如何访问AsyncTask中的自定义参数？

我想加载图像异步并在infowindow上显示它们。为此，我制作了一个自定义类来存储参数。我需要这个（标记，图像），但我的代码会抛出运行时异常说它无法调用存储在自定义类实例中的标记I上的getPosition。什么是使用AsyncTask自定义类实例参数的正确方法？如何访问AsyncTask中的自定义参数？

这是我的代码：

googleMap.setOnMarkerClickListener(new GoogleMap.OnMarkerClickListener() { 
        @Override 
        public boolean onMarkerClick(Marker marker) { 
         LatLng latLng = marker.getPosition(); 
         // find location id in database 
         Location location = dbhandler.getLocationByLatLng(latLng); 
         final int id = location.getId(); 
         addButton.setVisibility(View.VISIBLE); 
         addButton.setOnClickListener(new View.OnClickListener() { 
          @Override 
          public void onClick(View v) { 
           // open load image fragment 
           android.support.v4.app.FragmentManager fragmentManager = getActivity().getSupportFragmentManager(); 
           android.support.v4.app.FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction(); 

           LoadImageFragment fragment = new LoadImageFragment(); 
           // pass id to new fragment 
           Bundle bundle = new Bundle(); 
           bundle.putInt("id", id); 
           fragment.setArguments(bundle); 

           fragmentTransaction.replace(R.id.fragment_container, fragment); 
           fragmentTransaction.commit(); 
          } 
         }); 
         removeButton.setVisibility(View.VISIBLE); 
         removeButton.setOnClickListener(new View.OnClickListener() { 
          @Override 
          public void onClick(View v) { 
           // remove markers and images 
          } 
         }); 
         class TaskParams { 
          Marker marker; 
          Location location; 
          Image image; 

          TaskParams() { 
          } 

          public Location getLocation() { 
           return this.location; 
          } 
          public Marker getMarker() { 
           return this.marker; 
          } 
          public Image getImage(){ 
           return this.image; 
          } 
          public void setMarker(Marker marker) { 
           this.marker = marker; 
          } 

          public void setLocation(Location location) { 
           this.location = location; 
          } 

          public void setImage(Image image) { 
           this.image = image; 
          } 
         } 
         TaskParams taskParams = new TaskParams(); 
         taskParams.setMarker(marker); 
         new AsyncTask<TaskParams, Void, TaskParams>() { 
          @Override 
          protected TaskParams doInBackground(TaskParams... params) { 
           TaskParams tParams = params[0]; 
           Marker m = tParams.getMarker(); 
           LatLng latLng = m.getPosition(); 
           Location location = dbhandler.getLocationByLatLng(latLng); 

           tParams.setLocation(location); 


           return tParams; 
          } 
          // find image and text associated with Location 
          protected void onPostExecute(TaskParams taskParams) { 

           new AsyncTask<TaskParams, Void, TaskParams>() { 
            @Override 
            protected TaskParams doInBackground(TaskParams... params) { 
             TaskParams tParams = params[0]; 
             Location location = tParams.getLocation(); 
             try { 
              image = dbhandler.getImageByLocationId(location.getId()); 
              tParams.setImage(image); 
             } 
             catch (Exception ex){ 
              Log.d("debug", "failed to fetch image"); 
              image = null; 
             } 
             return tParams; 
            } 
            @Override 
            protected void onPostExecute(TaskParams taskParams) { 
             Image image = taskParams.getImage(); 
             // set image and description 
             if(image != null) { 
              infoImageView.setImageBitmap(image.getBitmap()); 
              infoTextView.setText(image.getDescription()); 

              Marker marker = taskParams.getMarker(); 
              marker.showInfoWindow(); 

              updateInfoWindow(image); 
             } 
            } 
           }.execute(taskParams); 
          } 
         }.execute(taskParams); 
         //marker.showInfoWindow(); 
         return true; 
        } 
       }); 

       // find Location in database 

       // Setting a custom info window adapter for the google map 
       googleMap.setInfoWindowAdapter(new InfoWindowAdapter() { 
        // Use default InfoWindow frame 
        @Override 
        public View getInfoWindow(Marker arg0) { 
         return null; 
        } 

        // Defines the contents of the InfoWindow 
        @Override 
        public View getInfoContents(Marker arg0) { 
         // Getting view from the layout file info_window_layout 
         View v = getActivity().getLayoutInflater().inflate(R.layout.info_window_layout, null); 

         // Getting the position from the marker 
         final LatLng latLng = arg0.getPosition(); 

         infoImageView = (ImageView) v.findViewById(R.id.infoImage); 
         infoTextView = (TextView) v.findViewById(R.id.infoText); 
         if(image != null) { 
          infoImageView.setImageBitmap(image.getBitmap()); 
          infoTextView.setText(image.getDescription()); 
         } 

         return v; 
        } 

       });

来源

2017-08-05 no-name

您可以覆盖的构造。喜欢的东西：

private class MyAsyncTask extends AsyncTask<Void, Void, Void> { 

public MyAsyncTask(boolean showLoading) { 
    super(); 
    // do stuff 
} 

// doInBackground() et al. 
}

然后，调用任务的时候，做这样的事情：

new MyAsyncTask(true).execute(maybe_other_params);

这比创建成员变量，因为它简化了任务调用更加有用。比较上面的代码：

MyAsyncTask task = new MyAsyncTask(); 
task.showLoading = false; 
task.execute();

来源

2017-08-05 14:20:44

如何访问AsyncTask中的自定义参数？

回答

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