why aren't the buttons aligning horizontally in the stackpanel? - wpf

Question

I have a list of buttons being generated from data, so there are a variable number of buttons. In an old version of the software I am overhauling, they used random custom controls but the result was that there was an infinitely growing horizontal scroller.
It appears I have the exact same XAML but it's not aligning each item horizontally, only vertically
<ScrollViewer Background="#33FFFFFF" HorizontalScrollBarVisibility="Visible" VerticalScrollBarVisibility="Disabled" >
<StackPanel Orientation="Horizontal">
<ItemsControl ItemsSource="{Binding Events}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<Button Margin="10" HorizontalAlignment="Stretch" Background="#FF1B1B1B" BorderThickness="5" BorderBrush="White" Command="{Binding Source={StaticResource Locator}, Path=EventSelector.ViewEventCommand}" CommandParameter="{Binding }">
<Grid Name="tileGridButton" Height="600" Width="400" Margin="5">
<Grid.RowDefinitions>
<RowDefinition Height="5*"></RowDefinition>
<RowDefinition Height="5*"></RowDefinition>
</Grid.RowDefinitions>
<Border Grid.Row="0" Name="tileImageBorder" Margin="5" BorderThickness="1" VerticalAlignment="Stretch" HorizontalAlignment="Center">
<Image Name="tileImage" Margin="0" Source="{Binding ImageURL}"/>
</Border>
<Grid Grid.Row="1" VerticalAlignment="Top">
<Grid.RowDefinitions>
<RowDefinition Height="6*"></RowDefinition>
<RowDefinition Height="4*"></RowDefinition>
</Grid.RowDefinitions>
<TextBlock Grid.Row="0" Name="tileText" Margin="5" Foreground="White" TextAlignment="Center" TextTrimming="CharacterEllipsis" TextWrapping="Wrap" FontSize="30" FontWeight="Bold" Text="{Binding Title}" />
<TextBlock Grid.Row="1" Name="tileDescription" Margin="5" Foreground="White" TextAlignment="Center" TextTrimming="CharacterEllipsis" TextWrapping="Wrap" FontSize="25" FontWeight="Bold" Text="{Binding EventTimeBegin}" />
</Grid>
</Grid>
</Button>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</StackPanel>
</ScrollViewer>

Answer 1

First of all your StackPanel is pretty much useless because it only contains a single item, the ItemsControl.
Instead you need to change your ItemsControl so that it uses a StackPanel as its method of laying out items inside the ItemsControl...
<ItemsControl ...>
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal"/>
<ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
.....