Java 如何使用多段线显示从当前位置到地图中已存储的目的地的路线，而无需单击地图来设置目的地

这是我的

main活动

，在点击目的地之前，它不会在地图加载时自动显示路线。我希望它使路线在开始时显示从当前位置到目的地的路线

public class MainActivity extends FragmentActivity implements LocationListener {

GoogleMap mGoogleMap;
ArrayList<LatLng> mMarkerPoints;
double mLatitude=27.7247789;
double mLongitude=85.320704;

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

    // Getting Google Play availability status
    int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(getBaseContext());

    if(status!=ConnectionResult.SUCCESS){ // Google Play Services are not available

        int requestCode = 10;
        Dialog dialog = GooglePlayServicesUtil.getErrorDialog(status, this, requestCode);
        dialog.show();

    }else { // Google Play Services are available

        // Initializing
        mMarkerPoints = new ArrayList<LatLng>();

        // Getting reference to SupportMapFragment of the activity_main
        SupportMapFragment fm = (SupportMapFragment)getSupportFragmentManager().findFragmentById(R.id.map);

        // Getting Map for the SupportMapFragment
        mGoogleMap = fm.getMap();

        // Enable MyLocation Button in the Map
        mGoogleMap.setMyLocationEnabled(true);


        // Getting LocationManager object from System Service LOCATION_SERVICE
        LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);

        // Creating a criteria object to retrieve provider
        Criteria criteria = new Criteria();

        // Getting the name of the best provider
        String provider = locationManager.getBestProvider(criteria, true);

        // Getting Current Location From GPS
        Location location = locationManager.getLastKnownLocation(provider);

        if(location!=null){
            onLocationChanged(location);
        }

        locationManager.requestLocationUpdates(provider, 20000, 0, this);

        // Setting onclick event listener for the map
        mGoogleMap.setOnMapClickListener(new OnMapClickListener() {

            @Override
            public void onMapClick(LatLng point) {

                // Already map contain destination location
                if(mMarkerPoints.size()>1){

                    FragmentManager fm = getSupportFragmentManager();
                    mMarkerPoints.clear();
                    mGoogleMap.clear();
                    LatLng startPoint = new LatLng(mLatitude, mLongitude);
                    drawMarker(startPoint);
                }

                drawMarker(point);

                // Checks, whether start and end locations are captured
                if(mMarkerPoints.size() >= 2){
                    LatLng origin = mMarkerPoints.get(0);
                    LatLng dest = mMarkerPoints.get(1);

                    // Getting URL to the Google Directions API
                    String url = getDirectionsUrl(origin, dest);

                    DownloadTask downloadTask = new DownloadTask();

                    // Start downloading json data from Google Directions API
                    downloadTask.execute(url);
                }
            }
        });
    }
}

private String getDirectionsUrl(LatLng origin,LatLng dest){

    // Origin of route
    String str_origin = "origin="+origin.latitude+","+origin.longitude;

    // Destination of route
    String str_dest = "destination="+dest.latitude+","+dest.longitude;

    // Sensor enabled
    String sensor = "sensor=false";

    // Building the parameters to the web service
    String parameters = str_origin+"&"+str_dest+"&"+sensor;

    // Output format
    String output = "json";

    // Building the url to the web service
    String url = "https://maps.googleapis.com/maps/api/directions/"+output+"?"+parameters;

    return url;
}

/** A method to download json data from url */
private String downloadUrl(String strUrl) throws IOException{
    String data = "";
    InputStream iStream = null;
    HttpURLConnection urlConnection = null;
    try{
        URL url = new URL(strUrl);

        // Creating an http connection to communicate with url
        urlConnection = (HttpURLConnection) url.openConnection();

        // Connecting to url
        urlConnection.connect();

        // Reading data from url
        iStream = urlConnection.getInputStream();

        BufferedReader br = new BufferedReader(new InputStreamReader(iStream));

        StringBuffer sb  = new StringBuffer();

        String line = "";
        while( ( line = br.readLine())  != null){
            sb.append(line);
        }

        data = sb.toString();

        br.close();

    }catch(Exception e){
        Log.d("Exception while downloading url", e.toString());
    }finally{
        iStream.close();
        urlConnection.disconnect();
    }
    return data;
}



/** A class to download data from Google Directions URL */
private class DownloadTask extends AsyncTask<String, Void, String>{

    // Downloading data in non-ui thread
    @Override
    protected String doInBackground(String... url) {

        // For storing data from web service
        String data = "";

        try{
            // Fetching the data from web service
            data = downloadUrl(url[0]);
        }catch(Exception e){
            Log.d("Background Task",e.toString());
        }
        return data;
    }

    // Executes in UI thread, after the execution of
    // doInBackground()
    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);

        ParserTask parserTask = new ParserTask();

        // Invokes the thread for parsing the JSON data
        parserTask.execute(result);

    }
}

/** A class to parse the Google Directions in JSON format */
private class ParserTask extends AsyncTask<String, Integer, List<List<HashMap<String,String>>> >{

    // Parsing the data in non-ui thread
    @Override
    protected List<List<HashMap<String, String>>> doInBackground(String... jsonData) {

        JSONObject jObject;
        List<List<HashMap<String, String>>> routes = null;

        try{
            jObject = new JSONObject(jsonData[0]);
            DirectionsJSONParser parser = new DirectionsJSONParser();

            // Starts parsing data
            routes = parser.parse(jObject);
        }catch(Exception e){
            e.printStackTrace();
        }
        return routes;
    }

    // Executes in UI thread, after the parsing process
    @Override
    protected void onPostExecute(List<List<HashMap<String, String>>> result) {
        ArrayList<LatLng> points = null;
        PolylineOptions lineOptions = null;

        // Traversing through all the routes
        for(int i=0;i<result.size();i++){
            points = new ArrayList<LatLng>();
            lineOptions = new PolylineOptions();

            // Fetching i-th route
            List<HashMap<String, String>> path = result.get(i);

            // Fetching all the points in i-th route
            for(int j=0;j<path.size();j++){
                HashMap<String,String> point = path.get(j);

                double lat = Double.parseDouble(point.get("lat"));
                double lng = Double.parseDouble(point.get("lng"));
                LatLng position = new LatLng(lat, lng);

                points.add(position);
            }

            // Adding all the points in the route to LineOptions
            lineOptions.addAll(points);
            lineOptions.width(2);
            lineOptions.color(Color.RED);

        }

        // Drawing polyline in the Google Map for the i-th route
        mGoogleMap.addPolyline(lineOptions);
    }
}


@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;
}

private void drawMarker(LatLng point){
    mMarkerPoints.add(point);

    // Creating MarkerOptions
    MarkerOptions options = new MarkerOptions();

    // Setting the position of the marker
    options.position(point);

    /**
     * For the start location, the color of marker is GREEN and
     * for the end location, the color of marker is RED.
     */
    if(mMarkerPoints.size()==1){
        options.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_GREEN));
    }else if(mMarkerPoints.size()==2){
        options.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_RED));
    }

    // Add new marker to the Google Map Android API V2
    mGoogleMap.addMarker(options);
}

@Override
public void onLocationChanged(Location location) {
    // Draw the marker, if destination location is not set
    if(mMarkerPoints.size() < 2){

        mLatitude = location.getLatitude();
        mLongitude = location.getLongitude();
        LatLng point = new LatLng(mLatitude, mLongitude);

        mGoogleMap.moveCamera(CameraUpdateFactory.newLatLng(point));
        mGoogleMap.animateCamera(CameraUpdateFactory.zoomTo(12));


        drawMarker(point);
    }

}

@Override
public void onProviderDisabled(String provider) {
    // TODO Auto-generated method stub
}

@Override
public void onProviderEnabled(String provider) {
    // TODO Auto-generated method stub
}

@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
    // TODO Auto-generated method stub
}
}

公共类MainActivity扩展FragmentActivity实现LocationListener{
谷歌地图；
ArrayList mMarkerPoints；
双曲率=27.7247789；
双倍长度=85.320704；
@凌驾
创建时受保护的void（Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
setContentView（R.layout.activity_main）；
//获取Google Play可用性状态
int status=GooglePlayServicesUtil.isGooglePlayServicesAvailable（getBaseContext（））；
如果（status！=ConnectionResult.SUCCESS）{//Google Play服务不可用
int requestCode=10；
Dialog Dialog=GooglePlayServicesUtil.getErrorDialog（状态、此、请求代码）；
dialog.show（）；
}其他{//Google Play服务可用
//初始化
mMarkerPoints=newarraylist（）；
//获取对活动\u main的SupportMapFragment的引用
SupportMapFragment fm=（SupportMapFragment）getSupportFragmentManager（）.findFragmentById（R.id.map）；
//正在获取SupportMapFragment的映射
mGoogleMap=fm.getMap（）；
//在地图中启用MyLocation按钮
mGoogleMap.setMyLocationEnabled（true）；
//从系统服务位置\u服务获取LocationManager对象
LocationManager LocationManager=（LocationManager）getSystemService（LOCATION\u服务）；
//创建条件对象以检索提供程序
标准=新标准（）；
//获取最佳提供商的名称
字符串提供程序=locationManager.getBestProvider（条件为true）；
//从GPS获取当前位置
Location Location=locationManager.getLastKnownLocation（提供者）；
如果（位置！=null）{
onLocationChanged（位置）；
}
locationManager.RequestLocationUpdate（提供程序，20000，0，此）；
//为映射设置onclick事件侦听器
setOnMapClickListener（新的OnMapClickListener（））{
@凌驾
公共空区（停车点）{
//地图已包含目标位置
如果（mMarkerPoints.size（）>1）{
FragmentManager fm=getSupportFragmentManager（）；
mMarkerPoints.clear（）；
mGoogleMap.clear（）；
LatLng startPoint=新LatLng（高度、长度）；
绘图标记（起点）；
}
绘图标记（点）；
//检查是否捕获开始和结束位置
如果（mMarkerPoints.size（）>=2）{
LatLng origin=mMarkerPoints.get（0）；
LatLng dest=mMarkerPoints.get（1）；
//获取Google Directions API的URL
字符串url=getDirectionsUrl（源、目标）；
DownloadTask DownloadTask=新的DownloadTask（）；
//开始从Google Directions API下载json数据
downloadTask.execute（url）；
}
}
});
}
}
私有字符串getDirectionsUrl（LatLng来源，LatLng目的地）{
//路线起点
字符串str_origin=“origin=“+origin.latitude+”，“+origin.longitude；
//路线目的地
字符串str_dest=“destination=”+dest.latitude+”，“+dest.longitude；
//传感器启用
字符串sensor=“sensor=false”；
//为web服务构建参数
字符串参数=str_origin+“&”+str_dest+“&”+传感器；
//输出格式
字符串输出=“json”；
//构建web服务的url
字符串url=”https://maps.googleapis.com/maps/api/directions/“+输出+”？“+参数；
返回url；
}
/**从url下载json数据的方法*/
私有字符串下载URL（字符串strUrl）引发IOException{
字符串数据=”；
InputStream iStream=null；
HttpURLConnection-urlConnection=null；
试一试{
URL=新URL（strUrl）；
//创建http连接以与url通信
urlConnection=（HttpURLConnection）url.openConnection（）；
//连接到url
urlConnection.connect（）；
//从url读取数据
iStream=urlConnection.getInputStream（）；
BufferedReader br=新的BufferedReader（新的InputStreamReader（iStream））；
StringBuffer sb=新的StringBuffer（）；
字符串行=”；
而（（line=br.readLine（））！=null）{
某人附加（行）；
}
data=sb.toString（）；
br.close（）；
}捕获（例外e）{
Log.d（“下载url时出现异常”，例如toString（））；
}最后{
iStream.close（）；
urlConnection.disconnect（）；
}
返回数据；
}
/**从Google Directions URL下载数据的类*/
私有类DownloadTask扩展了AsyncTask{
//在非ui线程中下载数据
@凌驾
受保护的字符串doInBackground（字符串…url）{
//用于存储来自web服务的数据
字符串数据=”；
试一试{
//从web服务获取数据
数据=下载url（url[0]）；
}捕获（例外e）{
Log.d（“后台任务”，例如toString（））；
}
返回数据；
}
//在UI线程中执行，在
//doInBackground（）
@凌驾
受保护的void onPostExecute（字符串结果）{
super.onPostExecute（结果）；
ParserTask ParserTask=新的ParserTask（）；
//调用线程以解析JSON数据
执行（结果）；
}
}
/**以JSON格式解析Google方向的类*/
私有类ParserT
locationManager.requestLocationUpdates(provider, 20000, 0, this);

Handler handler = new Handler();
Runnable runnable = new Runnable() {
    public void run() {
        // Already map contain destination location
            if(mMarkerPoints.size()>1){

                FragmentManager fm = getSupportFragmentManager();
                mMarkerPoints.clear();
                mGoogleMap.clear();
                LatLng startPoint = new LatLng(mLatitude, mLongitude);
                drawMarker(startPoint);
            }

            drawMarker(point);

            // Checks, whether start and end locations are captured
            if(mMarkerPoints.size() >= 2){
                LatLng origin = mMarkerPoints.get(0);
                LatLng dest = mMarkerPoints.get(1);

                // Getting URL to the Google Directions API
                String url = getDirectionsUrl(origin, dest);

                DownloadTask downloadTask = new DownloadTask();

                // Start downloading json data from Google Directions API
                downloadTask.execute(url);
            }               
    }
};
handler.postDelayed(runnable, 40000);