How to detect when a user completes changing WinRT XAML Slider value?

MainPage.xaml

<Page
    x:Class="WinAppThai_SliderEvent.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:WinAppThai_SliderEvent"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">
 
    <Grid Background="{StaticResource ApplicationPageBackgroundThemeBrush}">
        <StackPanel>
            <Slider x:Name="slider" ValueChanged="Slider_ValueChanged"/>
            <TextBlock x:Name="textBlock"/>
        </StackPanel>
    </Grid>
</Page>

MainPage.xaml.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;
 
namespace WinAppThai_SliderEvent
{
    public sealed partial class MainPage : Page
    {
        public MainPage()
        {
            this.InitializeComponent();
        }
 
        private DispatcherTimer _timer = null;
 
        private void Slider_ValueChanged(object sender, RangeBaseValueChangedEventArgs e)
        {
            Debug.WriteLine("Slider_ValueChanged");
 
            // If we have a timer and we are in this event handler, a user is still interact with the slider
            // we stop the timer
            if (_timer != null)
                _timer.Stop();                                       
            
            // we always create a new instance of DispatcherTimer
            _timer = new DispatcherTimer();
 
            // if one second passes, that means our user has stopped interacting with the slider
            // we do real event
            _timer.Interval = new TimeSpan(0, 0, 1);
            _timer.Tick += updateTextBlock;
             
            _timer.Start();
        }
        
        void updateTextBlock(object sender, object e)
        {
            Debug.WriteLine("updateTextBlock");
            var i = slider.Value;
            textBlock.Text = i.ToString();
 
            // Don't forget to stop the timer :-)
            _timer.Stop();
            _timer.Tick -= updateTextBlock;
        }
    }
}