Using UWP VisualStateManager with varables - xaml

Question

I can use VisualStateManager to change individual properties of controls. Something like this:
<VisualStateManager.VisualStateGroups>
<VisualStateGroup>
<VisualState>
<VisualState.StateTriggers>
<!--small window-->
<AdaptiveTrigger MinWindowHeight="0" MinWindowWidth="0"/>
</VisualState.StateTriggers>
<VisualState.Setters>
<Setter Target="Control1.FontSize" Value="13"/>
<Setter Target="Control2.FontSize" Value="13"/>
<Setter Target="Control3.FontSize" Value="13"/>
<Setter Target="Control4.FontSize" Value="13"/>
</VisualState.Setters>
</VisualState>
<VisualState>
<VisualState.StateTriggers>
<!--large window-->
<AdaptiveTrigger MinWindowHeight="665" MinWindowWidth="1000"/>
</VisualState.StateTriggers>
<VisualState.Setters>
<Setter Target="Control1.FontSize" Value="24"/>
<Setter Target="Control2.FontSize" Value="24"/>
<Setter Target="Control3.FontSize" Value="24"/>
<Setter Target="Control4.FontSize" Value="24"/>
</VisualState.Setters>
</VisualState>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
This works but is soooo much typing!
Is it possible to use VisualStateManager to set a value for the font and than refer to this variable in XAML?
Something like this:
<VisualStateManager.VisualStateGroups>
<VisualStateGroup>
<VisualState>
<VisualState.StateTriggers>
<!--small window-->
<AdaptiveTrigger MinWindowHeight="0" MinWindowWidth="0"/>
</VisualState.StateTriggers>
<VisualState.Setters>
<Setter Target="#MyFontSize" Value="13"/>
</VisualState.Setters>
</VisualState>
<VisualState>
<VisualState.StateTriggers>
<!--large window-->
<AdaptiveTrigger MinWindowHeight="665" MinWindowWidth="1000"/>
</VisualState.StateTriggers>
<VisualState.Setters>
<Setter Target="#MyFontSize" Value="24"/>
</VisualState.Setters>
</VisualState>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
I could then use #MyFontSize variable in XAML when designing controls and I could change it in one place.
<TextBlock x:Name="Control1" FontSize="#MyFontSize"/>
<TextBlock x:Name="Control2" FontSize="#MyFontSize"/>
<TextBlock x:Name="Control3" FontSize="#MyFontSize"/>
Is it possible to do something like this with UWP VisualStateManager?

Answer 1

Is it possible to use VisualStateManager to set a value for the font and than refer to this variable in XAML
I'm afraid you can't set variable within VisualStateManager, But for your scenario, we have a workaround that use Setting class as medium and effect other TextControl with MVVM bind.
For example
public class Setting : INotifyPropertyChanged
{
private double _fontSize = 10;
public double CFontSize
{
get { return _fontSize; }
set { _fontSize = value; OnPropertyChanged(); }
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
Usage
<Page.Resources>
<local:Setting x:Key="Setting" />
</Page.Resources>
<StackPanel>
<TextBlock
x:Name="BaseControl"
VerticalAlignment="Center"
FontSize="{Binding CFontSize, Source={StaticResource Setting}, Mode=TwoWay}"
Text="Hello" />
<TextBlock
x:Name="Control1"
VerticalAlignment="Center"
FontSize="{Binding CFontSize, Source={StaticResource Setting}, Mode=TwoWay}"
Text="How are you" />
<TextBlock
x:Name="Control2"
VerticalAlignment="Center"
FontSize="{Binding CFontSize, Source={StaticResource Setting}, Mode=TwoWay}"
Text="Fine thank you, and you?" />
<VisualStateManager.VisualStateGroups>
<VisualStateGroup>
<VisualState>
<VisualState.StateTriggers>
<!-- small window -->
<AdaptiveTrigger MinWindowHeight="0" MinWindowWidth="0" />
</VisualState.StateTriggers>
<VisualState.Setters>
<Setter Target="BaseControl.FontSize" Value="13" />
</VisualState.Setters>
</VisualState>
<VisualState>
<VisualState.StateTriggers>
<!-- large window -->
<AdaptiveTrigger MinWindowHeight="665" MinWindowWidth="1000" />
</VisualState.StateTriggers>
<VisualState.Setters>
<Setter Target="BaseControl.FontSize" Value="24" />
</VisualState.Setters>
</VisualState>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
</StackPanel>

Answer 2

Found a similar but simpler way to do this inspired by #Nico Zhu's approach. Sharing here in case someone else finds it useful.
My approach is to use one control as a template and bind all other controls of that type to it.
The VisualStateManager sets the property for the "master" controls:
<VisualStateManager.VisualStateGroups>
<VisualStateGroup>
<VisualState>
<VisualState.StateTriggers>
<!--VisualState to be triggered when window width is <665 effective pixels.-->
<AdaptiveTrigger MinWindowHeight="0" MinWindowWidth="0"/>
</VisualState.StateTriggers>
<VisualState.Setters>
<Setter Target="txtHeader.FontSize" Value="13"/>
<Setter Target="txtRegular.FontSize" Value="10"/>
</VisualState.Setters>
</VisualState>
<VisualState>
<VisualState.StateTriggers>
<AdaptiveTrigger MinWindowHeight="665" MinWindowWidth="1000"/>
</VisualState.StateTriggers>
<VisualState.Setters>
<Setter Target="txtHeader.FontSize" Value="20"/>
<Setter Target="txtRegular.FontSize" Value="16"/>
</VisualState.Setters>
</VisualState>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
All other controls can bind to "master" controls.
<TextBlock Text="My Header 1" FontSize="{Binding ElementName=txtHeader, Path=FontSize}" />
<TextBlock Text="My Header 2" FontSize="{Binding ElementName=txtHeader, Path=FontSize}" />
<TextBlock Text="My regular text 1" FontSize="{Binding ElementName=txtRegular, Path=FontSize}" />
<TextBlock Text="My regular text 2" FontSize="{Binding ElementName=txtRegular, Path=FontSize}" />
When a user resizes page, VisualStateManager will change the master controls, all others will get it through binding.
If you want to, you can create hidden controls just to server as templates.