Problems overwriting theme resources

Question

Hi,

i want my GridViewItems have rounded corners and maybe no select animation. After some time i found following site with a resource table for the GridView:
So i tryed to overwrite the corner cardius and the selectedborderbrush in my application resources but it does not work:

<Application.Resources>  
    <ResourceDictionary>  
        <ResourceDictionary.MergedDictionaries>  
            <XamlControlsResources xmlns="using:Microsoft.UI.Xaml.Controls" />  
            <ResourceDictionary Source="/Styles/FontSizes.xaml" />  
            <ResourceDictionary Source="/Styles/Thickness.xaml" />  
            <ResourceDictionary Source="/Styles/TextBlock.xaml" />  
        </ResourceDictionary.MergedDictionaries>  
        <CornerRadius x:Key="GridViewItemCornerRadius">15</CornerRadius>  
        <SolidColorBrush x:Key="GridViewItemSelectedBorderBrush" Color="Chartreuse" />  
    </ResourceDictionary>  
</Application.Resources>  

Why does that not work, and what's my alternative?

...

I found following which does work but it's bad because it overwrites all default styling instead of only selected values:
GridView.ItemContainerStyle -> Style TargetType=GridViewItem ->

<Setter Property="Template">  
    <Setter.Value>  
        <ControlTemplate TargetType="GridViewItem">  
            <GridViewItemPresenter SelectedBackground="Chartreuse" CornerRadius="15"/>  
        </ControlTemplate>  
    </Setter.Value>  
</Setter>  

 

Answer 1

I use WinUI3 and if found a working solution: Overwrite GridViewItem style with a BasedOn property pointing to the original style. Because my problem was it would overwrite all the other style until i found out about the "based on".