RangeError：使用 valueChanges.subscribe 时超出最大调用堆栈大小

我正在使用带有反应式表单的 Angular 5，并且需要使用 valueChanges 来动态禁用所需的验证

组件类：

export class UserEditor implements OnInit {

    public userForm: FormGroup;
    userName: FormControl;
    firstName: FormControl;
    lastName: FormControl;
    email: FormControl;
    loginTypeId: FormControl;
    password: FormControl;
    confirmPassword: FormControl;
...

ngOnInit() {
    this.createFormControls();
    this.createForm();
    this.userForm.get('loginTypeId').valueChanges.subscribe(

            (loginTypeId: string) => {
                console.log("log this!");
                if (loginTypeId === "1") {
                    console.log("disable validators");
                    Validators.pattern('^[0-9]{5}(?:-[0-9]{4})?$')]);
                    this.userForm.get('password').setValidators([]);
                    this.userForm.get('confirmPassword').setValidators([]);

                } else if (loginTypeId === '2') {
                    console.log("enable validators");
                    this.userForm.get('password').setValidators([Validators.required, Validators.minLength(8)]);
                    this.userForm.get('confirmPassword').setValidators([Validators.required, Validators.minLength(8)]);

                }

                this.userForm.get('loginTypeId').updateValueAndValidity();

            }

        )
}
createFormControls() {
    this.userName = new FormControl('', [
        Validators.required,
        Validators.minLength(4)
    ]);
    this.firstName = new FormControl('', Validators.required);
    this.lastName = new FormControl('', Validators.required);
    this.email = new FormControl('', [
      Validators.required,
      Validators.pattern("[^ @]*@[^ @]*")
    ]);
    this.password = new FormControl('', [
       Validators.required,
       Validators.minLength(8)
    ]);
    this.confirmPassword = new FormControl('', [
        Validators.required,
        Validators.minLength(8)
    ]);

}

createForm() {
 this.userForm = new FormGroup({
      userName: this.userName,
      name: new FormGroup({
        firstName: this.firstName,
        lastName: this.lastName,
      }),
      email: this.email,
      loginTypeId: this.loginTypeId,
      password: this.password,
      confirmPassword: this.confirmPassword
    });
}

但是，当我运行它时，我收到浏览器 JavaScript 错误

UserEditor.html:82 ERROR RangeError: Maximum call stack size exceeded
    at SafeSubscriber.tryCatcher (tryCatch.js:9)
    at SafeSubscriber.webpackJsonp.../../../../rxjs/_esm5/Subscription.js.Subscription.unsubscribe (Subscription.js:68)
    at SafeSubscriber.webpackJsonp.../../../../rxjs/_esm5/Subscriber.js.Subscriber.unsubscribe (Subscriber.js:124)
    at SafeSubscriber.webpackJsonp.../../../../rxjs/_esm5/Subscriber.js.SafeSubscriber.__tryOrUnsub (Subscriber.js:242)
    at SafeSubscriber.webpackJsonp.../../../../rxjs/_esm5/Subscriber.js.SafeSubscriber.next (Subscriber.js:186)
    at Subscriber.webpackJsonp.../../../../rxjs/_esm5/Subscriber.js.Subscriber._next (Subscriber.js:127)
    at Subscriber.webpackJsonp.../../../../rxjs/_esm5/Subscriber.js.Subscriber.next (Subscriber.js:91)
    at EventEmitter.webpackJsonp.../../../../rxjs/_esm5/Subject.js.Subject.next (Subject.js:56)
    at EventEmitter.webpackJsonp.../../../core/esm5/core.js.EventEmitter.emit (core.js:4319)
    at FormControl.webpackJsonp.../../../forms/esm5/forms.js.AbstractControl.updateValueAndValidity (forms.js:3377)

“记录这个！”被记录重复调用，就像递归调用一样，这就是为什么它们是堆栈错误

如果我删除 valueChanges.subscribe，则除了有条件地删除验证之外，代码还可以工作。

为什么它递归地调用 valueChanges.subscribe ？

如果您想订阅任何表单更改并仍然在其中运行 patchValue，那么您可以添加{emitEvent: false}patchValue 的选项，因此修补不会触发另一个更改检测

code:

this.formGroup
    .valueChanges
    .subscribe( _ => {
        this.formGroup.get( 'controlName' ).patchValue( _val, {emitEvent: false} );
    } );

附言。这也比逐一订阅每个表单控件以避免触发更改最大调用堆栈超出更繁琐。特别是如果您的表单有 100 个控件需要订阅。

现在进一步详细说明，如果您仍然需要在订阅内 updateValueAndValidity，那么我建议您使用distinctUntilChangedrxjs 运算符，仅在某些值发生变化时运行订阅。

可以在此处找到distinctUntilChanged 文档

https://www.learnrxjs.io/operators/filtering/distinctuntilchanged.html https://www.learnrxjs.io/operators/filtering/distinctuntilchanged.html

直到改变为止- 仅当当前值不同时才发出 比最后一次。

现在我们还必须将其设为自定义验证函数，因为默认情况下，distinctUntilChanged 通过指针验证对象，并且每次更改时指针都是新的。

this.formGroup
    .valueChanges
    .distinctUntilChanged((a, b) => JSON.stringify(a) === JSON.stringify(b))
    .subscribe( _ => {
        this.formGroup.get( 'controlName' ).patchValue( _val, {emitEvent: false} );
        this.formGroup.get( 'controlName' ).updateValueAndValidity();
    } );

瞧，我们正在修补和更新，而没有遇到最大调用堆栈！