Android drawing objects on screen and obtaining geometry data

问题

Has anybody experience on drawing objects, by vertices e.g. Polygons and obtaining their surface and perimeter.

The geometry will be drawn by hand using vertices or coordinates similar to https://play.google.com/store/apps/details?id=de.hms.xconstruction and then shapes formed. I need to obtain the surface of these closed shapes.

Is there any available example on the net?

Thanks in advance.

回答1:

I think the following piece of code could be a good start. It basically draws lines between all user touches:

public class TestActivity extends Activity {

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(new DrawingView(this));
}

class DrawingView extends SurfaceView {

    private final SurfaceHolder surfaceHolder;
    private final Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);

    private List<Point> pointsList = new ArrayList<Point>();

    public DrawingView(Context context) {
        super(context);
        surfaceHolder = getHolder();
        paint.setColor(Color.WHITE);
        paint.setStyle(Style.FILL);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (event.getAction() == MotionEvent.ACTION_DOWN) {
            if (surfaceHolder.getSurface().isValid()) {

                // Add current touch position to the list of points
                pointsList.add(new Point((int)event.getX(), (int)event.getY()));

                // Get canvas from surface
                Canvas canvas = surfaceHolder.lockCanvas();

                // Clear screen
                canvas.drawColor(Color.BLACK);

                // Iterate on the list
                for(int i=0; i<pointsList.size(); i++) {
                    Point current = pointsList.get(i);

                    // Draw points
                    canvas.drawCircle(current.x, current.y, 10, paint);

                    // Draw line with next point (if it exists)
                    if(i + 1 < pointsList.size()) {
                        Point next = pointsList.get(i+1);
                        canvas.drawLine(current.x, current.y, next.x, next.y, paint);
                    }
                }

                // Release canvas
                surfaceHolder.unlockCanvasAndPost(canvas);
            }
        }
        return false;
    }

}

来源：https://stackoverflow.com/questions/13305706/android-drawing-objects-on-screen-and-obtaining-geometry-data