Let's talk about the life cycle (function) in WeChat applet

This article will take you to take a look at the life cycle in the WeChat applet, what life cycle functions are there, and talk about its triggering time and what it does. I hope it will be helpful to everyone!

1. Life cycle

1. What is life cycle?

Life Cycle(Life Cycle) refers to the entire stage of an object from creation-> running-> destruction, emphasizing a time period

2. The life cycle of the mini program

• Startup of the mini program represents the life cycle Start
• Close of the applet, indicating the end of the life cycle
• The process of running the applet in the middle is the life of the applet Cycle

3. Mini program life cycle classification

• Application life cycle Specifically refers to the process of mini program starting --> running --> destruction

• Page life cycle Specifically refers to the loading--> rendering--> destruction process of each page in the mini program

• Note: The life cycle range of the page is small , the life cycle range of the application is larger

2. Life cycle function

1. What is a life cycle function?

• The built-in functions provided by the mini program framework will be automatically executed in sequence along with the life cycle

• Life cycle The role of the function:

  • Allows programmers to perform certain operations at specific life cycle time points
  • For example, when the page is just loaded, in the life cycle function Automatically initiate a data request to obtain the data of the current page

• Note: The life cycle emphasizes the time period, and the life cycle function emphasizes the time point.

2. Application life cycle function

• app.js is the entry file for mini program execution. The App() function must be called in app.js and can only be called once. Among them, the App() function is used to register and execute the applet.

• App(Object) function receives an Object Parameters, you can specify the life cycle function of the applet through this Object parameter

• Code in app.js

The code is as follows (example):

App({

  /**
   * 当小程序初始化完成时，会触发 onLaunch（全局只触发一次）
   */
  onLaunch: function () { },

  /**
   * 当小程序启动，或从后台进入前台显示，会触发 onShow
   */
  onShow: function (options) { },

  /**
   * 当小程序从前台进入后台，会触发 onHide
   */
  onHide: function () { },

  /**
   * 当小程序发生脚本错误，或者 api 调用失败时，会触发 onError 并带上错误信息
   */
  onError: function (msg) { }
})

3. Page life cycle

• Each mini program page must have its own .js file, and must call the Page() function, otherwise an error will be reported. Among them, the Page() function is used to register the mini program page.

• Page(Object) function receives an Object parameter. , you can specify the life cycle function of the page through this Object parameter

• page.js

The code is as follows (example):

//index.js
//获取应用实例
const app = getApp()

Page({

  /**
   * 页面的初始数据
   */
  data: { },

  /**
   * 生命周期函数--监听页面加载
   */
  onLoad: function (options) { },

  /**
   * 生命周期函数--监听页面初次渲染完成
   */
  onReady: function () { },

  /**
   * 生命周期函数--监听页面显示
   */
  onShow: function () { },

  /**
   * 生命周期函数--监听页面隐藏
   */
  onHide: function () { },

  /**
   * 生命周期函数--监听页面卸载
   */
  onUnload: function () { },

  /**
   * 页面相关事件处理函数--监听用户下拉动作
   */
  onPullDownRefresh: function () { },

  /**
   * 页面上拉触底事件的处理函数
   */
  onReachBottom: function () { },

  /**
   * 用户点击右上角分享
   */
  onShareAppMessage: function () { }
})

4. The entire life cycle of components

What are the life cycles of components? When are they different?

Life cycle	Parameters	Description
created	None	Executed when the component instance is just created
attached	None	Executed when the component instance enters the page node tree
ready	None	Executed after the component is laid out in the view layer
moved	None	Executed when the component instance is moved to another location in the node tree
detached	None	Executed when the component instance is removed from the page node tree
error	Object Error	Every Executed when a component method throws an error

5. 组件主要的生命周期函数

data在哪个生命周期中初始化完毕？

组件的生命周期，指的是组件自身的一些函数，这些函数在特殊的时间点或遇到一些特殊的框架事件时被自动触发。

最重要的生命周期是 created, attached, detached ，包含一个组件实例生命流程的最主要时间点。

• 组件实例刚刚被创建好时， created 生命周期被触发

  • 此时还不能调用 setData
  • 通常情况下，这个生命周期只应该用于给组件 this 添加一些自定义属性字段

• 在组件完全初始化完毕、进入页面节点树后， attached 生命周期被触发

  • this.data 已被初始化完毕
  • 这个生命周期很有用，绝大多数初始化工作可以在这个时机进行

• 在组件离开页面节点树后， detached 生命周期被触发

  • 退出一个页面时，会触发页面内每个自定义组件的detached 生命周期被触发
  • 如果组件还在页面节点树中，则 detached 会被触发。
  • 此时适合做一些清理性质的工作

6. lifetimes 节点

同时以两种方式声明生命周期函数，会执行哪个？

生命周期方法可以直接定义在 Component 构造器的第一级参数中，组件的的生命周期也可以在 lifetimes 字段内进行声明（这是推荐的方式，其优先级最高）

lifetimes: {
  attached () {
    console.log('在组件实例进入页面节点树')
  },
  detached () {
    console.log('在组件实例被从页面节点树移除')
  }
},

attached () {
  console.log('~~~~~在组件实例进入页面节点树')
},
detached () {
  console.log('~~~~~在组件实例被从页面节点树移除')
},

/**
 * 组件的初始数据
 */
data: {
  // rgb 的颜色值对象
  _rgb: {
    r: 0,
    g: 0,
    b: 0
  },
  // 根据 rgb 对象的三个属性，动态计算 fullColor 的值
  fullColor: '0, 0, 0'
}

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