有条件地在Angular 2反应形式的表单字段中实现验证

Question

我可以有条件地实现Angular 2反应形式的验证.我有这个带有3个formControl字段的反应形式,一个是选择,另外两个是名字和姓氏的输入文本.我想根据第一个字段"validateBy"的选择有条件地实现firstname和lastname的验证.如果用户选择'byFirstName',则只应验证firstName.如果用户选择'byLastName',则只应验证lastName.如果用户选择'byBoth',则应验证firstName和lastName.我为此创造了一个plunker.只有两个验证工作.

ngOnInit() {
this.myForm = this._fb.group({
  validateBy: ['byFirstName'],
  firstName:  ['', isFirstNameValid(() => (this.validateBy === 'byFirstName' || this.validateBy === 'byBoth'),
                     Validators.required)],
  lastName: ['', isLastNameValid(() => (this.validateBy === 'byLastName' || this.validateBy === 'byBoth'),
                     Validators.required)],
}); 

https://plnkr.co/edit/X0zOGf?p=preview

Answer 1

另一种方法是这样的.似乎对plunker工作

  ngOnInit() {
    this.myForm = this._fb.group({
      validateBy: ['byFirstName'],
      firstName:  [''],
      lastName: [''],
    });

    this.myForm.get('validateBy').valueChanges.subscribe(
        (validateBy : string) => {
          if (validateBy === 'byFirstName' || validateBy === 'byBoth') {
            this.myForm.get('firstName').setValidators([Validators.required]);
            this.myForm.get('firstName').updateValueAndValidity();
          }
          if (validateBy === 'byLastName' || validateBy == 'byBoth') {
            this.myForm.get('lastName').setValidators([Validators.required]);
            this.myForm.get('lastName').updateValueAndValidity();
          }

        };
      )
  }

Answer 2

问题是你的代码只计算表达式一次 - FormGroup创建时.您需要通过创建自定义验证器使其动态化,该验证器将在每次调用时评估表达式:

this.personForm= this.fb.group({
  firstName: ['', Validators.required];
  lastName:  [
    '', 
    conditionalValidator(
      (() => this.isValidationForLastName === true),
      Validators.required
    )
  ]
});

function conditionalValidator(condition: (() => boolean), validator: ValidatorFn): ValidatorFn {
  return (control: AbstractControl): {[key: string]: any} => {
    if (! condition()) {
      return null;
    }
    return validator(control);
  }
}