Use a string as Window Height in XAML - wpf

Question

I made a window with some parameters:
<Window x:Class="MsgBox"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MsgBox" Height="300" Width="500" Topmost="True" WindowStartupLocation="CenterScreen" WindowStyle="None" Loaded="MsgBox_Loaded">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="1*"></ColumnDefinition>
<ColumnDefinition Width="2*"></ColumnDefinition>
</Grid.ColumnDefinitions>
</Grid>
</Window>
I want to change the height and width to these calculated strings. It gets the users screenwidth and height and divide it by four.
Public ReadOnly Property PrimaryScreenWidth As Double
Get
Return System.Windows.SystemParameters.PrimaryScreenWidth
End Get
End Property
Public ReadOnly Property PrimaryScreenHeight As Double
Get
Return System.Windows.SystemParameters.PrimaryScreenHeight
End Get
End Property
Private MsgBoxWidth As String = PrimaryScreenWidth \ 4
Private MsgBoxHeight As String = PrimaryScreenHeight \ 4
How to set it to my window?
Height="{x:static MsgBoxHeight }" Width="{x:static MsgBoxWidth }" ??

Answer 1

If you want to do this, why don't you simply
Me.Height = MsgBoxHeight
Me.Width = MsgBoxWidth
when you calculated the properties?

Answer 2

The syntax you're showing and presumably want, with the curly braces:
Height="{x:static MsgBoxHeight }" Width="{x:static MsgBoxWidth }"
is called Markup Extension syntax, it allows using a markup extension class to set a property value. Here's how you'd do it. First step, create the markup extenssion class:
Public Class MsgBoxHeight
Inherits System.Windows.Markup.MarkupExtension
Public Sub New()
End Sub
Public Overrides Function ProvideValue(serviceProvider As IServiceProvider) As Object
Return System.Windows.SystemParameters.PrimaryScreenHeight / 4
End Function
End Class
Next you'll add a xmlns:local="clr-namespace=YourNamespace" to the <Windows>, then you'll be able to use it like this: Height="{local:MsgBoxHeight}".
The complete XAML for the Window would look like this:
<Window x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:WpfApplication6"
Title="MainWindow" Height="{local:MsgBoxHeight}" Width="525">
<Grid>
</Grid>
</Window>
Note
Using the Markup Extension means you're doing it from code. You are introducing a nice application-specific extension to XAML, but you need code for it to work. If you only need to do this for one Window it makes more sense to simply set the Height and Width of the window from the code-behind and not bother with the Markup Extension.