You can display data by binding controls in an HTML template to properties of an Angular component.

在 Angular 中最典型的数据显示方式,就是把 HTML 模板中的控件绑定到 Angular 组件的属性。

In this page, you'll create a component with a list of heroes. You'll display the list of hero names and conditionally show a message below the list.

本章中,你将创建一个英雄列表组件。 你将显示英雄名字的列表,并根据条件在列表下方显示一条消息。

The final UI looks like this:


Final UI



The demonstrates all of the syntax and code snippets described in this page.


Showing component properties with interpolation


The easiest way to display a component property is to bind the property name through interpolation. With interpolation, you put the property name in the view template, enclosed in double curly braces: {{myHero}}.

要显示组件的属性,最简单的方式就是通过插值表达式 (interpolation) 来绑定属性名。 要使用插值表达式,就把属性名包裹在双花括号里放进视图模板,如{{myHero}}

Follow the setup instructions for creating a new project named .


Then modify the file by changing the template and the body of the component.


When you're done, it should look like this:



import { Component } from '@angular/core'; @Component({ selector: 'my-app', template: ` <h1>{{title}}</h1> <h2>My favorite hero is: {{myHero}}</h2> ` }) export class AppComponent { title = 'Tour of Heroes'; myHero = 'Windstorm'; }

You added two properties to the formerly empty component: title and myHero.


The revised template displays the two component properties using double curly brace interpolation:


template: ` <h1>{{title}}</h1> <h2>My favorite hero is: {{myHero}}</h2> `

The template is a multi-line string within ECMAScript 2015 backticks (`). The backtick (`)—which is not the same character as a single quote (')—allows you to compose a string over several lines, which makes the HTML more readable.

模板是包在 ECMAScript 2015 反引号 (`) 中的一个多行字符串。 反引号 (`) — 注意,不是单引号 (') — 允许把一个字符串写在多行上, 使 HTML 模板更容易阅读。

Angular automatically pulls the value of the title and myHero properties from the component and inserts those values into the browser. Angular updates the display when these properties change.

Angular 自动从组件中提取titlemyHero属性的值,并且把这些值插入浏览器中。当这些属性发生变化时,Angular 就会自动刷新显示。

More precisely, the redisplay occurs after some kind of asynchronous event related to the view, such as a keystroke, a timer completion, or a response to an HTTP request.

严格来说,“重新显示”是在某些与视图有关的异步事件之后发生的,例如,按键、定时器完成或对 HTTP 请求的响应。

Notice that you don't call new to create an instance of the AppComponent class. Angular is creating an instance for you. How?

注意,我们没有调用 new 来创建AppComponent类的实例,是 Angular 替我们创建了它。那么它是如何创建的呢?

The CSS selector in the @Component decorator specifies an element named <my-app>. That element is a placeholder in the body of your index.html file:

注意@Component装饰器中指定的 CSS 选择器selector,它指定了一个叫my-app的元素。 该元素是index.htmlbody里的占位符。

src/index.html (body)

<body> <my-app>loading...</my-app> </body>

When you bootstrap with the AppComponent class (in ), Angular looks for a <my-app> in the index.html, finds it, instantiates an instance of AppComponent, and renders it inside the <my-app> tag.

当我们通过main.ts中的AppComponent类启动时,Angular 在index.html中查找一个<my-app>元素, 然后实例化一个AppComponent,并将其渲染到<my-app>标签中。

Now run the app. It should display the title and hero name:


Title and Hero

The next few sections review some of the coding choices in the app.


Template inline or template file?

内联 (inline) 模板还是模板文件?

You can store your component's template in one of two places. You can define it inline using the template property, or you can define the template in a separate HTML file and link to it in the component metadata using the @Component decorator's templateUrl property.

你可以在两种地方存放组件模板。 你可以使用template属性把它定义为内联的,或者把模板定义在一个独立的 HTML 文件中, 再通过@Component装饰器中的templateUrl属性, 在组件元数据中把它链接到组件。

The choice between inline and separate HTML is a matter of taste, circumstances, and organization policy. Here the app uses inline HTML because the template is small and the demo is simpler without the additional HTML file.

