244 lines
4.1 KiB
Markdown
244 lines
4.1 KiB
Markdown
# Frequently Used Modules
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#### Prerequisites
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#### 前提条件
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A basic understanding of [Bootstrapping](guide/bootstrapping).
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<hr>
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An Angular app needs at least one module that serves as the root module.
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As you add features to your app, you can add them in modules.
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The following are frequently used Angular modules with examples
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of some of the things they contain:
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<table>
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<tr>
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<th style="vertical-align: top">
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NgModule
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</th>
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<th style="vertical-align: top">
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Import it from
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</th>
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<th style="vertical-align: top">
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Why you use it
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</th>
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</tr>
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<tr>
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<td>
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<code>BrowserModule</code>
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</td>
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<td>
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<code>@angular/platform-browser</code>
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</td>
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<td>
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When you want to run your app in a browser
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</td>
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</tr>
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<tr>
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<td>
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<code>CommonModule</code>
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</td>
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<td>
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<code>@angular/common</code>
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</td>
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<td>
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When you want to use <code>NgIf</code>, <code>NgFor</code>
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</td>
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</tr>
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<tr>
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<td>
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<code>FormsModule</code>
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</td>
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<td>
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<code>@angular/forms</code>
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</td>
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<td>
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When you build template driven forms (includes <code>NgModel</code>)
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</td>
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</tr>
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<tr>
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<td>
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<code>ReactiveFormsModule</code>
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</td>
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<td>
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<code>@angular/forms</code>
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</td>
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<td>
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When building reactive forms
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</td>
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</tr>
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<tr>
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<td>
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<code>RouterModule</code>
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<code>RouterModule</code>（路由器模块）
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</td>
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<td>
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<code>@angular/router</code>
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</td>
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<td>
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For Routing and when you want to use <code>RouterLink</code>,<code>.forRoot()</code>, and <code>.forChild()</code>
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</td>
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</tr>
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<tr>
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<td>
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<code>HttpClientModule</code>
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</td>
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<td>
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<code>@angular/common/http</code>
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</td>
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<td>
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When you to talk to a server
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</td>
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</tr>
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</table>
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## Importing modules
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When you use these Angular modules, import them in `AppModule`,
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or your feature module as appropriate, and list them in the `@NgModule`
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`imports` array. For example, in the basic app generated by the CLI,
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`BrowserModule` is the first import at the top of the `AppModule`,
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`app.module.ts`.
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```typescript
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/* import modules so that AppModule can access them */
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import { BrowserModule } from '@angular/platform-browser';
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import { NgModule } from '@angular/core';
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import { AppComponent } from './app.component';
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@NgModule({
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declarations: [
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AppComponent
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],
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imports: [ /* add modules here so Angular knows to use them */
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BrowserModule,
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],
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providers: [],
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bootstrap: [AppComponent]
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})
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export class AppModule { }
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```
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The imports at the top of the array are JavaScript import statements
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while the `imports` array within `@NgModule` is Angular specific.
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For more information on the difference, see [JavaScript Modules vs. NgModules](guide/ngmodule-vs-jsmodule).
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## `BrowserModule` and `CommonModule`
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`BrowserModule` imports `CommonModule`, which contributes many common
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directives such as `ngIf` and `ngFor`. Additionally, `BrowserModule`
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re-exports `CommonModule` making all of its directives available
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to any module that imports `BrowserModule`.
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For apps that run in the browser, import `BrowserModule` in the
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root `AppModule` because it provides services that are essential
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to launch and run a browser app. `BrowserModule`’s providers
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are for the whole app so it should only be in the root module,
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not in feature modules. Feature modules only need the common
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directives in `CommonModule`; they don’t need to re-install app-wide providers.
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If you do import `BrowserModule` into a lazy loaded feature module,
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Angular returns an error telling you to use `CommonModule` instead.
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<figure>
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<img src="generated/images/guide/frequent-ngmodules/browser-module-error.gif" width=750 alt="BrowserModule error">
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</figure>
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<hr />
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## More on NgModules
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You may also be interested in the following:
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* [Bootstrapping](guide/bootstrapping).
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* [NgModules](guide/ngmodules).
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* [JavaScript Modules vs. NgModules](guide/ngmodule-vs-jsmodule).
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[JavaScript 模块与 NgModules](guide/ngmodule-vs-jsmodule).
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