wpf - Change theme at runtime

Question

I have a WPF application with a theme (ShinyRed.xaml) and I want to have a button that when clicked changes the theme to ShinyBlue.xaml

I load in the theme initially in App.xaml:

<Application.Resources>
    <ResourceDictionary Source="/Themes/ShinyBlue.xaml"/>
</Application.Resources>

How might I do this?

Answer 1

How you could do it:

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary x:Name="ThemeDictionary">
                <ResourceDictionary.MergedDictionaries>
                    <ResourceDictionary Source="/Themes/ShinyRed.xaml"/>
                </ResourceDictionary.MergedDictionaries>
            </ResourceDictionary>
        </ResourceDictionary.MergedDictionaries>
    <!-- ... -->

public partial class App : Application
{
    public ResourceDictionary ThemeDictionary
    {
        // You could probably get it via its name with some query logic as well.
        get { return Resources.MergedDictionaries[0]; }
    }

    public void ChangeTheme(Uri uri)
    {
        ThemeDictionary.MergedDictionaries.Clear();
        ThemeDictionary.MergedDictionaries.Add(new ResourceDictionary() { Source = uri });
    }

    //...
}

In your change method:

var app = (App)Application.Current;
app.ChangeTheme(new Uri("New Uri here"));