表单link

Template-driven formslink

表单是商业应用的支柱，你用它来执行登录、求助、下单、预订机票、安排会议，以及不计其数的其它数据录入任务。

Forms are the mainstay of business applications. You use forms to log in, submit a help request, place an order, book a flight, schedule a meeting, and perform countless other data-entry tasks.

在开发表单时，创建数据方面的体验是非常重要的，它能指引用户明晰、高效的完成工作流程。

In developing a form, it's important to create a data-entry experience that guides the user efficiently and effectively through the workflow.

模板驱动表单简介link

Introduction to Template-driven formslink

开发表单需要设计能力（那超出了本章的范围），而框架支持双向数据绑定、变更检测、验证和错误处理，而本章你将会学到它们。

Developing forms requires design skills (which are out of scope for this page), as well as framework support for two-way data binding, change tracking, validation, and error handling, which you'll learn about on this page.

这个页面演示了如何从草稿构建一个简单的表单。这个过程中你将学会如何：

This page shows you how to build a simple form from scratch. Along the way you'll learn how to:

• 用组件和模板构建 Angular 表单

  Build an Angular form with a component and template.

• 用 ngModel 创建双向数据绑定，以读取和写入输入控件的值

  Use ngModel to create two-way data bindings for reading and writing input-control values.

• 跟踪状态的变化，并验证表单控件

  Track state changes and the validity of form controls.

• 使用特殊的 CSS 类来跟踪控件的状态并给出视觉反馈

  Provide visual feedback using special CSS classes that track the state of the controls.

• 向用户显示验证错误提示，以及启用/禁用表单控件

  Display validation errors to users and enable/disable form controls.

• 使用模板引用变量在 HTML 元素之间共享信息

  Share information across HTML elements using template reference variables.

你可以运行在线例子 / 下载范例，在 Stackblitz 中试用并下载本页的代码。

You can run the在线例子 / 下载范例in Stackblitz and download the code from there.

模板驱动表单link

Template-driven formslink

通常，使用 Angular 模板语法编写模板，结合本章所描述的表单专用指令和技术来构建表单。

You can build forms by writing templates in the Angular template syntax with the form-specific directives and techniques described in this page.

利用 Angular 模板，可以构建几乎所有表单 — 登录表单、联系人表单…… 以及任何的商务表单。 可以创造性地摆放各种控件、把它们绑定到数据、指定校验规则、显示校验错误、有条件的禁用或 启用特定的控件、触发内置的视觉反馈等等，不胜枚举。

You can build almost any form with an Angular template—login forms, contact forms, and pretty much any business form. You can lay out the controls creatively, bind them to data, specify validation rules and display validation errors, conditionally enable or disable specific controls, trigger built-in visual feedback, and much more.

它用起来很简单，这是因为 Angular 处理了大多数重复、单调的任务，这让你可以不必亲自操刀、身陷其中。

Angular makes the process easy by handling many of the repetitive, boilerplate tasks you'd otherwise wrestle with yourself.

你将学习构建如下的“模板驱动”表单：

You'll learn to build a template-driven form that looks like this:

这里是英雄职业介绍所，使用这个表单来维护候选英雄们的个人信息。每个英雄都需要一份工作。 公司的使命就是让合适的英雄去应对恰当的危机！

The Hero Employment Agency uses this form to maintain personal information about heroes. Every hero needs a job. It's the company mission to match the right hero with the right crisis.

表单中的三个字段，其中两个是必填的。必填的字段在左侧有个绿色的竖条，方便用户分辨哪些是必填项。

Two of the three fields on this form are required. Required fields have a green bar on the left to make them easy to spot.

如果删除了英雄的名字，表单就会用醒目的样式把验证错误显示出来。

If you delete the hero name, the form displays a validation error in an attention-grabbing style:

注意，提交按钮被禁用了，而且输入控件左侧的“必填”条从绿色变为了红色。

Note that the Submit button is disabled, and the "required" bar to the left of the input control changes from green to red.

你将一点点构建出此表单：

You'll build this form in small steps:

1. 创建 Hero 模型类

   Create the Hero model class.

2. 创建控制此表单的组件。

   Create the component that controls the form.

3. 创建具有初始表单布局的模板。

   Create a template with the initial form layout.

4. 使用 ngModel 双向数据绑定语法把数据属性绑定到每个表单输入控件。

   Bind data properties to each form control using the ngModel two-way data-binding syntax.

