Angular 9 References/ Forms
References

ControlValueAccessor

This is the documentation for Angular 9.
You can switch to the latest version Angular 10.

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