进度对话框在异步任务中的片段中不起作用

Question

进度对话框工作正常，但是我使用setUserVisibleHint并在该函数中执行了我的AsyncTask但是在应用程序午餐后，我收到了这个错误：

所以我研究了这个，并在堆栈中看到了很多关于流的帖子以及像AsyncTask中的make context或构造函数这样的解决方案，但是没有人不工作。

这是我的片段：

 public class maghalat extends Fragment {

private View myFragmentView;
private RecyclerView recyclerView;
private DataAdapter adapter;
private String TAG = MainActivity.class.getSimpleName();
public ProgressDialog pDialog;
List<jsonContent> listcontent=new ArrayList<>();

public int dog=1;
public String url = "http://memaraneha.com;

public int id;


private boolean isFragmentLoaded=false;

public Context context;

@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);
    if (getActivity() != null){
    if (isVisibleToUser && !isFragmentLoaded ) {

        new GetContacts(context).execute();

        isFragmentLoaded = true;
    }
    }
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    myFragmentView = inflater.inflate(R.layout.maghalat, container, false);

    context= container.getContext();
    return myFragmentView;
}


public class GetContacts extends AsyncTask<Void, Void, Void> {


public GetContacts(Context context) {

}

@Override
    protected void onPreExecute() {
        super.onPreExecute();
        // Showing progress dialog
        pDialog = new ProgressDialog(context);
        pDialog.setMessage("Please wait...");
        pDialog.setCancelable(false);
        pDialog.show();
    }

    @Override
    protected Void doInBackground(Void... arg0) {

        HttpHandler sh = new HttpHandler();

        // Making a request to url and getting response
        String jsonStr = sh.makeServiceCall(url);


        Log.e(TAG, "Response from url: " + jsonStr);

        if (jsonStr != null) {
            try {

                JSONObject jsonObj = new JSONObject(jsonStr);


                 id=jsonObj.getInt("pages");


                JSONArray posts = jsonObj.getJSONArray("posts");
                for (int i = 0; i < posts.length(); i++) {
                    JSONObject c = posts.getJSONObject(i);

                    jsonContent jsonContent=new jsonContent();

                    jsonContent.title=c.getString("title");

                    //img
                    JSONObject post_img=c.getJSONObject("thumbnail_images");
                    for (int j=0;j<post_img.length();j++)
                    {
                        JSONObject v=post_img.getJSONObject("mom-portfolio-two");
                        jsonContent.imgurl=v.getString("url");
                    }
                    jsonContent.pages=id;
                    jsonContent.curpage=dog;
                    listcontent.add(jsonContent);

                }

            } catch (final JSONException e) {
                Log.e(TAG, "Json parsing error: " + e.getMessage());
                getActivity().runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        Toast.makeText(getActivity().getApplicationContext(),
                                "Json parsing error: " + e.getMessage(),
                                Toast.LENGTH_LONG)
                                .show();
                    }
                });
            }
        } else {
            Log.e(TAG, "Couldn't get json from server.");
            getActivity().runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    Toast.makeText(getActivity().getApplicationContext(),
                            "Couldn't get json from server. Check LogCat for possible errors!",
                            Toast.LENGTH_LONG)
                            .show();
                }
            });
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        super.onPostExecute(result);

        pDialog.dismiss();


    }
}

Answer 1

问题从这里开始

 @Override
public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);
    if (isVisibleToUser && !isFragmentLoaded ) {

        new GetContacts().execute();

        isFragmentLoaded = true;
    }
}

你应该在这里检查 getActivity（） null或不

 @Override
public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);
    if (getActivity() != null)
     {
        if (isVisibleToUser && !isFragmentLoaded ) {

            new GetContacts().execute();

            isFragmentLoaded = true;
        }
    }
else
  {
     // NPE. You Must pass Context
   }
} 

<强>其次

检查您的onAttach方法。在这里传递上下文

修改

将Context context;声明为全局。 然后将context= container.getContext();放入 onCreateView 部分

最后，您可以调用上下文而不是 getActivity（）;

Answer 2

尝试在userVisibleHint（）;

中初始化pDialog

    @Override
    public void setUserVisibleHint(boolean isVisibleToUser) {
        super.setUserVisibleHint(isVisibleToUser);
        if (isVisibleToUser) {
    pDialog = new ProgressDialog(getActivity());
            new GetContacts().execute();


        }
    }

在预执行中

 @Override
    protected void onPreExecute() {
        super.onPreExecute();

if(pDialog ==null)
{
pDialog = new ProgressDialog(getActivity());
}

        pDialog.setMessage("Please wait...");
        pDialog.setCancelable(false);
        pDialog.show();
    }

Answer 3

尝试使用Context。可能是getActivity（）返回null。使用Context方法

中的onAttach

private Context context;
...
...
@Override
public void onAttach(Context context) {
    super.onAttach(context);
    this.context = context;
}

传递context

pDialog = new ProgressDialog(context);