Change the DropDownList Icon When the Popup is Opened

Environment

Product

DropDownList for Blazor, ComboBox for Blazor, MultiColumnComboBox for Blazor, MultiSelect for Blazor

Description

I want to change the icon of the DropDownList when the popup is opened.

Specifically, I want the icon to point up when the dropdown is expanded and to point down when the dropdown is collapsed. How to achieve this?

Solution

To change the DropDownList icon when the popup is opened, follow these steps:

1. Handle the OnOpen and OnClose events of the DropDownList component.
2. Declare a flag to save the opened or closed state of the popup.
3. Toggle the flag value in the OnOpen and OnClose event handlers.
4. Use CSS to change the icon based on the flag value. Conditionally add a <style> tag to achieve this.
   • All components, including the DropDownList, use SVG icons. To change the icon, you can alter the path of the <svg> element.
   • To get the path of the desired icon, render an SvgIcon component, inspect it, and copy its path.

Change the DropDownList icon when expanded

@if (isPopupOpen)
{
    <style>
        .custom-dropdown-icon .k-input-button .k-svg-icon svg path {
            d: path("m256 160 128 192H128l128-192z");
        }
    </style>
}

Desired icon to include conditionally: <TelerikSvgIcon Icon="@SvgIcon.CaretAltDown"></TelerikSvgIcon>

<br />

<TelerikDropDownList Class="custom-dropdown-icon"
                     Data="@DropDownListData"
                     OnOpen="OnDropDownListPopupOpen"
                     OnClose="@OnDropDownListPopupClose"
                     @bind-Value="@DropDownListValue"
                     Width="300px">
</TelerikDropDownList>

@code {
    private string DropDownListValue { get; set; }

    private List<string> DropDownListData { get; set; } = new List<string>() { "first", "second", "third" };

    private bool isPopupOpen { get; set; }

    private void OnDropDownListPopupOpen(DropDownListOpenEventArgs args)
    {
        isPopupOpen = true;
    }

    private void OnDropDownListPopupClose(DropDownListCloseEventArgs args)
    {
        isPopupOpen = false;
    }
}