AsyncTask - 直到 doInBackground 完成后才调用 onProgressUpdate

Question

我搜索了其他帖子，但没有找到任何描述我的特定问题的帖子。其中许多是指从 doInBackground 调用 publishProgress。我正在从 onPreExecute 调用 publishProgress，期望显示一个对话框以通知用户正在获取数据。 AsyncTask 正在从用户从 Spinner 中进行选择启动。 UI 不会显示对话框，而是冻结直到 AsyncTask 完成。我已在日志消息中添加，看起来虽然在 onPreExecute 中调用了 publishProgress，但直到 doInBackground 完成后才会执行 onProgressUpdate。

活动：

public class MainActivity extends Activity implements OnItemSelectedListener{

private Spinner spinner;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

}



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

    spinner = (Spinner)findViewById(R.id.spinner);
    SpinnerAdapter adapter = new CustomSpinnerAdapter<String>(this, new String[]{"one", "two", "three"});
    spinner.setAdapter(adapter);
    spinner.setOnItemSelectedListener(this);

}



@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@SuppressLint("NewApi")
@Override
public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
    try{
        FetchDataTask fetchDataTask = new FetchDataTask();
        if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB){
            fetchDataTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, "data");
        } else{
            fetchDataTask.execute("data");
        }
        fetchDataTask.await();
    } catch (InterruptedException e){
        e.printStackTrace();
    }
}

@Override
public void onNothingSelected(AdapterView<?> arg0) {
    // TODO Auto-generated method stub

}

public class FetchDataTask extends AsyncTask<String, Integer, Boolean> {

    private  final String TAG = FetchDataTask.class.getSimpleName();
    private  final Integer FETCHING_DATA = 1;

    CountDownLatch countDownLatch = new CountDownLatch(1);
    ProgressDialog dialog;

    @Override
    protected void onPostExecute(Boolean result) {
        super.onPostExecute(result);
        Log.d(TAG,"Exiting onPostExecute");     
        dialog.dismiss();       
    }

    @Override
    protected void onPreExecute() {
        // TODO Auto-generated method stub
        super.onPreExecute();
        publishProgress(FETCHING_DATA);
        Log.d(TAG, "Exiting onPreExecute");
    }

    @Override
    protected void onProgressUpdate(Integer... values) {
        super.onProgressUpdate(values);
        dialog = ProgressDialog.show(MainActivity.this, "Fetching", "Data");
        Log.d(TAG, "Exiting onProgressUpdate");

    }

    @Override
    protected Boolean doInBackground(String... arg0) {

        /*
         *  Fetching data here
         */

        Log.d(TAG, "Exiting doInBackground");
        countDownLatch.countDown();
        return true;
    }

    public void await() throws InterruptedException{
        countDownLatch.await();
    }

}
}

旋转器：

public class CustomSpinnerAdapter<T> implements SpinnerAdapter {

Context context;
T[] values;

public CustomSpinnerAdapter(Context context, T[] values){
    this.context = context;
    this.values = values;
    for(T value: this.values){
        Log.d("Spinner", value.toString());
    }
}

@Override
public int getCount() {
    // TODO Auto-generated method stub
    return values.length;
}

@Override
public Object getItem(int position) {
    // TODO Auto-generated method stub
    return values[position];
}

@Override
public long getItemId(int position) {
    // TODO Auto-generated method stub
    return position;
}

@Override
public int getItemViewType(int position) {
    // TODO Auto-generated method stub
    return android.R.layout.simple_spinner_dropdown_item;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    // TODO Auto-generated method stub
    TextView v = new TextView(context);
    v.setTextColor(Color.BLACK);
    v.setText(values[position].toString());
    return v;
}

@Override
public int getViewTypeCount() {
    // TODO Auto-generated method stub
    return 1;
}

@Override
public boolean hasStableIds() {
    // TODO Auto-generated method stub
    return false;
}

@Override
public boolean isEmpty() {
    // TODO Auto-generated method stub
    return false;
}

@Override
public void registerDataSetObserver(DataSetObserver observer) {
    // TODO Auto-generated method stub

}

@Override
public void unregisterDataSetObserver(DataSetObserver observer) {
    // TODO Auto-generated method stub

}

@Override
public View getDropDownView(int position, View convertView, ViewGroup parent) {
    // TODO Auto-generated method stub
    return this.getView(position, convertView, parent);
}

}

观点：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content">

<Spinner
    android:id="@+id/spinner"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
     />

</RelativeLayout>

我认为这可能与从 Spinner 选择中执行 AsyncTask 有关，因为仅在 Activity 中执行它而不将其连接到 Spinner 不会出现此问题。任何帮助将不胜感激。

Answer 1

您不会继续显示进度更新对话框，而是显示它onPreExecute 更新它onProgressUpdate 并隐藏它onPostExecute 或cancel。在您的情况下，您不需要发布进度，因为 progressBar 是不确定的

    @Override
    protected void onPreExecute()
    {
        super.onPreExecute();
        Log.d(TAG, "Exiting onPreExecute");
        dialog = ProgressDialog.show(MainActivity.this, "Fetching", "Data");
    }

    @Override
    protected Boolean doInBackground(String... arg0)
    {
        Log.d(TAG, "Exiting doInBackground");
        countDownLatch.countDown();
        //publishProgress(x);
        return true;
    }

    public void await() throws InterruptedException
    {
        countDownLatch.await();
    }

    @Override
    protected void onProgressUpdate(Integer... values)
    {
        super.onProgressUpdate(values);
        Log.d(TAG, "Exiting onProgressUpdate");
        // update progressbar value
        // ex progresssBar.setProgress(values[0]);

    }
    @Override
    protected void onPostExecute(Boolean result)
    {
        super.onPostExecute(result);
        Log.d(TAG,"Exiting onPostExecute");     
        dialog.dismiss();       
    }