Mat-Checkbox 绑定 model 可以是可选的还是 null？

Question

Hi all I am new to angular, which I created a dynamic list of checkboxes. Because there are times which I will get the selected value from API which I need to bind to the checkboxes. Thus I will have the code like below

<div *ngFor="let b of result?.category">
                        <mat-checkbox (change)="onChangeCheckbox($event)" [value]="b.RefAccess?.accessId"
                            [checked]="b.RefAccess?.selected" [(ngModel)]="b.BoRefAccess?.selected"
                            [ngModelOptions]="{standalone: true}">
                            {{b.BoRefAccess?.accessDesc}}
                        </mat-checkbox>
                    </div>

Error "Empty expressions are not allowed ng , Parser Error: The '?.' operator cannot be used in the assignment at column 25 in [b.BoRefAccess?.selected=$event] in..."

My main problem now is the ngModel binding can not be optional but I need it to be optional because there are times API will give me null list item. So I not sure how to handle it.

I also came across another method which keep track on the onChange event but it will only consist checkboxes that being onChanged, those are selected is not included.

Answer 1

So, I'm thinking maybe you could create another variable to bind with ngModel. In the function onChangeCheckbox you created, you could update the value of b.RefAccess.selected if it's different from null.

Answer 2

The elvis operator can't be used for assignment. You should declare it in a more explicit way.

Instead of

[(ngModel)]="b.BoRefAccess?.selected"

Use

[ngModel]="b.BoRefAccess?.selected" (ngModelChange)="b.BoRefAccess.selected=$event"