5. 往每个表单输入控件上添加 name 属性 (attribute)。

   Add a name attribute to each form-input control.

6. 添加自定义 CSS 来提供视觉反馈。

   Add custom CSS to provide visual feedback.

7. 显示和隐藏有效性验证的错误信息。

   Show and hide validation-error messages.

8. 使用 ngSubmit 处理表单提交。

   Handle form submission with ngSubmit.

9. 禁用此表单的提交按钮，直到表单变为有效。

   Disable the form’s Submit button until the form is valid.

准备工作link

Setuplink

创建一个名为 angular-forms 的新项目：

Create a new project named angular-forms:

      
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      ng new angular-forms
    

创建 Hero 模型类link

Create the Hero model classlink

当用户输入表单数据时，需要捕获它们的变化，并更新到模型的实例中。 除非知道模型里有什么，否则无法设计表单的布局。

As users enter form data, you'll capture their changes and update an instance of a model. You can't lay out the form until you know what the model looks like.

最简单的模型是个“属性包”，用来存放应用中一件事物的事实。 这里使用三个必备字段 (id、name、power)，和一个可选字段 (alterEgo，译注：中文含义是第二人格，例如 X 战警中的 Jean / 黑凤凰)。

A model can be as simple as a "property bag" that holds facts about a thing of application importance. That describes well the Hero class with its three required fields (id, name, power) and one optional field (alterEgo).

使用 Angular CLI 命令 ng generate class生成一个名叫 Hero 的新类：

Using the Angular CLI command ng generate class, generate a new class named Hero:

      
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      ng generate class Hero
    

内容如下：

With this content:

      
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      export class Hero {

  constructor(
    public id: number,
    public name: string,
    public power: string,
    public alterEgo?: string
  ) {  }

}
    

这是一个少量需求和零行为的贫血模型。对演示来说很完美。

It's an anemic model with few requirements and no behavior. Perfect for the demo.

TypeScript 编译器为每个 public 构造函数参数生成一个公共字段，在创建新的英雄实例时，自动把参数值赋给这些公共字段。

The TypeScript compiler generates a public field for each public constructor parameter and automatically assigns the parameter’s value to that field when you create heroes.

alterEgo 是可选的，调用构造函数时可省略，注意 alterEgo? 中的问号 (?)。

The alterEgo is optional, so the constructor lets you omit it; note the question mark (?) in alterEgo?.

可以这样创建新英雄：

You can create a new hero like this:

      
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      let myHero =  new Hero(42, 'SkyDog',
                       'Fetch any object at any distance',
                       'Leslie Rollover');
console.log('My hero is called ' + myHero.name); // "My hero is called SkyDog"
    

创建表单组件link

Create a form componentlink

Angular 表单分为两部分：基于 HTML 的模板和组件类，用来程序处理数据和用户交互。 先从组件类开始，是因为它可以简要说明英雄编辑器能做什么。

An Angular form has two parts: an HTML-based template and a component class to handle data and user interactions programmatically. Begin with the class because it states, in brief, what the hero editor can do.

使用 Angular CLI 命令 ng generate class生成一个名叫 HeroForm 的新组件：

Using the Angular CLI command ng generate component, generate a new component named HeroForm:

      
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      ng generate component HeroForm
    

内容如下：

With this content:

      
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      import { Component } from '@angular/core';

import { Hero }    from '../hero';

@Component({
  selector: 'app-hero-form',
  templateUrl: './hero-form.component.html',
  styleUrls: ['./hero-form.component.css']
})
export class HeroFormComponent {

  powers = ['Really Smart', 'Super Flexible',
            'Super Hot', 'Weather Changer'];

  model = new Hero(18, 'Dr IQ', this.powers[0], 'Chuck Overstreet');

  submitted = false;

  onSubmit() { this.submitted = true; }

  // TODO: Remove this when we're done
  get diagnostic() { return JSON.stringify(this.model); }
}
    

这个组件没有什么特别的地方，没有表单相关的东西，与之前写过的组件没什么不同。

There’s nothing special about this component, nothing form-specific, nothing to distinguish it from any component you've written before.

只要用前面章节中学过的 Angular 概念，就可以完全理解这个组件：

Understanding this component requires only the Angular concepts covered in previous pages.

• 这段代码导入了 Angular 核心库以及你刚刚创建的 Hero 模型。

  The code imports the Angular core library and the Hero model you just created.

