What event fires when user lifts finger from ScrollViewer on touch capable screens

Question

I'm finding that when I tap the ScrollViewer, the PointerPressed and PointerExited events fires as expected. But, if I scroll in any direction after touching the screen and lift my finger, no event fires except for PointerCaptureLost which prematurely fires as soon as I scroll.

When I capture the pointer ID and poll the status of the PointerPoint with a timer, the IsInContact flag remains true, even after I lift my finger after scrolling. It works as expected when I simply tap the screen.

ManipulationCompleted has the same effect as above, and I cannot use the ViewChanged event since this fires before I lift my finger.

Is this a bug or am I missing something here? Is there another way I can detect when a user has lifted their finger off the screen? This is driving me bananas.

Sample code below. You'll need to use the simulator in touch-mode or have a touch capable screen to test:

Code:

using System;
using Windows.UI.Input;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Input;

namespace App1
{
    public sealed partial class MainPage : Page
    {

        private readonly DispatcherTimer pointerTimer = new DispatcherTimer();
        private uint? CurrentPointerID; //container for the current pointer id when user makes contact with the screeen

        public MainPage()
        {
            this.InitializeComponent();

            scrollviewer.PointerPressed += scrollviewer_PointerPressed;
            scrollviewer.PointerMoved += scrollviewer_PointerMoved;
            scrollviewer.PointerExited += scrollviewer_PointerExited;
            scrollviewer.PointerReleased += scrollviewer_PointerReleased;
            scrollviewer.PointerCaptureLost += scrollviewer_PointerCaptureLost;
            scrollviewer.PointerCanceled += scrollviewer_PointerCanceled;


            pointerTimer.Tick += pointerTimer_Tick;
            pointerTimer.Interval = TimeSpan.FromMilliseconds(300);
            pointerTimer.Start();


        }

        #region ScrollViewer Events

        void scrollviewer_PointerMoved(object sender, PointerRoutedEventArgs e)
        {
            EventCalledTextBlock.Text = "Pointer Moved";
        }

        void scrollviewer_PointerExited(object sender, PointerRoutedEventArgs e)
        {
            EventCalledTextBlock.Text = "Pointer Exited";
        }

        void scrollviewer_PointerPressed(object sender, PointerRoutedEventArgs e)
        {
            CurrentPointerID = e.Pointer.PointerId;
            EventCalledTextBlock.Text = "Pointer Pressed";
        }

        void scrollviewer_PointerCanceled(object sender, PointerRoutedEventArgs e)
        {
            EventCalledTextBlock.Text = "Pointer Canceled";
        }

        void scrollviewer_PointerCaptureLost(object sender, PointerRoutedEventArgs e)
        {
            EventCalledTextBlock.Text = "Capture Lost";
        }

        void scrollviewer_PointerReleased(object sender, PointerRoutedEventArgs e)
        {
            EventCalledTextBlock.Text = "Pointer Released";
        }
        #endregion



        void pointerTimer_Tick(object sender, object e)
        {
            if (!CurrentPointerID.HasValue)
            {
                PollingTextBlock.Text = string.Empty;
                return;
            }

            try
            {
                var pointerPoint = PointerPoint.GetCurrentPoint(CurrentPointerID.Value);

                PollingTextBlock.Text = pointerPoint.IsInContact ? "Is In Contact" : "Not in Contact";
            }
            catch (Exception ex)
            {
                //This exception is raised when the user lifts finger without dragging.
                //assume finger is not in contact with screen
                PollingTextBlock.Text = "Not in Contact";
            }
        }

    }
}

XAML:

 <Page
    x:Class="App1.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:App1"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}" Name="grid">
        <Grid.RowDefinitions>
            <RowDefinition Height="113*"/>
            <RowDefinition Height="655*"/>
        </Grid.RowDefinitions>
        <ScrollViewer x:Name="scrollviewer" VerticalScrollBarVisibility="Disabled" HorizontalScrollBarVisibility="Visible" Grid.Row="1" >
            <Rectangle Fill="#FF3783CF" Height="100" Stroke="#FF33D851" Width="{Binding ElementName=grid, Path=ActualWidth}" Margin="100" StrokeThickness="4" />
        </ScrollViewer>
        <StackPanel Orientation="Vertical" Margin="45,25,0,0">
            <StackPanel Orientation="Horizontal">
            <TextBlock  HorizontalAlignment="Left" TextWrapping="Wrap" Text="Event Called:" VerticalAlignment="Top" FontSize="24" Margin="0,0,20,0"/>
            <TextBlock x:Name="EventCalledTextBlock" HorizontalAlignment="Left" TextWrapping="Wrap" VerticalAlignment="Top" FontSize="24"/>
        </StackPanel>
        <StackPanel Orientation="Horizontal">
            <TextBlock  HorizontalAlignment="Left" TextWrapping="Wrap" Text="Polling Value:" VerticalAlignment="Top" FontSize="24" Margin="0,0,20,0"/>
            <TextBlock x:Name="PollingTextBlock" HorizontalAlignment="Left" TextWrapping="Wrap" VerticalAlignment="Top" FontSize="24"/>
        </StackPanel>
    </StackPanel>

    </Grid>
</Page>

Answer 1

I stumbled upon this question since I was struggling with a similar problem. I have a ScrollViewer which has several images in it and I wanted to know what images are shown at the moment the ScrollViewer stops moving...

In the end I did used the ScrollViewer.ViewChanged event. This event keeps triggering untill it has finished with scrolling.

I actually am only interested in the last of these events, but since there is no event that triggers only on that particular moment I need to respond to this one and check for myself if this is the appropriate moment to take actions.

I hope this helps.

ScrollViewer.ViewChanged event: https://msdn.microsoft.com/en-us/library/windows/apps/windows.ui.xaml.controls.scrollviewer.viewchanged?f=255&MSPPError=-2147217396