在angular2

Question

是新形式的異步驗證，angular2，我想驗證來自服務器的電子郵件地址，但它沒有

這是我的形式

this.userform = this._formbuilder.group({ 
    email: ['', [Validators.required], [this._validationService.emailExistsValidator.bind(this)]], 
}); 

然後_ValidationService我有 驗證服務是與@Injector

@Injectable() 
    export class ValidationService{ 

    constructor(
private _authService:AuthService 
){} 

emailExistsValidator(control) { 
    if (control.value != undefined) { 
    return this._authService.checkExists("email") 
     .map(response => { 
     if (!response) { 
      return {'emailNotExists': true}; 
     } 
     }); 
    } 
    } 
} 

服務而在authservice我有（其被另一服務執行HTTP請求）

@Injectable() 
export class AuthService { 

checkExists(value):Observable<any>{ 
return this._http.get(this.authurl+value) 
    .map(response => { 
    return response //this is either true or false 
    }); 
} 

} 

我已按照建立我的表格This link但它無法

返回的錯誤是

Cannot read property 'checkExists' of undefined 
at UsersComponent.webpackJsonp.187. 
ValidationService.emailExistsValidator 

可能是錯的什麼

Answer 1

如果this應指向ValidationService， bind()需要爲

this.userform = this._formbuilder.group({ 
    email: ['', [Validators.required], [this._validationService.emailExistsValidator.bind(this._validationService)]], 
});