• @Component 选择器“hero-form”表示可以用 <app-hero-form> 标签把这个表单放进父模板。

  The @Component selector value of "app-hero-form" means you can drop this form in a parent template with a <app-hero-form> tag.

• templateUrl 属性指向一个独立的 HTML 模板文件。

  The templateUrl property points to a separate file for the template HTML.

• 你定义了一些用来演示的，关于 model 和 powers 的模拟数据。

  You defined dummy data for model and powers, as befits a demo.

接下来，你可以注入一个数据服务，以获取或保存真实的数据，或者把这些属性暴露为输入属性和输出属性（参见Template Syntax中的输入和输出属性）来绑定到一个父组件。这不是现在需要关心的问题，未来的更改不会影响到这个表单。

Down the road, you can inject a data service to get and save real data or perhaps expose these properties as inputs and outputs (see Input and output properties on the Template Syntax page) for binding to a parent component. This is not a concern now and these future changes won't affect the form.

• 你添加一个 diagnostic 属性，以返回这个模型的 JSON 形式。在开发过程中，它用于调试，最后清理时会丢弃它。

  You added a diagnostic property to return a JSON representation of the model. It'll help you see what you're doing during development; you've left yourself a cleanup note to discard it later.

修改 app.module.tslink

Revise app.module.tslink

app.module.ts 定义了应用的根模块。其中标识即将用到的外部模块，以及声明属于本模块中的组件，例如 HeroFormComponent。

app.module.ts defines the application's root module. In it you identify the external modules you'll use in the application and declare the components that belong to this module, such as the HeroFormComponent.

因为模板驱动的表单位于它们自己的模块，所以在使用表单之前，需要将 FormsModule 添加到应用模块的 imports 数组中。

Because template-driven forms are in their own module, you need to add the FormsModule to the array of imports for the application module before you can use forms.

对它做如下修改：

Update it with the following:

      
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import { NgModule }      from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule }   from '@angular/forms';
 
import { AppComponent }  from './app.component';
import { HeroFormComponent } from './hero-form/hero-form.component';
 
@NgModule({
  imports: [
    BrowserModule,
    FormsModule
  ],
  declarations: [
    AppComponent,
    HeroFormComponent
  ],
  providers: [],
  bootstrap: [ AppComponent ]
})
export class AppModule { }
    

修改 app.component.tslink

Revise app.component.htmllink

AppComponent 是应用的根组件，HeroFormComponent 将被放在其中。

AppComponent is the application's root component. It will host the new HeroFormComponent.

把模板中的内容替换成如下代码：

Replace the contents of its template with the following:

      
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      <app-hero-form></app-hero-form>
    

创建初始 HTML 表单模板link

Create an initial HTML form templatelink

修改模板文件，内容如下：

Update the template file with the following contents:

      
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<div class="container">
    <h1>Hero Form</h1>
    <form>
      <div class="form-group">
        <label for="name">Name</label>
        <input type="text" class="form-control" id="name" required>
      </div>
 
      <div class="form-group">
        <label for="alterEgo">Alter Ego</label>
        <input type="text" class="form-control" id="alterEgo">
      </div>
 
      <button type="submit" class="btn btn-success">Submit</button>
 
    </form>
</div>
    

这只是一段普通的旧式 HTML 5 代码。这里有两个 Hero 字段，name 和 alterEgo，供用户输入。

The language is simply HTML5. You're presenting two of the Hero fields, name and alterEgo, and opening them up for user input in input boxes.

Name <input> 控件具有 HTML5 的 required 属性；但 Alter Ego <input> 控件没有，因为 alterEgo 字段是可选的。

The Name <input> control has the HTML5 required attribute; the Alter Ego <input> control does not because alterEgo is optional.

在底部添加个 Submit 按钮，它还带一些 CSS 样式类。

You added a Submit button at the bottom with some classes on it for styling.

你还没有真正用到 Angular。没有绑定，没有额外的指令，只有布局。

You're not using Angular yet. There are no bindings or extra directives, just layout.

container、form-group、form-control 和 btn 类来自 Twitter Bootstrap。这些类纯粹是装饰品。 Bootstrap 为这个表单提供了一些样式。

The container, form-group, form-control, and btn classes come from Twitter Bootstrap. These classes are purely cosmetic. Bootstrap gives the form a little style.

