Add TabAssist.UseHeaderPadding to enable/disable new behavior

The feature is on by default

Author: nicolaihenriksen

src/MaterialDesignThemes.Wpf/Behaviors/Internal/TabControlHeaderScrollBehavior.cs

@@ -94,6 +94,8 @@ bool IsMovingForward()
 
     private void AddPaddingToScrollableContentIfWiderThanViewPort()
     {
+        if (TabAssist.GetUseHeaderPadding(TabControl) == false)
+            return;
         if (ScrollableContent is null)
             return;
 
@@ -128,6 +130,8 @@ protected override void OnDetaching()
 
     private void AssociatedObject_ScrollChanged(object sender, ScrollChangedEventArgs e)
     {
+        if (TabAssist.GetUseHeaderPadding(TabControl) == false)
+            return;
         TimeSpan duration = TabAssist.GetScrollDuration(TabControl);
         if (duration == TimeSpan.Zero)
             return;

src/MaterialDesignThemes.Wpf/Internal/PaddedBringIntoViewStackPanel.cs

@@ -25,11 +25,23 @@ public double HeaderPadding
         DependencyProperty.Register(nameof(HeaderPadding),
             typeof(double), typeof(PaddedBringIntoViewStackPanel), new PropertyMetadata(0d));
 
+    public bool UseHeaderPadding
+    {
+        get => (bool)GetValue(UseHeaderPaddingProperty);
+        set => SetValue(UseHeaderPaddingProperty, value);
+    }
+
+    public static readonly DependencyProperty UseHeaderPaddingProperty =
+        DependencyProperty.Register(nameof(UseHeaderPadding), typeof(bool), typeof(PaddedBringIntoViewStackPanel), new PropertyMetadata(false));
+
     public PaddedBringIntoViewStackPanel()
         => AddHandler(FrameworkElement.RequestBringIntoViewEvent, new RoutedEventHandler(OnRequestBringIntoView), false);
 
     private void OnRequestBringIntoView(object sender, RoutedEventArgs e)
     {
+        if (!UseHeaderPadding)
+            return;
+
         if (e.OriginalSource is FrameworkElement child && child != this)
         {
             e.Handled = true;

src/MaterialDesignThemes.Wpf/TabAssist.cs

@@ -73,6 +73,15 @@ public static void SetHeaderBehavior(DependencyObject obj, TabControlHeaderBehav
     public static double GetHeaderPadding(DependencyObject obj)
         => (double)obj.GetValue(HeaderPaddingProperty);
 
+    public static bool GetUseHeaderPadding(DependencyObject obj)
+        => (bool)obj.GetValue(UseHeaderPaddingProperty);
+
+    public static void SetUseHeaderPadding(DependencyObject obj, bool value)
+        => obj.SetValue(UseHeaderPaddingProperty, value);
+
+    public static readonly DependencyProperty UseHeaderPaddingProperty =
+        DependencyProperty.RegisterAttached("UseHeaderPadding", typeof(bool), typeof(TabAssist), new PropertyMetadata(false));
+
     public static void SetHeaderPadding(DependencyObject obj, double value)
         => obj.SetValue(HeaderPaddingProperty, value);
 

src/MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.TabControl.xaml

@@ -44,7 +44,8 @@
           </b:Interaction.Behaviors>
           <internal:PaddedBringIntoViewStackPanel x:Name="ScrollableContent"
                                                   ScrollDirection="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(behaviorsInternal:TabControlHeaderScrollBehavior.ScrollDirection)}"
-                                                  HeaderPadding="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:TabAssist.HeaderPadding)}">
+                                                  HeaderPadding="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:TabAssist.HeaderPadding)}"
+                                                  UseHeaderPadding="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:TabAssist.UseHeaderPadding)}">
             <UniformGrid x:Name="CenteredHeaderPanel"
                                      HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                                      Margin="{Binding Path=(wpf:TabAssist.HeaderPanelMargin), RelativeSource={RelativeSource TemplatedParent}}"
@@ -237,6 +238,7 @@
     <Setter Property="wpf:TabAssist.HasUniformTabWidth" Value="False" />
     <!-- MD spec says 52 DP, but that seems a little excessive in practice -->
     <Setter Property="wpf:TabAssist.HeaderPadding" Value="40" />
+    <Setter Property="wpf:TabAssist.UseHeaderPadding" Value="True" />
     <Setter Property="wpf:TabAssist.ScrollDuration" Value="0:0:0.250" />
 
     <Style.Triggers>