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API > @angular/core

ExistingProvider

Configures the Injector to return a value of another useExisting token.

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      interface ExistingProvider extends ExistingSansProvider {
  provide: any
  multi?: boolean
}

说明

For more details, see the "Dependency Injection Guide".

属性

属性说明
provide: any

An injection token. (Typically an instance of Type or InjectionToken, but can be any).

multi?: boolean

If true, then injector returns an array of instances. This is useful to allow multiple providers spread across many files to provide configuration information to a common token.

使用说明

Example

class Greeting { salutation = 'Hello'; } class FormalGreeting extends Greeting { salutation = 'Greetings'; } const injector = Injector.create([ {provide: FormalGreeting, deps: []}, {provide: Greeting, useExisting: FormalGreeting} ]); expect(injector.get(Greeting).salutation).toEqual('Greetings'); expect(injector.get(FormalGreeting).salutation).toEqual('Greetings'); expect(injector.get(FormalGreeting)).toBe(injector.get(Greeting));
      
      
  1. class Greeting {
  2.   salutation = 'Hello';
  3. }
  4.  
  5. class FormalGreeting extends Greeting {
  6.   salutation = 'Greetings';
  7. }
  8.  
  9. const injector = Injector.create([
  10.   {provide: FormalGreeting, deps: []}, {provide: Greeting, useExisting: FormalGreeting}
  11. ]);
  12.  
  13. expect(injector.get(Greeting).salutation).toEqual('Greetings');
  14. expect(injector.get(FormalGreeting).salutation).toEqual('Greetings');
  15. expect(injector.get(FormalGreeting)).toBe(injector.get(Greeting));

Multi-value example

const locale = new InjectionToken<string[]>('locale'); const injector = Injector.create([ {provide: locale, multi: true, useValue: 'en'}, {provide: locale, multi: true, useValue: 'sk'}, ]); const locales: string[] = injector.get(locale); expect(locales).toEqual(['en', 'sk']);
      
      const locale = new InjectionToken<string[]>('locale');
const injector = Injector.create([
  {provide: locale, multi: true, useValue: 'en'},
  {provide: locale, multi: true, useValue: 'sk'},
]);

const locales: string[] = injector.get(locale);
expect(locales).toEqual(['en', 'sk']);