要添加样式表，就打开 styles.css，并把下列代码添加到顶部：

To add the stylesheet, open styles.css and add the following import line at the top:

      
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      @import url('https://unpkg.com/bootstrap@3.3.7/dist/css/bootstrap.min.css');
    

用 ngFor 添加超能力link

Add powers with *ngForlink

英雄必须从认证过的固定列表中选择一项超能力。 这个列表位于 HeroFormComponent 中。

The hero must choose one superpower from a fixed list of agency-approved powers. You maintain that list internally (in HeroFormComponent).

在表单中添加 select，用 ngFor 把 powers 列表绑定到列表选项。 之前的显示数据一章中见过 ngFor。

You'll add a select to the form and bind the options to the powers list using ngFor, a technique seen previously in the Displaying Data page.

在 Alter Ego 的紧下方添加如下 HTML：

Add the following HTML immediately below the Alter Ego group:

      
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      <div class="form-group">
  <label for="power">Hero Power</label>
  <select class="form-control" id="power" required>
    <option *ngFor="let pow of powers" [value]="pow">{{pow}}</option>
  </select>
</div>
    

列表中的每一项超能力都会渲染成 <option> 标签。 模板输入变量 pow 在每个迭代指向不同的超能力，使用双花括号插值表达式语法来显示它的名称。

This code repeats the <option> tag for each power in the list of powers. The pow template input variable is a different power in each iteration; you display its name using the interpolation syntax.

使用 ngModel 进行双向数据绑定link

Two-way data binding with ngModellink

如果立即运行此应用，你将会失望。

Running the app right now would be disappointing.

因为还没有绑定到某个英雄，所以看不到任何数据。 解决方案见前面的章节。 显示数据介绍了属性绑定。 用户输入介绍了如何通过事件绑定来监听 DOM 事件，以及如何用显示值更新组件的属性。

You don't see hero data because you're not binding to the Hero yet. You know how to do that from earlier pages. Displaying Data teaches property binding. User Input shows how to listen for DOM events with an event binding and how to update a component property with the displayed value.

现在，需要同时进行显示、监听和提取。

Now you need to display, listen, and extract at the same time.

虽然可以在表单中再次使用这些技术。 但是，这里将介绍个新东西，[(ngModel)] 语法，使表单绑定到模型的工作变得超级简单。

You could use the techniques you already know, but instead you'll use the new [(ngModel)] syntax, which makes binding the form to the model easy.

找到 Name 对应的 <input> 标签，并且像这样修改它：

Find the <input> tag for Name and update it like this:

      
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      <input type="text" class="form-control" id="name"
       required
       [(ngModel)]="model.name" name="name">
TODO: remove this: {{model.name}}
    

聚焦到绑定语法 [(ngModel)]="..." 上。

Focus on the binding syntax: [(ngModel)]="...".

你需要更多的工作来显示数据。在表单中声明一个模板变量。往 <form> 标签中加入 #heroForm="ngForm"，代码如下：

You need one more addition to display the data. Declare a template variable for the form. Update the <form> tag with #heroForm="ngForm" as follows:

      
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      <form #heroForm="ngForm">
    

heroForm 变量是一个到 NgForm 指令的引用，它代表该表单的整体。

The variable heroForm is now a reference to the NgForm directive that governs the form as a whole.

如果现在运行这个应用，开始在姓名输入框中键入，添加和删除字符，将看到它们从插值结果中显示和消失。 某一瞬间，它可能是这样的：

If you ran the app now and started typing in the Name input box, adding and deleting characters, you'd see them appear and disappear from the interpolated text. At some point it might look like this:

诊断信息可以证明，数据确实从输入框流动到模型，再反向流动回来。

The diagnostic is evidence that values really are flowing from the input box to the model and back again.

注意，<input> 标签还添加了 name 属性 (attribute)，并设置为 "name"，表示英雄的名字。 使用任何唯一的值都可以，但使用具有描述性的名字会更有帮助。 当在表单中使用 [(ngModel)] 时，必须要定义 name 属性。

Notice that you also added a name attribute to the <input> tag and set it to "name", which makes sense for the hero's name. Any unique value will do, but using a descriptive name is helpful. Defining a name attribute is a requirement when using [(ngModel)] in combination with a form.

