A brief analysis of several ways of communicating between slots and parent-child components in mini programs

This article will introduce to you the slots in the WeChat applet and several methods of parent-child component communication. I hope it will be helpful to you!

Today we will take a look at the communication between slots and parent-child components in the mini program, and see what the differences are with vue? [Related learning recommendations: 小program development tutorial]

1. Slot

1. What is a slot ?

In the wxml structure of a custom component, a node (slot) can be provided to host the wxml## provided by the component user. # Structure

#In fact, the slot, to put it more simply, is the process of

the sub-component digging the hole and the parent component filling the hole . When the parent component uses the child component, it determines some layout display inside the child component

The child component fills the hole by digging holes
• The parent component fills the hole through the content in the middle of the component tag

2. Single slot

In the applet, by default only one is allowed in each custom component

slot Placeholder, this limit on the number is called a single slot

By default, there can only be one
• in a component's wxml slot
When you need to use multiple
• slot, you can declare the enablement in the component
js
• Note: small Currently, there are only default slots and multiple slots in the program. Scope slots are not supported at the moment.

The code is as follows (example):

<!-- 组件的封装者 -->
<view class="wrapper">
  <view>这里是组件的内部节点</view>
  <!-- 对于不确定的内容，可以使用<slot>进行占位，具体的内容由组件的使用者决定 -->
  <slot></slot>
</view>

<!-- 组件的使用者 -->
<component-tag-name>
  <!-- 这部分内容将被放置在组件<slot>的位置上 -->
  <view>这里是插入到组件slot的内容</view>
</component-tag-name>

3. Start multiple slots

In the custom component of the applet, when you need to use multiple slots, you can

in the .js file of the component

The code is as follows (example):

Component({
  options: {
    multipleSlots: true // 在组件定义时的选项中启用多 slot 支持
  }，
  properties: { /* ... */ },
  methods: { /* ... */ }
})

4. Define multiple slots

Can be in the component's

.wxml Use multiple tags in to distinguish different slots with different name

The code is as follows (example):

<!-- 组件模板 -->
<view class="wrapper">
  <!-- name 为 before 的第一个 slot 插槽 -->
  <slot name="before"></slot>
  <view>这是一段固定的文本内容</view>
  <!-- name 为 after 的第二个 slot 插槽 -->
  <slot name="after"></slot>
</view>

2. Father and son Component communication

1. Parent-child component communication

• Property binding Used for parent components to set data to specified properties of child components. Only

  JSON compatible data can be set (only data can be passed, methods cannot be passed)

• Event binding Certainly Used for child components to pass data to parent components. You can pass any data (including arrays and methods)

• Get the component instance The parent component can also obtain the child component instance object through

  this.selectComponent() so that it can directly access any data and methods of the child component

2. Attribute binding

#Transfer data Property binding is used to transfer values ​​​​from parent to child, and can only pass common types of data. Methods cannot be passed to child components.

The code is as follows (example):

// 父组件的 data 节点
data: {
  count: 0
}

// 父组件的wxml 结构
<my-test3 count="{{count}}"></my-test3>
<view>~~</view>
<view>父组件中，count值为：{{count}}</view>

Accept data

The subcomponent declares the corresponding properties in the properties node and uses The code is as follows (example):

// 子组件的 properties 节点
properties: {
  count: Number
}

// 子组件的 wxml 结构
<text>子组件中，count值为：{{count}}</text>

3. The core implementation steps of event binding

Event binding is used to realize the transmission from child to parent Value, any type of data can be passed. The usage steps are as follows:

In
• js of parent component, define a function, which will be passed to the child component in the form of a custom event
In
• wxml of the parent component, pass the function reference defined in step 1 to the child component## in the form of a custom event #In
js
• of subcomponent, by calling this.triggerEvent('custom event name', {/* parameter object*/}), Data is sent to the parent componentIn the
js
• of the parent component, the data passed by the child component is obtained through e.detail

4. The core implementation code of event binding

Step 1: In the

js
• of the parent component, define a function , this function will be passed to the child component in the form of a custom event
The code is as follows (example):

// 父组件中定义 syncCount 方法
// 将来，这个方法会被传递给子组件，供子组件进行调用
syncCount() {
  console.log('syncCount')
},

Step 2: In the parent component's

In wxml
• , pass the function reference defined in step 1 to the sub-component in the form of a custom event
The code is as follows (example):

<!-- 使用 bind: 自定义事件名称(推荐：结构清晰) -->
<my-test3 count="{{count}}" bind:sync="syncCount"></my-test3>
<!-- 或在 bind 后面直接协商自定义事件名称 -->
<my-test3 count="{{count}}" bindsync="syncCount"></my-test3>

Step 3: In

js
• of subcomponent, by calling this.triggerEvent('custom event name', {/* parameter object*/}), send data to the parent component
The code is as follows (example):

// 子组件的wxml结构
<text>子组件中，count值为：{{count}}</text>
<button type="primary" bindtap="addCount">+1</button>

// 子组件中的 js 代码
methods: {
  addCount() {
    this.setData({
      count: this.properties.count + 1
    })
    this.triggerEvent(&#39;sync&#39;, {value: this.properties.count})
  }
}

• 步骤 4：在父组件的 js 中，通过 e.detail 获取到子组件传递过来的数据

代码如下（示例）：

syncCount(e) {
  // console.log(e.detail.value)
  this.setData({
    count: e.detail.value
  })
}

5. 使用 selectComponent 获取组件实例

父组件如何获得子组件实例？

可在父组件里调用  this.selectComponent("id或class选择器")，获取子组件的实例对象，从而直接访问子组件的任意数据和方法。调用时需要传入一个选择器，例如  this.selectComponent(".my-component")

代码如下（示例）：

// wxml结构
<my-test3 count="{{count}}" bind:sync="syncCount" class="customA" id="cA"></my-test3>
<button bindtap="getChild">获取子组件实例</button>

getChild() { // 按钮的tap事件处理函数
  // 切记下面参数不能传递标签选择器 &#39;my-test3&#39;,不然返回的是 null
  const child = this.selectComponent(&#39;.customA&#39;) // 也可以传递 id 选择器 #cA
  child.setData({ count: child.properties.count + 1 }) // 调用子组件的 setData 方法
  child.addCount() // 调用子组件的 addCount 方法 
}

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