如何在android中使用Canvas动画绘制视图？

public class CustomView extends View {
    private Paint paint;
    private float radius;

    public CustomView(Context context) {
        super(context);
        init();
    }

    public CustomView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        paint = new Paint();
        paint.setColor(Color.RED);
        paint.setAntiAlias(true);
        radius = 0;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        // 绘制一个圆形
        canvas.drawCircle(getWidth() / 2, getHeight() / 2, radius, paint);
    }

    public void startAnimation() {
        ValueAnimator animator = ValueAnimator.ofFloat(0, 200);
        animator.setDuration(1000);
        animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                radius = (float) animation.getAnimatedValue();
                invalidate(); // 触发重绘
            }
        });
        animator.start();
    }
}