Question

我想加载图片异步并在infowindow上显示它们。为此我创建了一个自定义类来存储参数。我需要这个（标记，图像），但是我的代码抛出运行时异常，说它不能在我存储在自定义类实例中的标记上调用getPosition 。使用自定义类实例参数的正确使用AsyncTask 的方法是什么？

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;
                    }

                });

Answer 1

您可以覆盖构造函数。类似的东西：

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

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

// doInBackground() et al.
}

然后，在调用任务时，执行以下操作：

new MyAsyncTask(true).execute(maybe_other_params);

这比创建成员变量更有用，因为它简化了任务调用。将上面的代码与：

进行比较

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

如何在AsyncTask中访问自定义参数？

1 个答案: