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625 lines
16 KiB
Markdown
625 lines
16 KiB
Markdown
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---
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title: 01-数据库的基础知识
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publish: false
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---
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## 子组件的定义和注册
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我们在本文的第一段中，通过`Vue.component`形式定义的是**全局组件**。这一段中，我们来讲一下**子组件**。
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### 在父组件中定义子组件
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比如说，一个`账号`模块是父组件，里面分为`登陆`模块和`注册`模块，这两个晓得模块就可以定义为子组件。
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需要注意的是作用域的问题：我们在父组件中定义的子组件，只能在当前父组件的模板中使用；在其他的组件，甚至根组件中，都无法使用。
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```html
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<meta http-equiv="X-UA-Compatible" content="ie=edge">
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<title>Document</title>
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<script src="vue2.5.16.js"></script>
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</head>
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<body>
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<div id="app">
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<account>
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</account>
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</div>
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<script>
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//定义、注册组件
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Vue.component('account', {
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template: '<div><h2>账号模块</h2> <login></login></div>',
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components: {
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'login': {
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template: '<h3>登录模块</h3>'
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}
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}
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});
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new Vue({
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el: '#app'
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});
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</script>
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</body>
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</html>
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```
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我们发现，既然是定义父亲`<account>`的子组件，那么，子组件`<login>`的调用，只能写在父组件`<account>`的`template`模板中。
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显示效果：
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### 在 Vue 根实例中定义子组件
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当然，我们还可以这样做：把整个 Vue 对象当成父亲，这样的话，就可以在 Vue 示例中定义一个子组件。如下：
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```html
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<meta http-equiv="X-UA-Compatible" content="ie=edge">
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<title>Document</title>
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<script src="vue2.5.16.js"></script>
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</head>
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<body>
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<div id="app">
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<login> </login>
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</div>
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<script>
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new Vue({
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el: '#app',
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//在Vue实例中定义子组件
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components: { // components 是关键字，不能改
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'login': {
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template: '<h3>登录模块</h3>'
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}
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}
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});
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</script>
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</body>
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</html>
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```
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这样写的话，我们定义的子组件`<login>`在整个`#app`区域，都是可以使用的。
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上面的代码，还有**另外一种写法**：（把子组件的模板定义，存放到变量中）【重要】
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```html
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<meta http-equiv="X-UA-Compatible" content="ie=edge">
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<title>Document</title>
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<script src="vue2.5.16.js"></script>
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</head>
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<body>
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<div id="app">
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<login> </login>
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</div>
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<script>
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//通过变量接收定义的子组件
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var myLogin = {
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template: '<h3>登录模块</h3>' // template 是关键字，不能改
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}
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new Vue({
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el: '#app',
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//在Vue实例中定义子组件
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components: { // components 是关键字，不能改
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'login': myLogin
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}
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});
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</script>
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</body>
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</html>
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```
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注意，在定义子组件时，关键字`components`不要写错了。
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## 组件之间的动态切换（暂略）
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我们可以利用`<component> `标签的`:is`参数来进行组件之间的切换。
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## 父组件向子组件传递数据
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我们要记住：父组件通过**属性**的形式，向子组件传递数据。
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**引入**：
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我们先来看这样一段代码：
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```html
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<meta http-equiv="X-UA-Compatible" content="ie=edge">
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<title>Document</title>
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</head>
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<script src="vue2.5.16.js"></script>
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<body>
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<div id="app">
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<!-- 这里是父组件的范围，自定义一个数值 number -->
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<counter number="1+2"> </counter>
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<counter number="10+20"> </counter>
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</div>
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<script>
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var myCounter = {
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//【重要】这里是子组件的范围，无法直接获取父组件中的 number
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template: '<div>我是子组件。{{number}}</div>'
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}
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var vm = new Vue({
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el: '#app',
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components: {
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'counter': myCounter
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}
