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API > @angular/core

ExistingProvider

配置此 Injector 以返回另一个 useExisting 令牌的值。

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

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

  // 继承自 core/ExistingSansProvider
  useExisting: any
}

参见

属性

属性说明
provide: any

注入令牌。通常是 Type 或 InjectionToken 的实例，但也可以是 any 实例。

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

multi?: boolean

如果为 true，则注入器返回实例数组。这对于允许多个提供者散布在多个文件中，以向某个公共令牌提供配置信息很有用。

When true, 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

      
      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));

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']);