03.3 精通自定义 View 之属性动画——ofObject

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public static ValueAnimator ofObject(TypeEvaluator evaluator, Object... values)

3.3.1 示例：字母从 A 变化到 Z

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private void startAnim() {
    ValueAnimator animator = ValueAnimator.ofObject(new CharEvaluator(),
            Character.valueOf('A'), Character.valueOf('Z'));
    animator.setDuration(3000);
    animator.setInterpolator(new AccelerateInterpolator());
    animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
        @Override
        public void onAnimationUpdate(ValueAnimator animation) {
            char text = (Character) animation.getAnimatedValue();
            mView.setText(String.valueOf(text));
        }
    });
    animator.start();
}
public class CharEvaluator implements TypeEvaluator<Character> {
    @Override
    public Character evaluate(float fraction,Character startValue,Character endValue){
        int startInt = (int) startValue;
        int endInt = (int) endValue;
        int value = (int) (startInt + fraction * (endInt - startInt));
        return (char) value;
    }
}

3.3.2 示例：抛物动画

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private void startAnim() {
    ValueAnimator animator = ValueAnimator.ofObject(new FallingBallEvaluator(),
            new Point(0, mTop), new Point(500, 500));
    animator.setDuration(3000);
    animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
        @Override
        public void onAnimationUpdate(ValueAnimator animation) {
            Point p = (Point) animation.getAnimatedValue();
            mView.layout(p.x, p.y, p.x + mView.getWidth(), p.y + mView.getHeight());
        }
    });
    animator.start();
}
public class FallingBallEvaluator implements TypeEvaluator<Point> {
    private Point point = new Point();
    @Override
    public Point evaluate(float fraction, Point startValue, Point endValue) {
        point.x = (int)(startValue.x + fraction * (endValue.x - startValue.x));
        if (fraction * 2 < 1) {
            point.y = (int)(startValue.y + fraction * 2 * (endValue.y - startValue.y));
        } else {
            point.y = endValue.y;
        }
        return point;
    }
}