从异步任务返回时，片段未附加到活动

Question

I have added three fragment inside A_Activity. These are fragment_1, fragment_2, fragment_3

from fragment_1 I am calling an async class async_class

Here is my Fragment_1:

public class Fragment_1 extends Fragment {

ListView listView;
private TrainingGetData mTrainingGetData = null;
Context mContext;

public Fragment_1(){
}

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

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_1, container, false);

    mTrainingGetData = new TrainingGetData(getContext());
    mTrainingGetData.execute((String) null);
    return view;
}


public void setTitle(Context context, ArrayList<String> ids, ArrayList<String> titles, final ArrayList<String> urls){

    final Activity activity=(Activity) context;
    final ArrayAdapter adapter=new ArrayAdapter(context, android.R.layout.simple_list_item_1, titles);
    listView=(ListView) ((Activity) context).findViewById(R.id.listView_1);
    listView.setAdapter(adapter);

    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            Intent myIntent = new Intent(activity, AnotherActivity.class);
            myIntent.putExtra("url", urls.get(position));
    startActivity(myIntent);
        });
}

}

In the async class I do some task in the background and in post execude I have added these code

public class TrainingGetData extends AsyncTask<String, String, String> {
Fragment_1 fragment_1=new Fragment_1();

public TrainingGetData(Context context){
    mContext=context;
}

@Override
protected String doInBackground(String... params) {

    try {
        //do the processing
    }
    catch (JSONException e) {
        e.printStackTrace();
        return "JSON Data Parse Error";
    }
    catch (Exception e){
        e.printStackTrace();
        return "Unknown Error: Insert/Update Failed";
    }
    return null;
}

@Override
protected void onPostExecute(String message) {

    if(success == 0 && message.equals("No files found")){
        Toast.makeText(mContext, "Sorry No Data Found", Toast.LENGTH_SHORT).show();
    }

    if(success==1) {
        //do the processing
        fragment_1.setTitle(mContext, ids, titles, urls);
    }
}
}

But when I return to the fragment_1 setTitle method and click on any list item it shows that the fragment_1 is not attached to the Activity.

What went wrong? How can I solve this?

Thanks

Answer 1

But when I return to the fragment_1 setTitle method and click on any list item it shows that the fragment_1 is not attached to the Activity

Because currently creating new object of Fragment_1 for calling setTitle method.

Pass current Fragment Context in TrainingGetData class in same way as passing Context then call setTitle method. like:

Fragment_1 fragment_1;

public TrainingGetData(Context context,Fragment_1 fragment_1){
    mContext=context;
    this.fragment_1=fragment_1;
}

and create TrainingGetData object:

mTrainingGetData = new TrainingGetData(getContext(),Fragment_1.this);

Answer 2

You're getting the error because the fragment_1 object of your Fragment Fragment_1 has been instantiated inside your AsyncTask TrainingGetData. This is not the Fragment object which is connected to your Activity .

In order to solve the issue, you need to initialise fragment_1 object as shown below:

    fragment_1 = (Fragment) mContext;

Write the above line of code in the Constructor of AsyncTask TrainingGetData.

Answer 3

As you are creating new instance of fragment.

 Fragment_1 fragment_1=new Fragment_1();

these is not going to work

use fragment instance in TrainingGetData constructor and used it

  public TrainingGetData(Context context, Fragment_1  fragment_1) {
        mContext = context;
        this.fragment_1 = fragment_1;
    }