# Value Binding

The DropDownList value can either be a [primitive (strings, numbers, or other)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Primitive_values) or a [complex value (objects)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Objects).

To set the value, apply any of the following approaches:

* Use the [`value`](https://www.telerik.com/kendo-angular-ui-develop/components/dropdowns/api/dropdownlistcomponent#value) property. If the value is set through the `value` property, you have to hook up to the [`valueChange`](https://www.telerik.com/kendo-angular-ui-develop/components/dropdowns/api/dropdownlistcomponent#valuechange) event and manually update the value of the `value` property.
* Use the [`ngModel`](https://angular.dev/guide/forms) value binding. If the value is set by the `ngModel` value binding, the framework will automatically update the corresponding field from the model after the value of the component changes.
* Use the [`formControlName`](https://angular.dev/api/forms/FormControlName) value binding available in the [Reactive forms](https://angular.dev/guide/forms/reactive-forms). If the value is set by the `formControlName` value binding, the framework will automatically update the corresponding field from the form model after the value of the component changes.

> The DropDownList does not support the simultaneous usage of the `value` property and the `ngModel` value binding.

When binding the DropDownList value, the component provides options for:

* [Using primitive values (strings, numbers, or other)](https://www.telerik.com/kendo-angular-ui-develop/components/dropdowns/dropdownlist/value-binding#primitive-values)
* [Using complex values (objects)](https://www.telerik.com/kendo-angular-ui-develop/components/dropdowns/dropdownlist/value-binding#object-values)
* [Using primitive values from object fields](https://www.telerik.com/kendo-angular-ui-develop/components/dropdowns/dropdownlist/value-binding#primitive-values-from-object-fields)
* [Handling invalid value errors](https://www.telerik.com/kendo-angular-ui-develop/components/dropdowns/dropdownlist/value-binding#invalid-value-errors)

## Primitive Values

If the DropDownList is bound to a dataset of primitives, its value will be a primitive of the same type.

Primitive data types include:

* `String`
* `Number`
* `Undefined`
* `Null`

The following snippet shows how to set a pre-selected value using the `[value]` input.

```html app.component.html
<kendo-dropdownlist
    [data]="sizes"
    [value]="selectedSize">
</kendo-dropdownlist>
```

```typescript app.component.ts
public sizes: string[] = ['Small', 'Medium', 'Large'];
public selectedSize = 'Medium';
```

The following example demonstrates primitive value binding with the DropDownList.

[Demo Source](https://demos.telerik.com/kendo-angular-ui/demos/dropdowns/dropdownlist/value_binding/source.txt)

## Object Values

If the DropDownList is bound to a dataset of objects, its value will be an object of the same type.

> When the selected item is an object, always specify `valueField`. If you do not set a value for the field, the DropDownList will compare the items by reference, which may complicate debugging. For example, the selected value will not be applied, if it does not reference the exact passed `data` object.

The following snippet shows how to use `[value]` with an object dataset. The pre-selected item must reference the same object instance present in `data`.

```html app.component.html

<kendo-dropdownlist
    [data]="statuses"
    textField="label"
    valueField="code"
    [value]="selectedStatus">
</kendo-dropdownlist>
```

```typescript app.component.ts
public statuses = [
    { code: 'active', label: 'Active' },
    { code: 'inactive', label: 'Inactive' },
    { code: 'pending', label: 'Pending' }
];
public selectedStatus = this.statuses[0];
```

The following example demonstrates object value binding with the DropDownList.

[Demo Source](https://demos.telerik.com/kendo-angular-ui/demos/dropdowns/dropdownlist/value_binding/object_values/source.txt)

## Primitive Values from Object Fields

If the DropDownList is bound to a dataset of objects and the [`valuePrimitive`](https://www.telerik.com/kendo-angular-ui-develop/components/dropdowns/api/dropdownlistcomponent#valueprimitive) property is set to `true`, the value of the component will be extracted from the [`valueField`](https://www.telerik.com/kendo-angular-ui-develop/components/dropdowns/api/dropdownlistcomponent#valuefield) of the objects. Use this approach to store only a scalar identifier (for example, a status code) rather than the full object.

The following snippet shows how to store only the `code` string. The DropDownList still displays the `label`, but the bound value is a plain string that is easier to persist or send to an API.

```html app.component.html

<kendo-dropdownlist
    [data]="statuses"
    textField="label"
    valueField="code"
    [valuePrimitive]="true"
    [value]="selectedCode">
</kendo-dropdownlist>
```

```typescript app.component.ts
public statuses = [
    { code: 'active', label: 'Active' },
    { code: 'inactive', label: 'Inactive' },
    { code: 'pending', label: 'Pending' }
];
public selectedCode = 'active';
```

The following example demonstrates how to bind a DropDownList to object data while keeping the selected value as a primitive.

[Demo Source](https://demos.telerik.com/kendo-angular-ui/demos/dropdowns/dropdownlist/value_binding/primitive_values_from_object_fields/source.txt)

## Invalid Value Errors

If the value which is assigned through the `[value]` or `[(ngModel)]` inputs does not match the expected type, the DropDownList throws a JavaScript error.

In the following example, the component has both its `[valueField]` and `[textField]` specified, which implies that the `[data]` will contain objects. Because the `[valuePrimitive]` is not explicitly set to `true`, the DropDownList expects an object value. Instead, a number is provided and, as a result, a JavaScript exception occurs.

[Demo Source](https://demos.telerik.com/kendo-angular-ui/demos/dropdowns/dropdownlist/value_binding/invalid_value_errors/source.txt)

To fix the JavaScript issue, either:

* Change the value type, or
* Update the settings of the component.

The following table lists the valid configuration scenarios.

| Value     | \[Data]    | \[ValuePrimitive]                             |
| :-------- | :--------- | :-------------------------------------------- |
| primitive | primitives | Not set (automatically calculated as `true`)  |
| object    | objects    | Not set (automatically calculated as `false`) |
| primitive | objects    | `true`  (manually set by the developer)       |

## Suggested Links

* [API Reference of the DropDownList](https://www.telerik.com/kendo-angular-ui-develop/components/dropdowns/api/dropdownlistcomponent)