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});
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</script>
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</body>
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</html>
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```
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上方代码中，我想把父组件里 number 的数值传递给子组件，直接这样写，是看不到效果的：
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**1、父组件传值给子组件**：
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要通过 props 属性将number进行传递给子组件才可以。代码如下：
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```html
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<meta http-equiv="X-UA-Compatible" content="ie=edge">
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<title>Document</title>
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</head>
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<script src="vue2.5.16.js"></script>
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<body>
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<div id="app">
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<!-- 这里是父组件的范围，自定义一个数值 number -->
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<counter :number="1+2"> </counter>
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<counter :number="10+20"> </counter>
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</div>
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<script>
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var myCounter = {
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//这里是子组件的范围
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props: ['number'], //通过 props 属性将父亲的 number 数据传递给子组件
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template: '<div>我是子组件。{{number}}</div>'
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}
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var vm = new Vue({
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el: '#app',
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components: {
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'counter': myCounter
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}
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});
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</script>
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</body>
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</html>
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```
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在`<counter>`标签中，要注意`:number`里的冒号。加上冒号，那么引号里的内容就是表达式（期望的结果）；否则，引号的内容只是字符串：
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**2、子组件获取了父组件的数据后，进行求和操作**：
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上方代码中，子组件已经获取了父组件的两个number，现在要求：每点击一次子组件，在子组件中将数据加 1。
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一般人可能会这样写：（不推荐的写法：子组件直接修改父组件中的数据）
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```javascript
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var myCounter = {
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//这里是子组件的范围
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props: ['number'], //通过 props 属性将父亲的数据传递给子组件
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template: '<div @click="addClick">我是子组件。{{number}}</div>',
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methods: {
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addClick: function () {
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this.number ++; //这种写法不推荐。不建议直接操作父组件中的数据
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}
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}
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}
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```
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上方代码的写法不推荐，因为不建议直接操作父组件中的数据。虽然数据操作成功，但是控制台会报错：
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img.png
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这样涉及到**单向数据流**的概念：
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- 父组件可以传递参数给子组件，但是反过来，子组件不要去修改父组件传递过来的参数。因为同一个参数，可能会传递给多个子组件，避免造成修改的冲突。
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既然如此，我可以把父组件中的数据，在子组件中创建**副本**，然后我们去修改这个副本，就不会造成影响了。最终，完整版代码如下：
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```html
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<meta http-equiv="X-UA-Compatible" content="ie=edge">
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<title>Document</title>
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</head>
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<script src="vue2.5.16.js"></script>
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<body>
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<div id="app">
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<!-- 这里是父组件的范围，自定义一个数值 number -->
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<counter :number="1+2"> </counter>
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<counter :number="10+20"> </counter>
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</div>
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<script>
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var myCounter = {
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//这里是子组件的范围
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props: ['number'], //通过 props 属性将父亲的数据传递给子组件
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data: function () {
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return {
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number2: this.number
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}
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},
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template: '<div @click="addClick">我是子组件。{{number2}}</div>',
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methods: {
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addClick: function () {
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this.number2 ++; //操作和修改number的副本
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}
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}
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}
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var vm = new Vue({
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el: '#app',
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components: {
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'counter': myCounter
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},
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});
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</script>
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</body>
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</html>
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```
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## 子组件向父组件传值
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我们要记住：子组件通过**事件触发**的形式，向父组件传值。
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**案例1:**子组件给父组件传递数据
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```html
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<meta http-equiv="X-UA-Compatible" content="ie=edge">
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<title>Document</title>
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<script src="vue2.5.16.js"></script>
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</head>
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<body>
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<div id="app">
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<!-- 在外层监听`mysend`事件，进而出发外层的 getData 方法 -->
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<counter v-on:mysend="getData"> </counter>
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</div>
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<script>
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Vue.component('counter', {
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template: '<div @click = "addClick">发送数据给父组件</div>', //当组件被点击时，触发 addClick 方法
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methods: {
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addClick: function () {
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//第一个参数为键(注意，要小写，不能大写)，第二个参数为值
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this.$emit('mysend', 'smyhvae'); //通过键`mysend`事件通知外面，将值`smyhvae`传给父组件
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}
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}
