Question

我是Java的新手，因为这个问题属于我工作的时间敏感项目，所以我没有时间学习AsyncTasks的所有内容。所以我的问题是：

如何使用以下代码构建AsyncTask？

目标是在地图上绘制路线。我用ArrayList填充了两个Geopoints（路线的起始位置和目的地）。 roadManager应该将这些航点发送给服务器，该服务器将回送路线。

buildRoadOverlay是最终在地图上绘制路线的方法。

    RoadManager roadManager = new OSRMRoadManager(this);

    ArrayList<GeoPoint> waypoints = new ArrayList<GeoPoint>();
    GeoPoint myLocation = new GeoPoint(51.488978, 6.746994);
    waypoints.add(Location);
    waypoints.add(myLocation);
    Road road = roadManager.getRoad(waypoints);

我想这必须进入onPostExecute方法，对吧？：

    Polyline roadOverlay = RoadManager.buildRoadOverlay(road);
    map.getOverlays().add(roadOverlay);

来自上层代码的变量location来自不同的方法，我打算从中启动异步任务。这意味着，我需要在调用它时将变量传递给AsyncTask，我也不确定该怎么做。

这是变量location：

的初始化

GeoPoint Location = new GeoPoint(Double.parseDouble(place.getLongitude()), 
    Double.parseDouble(place.getLatitude()));

Answer 1

将耗时的任务放在onPostExecute（）的doInBackground（），udpate视图中。

public void drawRouteAsync() {
    GeoPoint location = new GeoPoint(Double.parseDouble(place.getLongitude()),
            Double.parseDouble(place.getLatitude()));
    GeoPoint myLocation = new GeoPoint(51.488978, 6.746994);

    new RouteAsyncTask().execute(location, myLocation);
}

private class RouteAsyncTask extends AsyncTask<GeoPoint, Void, Road> {
    @Override
    protected Road doInBackground(GeoPoint... params) {
        ArrayList<GeoPoint> waypoints = new ArrayList<GeoPoint>();
        waypoints.add(params[0]); // location
        waypoints.add(params[1]); // myLocation
        RoadManager roadManager = new OSRMRoadManager(mContext); // your context
        Road road = roadManager.getRoad(waypoints); // time consuming
        return road;
    }

    @Override
    protected void onPostExecute(Road road) {
        Polyline roadOverlay = RoadManager.buildRoadOverlay(road);
        map.getOverlays().add(roadOverlay); // update view
    }
}

Answer 2

AsyncTask 有3个重要方法：

protected void onPreExecute() //主线程
protected E doInBackground(T... params) // async thread
protected void onPostExecute(E result) //主线程

E和T将在实施过程中定义。

知道这一点，你的AsincTask应该看起来像这样：

public class GetRouteTask extends AsyncTask<GeoPoint, Void, Integer> {

    private Context mContext;
    private OnGetRouteCompleted delegate;
    private Road route;

    public GetRouteTask (Context context, OnGetRouteCompleted delegate) {
        this.delegate = delegate;
        this.mContext = context;
    }

    @Override
    protected Integer doInBackground(GeoPoint... params) {
        ArrayList<GeoPoint> wayPoints = new ArrayList<GeoPoint>();
        wayPoints.add(params[0]); // pointFrom 
        wayPoints.add(params[1]); // pointTo 

        try {
            RoadManager roadManager = new OSRMRoadManager(mContext);
            route = roadManager.getRoad(waypoints);
            return 1;
        } catch (JSONException e) {
            return -1;
        }
    }

    @Override
    protected void onPostExecute(Integer success) {
        if (success == 1) {
            delegate.onGetRouteCompleted(true, route);
        } else {
            delegate.onGetRouteCompleted(false, null);
        }
        Polyline roadOverlay = RoadManager.buildRoadOverlay(road);
        map.getOverlays().add(roadOverlay); // update view
    }

    public interface OnGetRouteCompleted {
        public void onGetRouteCompleted(boolean success, Route route);
    }
}

这就是你如何使用它：

public class SomeActivity extend Activity implements OnGetRouteCompleted {

    // Methods and properties...

    public void drawRouteAsync() {
        GeoPoint pointFrom = new GeoPoint(51.489878, 6.143294);
        GeoPoint pointTo = new GeoPoint(51.488978, 6.746994);

        new GetRouteTask(getApplicationContext(), this).execute(new GeoPoint(){pointFrom , pointTo});
    }

    @Override
    public void onGetRouteCompleted(boolean success, Route route) {
        if (success) {
            Polyline roadOverlay = RoadManager.buildRoadOverlay(route);
            map.getOverlays().add(roadOverlay); // update view
        }
    }
}

如何正确创建AsyncTask

2 个答案: