java - 位置每 35 秒更新一次，并在当前位置上画一个圆圈

Question

目前我正在我的当前位置上绘制一个圆，位置每改变35秒并且移动10米的距离。

所以我在 LocationChanged 下实现了这个功能，一旦位置发生变化(移动 35 秒和 10 米)，我在谷歌地图上的当前位置绘制一个 Circle 。

问题陈述:-

我的应用程序运行很慢。有时我的应用程序会挂起？可能是因为我的代码按照我在下面编写的方式效率不高？

基本上，我只需要在每移动 35 秒和 10 米的距离后在当前位置上绘制一个圆圈。

我的代码有问题吗？任何想法，比如我应该如何改进它，让它顺利运行。

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

    locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);    

    locationListener = new GPSLocationListener();

    locationManager.requestLocationUpdates(
            LocationManager.GPS_PROVIDER, 
            35000, 
            10, 
            locationListener);

    mapView = (MapView) findViewById(R.id.mapView);
    listView = (ListView) findViewById(R.id.mylist);
    mapView.setStreetView(true);
    mapView.setBuiltInZoomControls(true);
    mapController = mapView.getController();
    mapController.setZoom(15);
}

private class GPSLocationListener implements LocationListener {
    @Override
    public void onLocationChanged(Location location) {
        if (location != null) {
            GeoPoint point = new GeoPoint(
                    (int) (location.getLatitude() * 1E6), 
                    (int) (location.getLongitude() * 1E6));

            findUsersInCurrentRadius(4,location.getLatitude(),location.getLongitude());

            mapController.animateTo(point);
            mapController.setZoom(15);

            // add marker
            MapOverlay mapOverlay = new MapOverlay(this,android.R.drawable.star_on);
            mapOverlay.setPointToDraw(point);
            List<Overlay> listOfOverlays = mapView.getOverlays();
            listOfOverlays.clear();
            listOfOverlays.add(mapOverlay);

            String address = ConvertPointToLocation(point);
            Toast.makeText(getBaseContext(), address, Toast.LENGTH_SHORT).show();

            mapView.invalidate();
        }
    }

    @Override
    public void onProviderDisabled(String provider) {
    }

    @Override
    public void onProviderEnabled(String provider) {
    }

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {
    }
}

这是我的 MapOverlay 类，我正在其中绘制一个圆。

class MapOverlay extends Overlay {
    private GeoPoint pointToDraw;
    int[] imageNames=new int[6];

    public MapOverlay(GPSLocationListener gpsLocationListener, int currentUser) {
        imageNames[0]=currentUser;
    }

    public void setPointToDraw(GeoPoint point) {
        pointToDraw = point;
    }

    public GeoPoint getPointToDraw() {
        return pointToDraw;
    }

    @Override
    public boolean draw(Canvas canvas, MapView mapView, boolean shadow, long when) {
        super.draw(canvas, mapView, shadow);
        //---translate the GeoPoint to screen pixels---
        Point screenPts = new Point();
        mapView.getProjection().toPixels(pointToDraw, screenPts);
        //--------------draw circle----------------------
        Point pt = mapView.getProjection().toPixels(pointToDraw,screenPts);
        Paint circlePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        circlePaint.setColor(0x30000000);
        circlePaint.setStyle(Style.FILL_AND_STROKE);

        int totalCircle=4;
        int radius=40;
        int centerimagesize=35;

        for (int i = 1; i <= totalCircle; i ++) { 
            canvas.drawCircle(screenPts.x,screenPts.y, i*radius, circlePaint); 
        } 

        canvas.drawBitmap(BitmapFactory.decodeResource(getResources(),imageNames[0]), (screenPts.x-(centerimagesize/2)),(screenPts.y-(centerimagesize/2)), null);

        super.draw(canvas,mapView,shadow);

        return true;
    }


}

更新代码:-

private MapView mapView;
private ListView listView;

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

    mapView = (MapView) findViewById(R.id.mapView);
    listView = (ListView) findViewById(R.id.mylist);

    locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);    

    locationListener = new GPSLocationListener(mapView);

    locationManager.requestLocationUpdates(
            LocationManager.GPS_PROVIDER, 
            35000, 
            0, 
            locationListener);


    mapView.setStreetView(true);
    mapView.setBuiltInZoomControls(true);
    mapController = mapView.getController();
    mapController.setZoom(15);
}


    private class GPSLocationListener implements LocationListener {

    MapOverlay mapOverlay;

    public GPSLocationListener(MapView mapView) {
        mapOverlay = new MapOverlay(this,android.R.drawable.star_on);
        List<Overlay> listOfOverlays = mapView.getOverlays();
        listOfOverlays.add(mapOverlay);
    }

    @Override
    public void onLocationChanged(Location location) {
        if (location != null) {
            GeoPoint point = new GeoPoint(
                    (int) (location.getLatitude() * 1E6), 
                    (int) (location.getLongitude() * 1E6));

            mapController.animateTo(point);
            mapController.setZoom(15);

            // **See no need to make a new Object here**
            mapOverlay.setPointToDraw(point);
            mapView.invalidate();
        }
    }

    @Override
    public void onProviderDisabled(String provider) {
    }

    @Override
    public void onProviderEnabled(String provider) {
    }

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {
    }
}


    class MapOverlay extends Overlay {
    private GeoPoint pointToDraw;
    int[] imageNames=new int[6];
    private Point mScreenPoints;
    private Bitmap mBitmap;
    private Paint mCirclePaint;


    public MapOverlay(GPSLocationListener gpsLocationListener, int currentUser) {
        imageNames[0]=currentUser;
        mCirclePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mCirclePaint.setColor(0x30000000);
        mCirclePaint.setStyle(Style.FILL_AND_STROKE);
        mBitmap = BitmapFactory.decodeResource(getResources(),imageNames[0]);
        mScreenPoints = new Point();
    }

    public void setPointToDraw(GeoPoint point) {
        pointToDraw = point;
    }

    public GeoPoint getPointToDraw() {
        return pointToDraw;
    }

    public boolean draw(Canvas canvas, MapView mapView, boolean shadow, long when) {
        super.draw(canvas, mapView, shadow);
        mScreenPoints = mapView.getProjection().toPixels(pointToDraw, mScreenPoints);

        int totalCircle=4;
        int radius=40;
        int centerimagesize=35;

        for (int i = 1; i <= totalCircle; i ++) { 
            canvas.drawCircle(mScreenPoints.x,mScreenPoints.y, i*radius, mCirclePaint); 
        } 

        canvas.drawBitmap(mBitmap, (mScreenPoints.x-(centerimagesize/2)),(mScreenPoints.y-(centerimagesize/2)), null);
        super.draw(canvas,mapView,shadow);

        return true;
    }


} 

Answer 1

画画时要注意以下几点:

1. 不要阻塞主 UI 线程
2. 记住回收对象。
3. 记住回收对象。
4. 并始终记住回收对象。

可能的 UI 线程阻塞

这段代码看起来像是在 onLocationChanged() 的回调上调用一个可能代价高昂的操作，这样做真的很危险，因为您可能最终会陷入 ANR。这可能应该在后台 AsyncTask 上完成，然后在它的结果上显示 toast。

String address = ConvertPointToLocation(point);
Toast.makeText(getBaseContext(), address, Toast.LENGTH_SHORT).show();

更好地管理 map 上的资源

不要每次都添加一个新的叠加层，而是确保回收实例并重置它的位置。

private class GPSLocationListener implements LocationListener {
    MapOverlay mOverlay;

    public GPSLocationListener() {

    }

   @Override
   public void onLocationChanged(Location location) {
    if (location != null) {
        GeoPoint point = new GeoPoint(
                (int) (location.getLatitude() * 1E6), 
                (int) (location.getLongitude() * 1E6));

        findUsersInCurrentRadius(4,location.getLatitude(),location.getLongitude());

        mapController.animateTo(point);
        mapController.setZoom(15);

        if (mOverlay == null) {
            // Add this marker to the list of overlays always.
            // This stuff never changes so there is no need to do this logic
            // Every 30 secs. Loading images is **Expensive**
            mOverlay = mMapOverlay = new MapOverlay(this,android.R.drawable.star_on);
            List<Overlay> listOfOverlays = mapView.getOverlays();
            listOfOverlays.add(mMapOverlay);
        }
        // **See, no need to make a new Object here**
        mOverlay.setPointToDraw(point);

        // This can probably be done at another time.
        // String address = ConvertPointToLocation(point);
        // Toast.makeText(getBaseContext(), address, Toast.LENGTH_SHORT).show();

        mapView.invalidate();
    }

此代码可以重用此标记并仅更新其位置。如果它不在列表中，您应该只创建一个。

画得更好

好的，接下来请记住，如果没有必要，请不要在 onDraw() 方法中创建对象。一旦标记知道要绘制到哪里，您应该缓存所有内容，以便您可以专注于绘图。例如:

public class MapOverlay {

    private GeoPoint pointToDraw;
    int[] imageNames=new int[6];
    // This is the cached Point on the screen that will get refilled on every draw
    private Point mScreenPoints;
    // This is the cached decoded bitmap that will be drawn each time
    private Bitmap mBitmap;
    // Cached Paint
    private Paint mCirclePaint;

    public MapOverlay(GPSLocationListener gpsLocationListener, int currentUser) {
      imageNames[0]=currentUser;
      // This only needs to be made here, once. It never needs to change.
      mCirclePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
      mCirclePaint.setColor(0x30000000);
      mCirclePaint.setStyle(Style.FILL_AND_STROKE);
      // We only need to load this image once and then just keep drawing it when dirtyed.
      mBitmap = BitmapFactory.decodeResource(context.getResources(),imageNames[0]);
      // This Point object will be changed every call to toPixels(), but the instance can be recycled
      mScreenPoints = new Point();
    }

    public void setPointToDraw(GeoPoint point) {
      pointToDraw = point;
    }

    public GeoPoint getPointToDraw() {
      return pointToDraw;
    }

    public boolean draw(Canvas canvas, MapView mapView, boolean shadow, long when) {
      super.draw(canvas, mapView, shadow);
      // In the case where nothing has been set yet, don't do any drawing
      if (pointToDraw == null) {
         return true;
      }
      //--------------draw circle----------------------
      mScreenPoints = mapView.getProjection().toPixels(pointToDraw, mScreenPoints);

      int totalCircle=4;
      int radius=40;
      int centerimagesize=35;

      for (int i = 1; i <= totalCircle; i ++) { 
          canvas.drawCircle(screenPts.x,screenPts.y, i*radius, mCirclePaint); 
      } 

      canvas.drawBitmap(mBitmap, (screenPts.x-(centerimagesize/2)),(screenPts.y-(centerimagesize/2)), null);
      super.draw(canvas,mapView,shadow);

      return true;
    }