到底选择内联 HTML 还是独立 HTML 取决于个人喜好、具体状况和组织级策略。 上面的应用选择内联 HTML ,是因为模板很小,而且没有额外的 HTML 文件显得这个演示简单些。

In either style, the template data bindings have the same access to the component's properties.


Constructor or variable initialization?


Although this example uses variable assignment to initialize the components, you can instead declare and initialize the properties using a constructor:


src/app/app-ctor.component.ts (class)

export class AppCtorComponent { title: string; myHero: string; constructor() { this.title = 'Tour of Heroes'; this.myHero = 'Windstorm'; } }

This app uses more terse "variable assignment" style simply for brevity.


Showing an array property with *ngFor


To display a list of heroes, begin by adding an array of hero names to the component and redefine myHero to be the first name in the array.


src/app/app.component.ts (class)

export class AppComponent { title = 'Tour of Heroes'; heroes = ['Windstorm', 'Bombasto', 'Magneta', 'Tornado']; myHero = this.heroes[0]; }

Now use the Angular ngFor directive in the template to display each item in the heroes list.

接着,在模板中使用 Angular 的ngFor指令来显示heroes列表中的每一项。

src/app/app.component.ts (template)

template: ` <h1>{{title}}</h1> <h2>My favorite hero is: {{myHero}}</h2> <p>Heroes:</p> <ul> <li *ngFor="let hero of heroes"> {{ hero }} </li> </ul> `

This UI uses the HTML unordered list with <ul> and <li> tags. The *ngFor in the <li> element is the Angular "repeater" directive. It marks that <li> element (and its children) as the "repeater template":

这个界面使用了由<ul><li>标签组成的无序列表。<li>元素里的*ngFor是 Angular 的“迭代”指令。 它将<li>元素及其子级标记为“迭代模板”:

<li *ngFor="let hero of heroes"> {{ hero }} </li>

Don't forget the leading asterisk (*) in *ngFor. It is an essential part of the syntax. For more information, see the Template Syntax page.

不要忘记*ngFor中的前导星号 (*)。它是语法中不可或缺的一部分。 更多信息,见模板语法

Notice the hero in the ngFor double-quoted instruction; it is an example of a template input variable. Read more about template input variables in the microsyntax section of the Template Syntax page.

注意看ngFor双引号表达式中的hero,它是一个模板输入变量。 更多模板输入变量的信息,见模板语法中的 微语法 (microsyntax)

Angular duplicates the <li> for each item in the list, setting the hero variable to the item (the hero) in the current iteration. Angular uses that variable as the context for the interpolation in the double curly braces.

Angular 为列表中的每个条目复制一个<li>元素,在每个迭代中,把hero变量设置为当前条目(英雄)。 Angular 把hero变量作为双花括号插值表达式的上下文。

In this case, ngFor is displaying an array, but ngFor can repeat items for any iterable object.

本例中,ngFor用于显示一个“数组”, 但ngFor可以为任何可迭代的 (iterable) 对象重复渲染条目。

Now the heroes appear in an unordered list.



Creating a class for the data


The app's code defines the data directly inside the component, which isn't best practice. In a simple demo, however, it's fine.

应用代码直接在组件内部直接定义了数据。 作为演示还可以,但它显然不是最佳实践。

At the moment, the binding is to an array of strings. In real applications, most bindings are to more specialized objects.


To convert this binding to use specialized objects, turn the array of hero names into an array of Hero objects. For that you'll need a Hero class.


Create a new file in the app folder called with the following code:


src/app/hero.ts (excerpt)

export class Hero { constructor( public id: number, public name: string) { } }

You've defined a class with a constructor and two properties: id and name.


It might not look like the class has properties, but it does. The declaration of the constructor parameters takes advantage of a TypeScript shortcut.

它可能看上去不像是有属性的类,但它确实有,利用的是 TypeScript 提供的简写形式 —— 用构造函数的参数直接定义属性。

Consider the first parameter:


src/app/hero.ts (id)

public id: number,

That brief syntax does a lot:


Using the Hero class

使用 Hero 类

After importing the Hero class, the AppComponent.heroes property can return a typed array of Hero objects:


src/app/app.component.ts (heroes)

heroes = [ new Hero(1, 'Windstorm'), new Hero(13, 'Bombasto'), new Hero(15, 'Magneta'), new Hero(20, 'Tornado') ]; myHero = this.heroes[0];

Next, update the template. At the moment it displays the hero's id and name. Fix that to display only the hero's name property.

