[ngModel] 和 (ngModelChange) 如何协同工作? [英] How [ngModel] and (ngModelChange) work together?

问题描述

我是 angular 的新手，我正在学习 Angular 6.我了解 ngModel.但是当我尝试使用 ngModelChange 时，提出了一些问题.

I am new to angular and I am learning Angular 6. I understood about ngModel. But while I was experimenting with ngModelChange, some questions raised.

我有一个 html 元素HTML

I have an html element HTML

<input #input  type="text" [value]="name" [(ngModel)] ="name" (ngModelChange) ="change(input.value)"/>

打字稿

change(event :any) {
    this.name = event;
    console.log(this.name);
}

更改 input 中的值后，我可以看到 name 属性的更改.

Upon changing the value in the input , I can see the changes with the name property.

当我将 html 代码更改为

When I changed the html code to

HTML

<input #input type="text" [value]="name"  [ngModel] ="name" 
(ngModelChange)="change(input.value)" />
{{ name }}

TS

change(event :any) {
    this.name = event;
    console.log(this.name);
}

它在控制台和 UI 中按预期工作正常.

It's working fine as expected in the console and in the UI.

问题 1

<input #input  type="text" [value]="name" [(ngModel)] ="name" 
(ngModelChange) ="change(input.value)"/>

&

<input #input type="text" [value]="name"  [ngModel] ="name" 
(ngModelChange)="change(input.value)" />

一样吗??

问题 2.

当我删除 [ngModel] 指令时.ngModelChange 没有被触发.必须拥有 [ngModel] 吗?如果是，为什么?

When I remove the [ngModel] directive. The ngModelChange is not getting triggered. Is it mandatory to have [ngModel]? If yes,Why?

HTML

<input #input type="text" [value]="name" 
(ngModelChange)="change(input.value)" />
<br/>
<br/>
{{ name }}

TS

change(event: any) {
     this.name = event;
     console.log(this.name);
 }

这将是一个很大的帮助.提前致谢.

This would be a great help. Thanks in Advance.

推荐答案

当元素具有名为 x 的可设置属性和名为 xChange 的相应事件时，[()] 语法很容易演示.这是一个适合这种模式的 SizerComponent.它有一个 size value 属性和一个伴随 sizeChange 事件

The [()] syntax is easy to demonstrate when the element has a settable property called x and a corresponding event named xChange. Here's a SizerComponent that fits this pattern. It has a size value property and a companion sizeChange event

https://angular.io/guide/template-syntax#basics-of-two-way-binding

所以，它们是等价的.

<input [(ngModel)]="name"/>
<input [ngModel]="name" (ngModelChange) ="name = $event"/>

但是如果没有对应的属性，那么xChange将不起作用.

But if there is no corresponding property, then xChange will not work.

<input (ngModelChange) ="name = $event"/>

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