WPF resize issues when using RowDefinition Height="*" in Grid - wpf

Question

UPDATE I added the UserControl definition to the XAML.
I've noticed some strange behavior in a couple of WPF applications I've created lately, that seem to be related to using "*" for a Grid row height or column width.
The behavior I'm referring to is when trying to expand items in a control (like a treeview), the entire window will resize its height instead of creating a scrollbar. So if I just run the application, and start expanding nodes, when the items extend beyond the visible portion of the UI then the window will resize.
BUT if I resize the window first, or even just click on the bottom or right border (without actually resizing), then it will behave normally and leave the window height alone, with a scrollbar on the treeview.
<UserControl x:Class="ProjectZ.Views.GenericDefinitionView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:cal="http://www.caliburnproject.org"
xmlns:xctk="http://schemas.xceed.com/wpf/xaml/toolkit"
xmlns:xcad="http://schemas.xceed.com/wpf/xaml/avalondock"
xmlns:local="clr-namespace:ProjectZ"
xmlns:behaviors="clr-namespace:ProjectZ.Behaviors"
mc:Ignorable="d" d:DesignHeight="600" d:DesignWidth="600">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="20" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Menu Grid.Row="0" Name="mnuMainMenu" IsMainMenu="True">
... menu stuff
</Menu>
<xcad:DockingManager ... />
</Grid>
</UserControl>
I've played around with it and it seems to always start happening after I've used the "*" value for a grid row height or a column width. If I take that out, it seems to behave normally.
Has anyone else run into this? Any ideas what I'm doing wrong or could do differently to fix this? The only other information I think might be relevant is that this is using Caliburn.Micro. The only settings passed to the window when launching are: MinHeight, MinWidth, Title, and Icon.

Answer 1

The problem is that you never specify a height in the visual tree above the element.
Your UserControl or the Window that's created needs a specific height if you want to use star sizing effectively. Otherwise, a height is "chosen" at runtime, but the Window is effectively set to size by content. As you change items, the Window resizes.
As soon as you touch a border, the Height is being set (whether or not you resize), in which case it then dictates the layout correctly.
If you specify a default height for the Window as its created, the issue will likely resolve itself.

Answer 2

The resizing must be caused by the code:
<UserControl
//...stuff>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="*" />
</Grid.RowDefinitions>
</Grid>
</UserControl>
Where the < * > can be understood as "Take the rest of all available space, after placing all the other elements first". So when you add another element in the control the view will set itself and the the
<RowDefinition Height="*" />
Will resize itself acordingly to take the remainder of space available. To remove this you can just set a specific height for the row or another idea will be to add another Grid inside the row definition so that it won't resize since it will always be inside the row, but still have all of it's functionality.