为第二人格和超能力属性添加类似的 [(ngModel)] 绑定和 name 属性。 抛弃输入框的绑定消息，在组件顶部添加到 diagnostic 属性的新绑定。 这样就能确认双向数据绑定在整个 Hero 模型上都能正常工作了。

Add similar [(ngModel)] bindings and name attributes to Alter Ego and Hero Power. You'll ditch the input box binding message and add a new binding (at the top) to the component's diagnostic property. Then you can confirm that two-way data binding works for the entire hero model.

修改之后，这个表单的核心是这样的：

After revision, the core of the form should look like this:

      
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      {{diagnostic}}
<div class="form-group">
  <label for="name">Name</label>
  <input type="text" class="form-control" id="name"
         required
         [(ngModel)]="model.name" name="name">
</div>

<div class="form-group">
  <label for="alterEgo">Alter Ego</label>
  <input type="text"  class="form-control" id="alterEgo"
         [(ngModel)]="model.alterEgo" name="alterEgo">
</div>

<div class="form-group">
  <label for="power">Hero Power</label>
  <select class="form-control"  id="power"
          required
          [(ngModel)]="model.power" name="power">
    <option *ngFor="let pow of powers" [value]="pow">{{pow}}</option>
  </select>
</div>
    

如果现在运行本应用，修改 Hero 模型的每个属性，表单是这样的：

If you run the app now and change every hero model property, the form might display like this:

表单顶部的诊断信息反映出所做的一切更改。

The diagnostic near the top of the form confirms that all of your changes are reflected in the model.

表单顶部的 {{diagnostic}} 绑定已经完成了它的使命，删除它。

Delete the {{diagnostic}} binding at the top as it has served its purpose.

通过 ngModel 跟踪修改状态与有效性验证link

Track control state and validity with ngModellink

在表单中使用 ngModel 可以获得比仅使用双向数据绑定更多的控制权。它还会告诉你很多信息：用户碰过此控件吗？它的值变化了吗？数据变得无效了吗？

Using ngModel in a form gives you more than just two-way data binding. It also tells you if the user touched the control, if the value changed, or if the value became invalid.

NgModel 指令不仅仅跟踪状态。它还使用特定的 Angular CSS 类来更新控件，以反映当前状态。 可以利用这些 CSS 类来修改控件的外观，显示或隐藏消息。

The NgModel directive doesn't just track state; it updates the control with special Angular CSS classes that reflect the state. You can leverage those class names to change the appearance of the control.

往姓名 <input> 标签上添加名叫 spy 的临时模板引用变量， 然后用这个 spy 来显示它上面的所有 CSS 类。

Temporarily add a template reference variable named spy to the Name <input> tag and use it to display the input's CSS classes.

      
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      <input type="text" class="form-control" id="name"
  required
  [(ngModel)]="model.name" name="name"
  #spy>
<br>TODO: remove this: {{spy.className}}
    

现在，运行本应用，并让姓名输入框获得焦点。 然后严格按照下面四个步骤来做：

Now run the app and look at the Name input box. Follow these steps precisely:

1. 查看输入框，但别碰它。

   Look but don't touch.

2. 点击输入框，然后点击输入框外面。

   Click inside the name box, then click outside it.

3. 在名字的末尾添加些斜杠。

   Add slashes to the end of the name.

4. 删除名字。

   Erase the name.

动作和它对应的效果如下：

The actions and effects are as follows:

你会看到下列转换及其类名：

You should see the following transitions and class names:

(ng-valid | ng-invalid)这一对是最有趣的部分，因为当数据变得无效时，你希望发出强力的视觉信号， 还想要标记出必填字段。可以通过加入自定义 CSS 来提供视觉反馈。

The ng-valid/ng-invalid pair is the most interesting, because you want to send a strong visual signal when the values are invalid. You also want to mark required fields. To create such visual feedback, add definitions for the ng-* CSS classes.

删除模板引用变量 #spy 和 TODO，因为它们已经完成了使命。

Delete the #spy template reference variable and the TODO as they have served their purpose.

