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