Moving a complicated XAML binding to a Style Setter - wpf

Question

I'm using a checkbox with a custom style and control template. I would like to move the height and width bindings over to the style as well, but I can't seem to get it right.
Here's the checkbox XAML
<CheckBox Style="{StaticResource MyCheckStyle}"
HorizontalAlignment="Center"
Height="{Binding FontSize,
Source={x:Static gap:Settings.Default},
Converter={StaticResource MyMathConverter},
ConverterParameter='x+10'}"
Width="{Binding ActualHeight, RelativeSource={RelativeSource Self}}"
IsChecked="{Binding ValueT, Mode=TwoWay, UpdateSourceTrigger=LostFocus}"
/>
I'm trying to achieve a check box whose height in pixels is 10 larger than the current font size in points (a hack but please ignore that for now).
I'm binding Width to ActualHeight so that they'll always be square (my custom template would allow any size otherwise)
I'm using a converter (Ivan Krivyakov's MathConverter) to do the math.
The size I'm binding to is stored in a static instance of a Settings class generated from a Settings file.
MyCheckStyle is currently as follows:
<Style x:Key="MyCheckStyle" TargetType="{x:Type CheckBox}">
<Setter Property="HorizontalContentAlignment" Value="Stretch"/>
<Setter Property="VerticalContentAlignment" Value="Stretch"/>
<Setter Property="Template" Value="{StaticResource MyCheckBoxTemplate}" />
</Style>
So far, this all works perfectly. But my attempt at moving the Width Binding to the style crashes the application:
<!-- WIDTH BINDING. CAUSES A CRASH DUE TO ACCESS VIOLATION -->
<Setter Property="Width">
<Setter.Value>
<Binding>
<Binding.Source>
<RelativeSource Mode="Self"/>
</Binding.Source>
<Binding.Path>
<PropertyPath Path="ActualHeight"/>
</Binding.Path>
</Binding>
</Setter.Value>
</Setter>
My attempts at the moving the Height binding are a complete failure. I can't figure out how to replicate the "x:Static" markup extension in element syntax, among other things. Intellisense/ReSharper isn't helping me much.
<Setter Property="Height">
<Setter.Value>
<Binding>
<!-- NO IDEA WHAT TO PUT HERE? -->
</Binding>
</Setter.Value>
</Setter>
</Style>
Anyone able to set me right? Is what I'm doing possible?

Answer 1

Have you ever done
Prop="{Binding Source={RelativeSouce ...}}"?
Nope. It's not Source, it's RelativeSource. The curly brace markup-extension syntax sets the same properties as the XML element syntax, but with curly braces. That's all. If it's RelativeSource with curly braces, it's RelativeSource with angle brackets.
<Setter Property="Width">
<Setter.Value>
<Binding>
<!-- RelativeSource, not Source -->
<Binding.RelativeSource>
<RelativeSource Mode="Self"/>
</Binding.RelativeSource>
<Binding.Path>
<PropertyPath Path="ActualHeight"/>
</Binding.Path>
</Binding>
</Setter.Value>
</Setter>
For x:Static, that's another markup extension (a subclass of System.Windows.Markup.MarkupExtension). If markup extension class names have the Extension postfix, the XAML parser lets you omit the "Extension" part. So as it happens that class is actually named StaticExtension. If you want static member Foo.Bar in the local namespace, easy:
<x:StaticExtension Member="local:Foo.Bar" />
The Binding class is a subclass of MarkupExtension (via BindingBase), which is why you can use the curly-brace syntax with it. However, it doesn't have the "Extension" name postfix. That's optional. There's no particular consistency there.
Key point: Every one of these things is a class. XAML is a notation for instantiating instances of classes and initializing their properties with either scalar values, or with other class instances. Curly-brace markup extension syntax is a funny little addition -- but a useful one, as you can see comparing the XAML above with what I'm about to suggest as a replacement.
Now, that's all well worth knowing, but you don't need any of it here.
tl;dr
<Setter
Property="Width"
Value="{Binding ActualHeight, RelativeSource={RelativeSource Self}}"
/>
<Setter
Property="Height"
Value="{Binding FontSize,
Source={x:Static gap:Settings.Default},
Converter={StaticResource MyMathConverter},
ConverterParameter='x+10'}"
/>
Done.