添加用于视觉反馈的自定义 CSSlink

Add custom CSS for visual feedbacklink

可以在输入框的左侧添加带颜色的竖条，用于标记必填字段和无效输入：

You can mark required fields and invalid data at the same time with a colored bar on the left of the input box:

在新建的 forms.css 文件中，添加两个样式来实现这一效果。把这个文件添加到项目中，与 index.html 相邻。

You achieve this effect by adding these class definitions to a new forms.css file that you add to the project as a sibling to index.html:

      
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      .ng-valid[required], .ng-valid.required  {
  border-left: 5px solid #42A948; /* green */
}

.ng-invalid:not(form)  {
  border-left: 5px solid #a94442; /* red */
}
    

修改 index.html 中的 <head>，以包含这个样式表：

Update the <head> of index.html to include this style sheet:

      
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      <link rel="stylesheet" href="assets/forms.css">
    

显示和隐藏验证错误信息link

Show and hide validation error messageslink

你还能做的更好。“Name” 输入框是必填的，清空它会让左侧的条变红。这表示某些东西是错的，但用户不知道错在哪里，或者如何纠正。 可以借助 ng-invalid 类来给出有用的提示。

You can improve the form. The Name input box is required and clearing it turns the bar red. That says something is wrong but the user doesn't know what is wrong or what to do about it. Leverage the control's state to reveal a helpful message.

当用户删除姓名时，应该是这样的：

When the user deletes the name, the form should look like this:

要达到这个效果，在 <input> 标签中添加：

To achieve this effect, extend the <input> tag with the following:

• 模板引用变量

  A template reference variable.

• “is required”消息，放在邻近的 <div> 元素中，只有当控件无效时，才显示它。

  The "is required" message in a nearby <div>, which you'll display only if the control is invalid.

下面这个例子中把一条错误信息添加到了name输入框中：

Here's an example of an error message added to the name input box:

      
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      <label for="name">Name</label>
<input type="text" class="form-control" id="name"
       required
       [(ngModel)]="model.name" name="name"
       #name="ngModel">
<div [hidden]="name.valid || name.pristine"
     class="alert alert-danger">
  Name is required
</div>
    

模板引用变量可以访问模板中输入框的 Angular 控件。 这里，创建了名叫 name 的变量，并且赋值为 "ngModel"。

You need a template reference variable to access the input box's Angular control from within the template. Here you created a variable called name and gave it the value "ngModel".

你把 div 元素的 hidden 属性绑定到 name 控件的属性，这样就可以控制“姓名”字段错误信息的可见性了。

You control visibility of the name error message by binding properties of the name control to the message <div> element's hidden property.

      
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      <div [hidden]="name.valid || name.pristine"
     class="alert alert-danger">
    

上例中，当控件是有效的 (valid) 或全新的 (pristine) 时，隐藏消息。 “全新的”意味着从它显示在表单中开始，用户还从未修改过它的值。

In this example, you hide the message when the control is valid or pristine; "pristine" means the user hasn't changed the value since it was displayed in this form.

这种用户体验取决于开发人员的选择。有些人会希望任何时候都显示这条消息。 如果忽略了 pristine 状态，就会只在值有效时隐藏此消息。 如果往这个组件中传入全新（空）的英雄，或者无效的英雄，将立刻看到错误信息 —— 虽然你还啥都没做。

This user experience is the developer's choice. Some developers want the message to display at all times. If you ignore the pristine state, you would hide the message only when the value is valid. If you arrive in this component with a new (blank) hero or an invalid hero, you'll see the error message immediately, before you've done anything.

有些人会为这种行为感到不安。它们希望只有在用户做出无效的更改时才显示这个消息。 如果当控件是“全新”状态时也隐藏消息，就能达到这个目的。 在往表单中添加新英雄时，将看到这种选择的重要性。

Some developers want the message to display only when the user makes an invalid change. Hiding the message while the control is "pristine" achieves that goal. You'll see the significance of this choice when you add a new hero to the form.

英雄的第二人格是可选项，所以不用改它。

The hero Alter Ego is optional so you can leave that be.

英雄的超能力选项是必填的。 只要愿意，可以往 <select> 上添加相同的错误处理。 但没有必要，这个选择框已经限制了“超能力”只能选有效值。

Hero Power selection is required. You can add the same kind of error handling to the <select> if you want, but it's not imperative because the selection box already constrains the power to valid values.

现在，你要在这个表单中添加新的英雄。 在表单的底部放置“New Hero（新增英雄）”按钮，并把它的点击事件绑定到组件上的 newHero 方法。

Now you'll add a new hero in this form. Place a New Hero button at the bottom of the form and bind its click event to a newHero component method.

