android - 如何使 AsyncTask 是静态的并与活动分开?
问题描述
我正在做一个从 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 2 倍 = AsyncTask 在我启动 Activity 时工作两次。我可以以某种方式运行它 1 次并且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?
解决方案
我还读到 AsyncTask 应该是静态的,该怎么做?
它没有说AsyncTask
应该是静态的。但确实,由于您已将DataLoader
类设置为 的内部类,因此通过将内部 DataLoader 类设置为静态类SpecialtyListActivity
,您可以获得轻微的性能优势。只需添加静态修饰符:
static class DataLoader extends AsyncTask<String, Void, Void>
像这样对类定义使其成为静态的。
您似乎认为DataLoader
AsyncTask 触发两次的原因是因为它以某种方式“附加”到您的活动中。您可以参考Activity 生命周期以获取更多信息。
我可以以某种方式运行它 1 次并且通常将其设为静态以便它不附加到 Activity 吗?
您可以将 AsyncTask 设为单独的类,而不是内部类或活动。(但这不会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“附加到活动”)。使用以下模式使您的 AsyncTask 与您的活动松散耦合。
作为 AsyncTask 的结果,将 DataLoader 的第三个泛型类型设为您想要的类型,在您的情况下,这将是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
}
}
另请参阅如何将 OnPostExecute() 的结果获取到主要活动,因为 AsyncTask 是一个单独的类?
至于您的 AsyncTask 触发两次,您可以在 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。
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