Not all styles are overwritten in my WPF controls - wpf

Question

I have a system where I use my WPF UI as a class library. I also use different usercontrols to control what the user see during the span of the UIs life cycle. These are all set in code. I then added a theme system where you could create a XAML ResourseDictionary file and use that to change the look on the UI. To apply the style, everytime I create the window or a user control, that FrameworkElement goes through this code:
public void ApplyStyle(FrameworkElement element)
{
var targetDir = element.Resources.MergedDictionaries.FirstOrDefault(d => d.Contains("SonaStyleDocument"));
if (targetDir != null && loadedResource != null)
{
element.Resources.MergedDictionaries.Remove(targetDir);
element.Resources.MergedDictionaries.Add(loadedResource);
}
}
In my view I do set a standard style document via the xaml code. I locate the default style in the code, remove it and add the new one. Now this works, and I can see the changes when I apply a external ResourceDictionary. However, for some reason my buttons does not react to the changes. They keep the same styles, even though it has been removed. Here is one of my buttons code:
<Button Style="{StaticResource KeyboardToggleButton}" Command="{Binding KeyboardToggleCommand}">
<Button.Content>...</Button.Content>
</Button>
It uses the style KeyboardToggleButton, which has the follow style in my default style document:
<Style TargetType="Button" x:Key="SonaButton">
...
</Style>
<Style TargetType="Button" x:Key="SonaPrimaryButton" BasedOn="{StaticResource SonaButton}">
<Setter Property="Template" Value="{StaticResource DxcPrimaryButtonTemplate}" />
...
</Style>
<Style TargetType="Button" x:Key="ManipulationButton" BasedOn="{StaticResource SonaPrimaryButton}">
...
</Style>
<Style TargetType="Button" BasedOn="{StaticResource ManipulationButton}" x:Key="KeyboardToggleButton" />
But I replace it with the following style(s):
<Style TargetType="Button" x:Key="SonaButton">
<Setter Property="Template" Value="{StaticResource RoundCornerTemplate}"></Setter>
</Style>
<Style TargetType="Button" x:Key="ManipulationButton" BasedOn="{StaticResource SonaButton}">
...
</Style>
<Style TargetType="Button" x:Key="KeyboardToggleButton" BasedOn="{StaticResource ManipulationButton}"/>
What could be going on here? They both have the same key for KeyboardToggleButton, though the templating is different and I can see that my other controls react fine to the new styles they get. I even tested just adding the new style and let the old one remain and that has the same result. The buttons just won't accept the new style.
Update:
So I was reading various articles about styles to see if I find some more information, and some article mentioned Dynamic resources. To isolate the problem I first remade my default style of one of my buttons to be very basic:
<Style TargetType="ButtonBase" x:Key="KeyboardToggleButton" />
And then changed the style I want to overwrite the default style, to just change the background:
<Style TargetType="Button" x:Key="KeyboardToggleButton">
<Setter Property="Background" Value="Yellow"/>
</Style>
With this setup nothing happened, but when I changed the Style from a StaticResource to DynamicResource, then it worked. However, this presented another problem. I tried testing this result on one of my other buttons with all substyles and control templates activated and the system throwsan exception in the code that adds the style:
System.InvalidOperationException: 'Property can not be null on Trigger.'
The style I try to use instead of the default style has a control template with triggers, to handle hover events, click event and more. My theory at this point is that I have had this problem also with the StaticResource, but the error is hidden and the system defaults directly to the old style. My issue with this theory is that I actively remove the default style before I enter in the new. Not removing the old style does not help.

Answer 1

I found the problem. The exception was indeed the answer, but only when I changed the code to apply each style individually. I should have followed the exception a bit more, but I had tunnel vision. The answer came from here: Why is the WPF property IsDefaulted not found?
I have first tried to change to buttonbase, but that does not work with the trigger "IsDefaulted". That will not resolve and the property will be null. Changing back to TargetType="Button" worked. No more exceptions. Then I also changed all style references to be dynamic and now all buttons (Except one, which I am looking into) have the correct style. It makes sense that it should be Dynamic as I change it during runtime.