将AsyncTask结果传递给Fragment中的onCreateView

Question

我的情况是:在我的onCreate()中，我想创建一个AsyncTask来检索WebService的数据并将其存储在ArrayList中(检索点为图)。

然后在我的onCreateView()中，我想使用ArrayList并迭代它来绘制点…

我想通过某种方式确保我等待AsyncTask在开始onCreateView()函数之前完成执行。然后我在onPostExecute中使用回调，但它不起作用。我读到关于在任务上使用get()，但是如果我使用get()方法UI将被阻塞。所以唯一可能的方法是在onPostExecute中使用回调方法。

但是我的代码在完成Aysnctask onCreateView执行并在这行获得NullPointer Exception (PF.size() != 0)之前是这样运行的。

package hello.aws.graphs;
import android.support.v7.app.AppCompatActivity;
import android.app.AlertDialog;
import android.app.ProgressDialog;
import hello.aws.login.WebService;
public class PFGraph extends AppCompatActivity implements AsyncTaskCompleteListener {
public static boolean errored = false;
static ProgressDialog dialog = null;

public static Menu menu;
static ArrayList<PFKVABean> PF;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_line_chart);
     getData();/*Getting data from webservice**/

    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction().add(R.id.container, new PlaceholderFragment()).commit();
    }

}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    Intent newIntent;

    switch (item.getItemId()) {

        case R.id.bb_menu_favorites:
        getData();/*Getting data from webservice**/
            break;
        case R.id.bb_menu_recent:
        getData();/*Getting data from webservice**/
            break;
        case R.id.bb_menu_recents:
            getData();/*Getting data from webservice**/
            break;
}
    return true;
}
public void getData()
{
    AsyncCallWS task = new AsyncCallWS(this);
        task.execute();
}

@java.lang.Override
public void onTaskComplete(Object result) {
    PF=(ArrayList)result;//Storing result of AsyncTask
    Log.e("check","check");
}

/**
 * A fragment containing a line chart.
 */
public static class PlaceholderFragment extends Fragment {
    private LineChartView chart;
    private LineChartData data;

    private int numberOfLines = 2;
    private boolean hasLines = true;
    private boolean hasPoints = true;
    private ValueShape shape = ValueShape.CIRCLE;
    private boolean isFilled = false;
    private boolean hasLabels = false;
    private boolean isCubic = false;
    private boolean hasLabelForSelected = false;


    public PlaceholderFragment() {

    }
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        setHasOptionsMenu(true);

        View rootView = inflater.inflate(R.layout.fragment_pf_graph, container, false);
        chart = (LineChartView) rootView.findViewById(R.id.chart);
        chart.setOnValueTouchListener(new ValueTouchListener());

        generateData();

        return rootView;
    }

    private void generateData() {
        chart.setZoomEnabled(true);
        chart.setZoomType(ZoomType.HORIZONTAL);
        List<Line> lines = new ArrayList<Line>();
        List<AxisValue> axisValues = new ArrayList<AxisValue>();
        if(!errored) {
            if (PF.size() != 0) {/******NULL Pointer Exception***/
            /****Here the logic for plotting the points on graph***/
        }
        else
        {
            Toast.makeText(getActivity(), "Error occured in invoking Webservice", Toast.LENGTH_LONG).show();
        }
    }
}
}

private class AsyncCallWS extends AsyncTask<String, Void, ArrayList> {
    private AsyncTaskCompleteListener<ArrayList> callback;
    public AsyncCallWS(AsyncTaskCompleteListener<ArrayList> cb) {
        this.callback = cb;
    }
    @java.lang.Override
    protected ArrayList doInBackground(String... params) {
        PF=WebService.GetWSData();
        return PF;
    }
    @Override
    protected void onPreExecute() {
        dialog = new ProgressDialog(PFGraph.this, R.style.MyTheme);
        dialog.setProgressStyle(android.R.style.Widget_ProgressBar_Small);
        dialog.setIndeterminateDrawable(getResources().getDrawable(R.drawable.cp_bar));
        dialog.setCancelable(false);
        dialog.show();
       // getSupportFragmentManager().beginTransaction().replace(R.id.container, new PlaceholderFragment()).commit();

    }

    @Override
    protected void onPostExecute(ArrayList PF) {
        if(dialog!=null||dialog.isShowing()) {
            dialog.dismiss();
            Log.e("v","v");
            callback.onTaskComplete(PF);//Sending result
        }
    }
}
}

Answer 1

将对generateData();的调用从onCreateView()移动到onTaskComplete()，以便仅在数组被填充后才调用