Angular2 rc6 Expression has changed after it was checked

Question

I have followed tutorial on http://almerosteyn.com/2016/04/linkup-custom-control-to-ngcontrol-ngmodel to create a custom element.

There is a form with two fields: one custom component and another component (input field) linked to the same field through ngmodel.

When I edit the value in the custom component, it throws the exception "ORIGINAL EXCEPTION: Expression has changed after it was checked. ". However, the change in the normal field triggers the change correctly to the custom element.

This is the code:

<custom-component [control]="surname1" [(ngModel)]="person.surname1" [name]="'surname1'" formControlName="surname1">Add surname:</custom-component>

<input type="text" name="surname2" id="surname2" formControlName="surname1" [(ngModel)]="person.surname1" />

And the custom element:

const noop = () => {};

export const CUSTOM_INPUT_CONTROL_VALUE_ACCESSOR: any = {
    provide: NG_VALUE_ACCESSOR,
    useExisting: forwardRef(() => MyInputComponent2),
    multi: true
};

@Component({
    selector: 'custom-component',
    template: `<label><ng-content></ng-content></label>
                    <input type="text"  name="{{name}}" [(ngModel)]="value" 
                        (ngModelChange)="changed($event)"

                        (blur)="onBlur()"
                    />
    `,
    providers: [CUSTOM_INPUT_CONTROL_VALUE_ACCESSOR]
})
export class CustomComponent implements ControlValueAccessor {

    @Input() control: FormControl;
    @Input() name: any;
    private innerValue: any = '';

    private onTouchedCallback: () => void = noop;
    private onChangeCallback: (_: any) => void = noop;

    //get accessor
    get value(): any {
        return this.innerValue;
    };

    //set accessor including call the onchange callback
    set value(v: any) {
        if (v !== this.innerValue) {
            this.innerValue = v;
            this.onChangeCallback(v);
        }
    }

    //Set touched on blur
    changed(event) {
        this.onTouchedCallback();
    }

    onBlur() {
        this.onTouchedCallback();
    }

    //From ControlValueAccessor interface
    writeValue(value: any) {
        if (value !== this.innerValue) {
            this.innerValue = value;
        }
    }

    //From ControlValueAccessor interface
    registerOnChange(fn: any) {
        this.onChangeCallback = fn;
    }

    //From ControlValueAccessor interface
    registerOnTouched(fn: any) {
        this.onTouchedCallback = fn;
    }
}

it solves when using enableProdMode(); but cant use this in development

****ERROR (Chrome output) :

core.umd.js:5995 EXCEPTION: Error in ./MFormComponent class MFormComponent - inline template:55:117 caused by: Expression has changed after it was checked. Previous value: 'surtest'. Current value: 'surtes'.

core.umd.js:5997 ORIGINAL EXCEPTION: Expression has changed after it was checked. Previous value: 'surtest'. Current value: 'surtes'

at ExpressionChangedAfterItHasBeenCheckedError.Error (native) at ExpressionChangedAfterItHasBeenCheckedError.BaseError [as constructor] (http://localhost:8085/templatetest/js/@angular/core/bundles/core.umd.js:1456:38) at new ExpressionChangedAfterItHasBeenCheckedError (http://localhost:8085/templatetest/js/@angular/core/bundles/core.umd.js:8078:20)

Can you please add the full error message. As far as I remember the error message contains information about the expression that caused the error. — Günter Zöchbauer

Günter Zöchbauer Günter Zöchbauer · Accepted Answer · 2016-09-13T09:50:42

I guess it's because you are using the same formControlName="surename1" for <custom-component> and <input>.
If you want to bind them to the same model, then only point ngModel to it but create a control for each one.

Angular2 rc6 Expression has changed after it was checked

1 Answers