker>> {

    private DataLoadListener mListener;

    DataLoader(Context context, DataLoadListener listener) {
        mContext = context;
        mListener = listener;
    }

    @Override
    protected ArrayList<Worker> doInBackground(String... params) {

         //download data...

         ArrayList<Worker> workersToReturn = new ArrayList<>();

         for (int i = 0; i < response.length(); i++) {
             //build worker object...
             workersToReturn.add(worker);
         }

         return workersToReturn;
    }

    @Override
    protected void onPostExecute(ArrayList<Worker> result) {
        listener.onDataLoaded(billItem);
    }

    //Your activity should implement this interface and override onDataLoaded() to
    //to receive the result when this AsyncTask completes.
    public interface DataLoadListener { 
        void onDataLoaded(ArrayList<Worker> workers);          
    }
}

public class SpecialtyListActivity extends AppCompatActivity implements DataLoader.DataLoadListener{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        //Pass both context and DataLoadListener to the constructor
        new DataLoader(this, this).execute(URL);
    }

    @Override
    public void onDataLoaded(ArrayList<Worker> workers) {
         listView.setAdapter(new SpecialtyListAdapter(context, layout, specialtyList));
         listView.setAdapter(adapter);
         adapter.notifyDataSetChanged();
         //Do other stuff
    }

}

另见 How to get the result of OnPostExecute() to main activity because AsyncTask is a separate class?

至于你的 AsyncTask 触发两次，你可以在 doInBackground 方法中添加一个断点并调试应用程序。查看调用堆栈以找出它被调用两次的原因。

如何使 AsyncTask 是静态的并与 activity 分开？

How to make AsyncTask is static and Separate from activity?

android

adapter

android-asynctask