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});
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new Vue({
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el: '#app',
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methods: {
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getData: function (input) { //通过括号里的参数，获取子组件传递过来的值
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console.log(input); //打印结果：smyhvae
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}
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}
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});
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</script>
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</body>
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</html>
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```
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**案例2**：获取子组件的DOM对象
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题目：给两个相同的子组件定义计数器，每点击一次，数值加1。然后在父组件中求和。
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步骤（1）：给两个相同的子组件定义计数器，每点击一次，数值加1。代码如下：
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```html
|
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<!DOCTYPE html>
|
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<html lang="en">
|
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<head>
|
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<meta charset="UTF-8">
|
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
|
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<meta http-equiv="X-UA-Compatible" content="ie=edge">
|
|||
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<title>Document</title>
|
|||
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<script src="vue2.5.16.js"></script>
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</head>
|
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<body>
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<div id="app">
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<counter> </counter>
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<counter> </counter>
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</div>
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<script>
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Vue.component('counter', {
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template: '<div @click = "addClick">当前计数：{{number}}</div>', //当组件被点击时，调用 addClick 方法
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data: function () {
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return {
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number: 0 //给组件定义一个数据：number
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}
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},
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methods: {
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addClick: function () {
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this.number++; //定义方法：每点击一次，number 的数值加 1
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}
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}
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});
|
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new Vue({
|
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el: '#app'
|
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});
|
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</script>
|
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</body>
|
|||
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</html>
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```
|
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步骤（2）：两个子组件的数值加 1 后，通知父组件。代码如下：
|
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|
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|
```html
|
|||
|
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<!DOCTYPE html>
|
|||
|
|
<html lang="en">
|
|||
|
|
|
|||
|
|
<head>
|
|||
|
|
<meta charset="UTF-8">
|
|||
|
|
<meta name="viewport" content="width=device-width, initial-scale=1.0">
|
|||
|
|
<meta http-equiv="X-UA-Compatible" content="ie=edge">
|
|||
|
|
<title>Document</title>
|
|||
|
|
<script src="vue2.5.16.js"></script>
|
|||
|
|
</head>
|
|||
|
|
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<body>
|
|||
|
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<div id="app">
|
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|
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<!-- 在外层监听`change`事件，进而出发外层的 myClick 方法 -->
|
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<counter @change="myMethod"> </counter>
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<counter @change="myMethod"> </counter>
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</div>
|
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|
<script>
|
|||
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|
|||
|
|
Vue.component('counter', {
|
|||
|
|
template: '<div @click = "addClick">当前计数：{{number}}</div>', //当组件被点击时，
|
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|
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|
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data: function () {
|
|||
|
|
return {
|
|||
|
|
number: 0 //给组件定义一个数据：number
|
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|
|
}
|
|||
|
|
},
|
|||
|
|
methods: {
|
|||
|
|
addClick: function () {
|
|||
|
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this.number++; //定义方法：每点击一次，number 的数值加 1
|
|||
|
|
this.$emit('change'); //通过这一行的`change`，通知外面，内部的 addClick 方法已经执行了
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
});
|
|||
|
|
|
|||
|
|
new Vue({
|
|||
|
|
el: '#app',
|
|||
|
|
methods: {
|
|||
|
|
myMethod: function () {
|
|||
|
|
console.log('触发父组件');
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
});
|
|||
|
|
</script>
|
|||
|
|
</body>
|
|||
|
|
|
|||
|
|
</html>
|
|||
|
|
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
上方代码中，通过关键字`emit`通知父组件，子组件里的 addClick 方法被执行了。父组件得知后，执行`myMethod()`方法（这个方法是在Vue实例中定义的，很好理解）
|
|||
|
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|
|||
|
|
步骤（3）：在父组件中求和
|
|||
|
|
|
|||
|
|
既然父组件已经得知子组件的 addClick 事件，那我们直接在父组件的`myMethod()`里定义求和的方法即可。
|
|||
|
|
|
|||
|
|
```html
|
|||
|
|
<!DOCTYPE html>
|
|||
|
|
<html lang="en">
|
|||
|
|
|
|||
|
|
<head>
|
|||
|
|
<meta charset="UTF-8">
|
|||
|
|
<meta name="viewport" content="width=device-width, initial-scale=1.0">
|
|||
|
|
<meta http-equiv="X-UA-Compatible" content="ie=edge">
|
|||
|
|
<title>Document</title>
|
|||
|
|
<script src="vue2.5.16.js"></script>
|
|||
|
|
</head>
|
|||
|
|
|
|||
|
|
<body>
|
|||
|
|
|
|||
|
|
<div id="app">
|
|||
|
|
<!-- 在外层监听`change`事件，进而触发外层的 myMethod 方法 -->
|
|||
|
|
<counter ref="one" @change="myMethod"> </counter>
|
|||
|
|
<counter ref="two" @change="myMethod"> </counter>
|
|||
|
|
<div>{{totalData}}</div>
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
<script>
|
|||
|
|
|
|||
|
|
Vue.component('counter', {
|
|||
|
|
template: '<div @click = "addClick">当前计数：{{number}}</div>', //当组件被点击时，触发 addClick方法
|
|||
|
|
|
|||
|
|
data: function () {
|
|||
|
|
return {
|
|||
|
|
number: 0 //给组件定义一个数据：number
|
|||
|
|
}
|
|||
|
|
},
|
|||
|
|
methods: {
|
|||
|
|
addClick: function () {
|
|||
|
|
this.number++; //定义方法：每点击一次，number 的数值加 1
|
|||
|
|
this.$emit('change'); //通过这一行自定义的`change`，通知外面，内部的 addClick 方法已经执行了
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
});
|
|||
|
|
|
|||
|
|
new Vue({
|
|||
|
|
el: '#app',
|
|||
|
|
data: {
|
|||
|
|
totalData: 0
|
|||
|
|
},
|
|||
|
|
methods: {
|
|||
|
|
myMethod: function () {
|
|||
|
|
console.log('触发父组件');
|
|||
|
|
//通过`$refs`获取子组件中各自的number数值
|
|||
|
|
var a1 = this.$refs.one.number;
|
|||
|
|
var a2 = this.$refs.two.number;
|
|||
|
|
//求和，存放在父组件的 totalData 中
|
|||
|
|
this.totalData = a1 + a2;
|
|||
|
|
|
|||
|
|
console.log();
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
});
|
|||
|
|
</script>
|
|||
|
|
</body>
|
|||
|
|
|
|||
|
|
</html>
|
|||
|
|
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
代码的关键：
|
|||
|
|
|
|||
|
|
- 在`<counter>`标签中，通过 `ref = "xxx"`属性，给各个组件起一个别名，代表组件的引用
|
|||
|
|
|
|||
|
|
- 在父函数`myMethod()`中，通过`this.$refs.xxx`获取组件的引用。我们看一下最后两行代码在控制台的输出便知：（组件里有 number 属性）
|
|||
|
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|
|||
|
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|
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|
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|
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|
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