      
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      <button type="button" class="btn btn-default" (click)="newHero()">New Hero</button>
    

      
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      newHero() {
  this.model = new Hero(42, '', '');
}
    

再次运行应用，点击 New Hero 按钮，表单被清空了。 输入框左侧的必填项竖条是红色的，表示 name 和 power 属性是无效的。 这可以理解，因为有一些必填字段。 错误信息是隐藏的，因为表单还是全新的，还没有修改任何东西。

Run the application again, click the New Hero button, and the form clears. The required bars to the left of the input box are red, indicating invalid name and power properties. That's understandable as these are required fields. The error messages are hidden because the form is pristine; you haven't changed anything yet.

输入名字，再次点击 New Hero 按钮。 这次，出现了错误信息！为什么？你不希望显示新（空）的英雄时，出现错误信息。

Enter a name and click New Hero again. The app displays a Name is required error message. You don't want error messages when you create a new (empty) hero. Why are you getting one now?

使用浏览器工具审查这个元素就会发现，这个 name 输入框并不是全新的。 表单记得你在点击 New Hero 前输入的名字。 更换了英雄对象并不会重置控件的“全新”状态。

Inspecting the element in the browser tools reveals that the name input box is no longer pristine. The form remembers that you entered a name before clicking New Hero. Replacing the hero object did not restore the pristine state of the form controls.

你必须清除所有标记，在调用 newHero() 方法后调用表单的 reset() 方法即可。

You have to clear all of the flags imperatively, which you can do by calling the form's reset() method after calling the newHero() method.

      
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      <button type="button" class="btn btn-default" (click)="newHero(); heroForm.reset()">New Hero</button>
    

现在点击“New Hero”重设表单和它的控制标记。

Now clicking "New Hero" resets both the form and its control flags.

使用 ngSubmit 提交该表单link

Submit the form with ngSubmitlink

在填表完成之后，用户还应该能提交这个表单。 “Submit（提交）”按钮位于表单的底部，它自己不做任何事，但因为有特殊的 type 值 (type="submit")，所以会触发表单提交。

The user should be able to submit this form after filling it in. The Submit button at the bottom of the form does nothing on its own, but it will trigger a form submit because of its type (type="submit").

现在这样仅仅触发“表单提交”是没用的。 要让它有用，就要把该表单的 ngSubmit 事件属性绑定到英雄表单组件的 onSubmit() 方法上：

A "form submit" is useless at the moment. To make it useful, bind the form's ngSubmit event property to the hero form component's onSubmit() method:

      
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      <form (ngSubmit)="onSubmit()" #heroForm="ngForm">
    

你已经定义了一个模板引用变量 #heroForm，并且把赋值为“ngForm”。 现在，就可以在“Submit”按钮中访问这个表单了。

You'd already defined a template reference variable, #heroForm, and initialized it with the value "ngForm". Now, use that variable to access the form with the Submit button.

你要把表单的总体有效性通过 heroForm 变量绑定到此按钮的 disabled 属性上，代码如下：

You'll bind the form's overall validity via the heroForm variable to the button's disabled property using an event binding. Here's the code:

      
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      <button type="submit" class="btn btn-success" [disabled]="!heroForm.form.valid">Submit</button>
    

重新运行应用。表单打开时，状态是有效的，按钮是可用的。

If you run the application now, you find that the button is enabled—although it doesn't do anything useful yet.

现在，如果你删除姓名，就会违反“必填姓名”规则，就会像以前那样显示出错误信息。同时，Submit 按钮也被禁用了。

Now if you delete the Name, you violate the "required" rule, which is duly noted in the error message. The Submit button is also disabled.

没感觉吗？再想一会儿。如果没有 Angular NgForm 的帮助，又该怎么让按钮的禁用/启用状态和表单的有效性关联起来呢？

Not impressed? Think about it for a moment. What would you have to do to wire the button's enable/disabled state to the form's validity without Angular's help?

对你来说，它就是这么简单：

For you, it was as simple as this:

1. 定义模板引用变量，放在（强化过的）form 元素上

   Define a template reference variable on the (enhanced) form element.

2. 从很多行之外的按钮上引用这个变量。

   Refer to that variable in a button many lines away.

切换两个表单区域（额外的奖励）link

Toggle two form regions (extra credit)link

提交表单还是不够激动人心。

Submitting the form isn't terribly dramatic at the moment.

来实现一些更炫的视觉效果吧。 隐藏掉数据输入框，显示一些别的东西。

For a more strikingly visual effect, hide the data entry area and display something else.

先把表单包裹进 <div> 中，再把它的 hidden 属性绑定到 HeroFormComponent.submitted 属性。

Wrap the form in a <div> and bind its hidden property to the HeroFormComponent.submitted property.

