Today I decided to finally try virtualized TreeView. To do that binding is required. So I decided to get 2 things test - HierarchicalDataTemplate based on types + virtualization.
I created a base class for some data. Created 2 derived classes from base class. Made 2 HierarchicalDataTemplate (1 for each derived class) to get different formatting of nodes. And running population of 10k nodes of 2 types.
Classes:
public class ListItem_Generic
{
public string Name { get; protected set; }
public ListItem_Generic(string Name = "") { this.Name = Name; }
}
public class ListItem_Single : ListItem_Generic
{
public ListItem_Single(string Name = "") : base(Name) { }
}
public class ListItem_Multi : ListItem_Generic
{
public List<ListItem_Generic> Items { get; protected set; }
public ListItem_Multi(string Name = "", List<ListItem_Generic> Items = null)
: base(Name)
{
if (Items == null)
this.Items = new List<ListItem_Generic>();
else
this.Items = new List<ListItem_Generic>(Items);
}
}
Generation of 10k 1st level nodes with some children, binding:
public MainWindow()
{
InitializeComponent();
// Create a list of sample items and populate them
var lst = new List<ListItem_Generic>();
int MaxHeaders = 10000;
var rnd = new Random();
// Now generate 10 000 records. First select random amount of headers
int HeadersCount = rnd.Next(MaxHeaders);
for (int i = 0; i < HeadersCount; i++)
{
var Childrencount = rnd.Next(100);
var children = new List<ListItem_Generic>();
for (int j = 0; j < Childrencount; j++)
children.Add(new ListItem_Single("Child #"+j+" of parent #"+i));
lst.Add(new ListItem_Multi("Header #" + i + " (" + Childrencount + ")", children));
}
for (int i = 0; i < MaxHeaders - HeadersCount; i++)
lst.Add(new ListItem_Single("Line #" + i));
// Bind lstView to lst
lstView.ItemsSource = lst;
lstView.UpdateLayout();
}
XAML with HierarchicalDataTemplates:
<Window x:Class="Test_DataTemplates.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:loc="clr-namespace:Test_DataTemplates"
Title="MainWindow" Height="350" Width="525">
<Grid>
<TreeView Name="lstView" VirtualizingPanel.IsVirtualizing="True">
<TreeView.Resources>
<HierarchicalDataTemplate DataType="{x:Type loc:ListItem_Multi}" ItemsSource="{Binding Path=Items}">
<Border Background="RosyBrown">
<TextBlock Text="{Binding Path=Name}" Foreground="White" FontWeight="Bold"/>
</Border>
</HierarchicalDataTemplate>
<HierarchicalDataTemplate DataType="{x:Type loc:ListItem_Single}">
<TextBlock Text="{Binding Path=Name}"/>
</HierarchicalDataTemplate>
</TreeView.Resources>
</TreeView>
</Grid>
</Window>
Everything works finely:
Yet, when scrolling to let's say header #1000 and expanding it - scroll position would jump to some other place making expanded node and its children NOT visible.
What did I do wrong? Is there any way to fix this?
Update: Removing virtualization also removes scrolling bug.
After having many issues with Tree virtualization in C# WPF (including major issue, that only the very first level gets virtualized) - I was not able to find a proper fix. Microsoft accepted a bug report and answered, that scrolling issue will get fixed in one of future releases.
As to the final solution to this for me personally - I've switched to own implementation of ListTreeView, i.e. using List and simulating tree. This solved all the issues with virtualization and with scrolling behavior. The only issue was - removal of many items after collapsing tree node. I had to implement a check if it's easier/faster to just recreate a fresh list instead of deleting items 1 by 1.
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