【关键词】
动画样式、透明度、image、stack
【问题背景】
快应用中想在图片切换时加入一些动画效果,使用stack组件下使用两个image组件堆叠,一个image组件通过动画样式设置透明度从1-0隐藏起来,另一张显示出来,从而来实现图片切换效果,但是,前一张图片会概率性地闪现,然后消失。问题代码如下:
<template>
<div class="page-wrapper">
<input type="button" class="button" onclick="onCallAnimationClick" value="Animation 动画" />
<stack style="width: 400px; height: 400px">
<image class="img" id="img1" src="{{imgUrl}}" oncomplete="imgcomplete"></image>
<image class="img" id="img2" if="{{ximg}}" src="{{preUrl}}" oncomplete="imgcomplete2" style="{{'opacity:' + preop + ';'}}"></image>
</stack>
</div>
</template>
<script>
export default {
data: {
imgsrc: ["../Common/logo.png",
"../Common/b.jpg",
"../Common/logo.png",
"../Common/b.jpg",
"../Common/logo.png",
],
imgUrl: '',
preUrl: '',
ximg: true,
preop: 0,
i: 0
},
onInit: function () {
this.imgUrl = this.imgsrc[0]
},
onCallAnimationClick() {
if (this.i > 3) {
this.i = 0;
this.imgUrl = this.imgsrc[this.i]
} else {
this.i++
this.imgUrl = this.imgsrc[this.i]
}
console.log('imgcomplete=', this.i)
},
imgcomplete() {
console.log('imgcomplete 1')
this.preop = 1
var options = {
duration: 500,
easing: 'linear',
delay: 0,
fill: 'forwards',
iterations: 1
}
var frames = [{
opacity: 1
},
{
opacity: 0
}];
var animation = this.$element('img2').animate(frames, options);
animation.play();
var self = this
animation.onfinish = function () {
console.log("imgcomplete animation onfinish");
self.ximg = false
self.preop = 0
setTimeout(() => {
self.ximg = true
self.preUrl = self.$element("img1").attr.src
}, 30);
}
},
imgcomplete2() {
console.log('imgcomplete 2')
setTimeout(() => {
this.preop = 1
}, 50);
},
}
</script>
<style>
.page-wrapper {
flex-direction: column;
justify-content: center;
align-items: center;
}
.img {
width: 100%;
height: 100%;
}
.button {
color: #20a0ff;
background-color: #ffffff;
padding: 10px 20px;
border: 1px solid #20a0ff;
border-radius: 40px;
}
</style>
【问题分析】
上述代码用两个image组件实现了图片切换时淡入淡出的动画效果,主要是通过透明度实现的。第二个image的css中设置了透明度,但是imgcomplete()方法中又对该image组件做了透明度动画,透明度值从1到0,同时代码中又将css中绑定的透明度变量preop设置为1。
当动画方法完成时间早于css实现的时间,就会出现这个情况。
【解决方案】
1、 将template中第二个image组件的style="{{'opacity:' + preop + ';'}}"去掉。
<image class="img" id="img2" if="{{ximg}}" src="{{preUrl}}" oncomplete="imgcomplete2" ></image>
2、 改为通过动画样式来调用,从0-1变化。
imgcomplete2() {
console.log('imgcomplete 2')
var options = {
duration: 10,
easing: 'linear',
delay: 0,
fill: 'forwards',
iterations: 1
}
var frames = [{
opacity: 0
},
{
opacity: 1
}];
var animation = this.$element('img2').animate(frames, options);
animation.play();
},