Question

I create custom WPF Expander inherited from common Expander. I have a file with styles at path MyAssembly/Theme/generic.xaml. I can see that styles are applied in designer but are not in running program.

MyExpander.xaml:

<Expander x:Class="Path.To.MyExpander"
    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">
    <Expander.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="pack://application:,,,/MyAssembly;component/Theme/generic.xaml"/>
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Expander.Resources>
    ...

generic.xaml:

<ResourceDictionary
    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"
    mc:Ignorable="d"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008">
    ...

code where I instanciate the expanders:

class Viewer
{
    private void GenerateExpanders()
    {
        this.Expanders.Children.Clear();
        foreach (...)
        {
            MyExpander ex = new MyExpander();
            ex.HeaderText.Text = "Sample";
            ex.HorizontalAlignment = System.Windows.HorizontalAlignment.Stretch;
            ex.IsExpanded = true;
            this.Expanders.Children.Add(ex);
        }
    }
}

All three files are in one assembly but class Viewer is instantiated in another assembly.
Is there something am I doing wrong?

Answer 1

I had

<Style TargetType="Expander"

but it should be

<Style TargetType="MyExpander"

I didn’t realise that it wasn’t Expander anymore – it was MyExpander (class MyExpander : Expander)