在Vue中使用v-for处理v-if的正确方法 [英] Correct way to handle v-if with v-for in Vue
问题描述
在这个例子中,我们应该如何处理 v-for
和 v-if
:
这里我的 data.json
:
[
{
image:'foo.jpg'
},
{
image:'foobar.jpg',
video :'bar.mp4'
},
{
image:'barfoo.jpg'
}
]
在我的vue模板中,我想渲染这样的内容:
数据:key =index>中的< div v-for =(item,key,index)
< img:src =item.image>
< video v-if =!! item.video:src =item.video>< / video>
< / div>
但是文档说,我们应该避免 v-if
使用 v-for
而改为使用计算值。但即使json条目没有视频,我也需要渲染图像。
这不是什么大问题,我找到了一个解决方案,但我'我想知道解决这个问题的最佳方法。
我认为你误解了这些文档。在这种情况下,使用 v-for
和 v-if
是有意义的,因为你总是要至少渲染< img>
,您可以渲染< video>
。该文档试图表明,如果 v-if
和 v-for
是完全相同的元素。
文档显示的示例试图让您剪切一个列表,该列表只显示3个总元素中的2个只有2个元素,并让计算出的道具告诉你什么时候有更多。否则,每次需要重新渲染时都必须遍历整个列表。
考虑这种差异:
< pre class =lang-js prettyprint-override>
// 1000个项目的数组,但只有1个项目有视频元素
const data = [0 ... 999];
data.push({
image:some.jpg,
video:some.mp4
});
<! -
我们总是呈现1000个项目,但只有一些会有视频
- >数据
:key =index>中的
< div
v-for =(item,key,index)
< img:src =item.image>
< video v-if =!! item.video:src =item.video>< / video>
< / div>
<! -
我们必须访问1000个元素,但
只有1个实际上最终会渲染
- >
< div
v-if =!! item.video
v-for =(item,key,index)数据
:key =index >
< img:src =item.image>
< video:src =item.video>< / video>
< / div>
How should we handle a v-for
combined with a v-if
in this exemple:
Here my data.json
:
[
{
image: 'foo.jpg'
},
{
image: 'foobar.jpg',
video: 'bar.mp4'
},
{
image: 'barfoo.jpg'
}
]
In my vue template, I'd like to render something like this:
<div v-for="(item, key, index) in data" : key="index">
<img :src="item.image">
<video v-if="!!item.video" :src="item.video"></video>
</div >
But as the documentation say, we should avoid v-if
with v-for
and instead use a computed value. But there I need to render the image even if the json entry doesn't have a video.
That's not a big deal, I've find a solution but I'd like to know the best way to handle this.
I think that you are misunderstanding the documentation. In this instance, it makes sense to use both v-for
and v-if
because you are always going to render at least the <img>
and you might render the <video>
. The documentation is trying to show that you should pre-filter a list of items if the v-if
and v-for
are on the exact same element.
The example the docs are showing are trying to get you to cut a list that would show only only 2 of the 3 total elements down to just 2 elements and letting the computed prop tell you when there are more. Otherwise you have to iterate through the entire list every time you need to re-render.
Consider this difference:
// An array of 1000 items but only 1 has a video element
const data = [0...999];
data.push({
image: "some.jpg",
video: "some.mp4"
});
<!--
We always render 1000 items but only some will have video
-->
<div
v-for="(item, key, index) in data"
:key="index">
<img :src="item.image">
<video v-if="!!item.video" :src="item.video"></video>
</div>
<!--
We have to visit 1000 elements but
only 1 will actually end up rendering
-->
<div
v-if="!!item.video"
v-for="(item, key, index) in data"
:key="index">
<img :src="item.image">
<video :src="item.video"></video>
</div>
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