85 lines
3.1 KiB
Markdown
85 lines
3.1 KiB
Markdown
# Sharing Modules
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#### Prerequisites
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A basic understanding of the following:
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* [Feature Modules](guide/feature-modules).
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* [JavaScript Modules vs. NgModules](guide/ngmodule-vs-jsmodule).
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* [Frequently Used Modules](guide/frequent-ngmodules).
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* [Routing and Navigation](guide/router).
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* [Lazy loading modules](guide/lazy-loading-ngmodules).
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<!--* Components (#TBD) We don’t have a page just on the concept of components, but I think one would be helpful for beginners.-->
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<hr>
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Creating shared modules allows you to organize and streamline your code. You can put commonly
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used directives, pipes, and components into one module and then import just that module wherever
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you need it in other parts of your app.
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Consider the following module from an imaginary app:
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```typescript
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import { CommonModule } from '@angular/common';
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import { NgModule } from '@angular/core';
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import { FormsModule } from '@angular/forms';
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import { CustomerComponent } from './customer.component';
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import { NewItemDirective } from './new-item.directive';
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import { OrdersPipe } from './orders.pipe';
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@NgModule({
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imports: [ CommonModule ],
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declarations: [ CustomerComponent, NewItemDirective, OrdersPipe ],
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exports: [ CustomerComponent, NewItemDirective, OrdersPipe,
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CommonModule, FormsModule ]
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})
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export class SharedModule { }
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```
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Note the following:
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请注意以下几点：
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* It imports the `CommonModule` because the module's component needs common directives.
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* It declares and exports the utility pipe, directive, and component classes.
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* It re-exports the `CommonModule` and `FormsModule`.
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By re-exporting `CommonModule` and `FormsModule`, any other module that imports this
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`SharedModule`, gets access to directives like `NgIf` and `NgFor` from `CommonModule`
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and can bind to component properties with `[(ngModel)]`, a directive in the `FormsModule`.
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Even though the components declared by `SharedModule` might not bind
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with `[(ngModel)]` and there may be no need for `SharedModule`
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to import `FormsModule`, `SharedModule` can still export
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`FormsModule` without listing it among its `imports`. This
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way, you can give other modules access to `FormsModule` without
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having to import it directly into the `@NgModule` decorator.
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### Using components vs services from other modules.
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There is an important distinction between using another module's component and
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using a service from another module. Import modules when you want to use
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directives, pipes, and components. Importing a module with services means that you will have a new instance of that service, which typically is not what you need (typically one wants to reuse an existing service). Use module imports to control service instantiation.
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The most common way to get a hold of shared services is through Angular
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[dependency injection](guide/dependency-injection), rather than through the module system (importing a module will result in a new service instance, which is not a typical usage).
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To read about sharing services, see [Providers](guide/providers).
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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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* [Providers](guide/providers).
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* [Types of Feature Modules](guide/module-types).
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