接着,更新一下模板。 现在它显示的是英雄的idname。 要修复它,只显示英雄的name属性就行了。

src/app/app.component.ts (template)

template: ` <h1>{{title}}</h1> <h2>My favorite hero is: {{myHero.name}}</h2> <p>Heroes:</p> <ul> <li *ngFor="let hero of heroes"> {{ hero.name }} </li> </ul> `

Our display looks the same, but now we know much better what a hero really is.


Conditional display with NgIf

通过 NgIf 进行条件显示

Sometimes an app needs to display a view or a portion of a view only under specific circumstances.


Let's change the example to display a message if there are more than three heroes.


The Angular ngIf directive inserts or removes an element based on a truthy/falsy condition. To see it in action, add the following paragraph at the bottom of the template:

Angular 的ngIf指令会根据一个布尔条件来显示或移除一个元素。 来看看实际效果,把下列语句加到模板的底部:

src/app/app.component.ts (message)

<p *ngIf="heroes.length > 3">There are many heroes!</p>

Don't forget the leading asterisk (*) in *ngIf. It is an essential part of the syntax. Read more about ngIf and * in the ngIf section of the Template Syntax page.

不要忘了*ngIf中的前导星号 (*)。它是本语法中不可或缺的一部分。 更多ngIf*的内容,见模板语法中的ngIf

The template expression inside the double quotes, *ngIf="heros.length > 3", looks and behaves much like TypeScript. When the component's list of heroes has more than three items, Angular adds the paragraph to the DOM and the message appears. If there are three or fewer items, Angular omits the paragraph, so no message appears. For more information, see the template expressions section of the Template Syntax page.

双引号中的模板表达式*ngIf="heros.length > 3",外观和行为很象 TypeScript。 当组件中的英雄列表有三个以上的条目时,Angular 把这个段落添加到 DOM 中,于是消息显示了出来。 更多信息,见模板语法中的模板表达式

Angular isn't showing and hiding the message. It is adding and removing the paragraph element from the DOM. That improves performance, especially in larger projects when conditionally including or excluding big chunks of HTML with many data bindings.

Angular 并不是在显示和隐藏这条消息,它是在从 DOM 中添加和移除这个段落元素。 这会提高性能,特别是在一些大的项目中有条件地包含或排除一大堆带着很多数据绑定的 HTML 时。

Try it out. Because the array has four items, the message should appear. Go back into and delete or comment out one of the elements from the hero array. The browser should refresh automatically and the message should disappear.

试一下。因为这个数组中有四个条目,所以消息应该显示出来。 回到app.component.ts,从英雄数组中删除或注释掉一个元素。 浏览器应该自动刷新,消息应该会消失。



Now you know how to use:


Here's the final code:


import { Component } from '@angular/core'; import { Hero } from './hero'; @Component({ selector: 'my-app', template: ` <h1>{{title}}</h1> <h2>My favorite hero is: {{myHero.name}}</h2> <p>Heroes:</p> <ul> <li *ngFor="let hero of heroes"> {{ hero.name }} </li> </ul> <p *ngIf="heroes.length > 3">There are many heroes!</p> ` }) export class AppComponent { title = 'Tour of Heroes'; heroes = [ new Hero(1, 'Windstorm'), new Hero(13, 'Bombasto'), new Hero(15, 'Magneta'), new Hero(20, 'Tornado') ]; myHero = this.heroes[0]; } export class Hero { constructor( public id: number, public name: string) { } } import { NgModule } from '@angular/core'; import { BrowserModule } from '@angular/platform-browser'; import { AppComponent } from './app.component'; @NgModule({ imports: [ BrowserModule ], declarations: [ AppComponent ], bootstrap: [ AppComponent ] }) export class AppModule { } import { platformBrowserDynamic } from '@angular/platform-browser-dynamic'; import { AppModule } from './app/app.module'; platformBrowserDynamic().bootstrapModule(AppModule);