有一个自定义验证器，它将一个值作为参数，并检查所属的控制值是否等于该参数值 . 表单是 reactive form ，应检查的值是表单中的现有控件值（fisrstname，lastname和email） .
问题是，当创建表单时，没有任何控件（fisrstname，lastname和email）具有值，因此null将被发送到验证函数，然后验证不起作用，应如何处理这种情况？我在考虑 custom async validator ，但不知道如何实施，如果考虑是正确的 .
custom validator
public static specialNameValidator(name: string): ValidatorFn {
return (control: AbstractControl): {[key: string]: any} => {
if (control.value) {
return name === control.value.toLowerCase()
? {['specialname'] : {value: control.value}}
: null;
}
};
}
form creation
private createForm(): void {
this.signupFrom = this.formBuilder.group({
firstname: new FormControl(null, Validators.required),
lastname: new FormControl(null, Validators.required),
country: new FormControl(null/*, Validators.required*/),
email: new FormControl(null, [Validators.required, Validators.email]),
password: new FormControl(null,
[Validators.required,
PasswordValidation.NoSpace(),
PasswordValidation.specialNameValidator(this.model.email),
PasswordValidation.specialNameValidator(this.model.first_name),
PasswordValidation.specialNameValidator(this.model.last_name)
]),
passwordconfirm: new FormControl(null, Validators.required)
},
// add a validator for the whole group
{ validator: PasswordValidation.PasswordMatch('password',
'passwordconfirm')});
}