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Followup fix for ScrollViewerAssist PR #4016

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Merged
nicolaihenriksen merged 4 commits into from
Mar 9, 2026
+107 −50
Merged

Followup fix for ScrollViewerAssist PR #4016

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d325710
Revert "Remove ScrollViewerAssist weak event handlers on WM_DESTROY (…
nicolaihenriksen Mar 8, 2026
daa34c9
Fix issue by for BubbleVerticalScroll
nicolaihenriksen Mar 5, 2026
84c7f99
Fix issue by for HorizontalScroll
nicolaihenriksen Mar 8, 2026
487cc2c
Cleanup: revert not needed signature change
nicolaihenriksen Mar 8, 2026
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157 changes: 107 additions & 50 deletions src/MaterialDesignThemes.Wpf/ScrollViewerAssist.cs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
using System.Windows.Interop;
using System.Windows.Interop;

namespace MaterialDesignThemes.Wpf;

Expand Down Expand Up @@ -64,25 +64,25 @@ public static PaddingMode GetPaddingMode(DependencyObject element)
private static readonly DependencyProperty HorizontalScrollHookProperty = DependencyProperty.RegisterAttached(
"HorizontalScrollHook", typeof(HwndSourceHook), typeof(ScrollViewerAssist), new PropertyMetadata(null));

private static readonly DependencyProperty HorizontalScrollSourceProperty = DependencyProperty.RegisterAttached(
"HorizontalScrollSource", typeof(HwndSource), typeof(ScrollViewerAssist), new PropertyMetadata(null));
private static readonly DependencyProperty BubbleVerticalScrollHookProperty = DependencyProperty.RegisterAttached(
"BubbleVerticalScrollHook", typeof(HwndSourceHook), typeof(ScrollViewerAssist), new PropertyMetadata(null));

public static readonly DependencyProperty SupportHorizontalScrollProperty = DependencyProperty.RegisterAttached(
"SupportHorizontalScroll", typeof(bool), typeof(ScrollViewerAssist), new PropertyMetadata(false, OnSupportHorizontalScrollChanged));

private static void OnSupportHorizontalScrollChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
//Based on: https://blog.walterlv.com/post/handle-horizontal-scrolling-of-touchpad-en.html
if (d is ScrollViewer scrollViewer)
if (d is ScrollViewer sv)
{
if (scrollViewer.IsLoaded)
if (sv.IsLoaded)
{
DoOnLoaded(scrollViewer);
DoOnLoaded(sv);
}
else
{
WeakEventManager<ScrollViewer, RoutedEventArgs>.AddHandler(scrollViewer, nameof(ScrollViewer.Loaded), OnLoaded);
WeakEventManager<ScrollViewer, RoutedEventArgs>.AddHandler(scrollViewer, nameof(ScrollViewer.Unloaded), OnUnloaded);
RegisterForLoadedEvent(sv);
RegisterForUnloadedEvent(sv);
}
}

Expand All @@ -94,10 +94,35 @@ static void OnLoaded(object? sender, RoutedEventArgs e)
}
}

static void UnregisterForLoadedEvent(ScrollViewer sv)
{
WeakEventManager<ScrollViewer, RoutedEventArgs>.RemoveHandler(sv, nameof(ScrollViewer.Loaded), OnLoaded);
}

static void RegisterForLoadedEvent(ScrollViewer sv)
{
// Avoid double registrations
UnregisterForLoadedEvent(sv);
WeakEventManager<ScrollViewer, RoutedEventArgs>.AddHandler(sv, nameof(ScrollViewer.Loaded), OnLoaded);
}

static void UnregisterForUnloadedEvent(ScrollViewer sv)
{
WeakEventManager<ScrollViewer, RoutedEventArgs>.RemoveHandler(sv, nameof(ScrollViewer.Unloaded), OnUnloaded);
}

static void RegisterForUnloadedEvent(ScrollViewer sv)
{
// Avoid double registrations
UnregisterForUnloadedEvent(sv);
WeakEventManager<ScrollViewer, RoutedEventArgs>.AddHandler(sv, nameof(ScrollViewer.Unloaded), OnUnloaded);
}

