在GWT中平滑类似jQuery的动画

Question

我正在玩GWT的动画课作为练习.我的目标不是为GWT创建另一个小部件/动画库.另外,我很清楚有很多库可以做到这一点.我要做的是学习如何做到这一点,而不是如何使用一些库.这仅用于教育目的....

话虽如此,我已经实现了一个简单的类,在一些小部件上执行4种不同的动画:淡入,淡出,滑入和滑出(遵循jQuery的动画模型).请参阅下面的代码,了解我是如何实现它的.

现场演示: http ://www.rodrigo-silveira.com/gwt-custom-animation/

我的问题:如果触发另一个动画,我怎样才能顺利[并成功]停止动画,并继续当前动画中旧动画停止的动画？

例如,如果在调用slideOut()时,slideIn()是一半,那么如何从小部件的自然高度50%开始滑出？我尝试保留一个始终跟踪当前进度的成员变量,以便我可以在新动画中使用它,但似乎无法正确使用它.有任何想法吗？

import com.google.gwt.animation.client.Animation;
import com.google.gwt.dom.client.Style.Unit;
import com.google.gwt.user.client.Element;

public class RokkoAnim extends Animation {

    private Element element;
    private int currentOp;
    private final static int FADE_OUT = 0;
    private final static int FADE_IN = 1;
    private final static int SLIDE_IN = 2;
    private final static int SLIDE_OUT = 3;


    public RokkoAnim(Element element) {
        this.element = element;
    }

    public void fadeOut(int durationMilli) {
        cancel();
        currentOp = RokkoAnim.FADE_OUT;
        run(durationMilli);
    }

    public void fadeIn(int durationMilli) {
        cancel();
        currentOp = RokkoAnim.FADE_IN;
        run(durationMilli);
    }

    public void slideIn(int durationMilli) {
        cancel();
        currentOp = RokkoAnim.SLIDE_IN;
        run(durationMilli);
    }

    public void slideOut(int durationMilli) {
        cancel();
        currentOp = RokkoAnim.SLIDE_OUT;
        run(durationMilli);
    }

    @Override
    protected void onUpdate(double progress) {
        switch (currentOp) {
        case RokkoAnim.FADE_IN:
            doFadeIn(progress);
            break;
        case RokkoAnim.FADE_OUT:
            doFadeOut(progress);
            break;
        case RokkoAnim.SLIDE_IN:
            doSlideIn(progress);
            break;
        case RokkoAnim.SLIDE_OUT:
            doSlideOut(progress);
            break;
        }
    }

    private void doFadeOut(double progress) {
        element.getStyle().setOpacity(1.0d - progress);
    }

    private void doFadeIn(double progress) {
        element.getStyle().setOpacity(progress);
    }

    private void doSlideIn(double progress) {
        double height = element.getScrollHeight();
        element.getStyle().setHeight(height * (1.0d - progress), Unit.PX);
    }

    private void doSlideOut(double progress) {
            // Hard coded value. How can I find out what
            // the element's max natural height is if it's 
            // currently set to height: 0 ?
        element.getStyle().setHeight(200 * progress, Unit.PX);
    }
}

用法

// 1. Get some widget
FlowPanel div = new FlowPanel();

// 2. Instantiate the animation, passing the widget
RokkoAnim anim = new RokkoAnim(div.getElement());

// 3. Perform the animation

// >> inside mouseover event of some widget:
anim.fadeIn(1500);

// >> inside mouseout event of some widget:
anim.fadeOut(1500);

Answer 1

您需要根据当前值(相当于+=或-=赋值)更新不透明度:

private void doFadeOut(double progress) {
    double opacity = element.getStyle().getOpacity();
    element.getStyle().setOpacity(opacity - 1.0d - progress);
}

private void doFadeIn(double progress) {
    double opacity = element.getStyle().getOpacity();
    element.getStyle().setOpacity(opacity + progress);
}