在地图上创建自定义叠加层

Question

我正在尝试在Android中复制Google地图的这一功能：

你可以在地图上看到一个圆圈，描绘了用户选择的范围。

在我的应用程序中，我还希望拖动器驻留在圆周上，可以拖动它来重新定义半径。

如果有人能告诉我如何在地图上绘制自定义可绘制叠加和2D图形，我可以自己做其他事情。

谢谢！

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Answer 1

好的，我试着在我自己身上做点什么，并把这段代码用来取得上述效果：

public class MarkerOverlay extends Overlay {

    Geocoder geoCoder = null;

    public MarkerOverlay() {
        super();
    }


    @Override
    public boolean onTap(GeoPoint geoPoint, MapView mapView){
        selectedLatitude = geoPoint.getLatitudeE6(); 
        selectedLongitude = geoPoint.getLongitudeE6();
        return super.onTap(geoPoint,mapView);
    }

    @Override
    public void draw(Canvas canvas, MapView mapV, boolean shadow){

        if(shadow){
            Projection projection = mapV.getProjection();
            Point pt = new Point();
            projection.toPixels(globalGeoPoint,pt);

            GeoPoint newGeos = new GeoPoint(selectedLat+(100),selectedLong); // adjust your radius accordingly
            Point pt2 = new Point();
            projection.toPixels(newGeos,pt2);
            float circleRadius = Math.abs(pt2.y-pt.y);

            Paint circlePaint = new Paint(Paint.ANTI_ALIAS_FLAG);

            circlePaint.setColor(0x30000000);
            circlePaint.setStyle(Style.FILL_AND_STROKE);
            canvas.drawCircle((float)pt.x, (float)pt.y, circleRadius, circlePaint);

            circlePaint.setColor(0x99000000);
            circlePaint.setStyle(Style.STROKE);
            canvas.drawCircle((float)pt.x, (float)pt.y, circleRadius, circlePaint);

            Bitmap markerBitmap = BitmapFactory.decodeResource(getApplicationContext().getResources(),R.drawable.pin);
            canvas.drawBitmap(markerBitmap,pt.x,pt.y-markerBitmap.getHeight(),null);

            super.draw(canvas,mapV,shadow);
        }
    }
}

这让我有以下效果：

使用的计算可能不是您想要的 它仅用于演示目的。
实际距离/距离计算也需要使用轴承，并有一些特定的公式 如果您对此有任何疑问，请与我们联系。

Answer 2

扩展班级ItemizedOverlay以覆盖draw()方法。绘制叠加层的Canvas会传递给该方法，您可以调用drawCircle或任何显示范围拖动器所需的内容。

Answer 3

用圆圈绘制图钉的示例代码：

public class MapDemoActivity extends MapActivity {
    MapView mapView;
    MapController mc;
    GeoPoint p;

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

    mapView = (MapView) findViewById(R.id.mapView);
    LinearLayout zoomLayout = (LinearLayout)findViewById(R.id.zoom);  
    View zoomView = mapView.getZoomControls(); 

    zoomLayout.addView(zoomView, 
        new LinearLayout.LayoutParams(
            LayoutParams.WRAP_CONTENT, 
            LayoutParams.WRAP_CONTENT)); 
    mapView.displayZoomControls(true);

    mc = mapView.getController();        
    String coordinates[] = {"28.38", "77.12"};
    double lat = Double.parseDouble(coordinates[0]);
    double lng = Double.parseDouble(coordinates[1]);

    p = new GeoPoint(
        (int) (lat * 1E6), 
        (int) (lng * 1E6));

    mc.animateTo(p);
    mc.setZoom(8); 
    //---Add a location marker---
    MapOverlay mapOverlay = new MapOverlay();
    List<Overlay> listOfOverlays = mapView.getOverlays();
    listOfOverlays.clear();
    listOfOverlays.add(mapOverlay);        
    mapView.invalidate();
    }

    class MapOverlay extends com.google.android.maps.Overlay
{
    @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(p, screenPts);
        //--------------draw circle----------------------            

        Point pt=mapView.getProjection().toPixels(p,screenPts);

        Paint circlePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        circlePaint.setColor(0x30000000);
        circlePaint.setStyle(Style.FILL_AND_STROKE);
        canvas.drawCircle(screenPts.x, screenPts.y, 50, circlePaint);           

        //---add the marker---
        Bitmap bmp = BitmapFactory.decodeResource(
            getResources(), R.drawable.pin);            
        canvas.drawBitmap(bmp, screenPts.x, screenPts.y-bmp.getHeight(), null);              
        super.draw(canvas,mapView,shadow);

        return true;

    }
}
@Override
protected boolean isRouteDisplayed() {
    // TODO Auto-generated method stub
    return false;
}
}