From e8f3263b75acee31d2ac3e8a0fca95ebd893fc18 Mon Sep 17 00:00:00 2001
From: Joachim Marder <joachim.marder@outlook.com>
Date: Sat, 20 Jan 2024 15:31:39 +0100
Subject: [PATCH] Fix for issue #1234: Access violation while changing the
 theme

---
 Demos/Advanced/Advanced.dsv                 | 10 +++++++
 Demos/Interfaces/charityevents.dsv          | 30 +++++++++++++++++++++
 Demos/Minimal/Minimal.dsv                   | 20 ++++++++++++++
 Demos/OLE/OLE.dsv                           | 10 +++++++
 Demos/Objects/MVCDemo.dsv                   | 10 +++++++
 Packages/RAD Studio 10.4+/VirtualTreesR.dsv | 20 ++++++++++++++
 Source/VirtualTrees.StyleHooks.pas          | 14 +++++++---
 7 files changed, 110 insertions(+), 4 deletions(-)
 create mode 100644 Demos/Advanced/Advanced.dsv
 create mode 100644 Demos/Interfaces/charityevents.dsv
 create mode 100644 Demos/Minimal/Minimal.dsv
 create mode 100644 Demos/OLE/OLE.dsv
 create mode 100644 Demos/Objects/MVCDemo.dsv
 create mode 100644 Packages/RAD Studio 10.4+/VirtualTreesR.dsv

diff --git a/Demos/Advanced/Advanced.dsv b/Demos/Advanced/Advanced.dsv
new file mode 100644
index 000000000..5751759b5
--- /dev/null
+++ b/Demos/Advanced/Advanced.dsv
@@ -0,0 +1,10 @@
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xTb3VyY2VcVmlydHVhbFRyZWVzLnBhcw==]
+Module=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+CursorX=42
+CursorY=667
+TopLine=611
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+
diff --git a/Demos/Interfaces/charityevents.dsv b/Demos/Interfaces/charityevents.dsv
new file mode 100644
index 000000000..1dc475e91
--- /dev/null
+++ b/Demos/Interfaces/charityevents.dsv
@@ -0,0 +1,30 @@
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xTb3VyY2VcVmlydHVhbFRyZWVzLnBhcw==]
+Module=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+CursorX=47
+CursorY=246
+TopLine=223
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xEZW1vc1xJbnRlcmZhY2VzXG15ZXZlbnRzLnBh
+cw==]
+Module=D:\Projects\Virtual-TreeView\Demos\Interfaces\myevents.pas
+CursorX=6
+CursorY=26
+TopLine=13
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Demos\Interfaces\myevents.pas
+
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xEZW1vc1xPYmplY3RzXE1WQ1BhbmVsLnBhcw==]
+Module=D:\Projects\Virtual-TreeView\Demos\Objects\MVCPanel.pas
+CursorX=21
+CursorY=74
+TopLine=52
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Demos\Objects\MVCPanel.pas
+
diff --git a/Demos/Minimal/Minimal.dsv b/Demos/Minimal/Minimal.dsv
new file mode 100644
index 000000000..6a4237da6
--- /dev/null
+++ b/Demos/Minimal/Minimal.dsv
@@ -0,0 +1,20 @@
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xTb3VyY2VcVmlydHVhbFRyZWVzLnBhcw==]
+Module=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+CursorX=42
+CursorY=667
+TopLine=626
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xEZW1vc1xNaW5pbWFsXE1haW4ucGFz]
+Module=D:\Projects\Virtual-TreeView\Demos\Minimal\Main.pas
+CursorX=1
+CursorY=1
+TopLine=1
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=
+
diff --git a/Demos/OLE/OLE.dsv b/Demos/OLE/OLE.dsv
new file mode 100644
index 000000000..68f02fe96
--- /dev/null
+++ b/Demos/OLE/OLE.dsv
@@ -0,0 +1,10 @@
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xEZW1vc1xPTEVcTWFpbi5wYXM=]
+Module=D:\Projects\Virtual-TreeView\Demos\OLE\Main.pas
+CursorX=1
+CursorY=1
+TopLine=1
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=
+
diff --git a/Demos/Objects/MVCDemo.dsv b/Demos/Objects/MVCDemo.dsv
new file mode 100644
index 000000000..e1eb2caf7
--- /dev/null
+++ b/Demos/Objects/MVCDemo.dsv
@@ -0,0 +1,10 @@
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xTb3VyY2VcVmlydHVhbFRyZWVzLnBhcw==]
+Module=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+CursorX=42
+CursorY=667
+TopLine=626
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+
diff --git a/Packages/RAD Studio 10.4+/VirtualTreesR.dsv b/Packages/RAD Studio 10.4+/VirtualTreesR.dsv
new file mode 100644
index 000000000..521437eae
--- /dev/null
+++ b/Packages/RAD Studio 10.4+/VirtualTreesR.dsv	
@@ -0,0 +1,20 @@
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xTb3VyY2VcVmlydHVhbFRyZWVzLnBhcw==]
+Module=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+CursorX=42
+CursorY=667
+TopLine=626
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Source\VirtualTrees.pas
+
+[ClosedView_RDpcUHJvamVjdHNcVmlydHVhbC1UcmVlVmlld1xEZW1vc1xPYmplY3RzXE1WQ1R5cGVzLnBhcw==]
+Module=D:\Projects\Virtual-TreeView\Demos\Objects\MVCTypes.pas
+CursorX=36
+CursorY=194
+TopLine=172
+LeftCol=1
+Elisions=
+Bookmarks=
+EditViewName=D:\Projects\Virtual-TreeView\Demos\Objects\MVCTypes.pas
+
diff --git a/Source/VirtualTrees.StyleHooks.pas b/Source/VirtualTrees.StyleHooks.pas
index 760eb4aff..a6ad04995 100644
--- a/Source/VirtualTrees.StyleHooks.pas
+++ b/Source/VirtualTrees.StyleHooks.pas
@@ -523,10 +523,16 @@ procedure TVclStyleScrollBarsHook.WMCaptureChanged(var Msg: TMessage);
 
 destructor TVclStyleScrollBarsHook.Destroy;
 begin
-  FVertScrollWnd.StyleHook := nil;
-  FreeAndNil(FVertScrollWnd);
-  FHorzScrollWnd.StyleHook := nil;
-  FreeAndNil(FHorzScrollWnd);
+  if Assigned(FVertScrollWnd) then
+  begin
+    FVertScrollWnd.StyleHook := nil;
+    FreeAndNil(FVertScrollWnd);
+  end;
+  if Assigned(FHorzScrollWnd) then
+  begin
+    FHorzScrollWnd.StyleHook := nil;
+    FreeAndNil(FHorzScrollWnd);
+  end;
   inherited;
 end;