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({

  /**
   * 當(dāng)小程序初始化完成時，會觸發(fā) onLaunch（全局只觸發(fā)一次）
   */
  onLaunch: function () { },

  /**
   * 當(dāng)小程序啟動，或從后臺進入前臺顯示，會觸發(fā) onShow
   */
  onShow: function (options) { },

  /**
   * 當(dāng)小程序從前臺進入后臺，會觸發(fā) onHide
   */
  onHide: function () { },

  /**
   * 當(dāng)小程序發(fā)生腳本錯誤，或者 api 調(diào)用失敗時，會觸發(fā) onError 并帶上錯誤信息
   */
  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
//獲取應(yīng)用實例
const app = getApp()

Page({

  /**
   * 頁面的初始數(shù)據(jù)
   */
  data: { },

  /**
   * 生命周期函數(shù)--監(jiān)聽頁面加載
   */
  onLoad: function (options) { },

  /**
   * 生命周期函數(shù)--監(jiān)聽頁面初次渲染完成
   */
  onReady: function () { },

  /**
   * 生命周期函數(shù)--監(jiān)聽頁面顯示
   */
  onShow: function () { },

  /**
   * 生命周期函數(shù)--監(jiān)聽頁面隱藏
   */
  onHide: function () { },

  /**
   * 生命周期函數(shù)--監(jiān)聽頁面卸載
   */
  onUnload: function () { },

  /**
   * 頁面相關(guān)事件處理函數(shù)--監(jiān)聽用戶下拉動作
   */
  onPullDownRefresh: function () { },

  /**
   * 頁面上拉觸底事件的處理函數(shù)
   */
  onReachBottom: function () { },

  /**
   * 用戶點擊右上角分享
   */
  onShareAppMessage: function () { }
})

4. The entire life cycle of components

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

5. 組件主要的生命周期函數(shù)

data在哪個生命周期中初始化完畢？

組件的生命周期，指的是組件自身的一些函數(shù)，這些函數(shù)在特殊的時間點或遇到一些特殊的框架事件時被自動觸發(fā)。

最重要的生命周期是 created, attached, detached ，包含一個組件實例生命流程的最主要時間點。

• 組件實例剛剛被創(chuàng)建好時， created 生命周期被觸發(fā)

  • 此時還不能調(diào)用 setData
  • 通常情況下，這個生命周期只應(yīng)該用于給組件 this 添加一些自定義屬性字段

• 在組件完全初始化完畢、進入頁面節(jié)點樹后， attached 生命周期被觸發(fā)

  • this.data 已被初始化完畢
  • 這個生命周期很有用，絕大多數(shù)初始化工作可以在這個時機進行

• 在組件離開頁面節(jié)點樹后， detached 生命周期被觸發(fā)

  • 退出一個頁面時，會觸發(fā)頁面內(nèi)每個自定義組件的detached 生命周期被觸發(fā)
  • 如果組件還在頁面節(jié)點樹中，則 detached 會被觸發(fā)。
  • 此時適合做一些清理性質(zhì)的工作

6. lifetimes 節(jié)點

同時以兩種方式聲明生命周期函數(shù)，會執(zhí)行哪個？

生命周期方法可以直接定義在 Component 構(gòu)造器的第一級參數(shù)中，組件的的生命周期也可以在 lifetimes 字段內(nèi)進行聲明（這是推薦的方式，其優(yōu)先級最高）

lifetimes: {
  attached () {
    console.log('在組件實例進入頁面節(jié)點樹')
  },
  detached () {
    console.log('在組件實例被從頁面節(jié)點樹移除')
  }
},

attached () {
  console.log('~~~~~在組件實例進入頁面節(jié)點樹')
},
detached () {
  console.log('~~~~~在組件實例被從頁面節(jié)點樹移除')
},

/**
 * 組件的初始數(shù)據(jù)
 */
data: {
  // rgb 的顏色值對象
  _rgb: {
    r: 0,
    g: 0,
    b: 0
  },
  // 根據(jù) rgb 對象的三個屬性，動態(tài)計算 fullColor 的值
  fullColor: '0, 0, 0'
}

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