动态画弧

Question

I draw an arc using onDraw(canvas) :

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

public class MyView extends View {

    public MyView(Context context) {
        super(context);
    }

    @Override
    public void onDraw(Сanvas canvas) {
        super.onDraw(canvas);
        float width = (float) getWidth();
        float height = (float) getHeight();
        float radius;
        if (width > height) {
            radius = height / 4;
        } else {
            radius = width / 4;
        }

        final Paint paint = new Paint();
        paint.setColor(Color.WHITE);
        paint.setStrokeWidth(50);
        paint.setStyle(Paint.Style.STROKE);

        float center_x, center_y;
        center_x = width / 2;
        center_y = height / 4;
        final RectF oval = new RectF();
        oval.set(center_x - radius, center_y - radius, center_x + radius,
                center_y + radius);

        paint.setStyle(Paint.Style.STROKE);
        center_x = width / 2;
        center_y = height * 3 / 4;
        oval.set(center_x - radius, center_y - radius, center_x + radius,
                center_y + radius);

        canvas.drawArc(oval, -90, 45, false, paint);
    }
}

Tell me, how to dynamically change the value of sweepAngle() == 45 in line canvas.drawArc(oval, -90, 45, false, paint) ?

Answer 1

One solution would be to have a sweepAngle field in your class, and use that instead of 45 in drawing the arc. Then have a timer that periodically adds to sweepAngle and redraws the canvas.