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Draw a Circle Graphic with ESRI Android SDK

14. November 2011 12:56 by Scott in Development, ESRI  //  Tags: , , ,   //   Comments (3)

I wrote this code a while back.  The requirement was to have a user draw a circle with the ESRI Android SDK.  Well, their Android SDK doesn't currently support drawing circles.  It draws all other types of polygons except for the circle.  So what does a Software Engineer do, we come up with our own implementation.

So for the world to see, here it is:

First we capture the OnMotionEvent and the comments are in line.

Hope this helps someone.

    public boolean onDragPointerMove(MotionEvent from, MotionEvent to) {

        if (tempCircleGraphic != null)
            _graphicsLayer.removeGraphic(tempCircleGraphic);

        // creates a new polygon to be drawn.
        _circleTemp = new Polygon();

        Point point = _map.toMapPoint(to.getX(), to.getY());

        // If the starting point is null, create a polyline and start a
        // path.
        if (_startPoint == null) {
            _startPoint = _map.toMapPoint(from.getX(), from.getY());
            // creates a polyline so we can measure the radius of the
            // person
            // drawing the circle.
            _polylineTemp = new Polyline();
            // starts the poly line
            _polylineTemp.startPath(_startPoint.getX(), _startPoint.getY());
        }
        // continues the draw of the poly line
        _polylineTemp.lineTo((float) point.getX(), (float) point.getY());

        // calculates the circle when getting ready to be drawn.
        int pointsAroundCircle = 50; // N
        double radius = _polylineTemp.calculateLength2D(); // radius
        for (int i = 0; i < pointsAroundCircle; i++) {
            double fi = 2 * Math.PI * i / pointsAroundCircle;
            double x = radius * Math.sin(fi + Math.PI) + _startPoint.getX();
            double y = radius * Math.cos(fi + Math.PI) + _startPoint.getY();
            if (i == 0) // starts the drawing of the circle. if
                        // beginning
                        // the for loop
                _circleTemp.startPath(x, y);
            else if (i == pointsAroundCircle - 1) // ends the circle
                                                    // when at
                                                    // the end of the
                // for loop.
                _circleTemp.closeAllPaths();
            else
                // continues drawing the cirlce while it iterates
                _circleTemp.lineTo(x, y);
        }
        // creates a new graphic and sets the geometry to a polygon.
        Graphic graphic = new Graphic();
        graphic.setGeometry(_circleTemp);

        int drawColor = getDrawColor();
        int transparentColor = Color.argb(POLYGON_ALPHA, Color.red(drawColor),
                Color.green(drawColor), Color.blue(drawColor));
        SimpleFillSymbol fillSymbol = new SimpleFillSymbol(transparentColor);
        graphic.setSymbol(fillSymbol);
        
        tempCircleGraphic = graphic;
        // add the updated graphic to graphics layer
        _graphicsLayer.addGraphic(graphic);

        // Refresh the graphics layer
        _graphicsLayer.postInvalidate();
        return true;

    }