Arrange error when item keep aspect ratio.

[CodingOctocat]

I'm developing an image gallery that can be previewed by thumbnails just like Explorer.

<wpftk:VirtualizingItemsControl
    Margin="0,2,0,0"
    ItemTemplate="{StaticResource ItemTemplate}"
    VirtualizingPanel.CacheLengthUnit="Item"
    VirtualizingPanel.CacheLength="1,1"
    VirtualizingPanel.ScrollUnit="Pixel"
    VirtualizingPanel.VirtualizationMode="Standard"
    ScrollViewer.HorizontalScrollBarVisibility="Disabled"
    ScrollViewer.VerticalScrollBarVisibility="Auto">
    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <wpftk:VirtualizingWrapPanel
                Orientation="Vertical"
                SpacingMode="None" 
                StretchItems="True">
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>
</wpftk:VirtualizingItemsControl>

ItemTemplate:

<DataTemplate x:key="ItemTemplate">
    <mycontrol:MyThumbnail ImageSource="xxx/yyy/zzz.jpg"/>
</DataTemplate>

Bind the Height of the MyThumbnail control to the Width so that it always remains 16:9.
And Arrange error(I will re-upload screenshots of the real situation when I have time):

I guess the reason lies in the dynamically changing height of the item.

I have tried the following solution and it works fine (but it not support virtualization):
WrapPanel with full width columns
UniformMinWidthWrapPanel

Version Info
Package Version 1.5.7
.NET Version: .NET 6
OS Version: Win11

[CodingOctocat]

Actual results:

[CodingOctocat]

When I drag the scrollbar:
It gets worse!

[sbaeumlisberger]

Hi, in order to support virtualization the panel currently requires all items to have the same size. There is already an issue with the aim to allow different sized items: #22 Unfortunately, I don't have time to work on it actively at the moment. Hopefully, this will change in the summer.

In order to solve your issue right now you have to make sure that all items are sized equally. Therefore you can use the ItemSize property or set some size constraints on item template.