Angular 11自定义ISBN验证器反应形式

Question

我正在为ISBN编号进行自定义验证，我已经有了检查编号的功能，并且可以通过控制台完美地向我提供响应，但我需要使用表单控件进行自定义验证以在视图中获取错误，在这一步中，当我编写ISBN编号时，此错误会显示在控制台中，这就像它检查错误，但不知道什么时候是正确的，它应该把空响应作为正确的ISBN编号，至少我在一些例子中看到了这一点。

core.js:6210 ERROR TypeError: Cannot read properties of null (reading 'CheckDigit')
at LibrosComponent_Template (libros.component.html:22)
at executeTemplate (core.js:9600)
at refreshView (core.js:9466)
at refreshComponent (core.js:10637)
at refreshChildComponents (core.js:9263)
at refreshView (core.js:9516)
at refreshEmbeddedViews (core.js:10591)
at refreshView (core.js:9490)
at refreshComponent (core.js:10637)
at refreshChildComponents (core.js:9263)

这是我的打字稿，

export class LibrosComponent implements OnInit {
//ISBN Validator
isbnValue: string = ""

firstFormGroup: FormGroup;
secondFormGroup: FormGroup;
constructor(
private _formBuilder: FormBuilder,
) {}
ngOnInit() {
this.firstFormGroup = this._formBuilder.group({
tituloControl: ['', Validators.required],
isbnControl: ['', Validators.required],
},
{ validator: this.isbnValidate });    
}

isbnValidate(g: FormGroup) {
var isbnValue = g.get('isbnControl').value
var subject = isbnValue;
// Checks for ISBN-10 or ISBN-13 format
var regex = /^(?:ISBN(?:-1[03])?:? )?(?=[0-9X]{10}$|(?=(?:[0-9]+[- ]){3})[- 0-9X]{13}$|97[89][0-9]{10}$|(?=(?:[0-9]+[- ]){4})[- 0-9]{17}$)(?:97[89][- ]?)?[0-9]{1,5}[- ]?[0-9]+[- ]?[0-9]+[- ]?[0-9X]$/;
if (regex.test(subject)) {
// Remove non ISBN digits, then split into an array
var chars = subject.replace(/[- ]|^ISBN(?:-1[03])?:?/g, "").split("");
// Remove the final ISBN digit from `chars`, and assign it to `last`
var last = chars.pop();
var sum = 0;
var check, i;
if (chars.length == 9) {
// Compute the ISBN-10 check digit
chars.reverse();
for (i = 0; i < chars.length; i++) {
sum += (i + 2) * parseInt(chars[i], 10);
}
check = 11 - (sum % 11);
if (check == 10) {
check = "X";
} else if (check == 11) {
check = "0";
}
} else {
// Compute the ISBN-13 check digit
for (i = 0; i < chars.length; i++) {
sum += (i % 2 * 2 + 1) * parseInt(chars[i], 10);
}
check = 10 - (sum % 10);
if (check == 10) {
check = "0";
}
}
if (check != last) {
return null;

} else {
return  g.get('isbnControl').setErrors( {CheckDigit: true} )

}
} else {
return g.get('isbnControl').setErrors( {Invalid: true} );
}
}
}

在我的HTML中，我有一些包含在表单中的输入：

<form class="form" [formGroup]="firstFormGroup">  
<div class="container-1">
<mat-form-field class="width">
<mat-label>Título</mat-label>
<input matInput formControlName="tituloControl" required>
</mat-form-field>
<mat-form-field class="width">
<mat-label>ISBN</mat-label>
<input matInput formControlName="isbnControl" required>
<mat-error *ngIf="firstFormGroup.controls['isbnControl'].pristine || firstFormGroup.controls.isbnControl.errors['CheckDigit']">Invalid ISBN check digit</mat-error>
<mat-error *ngIf="firstFormGroup.controls['isbnControl'].pristine || firstFormGroup.controls.isbnControl.errors['Invalid']">Invalid ISBN</mat-error>
</mat-form-field>
</form>

Answer 1

我已经找到了错误的解决方案，将.errors["]替换为hasError("(，.errors[]是读取包含验证错误的对象的属性。但首先，我必须使用hasError((方法评估该属性是否存在才能访问它