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模板语句

Template statements

模板语句是可在 HTML 中用于响应用户事件的方法或属性。使用模板语句,你的应用可以通过诸如显示动态内容或提交表单之类的动作吸引用户。

Template statements are methods or properties that you can use in your HTML to respond to user events. With template statements, your application can engage users through actions such as displaying dynamic content or submitting forms.

关于本指南中的语法和代码段的信息,请参阅Template syntaxTemplate syntax / 下载范例

See theTemplate syntaxTemplate syntax / 下载范例for the syntax and code snippets in this guide.

在以下示例中,模板语句 deleteHero() 出现在 = 号右侧的引号中,(event)="statement"

In the following example, the template statement deleteHero() appears in quotes to the right of the = symbol as in (event)="statement".

<button (click)="deleteHero()">Delete hero</button>
src/app/app.component.html
      
      <button (click)="deleteHero()">Delete hero</button>
    

当用户单击 Delete hero 按钮时,Angular 就会调用组件类中 deleteHero() 方法。

When the user clicks the Delete hero button, Angular calls the deleteHero() method in the component class.

你可以将模板语句与元素、组件或指令一起使用以响应事件。

You can use template statements with elements, components, or directives in response to events.

响应事件是 Angular 单向数据流的一个方面。你可以在单个事件循环中更改应用程序中的任何内容。

Responding to events is an aspect of Angular's unidirectional data flow. You can change anything in your application during a single event loop.

语法

Syntax

模板表达式一样,模板语句使用类似于 JavaScript 的语言。但是,模板语句的解析器与模板表达式的解析器有所不同。此外,模板语句解析器特别支持基本赋值 = 和带有分号 ; 的串联表达式。

Like template expressions, template statements use a language that looks like JavaScript. However, the parser for template statements differs from the parser for template expressions. In addition, the template statements parser specifically supports both basic assignment, =, and chaining expressions with semicolons, ;.

不允许使用以下 JavaScript 和模板表达式语法:

The following JavaScript and template expression syntax is not allowed:

  • new

  • 递增和递减运算符 ++--

    increment and decrement operators, ++ and --

  • 赋值运算符,例如 +=-=

    operator assignment, such as += and -=

  • 按位运算符,例如 |&

    the bitwise operators, such as | and &

  • 管道操作符

    the pipe operator

语句的上下文

Statement context

语句具有上下文 - 也就是语句所属应用中的特定部分。

Statements have a context—a particular part of the application to which the statement belongs.

语句只能引用语句上下文中的内容,通常是组件实例。例如,(click)="deleteHero()" 中的 deleteHero() 就是下面代码段中的组件方法之一。

Statements can refer only to what's in the statement context, which is typically the component instance. For example, deleteHero() of (click)="deleteHero()" is a method of the component in the following snippet.

<button (click)="deleteHero()">Delete hero</button>
src/app/app.component.html
      
      <button (click)="deleteHero()">Delete hero</button>
    

语句上下文还可以引用模板自身的上下文属性。在下面的示例中,组件的事件处理方法 onSave() 将模板自己的 $event 对象用作参数。在接下来的两行中, deleteHero() 方法接收了模板输入变量 hero 作为参数,而 onSubmit() 接收了模板引用变量 #heroForm 作为参数。

The statement context may also refer to properties of the template's own context. In the following example, the component's event handling method, onSave() takes the template's own $event object as an argument. On the next two lines, the deleteHero() method takes a template input variable, hero, and onSubmit() takes a template reference variable, #heroForm.

<button (click)="onSave($event)">Save</button> <button *ngFor="let hero of heroes" (click)="deleteHero(hero)">{{hero.name}}</button> <form #heroForm (ngSubmit)="onSubmit(heroForm)"> ... </form>
src/app/app.component.html
      
      <button (click)="onSave($event)">Save</button>
<button *ngFor="let hero of heroes" (click)="deleteHero(hero)">{{hero.name}}</button>
<form #heroForm (ngSubmit)="onSubmit(heroForm)"> ... </form>
    

在此示例中, $event 对象、hero#heroForm 的上下文都是其模板。

In this example, the context of the $event object, hero, and #heroForm is the template.

模板上下文中的名称优先于组件上下文中的名称。前面 deleteHero(hero) 中的 hero 是模板输入变量,而不是组件的 hero 属性。

Template context names take precedence over component context names. In the preceding deleteHero(hero), the hero is the template input variable, not the component's hero property.

模板语句最佳实践

Statement best practices

  • 简明

    Conciseness

    通过只使用方法调用或基本属性赋值,让模板语句最少化。

    Keep template statements minimal by using method calls or basic property assignments.

  • 在上下文中工作

    Work within the context

    模板语句的上下文可以是组件类实例或模板。因此,模板语句无法引用全局名称空间中的任何内容,例如 windowdocument。例如,模板语句不能调用 console.log()Math.max()

    The context of a template statement can be the component class instance or the template. Because of this, template statements cannot refer to anything in the global namespace such as window or document. For example, template statements can't call console.log() or Math.max().