Change Resource Dictionary in runtime - wpf

Question

I use Material design in my wpf. I change theme(Light/Dark) in runtime.
<materialDesign:DialogHost Identifier="RootDialog">
<materialDesign:DialogHost.Resources>
<Style TargetType="materialDesign:Card" BasedOn="{StaticResource {x:Type materialDesign:Card}}">
<Style.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.dark.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Style.Resources>
<Setter Property="Background" Value="{DynamicResource MaterialDesignCardBackground}" />
</Style>
</materialDesign:DialogHost.Resources>
<Grid>
<!--some code-->
</Grid>
</materialDesign:DialogHost>
I want change source of Resource Dictionary in runtime to
pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.light.xaml
How I can do this?

Answer 1

Define your Resource dictionary Apllication wide in App.xaml
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<!-- This is the default theme (useful for Designing)-->
<ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.dark.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
Change the Theme in code behind.
public Skin ChangeSkin()
{
// you might want to have some logic here to keep switching
ApplyResources("pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.light.xaml")
}
private void ApplyResources(string src)
{
App a = App.Current as App;
var dict = new ResourceDictionary() { Source = new Uri(src, UriKind.Relative) };
foreach (var mergeDict in dict.MergedDictionaries)
{
a.Resources.MergedDictionaries.Add(mergeDict);
}
foreach (var key in dict.Keys)
{
a.Resources[key] = dict[key];
}
}