static void DoOnLoaded(ScrollViewer sv)
{
if (GetSupportHorizontalScroll(sv))
{
RegisterForUnloadedEvent(sv);
RegisterHook(sv);
}
else
Expand All @@ -114,30 +139,23 @@ static void OnUnloaded(object? sender, RoutedEventArgs e)
}
}

static void RemoveHandlers(ScrollViewer scrollViewer)
{
WeakEventManager<ScrollViewer, RoutedEventArgs>.RemoveHandler(scrollViewer, nameof(ScrollViewer.Loaded), OnLoaded);
WeakEventManager<ScrollViewer, RoutedEventArgs>.RemoveHandler(scrollViewer, nameof(ScrollViewer.Unloaded), OnUnloaded);
}

static void RemoveHook(ScrollViewer scrollViewer)
static void RemoveHook(ScrollViewer sv)
{
if (scrollViewer.GetValue(HorizontalScrollHookProperty) is HwndSourceHook hook &&
scrollViewer.GetValue(HorizontalScrollSourceProperty) is HwndSource source)
var source = PresentationSource.FromVisual(sv) as HwndSource;
if (source is not null && sv.GetValue(HorizontalScrollHookProperty) is HwndSourceHook hook)
{
source.RemoveHook(hook);
scrollViewer.SetValue(HorizontalScrollHookProperty, null);
sv.SetValue(HorizontalScrollHookProperty, null);
}
}

static void RegisterHook(ScrollViewer scrollViewer)
static void RegisterHook(ScrollViewer sv)
{
RemoveHook(scrollViewer);
if (PresentationSource.FromVisual(scrollViewer) is HwndSource source)
RemoveHook(sv);
if (PresentationSource.FromVisual(sv) is HwndSource source)
{
HwndSourceHook hook = Hook;
scrollViewer.SetValue(HorizontalScrollSourceProperty, source);
scrollViewer.SetValue(HorizontalScrollHookProperty, hook);
sv.SetValue(HorizontalScrollHookProperty, hook);
source.AddHook(hook);
}

Expand All @@ -148,15 +166,15 @@ IntPtr Hook(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled
const int WM_NCDESTROY = 0x0082;
switch (msg)
{
case WM_MOUSEHWHEEL when scrollViewer.IsMouseOver:
case WM_MOUSEHWHEEL when sv.IsMouseOver:
int tilt = (short)((wParam.ToInt64() >> 16) & 0xFFFF);
scrollViewer.ScrollToHorizontalOffset(scrollViewer.HorizontalOffset + tilt);
sv.ScrollToHorizontalOffset(sv.HorizontalOffset + tilt);
return (IntPtr)1;
case WM_DESTROY:
case WM_NCDESTROY:
RemoveHandlers(scrollViewer);
var source = PresentationSource.FromVisual(scrollViewer) as HwndSource;
source?.RemoveHook(Hook);
UnregisterForLoadedEvent(sv);
UnregisterForUnloadedEvent(sv);
RemoveHook(sv);
break;
}
return IntPtr.Zero;
Expand All @@ -166,19 +184,19 @@ IntPtr Hook(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled

public static readonly DependencyProperty BubbleVerticalScrollProperty = DependencyProperty.RegisterAttached(
"BubbleVerticalScroll", typeof(bool), typeof(ScrollViewerAssist), new PropertyMetadata(false, OnBubbleVerticalScrollChanged));

private static void OnBubbleVerticalScrollChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
if (d is ScrollViewer scrollViewer)
if (d is ScrollViewer sv)
{
if (scrollViewer.IsLoaded)
if (sv.IsLoaded)
{
DoOnLoaded(scrollViewer);
DoOnLoaded(sv);
}
else
{
WeakEventManager<ScrollViewer, RoutedEventArgs>.AddHandler(scrollViewer, nameof(ScrollViewer.Loaded), OnLoaded);
WeakEventManager<ScrollViewer, RoutedEventArgs>.AddHandler(scrollViewer, nameof(ScrollViewer.Unloaded), OnUnloaded);
RegisterForLoadedEvent(sv);
RegisterForUnloadedEvent(sv);
}
}

