Introduced function IsUpdating which can be used instead of checking for flag tsUpdating or (fUpdateCount > 0). Issue #1013.

Author: joachimmarder

Source/VirtualTrees.pas

@@ -3130,6 +3130,7 @@   TBaseVirtualTree = class(TCustomControl)
     function IsEditing: Boolean;
     function IsMouseSelecting: Boolean;
     function IsEmpty: Boolean; inline;
+    function IsUpdating(): Boolean;
     function IterateSubtree(Node: PVirtualNode; Callback: TVTGetNodeProc; Data: Pointer; Filter: TVirtualNodeStates = [];
       DoInit: Boolean = False; ChildNodesOnly: Boolean = False): PVirtualNode;
     procedure LoadFromFile(const FileName: TFileName); virtual;
@@ -8431,7 +8432,7 @@ procedure TVirtualTreeColumns.Update(Item: TCollectionItem);
           Treeview.Invalidate;
         end;
 
-      if not (tsUpdating in Treeview.FStates) then
+      if not (Treeview.IsUpdating) then
         // This is mainly to let the designer know when a change occurs at design time which
         // doesn't involve the object inspector (like column resizing with the mouse).
         // This does NOT include design time code as the communication is done via an interface.
@@ -19727,7 +19728,7 @@ procedure TBaseVirtualTree.DoColumnResize(Column: TColumnIndex);
     if [hsColumnWidthTracking, hsResizing] * FHeader.States = [hsColumnWidthTracking] then
       UpdateWindow(Handle);
 
-    if not (tsUpdating in FStates) then
+    if not (IsUpdating) then
       UpdateDesigner; // design time only
 
     if Assigned(FOnColumnResize) and not (hsResizing in FHeader.States) then
@@ -23280,7 +23281,7 @@ procedure TBaseVirtualTree.InternalClearSelection();
   // It is possible that there are invalid node references in the selection array
   // if the tree update is locked and changes in the structure were made.
   // Handle this potentially dangerous situation by packing the selection array explicitely.
-  if FUpdateCount > 0 then
+  if IsUpdating then
   begin
     Count := PackArray(FSelection, FSelectionCount);
     if Count > -1 then
@@ -30019,6 +30020,12 @@ function TBaseVirtualTree.IsMouseSelecting: Boolean;
   Result := (tsDrawSelPending in FStates) or (tsDrawSelecting in FStates);
 end;
 
+function TBaseVirtualTree.IsUpdating: Boolean;
+// The tree does currently not update its window because a BeginUpdate has not yet ended.
+begin
+  Exit(UpdateCount > 0);
+end;
+
 //----------------------------------------------------------------------------------------------------------------------
 
 function TBaseVirtualTree.IterateSubtree(Node: PVirtualNode; Callback: TVTGetNodeProc; Data: Pointer;
@@ -32636,7 +32643,7 @@ procedure TBaseVirtualTree.UpdateHorizontalScrollBar(DoRepaint: Boolean);
 begin
   UpdateHorizontalRange;
 
-  if (FUpdateCount > 0) or not HandleAllocated then
+  if IsUpdating or not HandleAllocated then
     Exit;
 
   // Adjust effect scroll offset depending on bidi mode.
@@ -32743,7 +32750,7 @@ procedure TBaseVirtualTree.UpdateVerticalScrollBar(DoRepaint: Boolean);
 begin
   UpdateVerticalRange;
 
-  if (fUpdateCount > 0) then
+  if (IsUpdating) then
     Exit;
   Assert(GetCurrentThreadId = MainThreadId, 'UI controls like ' + Classname + ' and its scrollbars should only be manipulated through the main thread.');