How to use Resource Dictionary by its Key?

Question

I am trying to use my Resource Dictionary but it does not recognize the styles have created.

<Window.Resources>
    <RoutedUICommand x:Key="Add" Text="Add" />
    <RoutedUICommand x:Key="Cancel" Text="Cancel" />
    <RoutedUICommand x:Key="Exit" Text="Exit" />
    <ResourceDictionary x:Key="LightTheme" Source="/Themes/Light.xaml"/>
</Window.Resources>

When I delete x:Key from ResourceDictionary tag, it shows a message saying "Each dictionary must have an associated key"

But when I try to use one of my styles, it does not work.

<Button x:Name="AddNew" Style="{StaticResource RoundCorner}">

Answer 1

Merge the dictionary. To do that, you need to have an explicit ResourceDictionary element.

<Window.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="/Themes/Light.xaml"/>
        </ResourceDictionary.MergedDictionaries>

        <RoutedUICommand x:Key="Add" Text="Add" />
        <RoutedUICommand x:Key="Cancel" Text="Cancel" />
        <RoutedUICommand x:Key="Exit" Text="Exit" />

    </ResourceDictionary>
</Window.Resources>