      
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      <div [hidden]="submitted">
  <h1>Hero Form</h1>
  <form (ngSubmit)="onSubmit()" #heroForm="ngForm">

     <!-- ... all of the form ... -->

  </form>
</div>
    

主表单从一开始就是可见的，因为 submitted 属性是 false，直到提交了这个表单。 来自 HeroFormComponent 的代码片段证实了这一点：

The main form is visible from the start because the submitted property is false until you submit the form, as this fragment from the HeroFormComponent shows:

      
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      submitted = false;

onSubmit() { this.submitted = true; }
    

当点击 Submit 按钮时，submitted 标志会变成 true，并且表单像预想中一样消失了。

When you click the Submit button, the submitted flag becomes true and the form disappears as planned.

现在，当表单处于已提交状态时，需要显示一些别的东西。 在刚刚写的 <div> 包装下方，添加下列 HTML 语句：

Now the app needs to show something else while the form is in the submitted state. Add the following HTML below the <div> wrapper you just wrote:

      
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      <div [hidden]="!submitted">
  <h2>You submitted the following:</h2>
  <div class="row">
    <div class="col-xs-3">Name</div>
    <div class="col-xs-9">{{ model.name }}</div>
  </div>
  <div class="row">
    <div class="col-xs-3">Alter Ego</div>
    <div class="col-xs-9">{{ model.alterEgo }}</div>
  </div>
  <div class="row">
    <div class="col-xs-3">Power</div>
    <div class="col-xs-9">{{ model.power }}</div>
  </div>
  <br>
  <button class="btn btn-primary" (click)="submitted=false">Edit</button>
</div>
    

英雄又出现了，它通过插值表达式绑定显示为只读内容。 这一小段 HTML 只在组件处于已提交状态时才会显示。

There's the hero again, displayed read-only with interpolation bindings. This <div> appears only while the component is in the submitted state.

这段 HTML 包含一个 “Edit（编辑）”按钮，它的 click 事件绑定到了一个用于清除 submitted 标志的表达式。

The HTML includes an Edit button whose click event is bound to an expression that clears the submitted flag.

当点 Edit 按钮时，这个只读块消失了，可编辑的表单重新出现了。

When you click the Edit button, this block disappears and the editable form reappears.

小结link

Summarylink

本章讨论的 Angular 表单技术利用了下列框架特性来支持数据修改、验证和更多操作：

The Angular form discussed in this page takes advantage of the following framework features to provide support for data modification, validation, and more:

• Angular HTML 表单模板。

  An Angular HTML form template.

• 带有 @Component 装饰器的表单组件类。

  A form component class with a @Component decorator.

• 通过绑定到 NgForm.ngSubmit 事件属性来处理表单提交。

  Handling form submission by binding to the NgForm.ngSubmit event property.

• 模板引用变量，例如 #heroForm 和 #name。

  Template-reference variables such as #heroForm and #name.

• [(ngModel)] 语法用来实现双向数据绑定。

  [(ngModel)] syntax for two-way data binding.

• name 属性的用途是有效性验证和对表单元素的变更进行追踪。

  The use of name attributes for validation and form-element change tracking.

• 指向 input 控件的引用变量上的 valid 属性，可用于检查控件是否有效、是否显示/隐藏错误信息。

  The reference variable’s valid property on input controls to check if a control is valid and show/hide error messages.

• 通过绑定到 NgForm 的有效性状态，控制 Submit 按钮的禁用状态。

  Controlling the Submit button's enabled state by binding to NgForm validity.

• 定制 CSS 类来给用户提供无效控件的视觉反馈。

  Custom CSS classes that provide visual feedback to users about invalid controls.

下面是该应用最终版本的代码：

Here’s the code for the final version of the application:

      
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import { Component } from '@angular/core';
 
import { Hero }    from '../hero';
 
@Component({
  selector: 'app-hero-form',
  templateUrl: './hero-form.component.html',
  styleUrls: ['./hero-form.component.css']
})
export class HeroFormComponent {
 
  powers = ['Really Smart', 'Super Flexible',
            'Super Hot', 'Weather Changer'];
 
  model = new Hero(18, 'Dr IQ', this.powers[0], 'Chuck Overstreet');
 
  submitted = false;
 
  onSubmit() { this.submitted = true; }
 
  newHero() {
    this.model = new Hero(42, '', '');
  }
}