App.xaml

<Application x:Class="_3launch.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:_3launch"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <Style xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
               xmlns:markup="http://schemas.microsoft.com/winfx/2006/xaml"
               TargetType="ListBox" x:Key="ListStyle" BasedOn="{StaticResource {markup:Type ListBox}}">
            <Style.Triggers>
                <DataTrigger 
                    Binding="{Binding RelativeSource={markup:Static RelativeSource.Self}, Path=Items.Count}" 
                    Value="0">
                    <Setter Property="Template">
                        <Setter.Value>
                            <ControlTemplate>
                                <TextBlock Margin="10">No items to display</TextBlock>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Application.Resources>
</Application>