DxComboBox<TData, TValue>.TextChanging Event

Fires when the ComboBox editor’s text is being modified. Use this event to validate/cancel user input or item selection.

Namespace: DevExpress.Blazor

Assembly: DevExpress.Blazor.v25.2.dll

NuGet Package: DevExpress.Blazor

Declaration

[Parameter]
public Action<ParameterValueChangingEventArgs<string>> TextChanging { get; set; }

Event Data

The TextChanging event's data class is ParameterValueChangingEventArgs<String>. 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 ComboBox editor raises the TextChanging event before the TextChanged event. Both events fire when a user performs one of the following actions:

• Changes the editor’s text and removes focus from the ComboBox.
• Changes the editor’s text and presses Enter.
• Clicks the Clear button.
• Selects an item from the ComboBox editor’s drop-down window.

You can use the TextChanging event to validate/cancel user input or item selection. In the following example, the TextChanging event is used to validate text input with two rules:

• Prevents entering numbers.
• Limits text length to 15 characters.

Invalid text is not applied. Valid text changes are handled in the TextChanged event handler.

<DxComboBox Data="@Cities"
            TValue="string"
            TData="string"
            AllowUserInput="true"
            SearchMode="ListSearchMode.AutoSearch"
            Text="@Text"
            TextChanging="@OnTextChanging"
            TextChanged="@OnTextChanged">
</DxComboBox>

<div class="mt-2">
    Current text: <b>@Text</b>
</div>

@code {
    List<string> Cities = new() {
        "New York",
        "London",
        "Berlin",
        "Paris",
        "Tokyo"
    };

    string Text { get; set; } = "London";

    void OnTextChanging(ParameterValueChangingEventArgs<string> e) {
        // Prevent entering numbers in the text
        if (e.NewValue != null && e.NewValue.Any(char.IsDigit)) {
            e.NewValue = e.OldValue;
            return;
        }

        // Limit text length to 15 characters
        if (e.NewValue?.Length > 15) {
            e.NewValue = e.OldValue;
            return;
        }
    }

    void OnTextChanged(string newValue) {
        Text = newValue;
    }
}