ScrollViewer.ChangeView() not working on my vertically scrolling GridView?

Question

Hi,

Okay I have some simple XAML code to layout some rectangles in a GridView and have it scroll vertically.

    <Canvas x:Name="canvas" Width="1920" Height="1080">
            <GridView x:Name="gridView1" Width="1920" Height="1080" CanReorderItems="True" BorderThickness="1" BorderBrush="Red" SelectionMode="Multiple" ScrollViewer.VerticalScrollMode="Enabled">
                <GridView.ItemsPanel>
                    <ItemsPanelTemplate>
                        <WrapGrid x:Name="wrapGrid1" Orientation="Horizontal" HorizontalAlignment="Center" MaximumRowsOrColumns="4">
                        </WrapGrid>
                    </ItemsPanelTemplate>
                </GridView.ItemsPanel>
            </GridView>    
    </Canvas>    

I want to scroll to an vertical offset programmatically (actually I would like to animate the scroll but first things first). Here is my attempt to use the ChangeView method on the GridView's ScrollViewer ...

        public MainPage()
        {
            this.InitializeComponent();

            for (int i = 0; i < 40; i++)
            {
                Rectangle temp = new Rectangle();
                temp.Width = 400;
                temp.Height = 250;
                SolidColorBrush blueBrush = new SolidColorBrush(Windows.UI.Colors.Blue);
                temp.Fill = blueBrush;
                gridView1.Items.Add(temp);
            }

            this.Loaded += MainPage_Loaded;
        }

        async void MainPage_Loaded(object sender, RoutedEventArgs e)
        {
            await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, new Windows.UI.Core.DispatchedHandler(() =>
            {
                Double off = 1000;
                var scrollViewer = gridView1.GetFirstDescendantOfType<ScrollViewer>();
                scrollViewer.ChangeView(null, off, null);
            }));

        }

Not working :-(. Any idea what I'm doing wrong?
      

Answer 1

This appears to be a bug as far as I can tell. I don't think MS puts a lot of thought into vertically scrolling containers for winrt. I was able to get the ChangeView method to work with a simple horizontally scrolling grid. I don't think they bothered to make this work with GridViews that have a WrapGrid contained in them and are set to scroll vertically :-(

Answer 2

Yes,there is a little bit issue in ChangeView method. I guess because of the screen rendering timing. Sometimes  the ChangeView has been called before rendering completed.

you can try put ChangeView in gridView1 loaded.

 

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Answer 3

Hi duffybr,

Try following code to see if you can make it work.

XAML, I add a button for changeView method and display the scrollbar of the gridview.

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Canvas x:Name="canvas" Margin="191,60,37,-312">
            <GridView x:Name="gridView1"  CanReorderItems="True"
                      BorderThickness="1" BorderBrush="Red" SelectionMode="Multiple" 
                      ScrollViewer.VerticalScrollBarVisibility="Visible"
                      ScrollViewer.VerticalScrollMode="Enabled" Height="638" Width="1138">
                <GridView.ItemsPanel>
                    <ItemsPanelTemplate>
                        <WrapGrid x:Name="wrapGrid1" Orientation="Horizontal" HorizontalAlignment="Center" MaximumRowsOrColumns="4">
                        </WrapGrid>
                    </ItemsPanelTemplate>
                </GridView.ItemsPanel>
            </GridView>
        </Canvas>
        <Button Content="Button" HorizontalAlignment="Left" Height="78" Margin="55,91,0,0" VerticalAlignment="Top" Width="100" Click="Button_Click"/>
    </Grid>

CS, I add some time span to it.

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            TimeSpan period = TimeSpan.FromMilliseconds(10);

            Windows.System.Threading.ThreadPoolTimer.CreateTimer(async (source) =>{
                await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, new Windows.UI.Core.DispatchedHandler(() =>
                {
                    Double off = 1000;
                    var scrollViewer = gridView1.GetFirstDescendantOfType<ScrollViewer>();
                    scrollViewer.ChangeView(null, off, null);
                }));
            }, period);
        }
    }

Tested with my own device, works fine.

Actually as Bill wrote there is bit issue with screen rendering, now it works fine.

--James

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Answer 4

Okay, thanks for the update on that. I have moved on to using a horizontal scrolling grid to reduce complexity.