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Events

This article showcases the available events in the Telerik RangeSlider component:

StartValueChanged and EndValueChanged

StartValueChanged fires when the user moves the lower range of the slider, and EndValueChanged fires when the user changes the higher range of the slider.

The ValueChanged events fire every time the corresponding Value parameter changes. This happens while the user is dragging the handle or when they click on the track.

As of version 2.28.0 of Telerik UI for Blazor, the ValueChanged events fire continuously while the user is dragging the handle to ensure updating the value accordingly and deliver live UX. Thus, the component will re-render multiple times during the dragging process. If you want to avoid that, you can handle the OnChange event instead.

Handle the StartValueChanged and EndValueChanged to filter products

@* This example showcases one-way data binding by using Value and ValueChanged
    It also shows how you could filter data based on the user selection in the slider *@

from @StartValue to @EndValue
<br />
<br />

<TelerikRangeSlider StartValue="@StartValue" StartValueChanged="@( async (decimal v) => await StartValueChangedHandler(v) )"
                    EndValue="@EndValue" EndValueChanged="@( async (decimal v) => await EndValueChangedHandler(v) )"
                    SmallStep="10m" LargeStep="20m" Min="0m" Max="170m" Width="500px">
</TelerikRangeSlider>

<br />
<br />

<ul>
    @foreach (Product item in Products)
    {
        <li>Product @item.Name costs <strong>@item.Price.ToString("C2")</strong></li>
    }
</ul>

@code{
    decimal StartValue { get; set; } = 30m;
    decimal EndValue { get; set; } = 40m;

    List<Product> Products { get; set; } = new List<Product>();

    async Task StartValueChangedHandler(decimal v)
    {
        // update the view-model to let the change render
        // if you avoid that, you wil effectively cancel the event
        StartValue = v;

        Console.WriteLine($"The user has now chosen {v} for the LOWER range");

        await FilterProducts();
    }

    async Task EndValueChangedHandler(decimal v)
    {
        // update the view-model to let the change render
        // if you avoid that, you wil effectively cancel the event
        EndValue = v;

        Console.WriteLine($"The user has now chosen {v} for the HIGHER range");

        await FilterProducts();
    }

    //sample business logic follows below

    async Task FilterProducts()
    {
        Products = await MyService.GetProducts(StartValue, EndValue);
    }

    protected override async Task OnInitializedAsync()
    {
        await FilterProducts();
    }

    // this mimics an actual service
    public static class MyService
    {
        private static List<Product> _data { get; set; }
        public static async Task<List<Product>> GetProducts(decimal low, decimal high)
        {
            EnsureData();
            var filteredProducts = _data.Where(p => p.Price >= low && p.Price <= high);
            return await Task.FromResult(filteredProducts.ToList());
        }

        private static void EnsureData()
        {
            if (_data == null || _data.Count < 1)
            {
                _data = new List<Product>();
                for (int i = 1; i < 30; i++)
                {
                    _data.Add(new Product { Name = $" Name {i}", Price = 3.14m * i * 2 });
                }
            }
        }
    }

    public class Product
    {
        public decimal Price { get; set; }
        public string Name { get; set; }
    }
}

The event is an EventCallback and it can be synchronous (return void), or it can also be asynchronous and return async Task.

The lambda expression in the handler is required by the framework: https://github.com/aspnet/AspNetCore/issues/12226.

OnChange

The OnChange event represents a user action - confirmation of the current value. It fires when the user stops dragging the handle or when they click on the track.

The handler receives an object of type RangeSliderChangeEventArgs which exposes the following fields:

  • StartValue - the new lower value of the slider that marks the range start.
  • EndValue - the new higher value of the slider that marks the range end.

If you use two-way binding, this will effectively fire the StartValueChanged and EndValueChanged events while the user is dragging the handle. This will result in continuous component re-rendering. If you want to avoid that, use one-way binding and update the value for the view-model in the OnChange event handler.

The OnChange event is a custom event and does not interfere with bindings, so you can use it together with models and forms.

Handle the OnChange event to filter products

@* This example showcases one-way data binding and handling the OnChange event to update the view-model.
    If you want to update the value while the user drags the handle, you can additionally use two-way binding or handle the ValueChanged event.
    It also shows how you could filter data based on the user selection in the slider *@

from @StartValue to @EndValue
<br />
<br />

<TelerikRangeSlider StartValue="@StartValue"
                    EndValue="@EndValue"
                    OnChange="@OnChangeHandler"
                    SmallStep="10m" LargeStep="20m" Min="0m" Max="170m" Width="500px">
</TelerikRangeSlider>

<br />
<br />

<ul>
    @foreach (Product item in Products)
    {
        <li>Product @item.Name costs <strong>@item.Price.ToString("C2")</strong></li>
    }
</ul>

@code{
    decimal StartValue { get; set; } = 30m;
    decimal EndValue { get; set; } = 40m;

    List<Product> Products { get; set; } = new List<Product>();

    async Task OnChangeHandler(RangeSliderChangeEventArgs args)
    {
        // update the view-model to let the change render.
        // if you avoid that, you will effectively cancel the event
        StartValue = (decimal)args.StartValue;
        EndValue = (decimal)args.EndValue;

        Console.WriteLine($"The user has now chosen {StartValue} for the LOWER range and {EndValue} for the HIGHER range");

        await FilterProducts();
    }

    //sample business logic follows below

    async Task FilterProducts()
    {
        Products = await MyService.GetProducts(StartValue, EndValue);
    }

    protected override async Task OnInitializedAsync()
    {
        await FilterProducts();
    }

    // this mimics an actual service
    public static class MyService
    {
        private static List<Product> _data { get; set; }
        public static async Task<List<Product>> GetProducts(decimal low, decimal high)
        {
            EnsureData();
            var filteredProducts = _data.Where(p => p.Price >= low && p.Price <= high);
            return await Task.FromResult(filteredProducts.ToList());
        }

        private static void EnsureData()
        {
            if (_data == null || _data.Count < 1)
            {
                _data = new List<Product>();
                for (int i = 1; i < 30; i++)
                {
                    _data.Add(new Product { Name = $" Name {i}", Price = 3.14m * i * 2 });
                }
            }
        }
    }

    public class Product
    {
        public decimal Price { get; set; }
        public string Name { get; set; }
    }
}

The event is an EventCallback and it can be synchronous (return void), or it can also be asynchronous and return async Task.

See Also

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