DxComboBox<TData, TValue>.ValueChanging Event

Fires when the ComboBox’s selected value is being modified. Use this event to validate/cancel item selection.

Namespace: DevExpress.Blazor

Assembly: DevExpress.Blazor.v25.2.dll

NuGet Package: DevExpress.Blazor

Declaration

[Parameter]
public Action<ParameterValueChangingEventArgs<TValue>> ValueChanging { get; set; }

Event Data

The ValueChanging event's data class is ParameterValueChangingEventArgs<TValue>. The following properties provide information specific to this event:

Property	Description
NewValue	Gets or sets the new value being assigned to the parameter.
OldValue	Gets the current parameter value.

Remarks

The ValueChanging event fires before a new value is applied to the component (before the ValueChanged event). You can use this event to validate/cancel item selection.

The following code prevents selection of unavailable items. If a user tries to select an item that is marked as unavailable, the ComboBox’s value remains unchanged.

<DxComboBox Data="@Products"
            @bind-Value="@SelectedProduct"
            ValueChanging="@OnValueChanging"
            TextFieldName="@nameof(Product.Name)" />

@code {
    Product SelectedProduct { get; set; }
    IEnumerable<Product> Products { get; set; }

    protected override void OnInitialized() {
        Products = new List<Product> {
            new Product { Name = "Product 1", IsAvailable = true },
            new Product { Name = "Product 2", IsAvailable = false },
            new Product { Name = "Product 3", IsAvailable = true }
        };
        SelectedProduct = Products.First();
    }

    void OnValueChanging(ParameterValueChangingEventArgs<Product> e) {
        if (e.NewValue != null && !e.NewValue.IsAvailable) {
            e.NewValue = e.OldValue;
        }
    }

    public class Product {
        public string Name { get; set; }
        public bool IsAvailable { get; set; }
    }
}