对于单元测试:

spyOn(component.form, 'valid').and.returnValue(true);

你也可以将viewChild的“类型”更改为NgForm，如下所示:

@ViewChild('loginForm') loginForm: NgForm;

然后以@Julia提到的相同方式引用控件:

 private login(formData: any): void {
    this.authService.login(formData).subscribe(res => {
      alert(`Congrats, you have logged in. We don't have anywhere to send you right now though, but congrats regardless!`);
    }, error => {
      this.loginFailed = true; // This displays the error message, I don't really like this, but that's another issue.

      this.loginForm.controls['email'].setErrors({ 'incorrect': true});
      this.loginForm.controls['password'].setErrors({ 'incorrect': true});
    });
  }

将Errors设置为null将清除UI上的错误:

this.loginForm.controls['email'].setErrors(null);

补充茱莉亚·帕斯科娃的答案

在组件中设置验证错误:

formData.form.controls['email'].setErrors({'incorrect': true});

清除组件中的验证错误:

formData.form.controls['email'].setErrors(null);

使用null清除错误时要小心，因为这将覆盖所有错误。如果你想保留一些，你可能必须先检查是否存在其他错误:

if (isIncorrectOnlyError){
   formData.form.controls['email'].setErrors(null);
}

在我的反应式形式，我需要标记一个字段无效，如果另一个字段被选中。在ng版本7中，我做了以下工作:

    const checkboxField = this.form.get('<name of field>');
    const dropDownField = this.form.get('<name of field>');

    this.checkboxField$ = checkboxField.valueChanges
        .subscribe((checked: boolean) => {
            if(checked) {
                dropDownField.setValidators(Validators.required);
                dropDownField.setErrors({ required: true });
                dropDownField.markAsDirty();
            } else {
                dropDownField.clearValidators();
                dropDownField.markAsPristine();
            }
        });

所以在上面，当我选中这个框时，它会根据需要设置下拉框，并将其标记为脏。如果您不这样标记它，那么直到您尝试提交表单或与之交互时，它才会无效(错误)。

如果复选框被设置为false(未选中)，那么我们清除下拉菜单上所需的验证器，并将其重置为原始状态。

另外，记得取消订阅监控字段更改!

下面是一个有效的例子:

MatchPassword(AC: FormControl) {
  let dataForm = AC.parent;
  if(!dataForm) return null;

  var newPasswordRepeat = dataForm.get('newPasswordRepeat');
  let password = dataForm.get('newPassword').value;
  let confirmPassword = newPasswordRepeat.value;

  if(password != confirmPassword) {
    /* for newPasswordRepeat from current field "newPassword" */
    dataForm.controls["newPasswordRepeat"].setErrors( {MatchPassword: true} );
    if( newPasswordRepeat == AC ) {
      /* for current field "newPasswordRepeat" */
      return {newPasswordRepeat: {MatchPassword: true} };
    }
  } else {
    dataForm.controls["newPasswordRepeat"].setErrors( null );
  }
  return null;
}

createForm() {
  this.dataForm = this.fb.group({
    password: [ "", Validators.required ],
    newPassword: [ "", [ Validators.required, Validators.minLength(6), this.MatchPassword] ],
    newPasswordRepeat: [ "", [Validators.required, this.MatchPassword] ]
  });
}

Angular文档中的这个示例可能会有所帮助: <input type="text" id="name" name="name" class="form-control"

      required minlength="4" appForbiddenName="bob"
      [(ngModel)]="hero.name" #name="ngModel">

<div *ngIf="name.invalid && (name.dirty || name.touched)"
    class="alert">

  <div *ngIf="name.errors?.['required']">
    Name is required.
  </div>
  <div *ngIf="name.errors?.['minlength']">
    Name must be at least 4 characters long.
  </div>
  <div *ngIf="name.errors?.['forbiddenName']">
    Name cannot be Bob.
  </div>

</div>