Expand All @@ -190,10 +208,48 @@ static void OnLoaded(object? sender, RoutedEventArgs e)
}
}

static void UnregisterForLoadedEvent(ScrollViewer sv)
{
WeakEventManager<ScrollViewer, RoutedEventArgs>.RemoveHandler(sv, nameof(ScrollViewer.Loaded), OnLoaded);
}

static void RegisterForLoadedEvent(ScrollViewer sv)
{
// Avoid double registrations
UnregisterForLoadedEvent(sv);
WeakEventManager<ScrollViewer, RoutedEventArgs>.AddHandler(sv, nameof(ScrollViewer.Loaded), OnLoaded);
}

static void UnregisterForUnloadedEvent(ScrollViewer sv)
{
WeakEventManager<ScrollViewer, RoutedEventArgs>.RemoveHandler(sv, nameof(ScrollViewer.Unloaded), OnUnloaded);
}

static void RegisterForUnloadedEvent(ScrollViewer sv)
{
// Avoid double registrations
UnregisterForUnloadedEvent(sv);
WeakEventManager<ScrollViewer, RoutedEventArgs>.AddHandler(sv, nameof(ScrollViewer.Unloaded), OnUnloaded);
}

static void UnregisterForMouseWheelEvent(ScrollViewer sv)
{
sv.RemoveHandler(UIElement.MouseWheelEvent, (RoutedEventHandler)ScrollViewerOnMouseWheel);
}

static void RegisterForMouseWheelEvent(ScrollViewer sv)
{
// Avoid double registrations
UnregisterForMouseWheelEvent(sv);
sv.AddHandler(UIElement.MouseWheelEvent, (RoutedEventHandler)ScrollViewerOnMouseWheel, true);
}

static void DoOnLoaded(ScrollViewer sv)
{
if (GetBubbleVerticalScroll(sv))
{
RegisterForUnloadedEvent(sv);
RegisterForMouseWheelEvent(sv);
RegisterHook(sv);
}
else
Expand All @@ -206,29 +262,29 @@ static void OnUnloaded(object? sender, RoutedEventArgs e)
{
if (sender is ScrollViewer sv)
{
RemoveHook(sv);
UnregisterForUnloadedEvent(sv);
UnregisterForMouseWheelEvent(sv);
}
}

static void RemoveHandlers(ScrollViewer scrollViewer)
{
WeakEventManager<ScrollViewer, RoutedEventArgs>.RemoveHandler(scrollViewer, nameof(ScrollViewer.Loaded), OnLoaded);
WeakEventManager<ScrollViewer, RoutedEventArgs>.RemoveHandler(scrollViewer, nameof(ScrollViewer.Unloaded), OnUnloaded);
}

static void RemoveHook(ScrollViewer scrollViewer)
static void RemoveHook(ScrollViewer sv)
{
scrollViewer.RemoveHandler(UIElement.MouseWheelEvent, (RoutedEventHandler)ScrollViewerOnMouseWheel);
var source = PresentationSource.FromVisual(sv) as HwndSource;
if (source is not null && sv.GetValue(BubbleVerticalScrollHookProperty) is HwndSourceHook hook)
{
source.RemoveHook(hook);
sv.SetValue(BubbleVerticalScrollHookProperty, null);
}
}

static void RegisterHook(ScrollViewer scrollViewer)
static void RegisterHook(ScrollViewer sv)
{
RemoveHook(scrollViewer);
if (PresentationSource.FromVisual(scrollViewer) is HwndSource source)
RemoveHook(sv);
if (PresentationSource.FromVisual(sv) is HwndSource source)
{
HwndSourceHook hook = Hook;
source.AddHook(hook);
scrollViewer.AddHandler(UIElement.MouseWheelEvent, (RoutedEventHandler)ScrollViewerOnMouseWheel, true);
sv.SetValue(BubbleVerticalScrollHookProperty, hook);
}

IntPtr Hook(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
Expand All @@ -239,9 +295,10 @@ IntPtr Hook(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled
{
case WM_DESTROY:
case WM_NCDESTROY:
RemoveHandlers(scrollViewer);
var source = PresentationSource.FromVisual(scrollViewer) as HwndSource;
source?.RemoveHook(Hook);
UnregisterForMouseWheelEvent(sv);
UnregisterForLoadedEvent(sv);
UnregisterForUnloadedEvent(sv);
RemoveHook(sv);
break;
}
return IntPtr.Zero;
Expand Down
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