The ScrollViewer extent height is not updated based on its child size changed at run time when ScrollViewer vertical bar visibility is disabled.

Question

Hi Team,

• The ScrollViewer extent height is not updated based on its child size changed at run time when ScrollViewer vertical bar visibility is disabled.
• In this demo, added 2 ScrollViewer with vertical bar visibility is disabled and visible, when child panel size dynamically changed the ScrollViewer extent height updated properly only to the vertical scroll bar visibility enabled.
• As my requirement I need to disable the first scroll viewer vertical bar disabled (as the sticky left header for 2nd scroll viewer , its sticky in 2nd scroll viewer horizontal bar scrolled), so when scroll changed to 2nd Scroll viewer the left header scroll viewer scroll offset changed, but as the extent height not updated for vertical bar disabled , left header scroll viewer not scrolled properly.

Replication Procedure:

1. Add Xaml and C# shared code in beow.
2. Click Auto button in window(Changing child element size but extent height is not update in ScrollViewer_1).

Code snippet:

Xaml

   <Grid>  
        <Grid.ColumnDefinitions>  
            <ColumnDefinition Width="50"/>  
            <ColumnDefinition Width="*"/>  
            <ColumnDefinition Width="100"/>  
        </Grid.ColumnDefinitions>  
  
        <ScrollViewer  x:Name="ScrollViewer_1" Grid.Column="0" Width="50" Background="White"   
                       IsDeferredScrollingEnabled="False" VerticalScrollBarVisibility="Disabled">  
            <local:CustomStackPanel x:Name="customStackPanel1" Width="50" AutoHeight="False"/>  
        </ScrollViewer>  
        <ScrollViewer x:Name="ScrollViewer_2"  ScrollChanged="ScrollViewer_2_ScrollChanged"  Grid.Column="1" Background="White"   
                      IsDeferredScrollingEnabled="False" VerticalScrollBarVisibility="Visible" HorizontalScrollBarVisibility="Visible" >  
            <local:CustomStackPanel x:Name="customStackPanel2" Width="50" AutoHeight="False"/>  
        </ScrollViewer>  
        <Button Grid.Column="2" Height="40" Width="70" Content="Auto" Click="Button_Click"/>  
    </Grid>  

C#

public partial class MainWindow : Window  
{  
public MainWindow()  
{  
InitializeComponent();  
}  
  
private void Button_Click(object sender, RoutedEventArgs e)  
{  
        if (this.customStackPanel1.AutoHeight == true)  
        {  
            this.customStackPanel1.AutoHeight = false;  
            this.customStackPanel2.AutoHeight = false;  
        }  
else  
{  
            this.customStackPanel1.AutoHeight = true;  
            this.customStackPanel2.AutoHeight = true;  
        }  
              
}  
  
private void ScrollViewer_2_ScrollChanged(object sender, ScrollChangedEventArgs e)  
{  
        this.ScrollViewer_1.ScrollToVerticalOffset(e.VerticalOffset);  
}  
}  
  
public class CustomStackPanel : Panel, INotifyPropertyChanged  
{  
  
    private bool autoHeight = false;  
  
    public event PropertyChangedEventHandler PropertyChanged;  
  
    public bool AutoHeight  
    {  
        get  
        {  
            return autoHeight;  
  
        }  
        set  
        {  
            autoHeight = value;  
            OnAutoHeightChanged();  
        }  
    }  
  
    private void OnAutoHeightChanged()  
    {  
        this.InvalidateMeasure();  
    }  
  
    protected override Size MeasureOverride(Size availableSize)  
    {  
        double height;  
        var scrollViewer = this.Parent as ScrollViewer;  
        if (AutoHeight)  
        {  
            height = scrollViewer.ViewportHeight / 24;  
        }  
        else  
        {  
            height = 100;  
        }  
  
        if (this.Children.Count == 0)  
        {  
            this.GenerateCells();  
            scrollViewer.ScrollChanged += ScrollViewer_ScrollChanged;  
        }  
        else  
        {  
            this.UpdateCells();  
        }  
  
        for (int i = 0; i < this.Children.Count; i++)  
        {  
            this.Children[i].Measure(new Size(50, height));  
        }  
  
        return new Size(availableSize.Width, height * this.Children.Count);  
    }  
  
    private void ScrollViewer_ScrollChanged(object sender, ScrollChangedEventArgs e)  
    {  
        this.InvalidateMeasure();  
    }  
  
    protected override Size ArrangeOverride(Size finalSize)  
    {  
        double height;  
        var scrollViewer = this.Parent as ScrollViewer;  
        if (AutoHeight)  
        {  
            height = scrollViewer.ViewportHeight / 24;  
        }  
        else  
        {  
            height = 100;  
        }  
  
        for (int i = 0; i < this.Children.Count; i++)  
        {  
            var cell = this.Children[i] as CustomBorder;  
  
            cell.Arrange(new Rect(cell.ColumnIndex * 50, cell.RowIndex * height, 50, height));  
        }  
  
        return base.ArrangeOverride(finalSize);  
    }  
  
    private void GenerateCells()  
    {  
        for (int i = 0; i < 24; i++)  
        {  
            this.Children.Add(new CustomBorder()  
            {  
                IsEnsured = true,  
                ColumnIndex = 0,  
                RowIndex = i,  
                Content = i.ToString(),  
                Background = new SolidColorBrush(Colors.Gray),  
                BorderThickness = new Thickness() { Left = 5, Bottom = 5, Right = 5, Top = 5 }  
            });  
        }  
    }  
  
    private void UpdateCells()  
    {  
        var cells = new List<CustomBorder>();  
        foreach (CustomBorder item in this.Children)  
        {  
            item.IsEnsured = false;  
            cells.Add(item);  
  
        }  
  
        for (int i = 0; i < 24; i++)  
        {  
            CustomBorder cell = cells.FirstOrDefault(_cell => (_cell as CustomBorder).RowIndex == i && (_cell as CustomBorder).ColumnIndex == 0) as CustomBorder;  
  
            if (cell != null)  
            {  
                cell.IsEnsured = true;  
            }  
            else  
            {  
                CustomBorder resuseingCell = cells.FirstOrDefault(_cell => !(_cell as CustomBorder).IsEnsured) as CustomBorder;  
  
                if (resuseingCell == null)  
                {  
                    this.Children.Add(new CustomBorder()  
                    {  
                        IsEnsured = true,  
                        ColumnIndex = 0,  
                        RowIndex = i,  
                        Content = i.ToString(),  
                        Background = new SolidColorBrush(Colors.Gray),  
                        BorderThickness = new Thickness() { Left = 5, Bottom = 5, Right = 5, Top = 5 }  
  
                    });;  
                }  
                else  
                {  
                    resuseingCell.ColumnIndex = 0;  
                    resuseingCell.RowIndex = i;  
                    resuseingCell.IsEnsured = true;  
                }  
            }  
  
        }  
    }  
}  
  
public class CustomBorder : Button  
{  
    internal int ColumnIndex { get; set; }  
    internal int RowIndex { get; set; }  
    internal bool IsEnsured { get; set; }  
  
    public CustomBorder()  
    {  
        this.VerticalAlignment = VerticalAlignment.Stretch;  
        this.HorizontalAlignment = HorizontalAlignment.Stretch;  
    }  
}  

Sample: https://www.syncfusion.com/downloads/support/directtrac/general/ze/SCROLL~31173881063

Note: Here, VerticalScrollBarVisibility of ScrollViewer_1 is Disabled.

Could you please check and provide a solution for this?