Let's talk about how to use v-if in uniapp

In uniapp, v-if is an instruction used for conditional rendering. Its function is to determine whether to render elements to the page based on the result of the expression. If the expression evaluates to true, the element will be rendered, otherwise it will not be rendered.

Usage of v-if directive

The v-if directive can directly bind a Boolean value or bind an expression that returns a Boolean value. When the directive's expression is true, the element will be rendered, otherwise it will not be rendered.

The basic syntax for using the v-if directive is as follows:

<template>
   <div>
       <p>这段文字会被渲染</p>
   </div>
</template>
<script>
   export default {
       data() {
           return {
               isShow: true
           }
       },
   }
</script>

In the above code, the v-if directive is bound to a Boolean value isShow. When the value of isShow is true, p The element will be rendered to the page.

The difference between v-if and v-show

The same point: both are used to control the display state of elements, and determine whether to display the element based on the result of the expression.

Difference:

1. v-if dynamically adds or deletes elements, while v-show only modifies the display attribute of the element when showing and hiding it.
2. v-if during initial rendering, if the condition is false, the element will not be rendered, while v-show will render all elements and use the CSS display attribute to hide the element when the condition is not met.
3. v-if has higher overhead when switching, while v-show is more lightweight and suitable for elements that switch frequently.

To sum up, if you need to frequently switch the display state of an element on the page, it is recommended to use the v-show command. If you need to render all elements at once, or conditionally render an element, it is recommended to use the v-if directive.

Notes

When using the v-if instruction, you need to pay attention to the following points:

1. If you use the v-if instruction, you need to ensure that the instruction is The element has only one root node.
2. If the v-if and v-for instructions are used, the v-if instruction needs to be placed outside the v-for instruction.
3. When using the v-if directive, you need to note that the destruction and reconstruction of elements will cause performance overhead, so it is not recommended to use the v-if directive frequently in complex pages.

To sum up, v-if is a commonly used instruction in uniapp to control the display and hiding of elements. You need to pay attention to the precautions when using it, especially in terms of performance.

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