Angular

Question

我正在尝试构建我的 angular 应用程序，但由于这个错误而失败了

 ERROR in : Can't resolve all parameters for SimpleLookupAddEditFormComponent 
 in C:/Users/lastr/Source/Repos/SMATA/Code/ng/smata-ng/src/app/system- 
 list/simple-lookup-add-edit/simple-lookup-add-edit.component.ts: (?, [object 
 Object], [object Object], [object Object]).

这里是组件的代码。这是一个基础组件。这里有什么遗漏吗？也许构造函数属性有问题？

 import { Component, OnInit } from '@angular/core';
 import { SimpleLookupBaseService } from '../services/simple-lookup-base/simple-lookup-base.service';
 import { ActivatedRoute, Router } from '@angular/router';
 import validationEngine from "devextreme/ui/validation_engine";
 import notify from 'devextreme/ui/notify';

 @Component({
   selector: 'app-simple-lookup-add-edit',
   templateUrl: './simple-lookup-add-edit.component.html',
   styleUrls: ['./simple-lookup-add-edit.component.css']
 })
 export class SimpleLookupAddEditFormComponent implements OnInit {

   newSystemList: {};
   isEditMode:boolean = true;
   selectedSystemList: any;
   title: string;
   saveButtonText: string;
   isPopupVisible:boolean = false;
   entityId:any;

   constructor(
     protected _systemListTitle : string,
     protected _svc: SimpleLookupBaseService,
     protected _router: Router,
     protected _route: ActivatedRoute
   ) 
     {}
 ............
 .....
 }

Answer 1

ERROR in : Can't resolve all parameters for SimpleLookupAddEditFormComponent in C:/Users/lastr/Source/Repos/SMATA/Code/ng/smata-ng/src/app/system- list/simple-lookup-add-edit/simple-lookup-add-edit.component.ts: (?, [object Object], [object Object], [object Object]).

错误消息中的?问号告诉构造函数中哪个参数未知。

constructor(
 protected _systemListTitle : string,
 protected _svc: SimpleLookupBaseService,
 protected _router: Router,
 protected _route: ActivatedRoute
)

第一个参数触发 ? 问号。

string 类型不是可注入类型。 Angular 注入器使用参数的类型来推断应该使用的 injectable 提供程序。

要注入 string 参数，您必须在您的 NgModule 定义之一中提供一个标记。

export const LIST_TITLE: InjectionToken<string> = new InjectionToken<string>('LIST_TITLE');

@NgModule({
   providers: [{provide: LIST_TITLE, useValue: 'My List Title'}]
})

现在您可以手动将令牌注入构造函数。

constructor(
 @Inject(LIST_TITLE) protected _systemListTitle : string,
 protected _svc: SimpleLookupBaseService,
 protected _router: Router,
 protected _route: ActivatedRoute
)

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