Drawing a rectangle onto a Google Map

问题

My plan is to allow user to draw a rectangle onto a map in order to mark an area and later save it. I found a method to do it, but it does nothing. Here is how the code looks so far.

public class Map extends MapActivity{

private MapView mvMap;
MapController kontrol;
float xs, ys, xe, ye;
GeoPoint start, end;
private Paint paint = new Paint();
private boolean up = false;

@Override
protected void onCreate(Bundle arg0) {
    // TODO Auto-generated method stub
    super.onCreate(arg0);
    setContentView(R.layout.map);
    mvMap = (MapView) findViewById(R.id.mvMap);
    mvMap.setBuiltInZoomControls(true);
    paint.setStrokeWidth(2.0f);
//  
//  DrawOverlay t = new DrawOverlay();
//  List<Overlay> olList = mvMap.getOverlays();
//  olList.add(t);
    mvMap.getOverlays().add(new EmptyOverlay());
    mvMap.postInvalidate();
    kontrol = mvMap.getController();
    GeoPoint ja = new GeoPoint(52172722, 21071987);
    kontrol.animateTo(ja);
    kontrol.setZoom(11);
}

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

class DrawOverlay extends Overlay{
    public boolean onTouchEvent(MotionEvent e, MapView m){
        if(up = false){
            if(e.getAction() == MotionEvent.ACTION_DOWN){
                xs = ys = 0;
                xs = e.getX();
                ys = e.getY();
                start = mvMap.getProjection().fromPixels((int)xs,(int)ys);
                //draw(null, m, up);
            }
            if(e.getAction() == MotionEvent.ACTION_MOVE){
                xe = e.getX();
                ye = e.getY();
                end = mvMap.getProjection().fromPixels((int)xe,(int)ye);

            }
            if(e.getAction() == MotionEvent.ACTION_UP){
                up = true;
            }
        }
        return true;
    }

    @Override
    public boolean draw(Canvas canvas, MapView mapView, boolean shadow,
            long when) {

        if(start != null && end != null){
            //get the 2 geopoints defining the area and transform them to pixels
            //this way if we move or zoom the map rectangle will follow accordingly
            Point screenPts1 = new Point();
            mapView.getProjection().toPixels(start, screenPts1);
            Point screenPts2 = new Point();
            mapView.getProjection().toPixels(end, screenPts2);

            //draw inner rectangle
            paint.setColor(0x4435EF56);
            paint.setStyle(Style.FILL);
            canvas.drawRect(screenPts1.x, screenPts1.y, screenPts2.x, screenPts2.y, paint);
            //draw outline rectangle
            paint.setColor(0x88158923);
            paint.setStyle(Style.STROKE);
            canvas.drawRect(screenPts1.x, screenPts1.y, screenPts2.x, screenPts2.y, paint);
        }
        return true;
    }

}

public class EmptyOverlay extends Overlay {
    private float x1,y1;
    private Overlay overlay = null;

    public EmptyOverlay(){

    }

    @Override
    public boolean draw(Canvas canvas, MapView mapView, boolean shadow,
            long when) {
        // TODO Auto-generated method stub
        return super.draw(canvas, mapView, shadow, when);
    }

    @Override
    public boolean onTouchEvent(MotionEvent e, MapView mapView) {
    //  if(mv.isEditMode()){
            if(e.getAction() == MotionEvent.ACTION_DOWN){
                //when user presses the map add a new overlay to the map
                //move events will be catched by newly created overlay
                x1 = y1 = 0;
                x1 = e.getX();
                y1 = e.getY();

                overlay = new DrawOverlay();
                mapView.getOverlays().add(overlay);

            }
            if(e.getAction() == MotionEvent.ACTION_MOVE){
            }
            //---when user lifts his finger---
            if (e.getAction() == MotionEvent.ACTION_UP) {                

            }    
           // return true;
//      }
        return false;
    }
}

I will be grateful for any help.

回答1:

Use this code it will work for Your on drawing a rectangel with inside text over any mark location., this code will draw many rectangles for many friends which we have passed through overlay item,

      public void draw(android.graphics.Canvas canvas, MapView mapView,
                  boolean shadow)
{
    super.draw(canvas, mapView, shadow);

    // go through all OverlayItems and draw title for each of them
    for (OverlayItem item:mOverlays)
    {

        GeoPoint point = item.getPoint();
        Point markerBottomCenterCoords = new Point();
        mapView.getProjection().toPixels(point, markerBottomCenterCoords);

        /* Find the width and height of the title*/
        TextPaint paintText = new TextPaint();
        Paint paintRect = new Paint();

        Rect rect = new Rect(markerBottomCenterCoords.x,markerBottomCenterCoords.y,33,44);
        paintText.setTextSize(FONT_SIZE);
        paintText.getTextBounds(item.getTitle(), 0, item.getTitle().length(), rect);
       // rect.height()=34;
        rect.inset(-TITLE_MARGIN, -TITLE_MARGIN);
        int markerHeight=34;// this will place to a height of 34 athe top of the mark location
        rect.offsetTo(markerBottomCenterCoords.x - rect.width()/2, markerBottomCenterCoords.y - markerHeight - rect.height());

        paintText.setTextAlign(Paint.Align.CENTER);
        paintText.setTextSize(FONT_SIZE);
        paintText.setARGB(255, 255, 255, 255);
        paintRect.setARGB(255,148,0,211);//s(255, 178, 34, 34);
        paintRect.setTextAlign(Align.CENTER);
        canvas.drawRoundRect( new RectF(rect), 0, 29, paintRect);
       canvas.drawText(item.getTitle(), rect.left + rect.width() / 2,
                rect.bottom - TITLE_MARGIN, paintText);

    }
}

来源：https://stackoverflow.com/questions/10567058/drawing-a-rectangle-onto-a-google-map