@angular/forms

SelectControlValueAccessor

directive

The ControlValueAccessor for writing select control values and listening to select control changes. The value accessor is used by the FormControlDirective, FormControlName, and NgModel directives.

  
    class SelectControlValueAccessor extends BuiltInControlValueAccessor implements ControlValueAccessor {}

Using select controls in a reactive form

The following examples show how to use a select control in a reactive form.

Using select controls in a template-driven form

To use a select in a template-driven form, simply add an ngModel and a name attribute to the main <select> tag.

Customizing option selection

Angular uses object identity to select option. It's possible for the identities of items to change while the data does not. This can happen, for example, if the items are produced from an RPC to the server, and that RPC is re-run. Even if the data hasn't changed, the second response will produce objects with different identities.

To customize the default option comparison algorithm, <select> supports compareWith input. compareWith takes a function which has two arguments: option1 and option2. If compareWith is given, Angular selects option by the return value of the function.

          const selectedCountriesControl = new FormControl();

          <select [compareWith]="compareFn"  [formControl]="selectedCountriesControl">    <option *ngFor="let country of countries" [ngValue]="country">        {{country.name}}    </option></select>compareFn(c1: Country, c2: Country): boolean {    return c1 && c2 ? c1.id === c2.id : c1 === c2;}

Note: We listen to the 'change' event because 'input' events aren't fired for selects in IE, see: https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/input_event#browser_compatibility

value

any

compareWith

(o1: any, o2: any) => boolean

Tracks the option comparison algorithm for tracking identities when checking for changes.

writeValue

void

Sets the "value" property on the select element.

@paramvalueany

@returnsvoid

registerOnChange

void

Registers a function called when the control value changes.

@paramfn(value: any) => any

@returnsvoid

onChange

(_: any) => void

The registered callback function called when a change or input event occurs on the input element.

onTouched

() => void

The registered callback function called when a blur event occurs on the input element.

setProperty

void

Helper method that sets a property on a target element using the current Renderer implementation.

@paramkeystring

@paramvalueany

@returnsvoid

registerOnTouched

void

Registers a function called when the control is touched.

@paramfn() => void

@returnsvoid

setDisabledState

void

Sets the "disabled" property on the range input element.

@paramisDisabledboolean

@returnsvoid