ControlValueAccessor

Defines an interface that acts as a bridge between the Angular forms API and a native element in the DOM.

Implement this interface to create a custom form control directive that integrates with Angular forms.

Links & Tutorials

Interface

writeValue#

writeValue(obj: any): void

Writes a new value to the element.

This method is called by the forms API to write to the view when programmatic changes from model to view are requested.

Write a value to the element

The following example writes a value to the native DOM element.

writeValue(value: any): void {
this._renderer.setProperty(this._elementRef.nativeElement, 'value', value);
}

registerOnChange#

registerOnChange(fn: any): void

Registers a callback function that is called when the control's value changes in the UI.

This method is called by the forms API on initialization to update the form model when values propagate from the view to the model.

When implementing the registerOnChange method in your own value accessor, save the given function so your class calls it at the appropriate time.

Store the change function

The following example stores the provided function as an internal method.

registerOnChange(fn: (_: any) => void): void {
this._onChange = fn;
}

When the value changes in the UI, call the registered function to allow the forms API to update itself:

host: {
'(change)': '_onChange($event.target.value)'
}

registerOnTouched#

registerOnTouched(fn: any): void

Registers a callback function is called by the forms API on initialization to update the form model on blur.

When implementing registerOnTouched in your own value accessor, save the given function so your class calls it when the control should be considered blurred or "touched".

Store the callback function

The following example stores the provided function as an internal method.

registerOnTouched(fn: any): void {
this._onTouched = fn;
}

On blur (or equivalent), your class should call the registered function to allow the forms API to update itself:

host: {
'(blur)': '_onTouched()'
}

setDisabledState#

setDisabledState(isDisabled: boolean)?: void

Function that is called by the forms API when the control status changes to or from 'DISABLED'. Depending on the status, it enables or disables the appropriate DOM element.

The following is an example of writing the disabled property to a native DOM element:

setDisabledState(isDisabled: boolean): void {
this._renderer.setProperty(this._elementRef.nativeElement, 'disabled', isDisabled);
}