Worker thread from AsyncTask blocks UI thread

Question

I'm making an android application which downloads JSON file in the AsyncTask class after SEARCH BUTTON in Activity is clicked. And I want to display Progress Dialog on the Activity while downloading data. But on my AVD and device, actual action is different from my thought. See this video (about 1 minute) I uploaded. https://www.youtube.com/watch?v=qKyVGZ1FxIo&feature=youtube_gdata_player

In this video,after SEARCH BUTTON clicked the UI freeze for a while, and then ProgressDialog is shown for a very short moment and Toast is shown.

I want ProgressDialog to be shown right after click, and be dismissed right before Toast is shown.

ClickListner in Activity:

@Override
public void onClick(View v) {
    DownloadJSONFile task = new DownloadJSONFile(MainActivity.this);
    task.execute("1", "class", lectureName, teacherName, date, period, "");
}

AsyncTask:

import org.json.JSONArray;

import com.fc2.wiki.ap2012.komari.SearchResultActivity;

import android.app.ProgressDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.AsyncTask;
import android.widget.Toast;

public class DownloadJSONFile extends AsyncTask<String, Integer, JSONArray> {

private ProgressDialog dialog;
Context context;
JSONArray jsonArray;
boolean makeNewActivityFlag = true;

public DownloadJSONFile(Context context, boolean flag) {
    this.context = context;
    this.makeNewActivityFlag = flag;
}

@Override
protected void onPreExecute() {
    dialog = new ProgressDialog(this.context);
    dialog.setTitle("こまり");    //it's Japanese
    dialog.setMessage("通信中…");
    dialog.setIndeterminate(true);
    dialog.setCancelable(true);
    dialog.show();
}

doInBackground:

@Override
protected JSONArray doInBackground(String... keywords) {

    try {
        //for test
        while(!this.dialog.isShowing()){
            Thread.sleep(500);
        }

        //I will load JSON file here
        /*
        JSONArray jsonArray = UTaisakuDatabaseUtil.getInstance()
                .getJSONSearchResult(version, method, searchedLectureName,
                        searchedTeacherName, date, period, assessment);
        */

        //for test
        Thread.sleep(5000);

    } catch (NumberFormatException e) {
        // TODO 自動生成された catch ブロック
        e.printStackTrace();
    } catch (InterruptedException e) {
        // TODO 自動生成された catch ブロック
        e.printStackTrace();
    }

    return jsonArray;
}

onPostExecute:

@Override
protected void onPostExecute(JSONArray jsonArray) {

    this.jsonArray = jsonArray;
    if (this.dialog.isShowing())
        dialog.dismiss();

    if (this.makeNewActivityFlag) {

        // Intentを作成してSearchResultActivityへ
        if (jsonArray != null) {
            Intent intent = new Intent(this.context,
                    SearchResultActivity.class);
            intent.putExtra("LECTURE_NAME", searchedLectureName);
            intent.putExtra("TEACHER_NAME", searchedTeacherName);
            intent.putExtra("YOUBI", searchedDateString);
            intent.putExtra("PERIOD", searchedPeriodString);
            intent.putExtra("JSONARRAY", jsonArray.toString());
            context.startActivity(intent);
        } else

//in this test case,jsonArray is always null.So this Toast is always called
            Toast.makeText(context, "ファイルが取得できませんでした。", Toast.LENGTH_SHORT)
                    .show();
        }
    }
}

Any ideas?

Answer 1

I found a solution of my own problem! I used Context class in a field parameta of AsyncTask. I use Activity class instead of Context!All things are work fine.

public class DownloadJSONFile extends AsyncTask<String, Integer, JSONArray> {

    private ProgressDialog dialog;

    //this is the cause of bug
    //Context context;        

    //this is the answer
    Activity activity;

    JSONArray jsonArray;
    boolean makeNewActivityFlag = true;

    public DownloadJSONFile(Activity activity, boolean flag) {
        this.activity = activity;
        this.makeNewActivityFlag = flag;
    }
…
…
}

But I can't explain why it's work fine when using Activity class and not work fine when using Context class.Can someone explain this? If you have any ideas,please comment here.

Answer 2

Thanks for posting the solution, I had similar problem adopting the code taken from zxing/BarCodeReader. After removing the context from constructor parameters, sleeping is interrupted properly and does not stall the UI thread anymore:

  AutoFocusManager(Context context, Camera camera) {
    this.camera = camera;
    taskExec = new AsyncTaskExecManager().build();
    SharedPreferences sharedPrefs = PreferenceManager.getDefaultSharedPreferences(context);
    String currentFocusMode = camera.getParameters().getFocusMode();
    useAutoFocus =

        FOCUS_MODES_CALLING_AF.contains(currentFocusMode);
    Log.i(TAG, "Current focus mode '" + currentFocusMode + "'; use auto focus? " + useAutoFocus);
    start();
  }

       protected Object doInBackground(Object... voids) {
      try {
        Thread.sleep(AUTO_FOCUS_INTERVAL_MS);
      } catch (InterruptedException e) {
        // continue
      }
      synchronized (AutoFocusManager.this) {
        if (active) {
          start();
        }
      }
      return null;
    }