NG_VALIDATORS和驗證器之間的區別（類）

Question

我對NG_VALIDATORS的用法感到困惑，我知道它是一個提供者令牌。但它有什麼用途？形式校驗器類與它有什麼不同？

https://github.com/angular/angular/blob/4.3.3/packages/forms/src/validators.ts

Answer 1

你有兩種方式來驗證添加到表單控件。通過指定它們作爲參數來表單控件使用勢在必行的方法：

const ctrl = new FormControl('', Validators.required); 

或聲明通過使用模板中驗證特定指令：

<input [formControl]='ctrl' required> 

NG_VALIDATORS該令牌在第二種情況下使用。這些令牌由驗證器指令required,email定義。並且它們在形式指令 - NgForm,NgModel和NgModelGroup創建的噴油器上定義。請參閱How exactly works the services hierarchy in this Angular 2 application?瞭解更多關於創建自己的噴油器的指令。

export const EMAIL_VALIDATOR: any = { 
    provide: NG_VALIDATORS, 
    useExisting: forwardRef(() => EmailValidator), 
    multi: true 
}; 
@Directive({ 
    selector: '[email]...', 
    providers: [EMAIL_VALIDATOR] <------------- 
}) 
export class EmailValidator implements Validator { 

---

export const REQUIRED_VALIDATOR: Provider = { 
    provide: NG_VALIDATORS, 
    useExisting: forwardRef(() => RequiredValidator), 
    multi: true 
}; 
@Directive({ 
    selector: 
     '[required]...', 
    providers: [REQUIRED_VALIDATOR], <------------- 
}) 
export class RequiredValidator implements Validator { 

---

角反應和模板驅動的形式指令（NgForm，NgModel和NgModelGroup）使用注入驗證：

全內置和自定義驗證使用此令牌註冊此令牌：

export class NgForm extends ControlContainer implements Form { 
    ...  
    constructor(
     @Optional() @Self() @Inject(NG_VALIDATORS) validators: any[], 

---

export class NgModel extends NgControl implements OnChanges, 
    ... 
    constructor(@Optional() @Self() @Inject(NG_VALIDATORS) validators..., 

---

export class NgModelGroup extends AbstractFormGroupDirective implements ... { 
    ... 
    constructor(
     @Optional() @Self() @Inject(NG_VALIDATORS) validators: any[], 

這同樣適用於在NG_ASYNC_VALIDATORS令牌。