Occasional Access Violation in GetDisplayRect

[romankassebaum]

From time to time I'm getting an access violation in TBaseVirtualTree.GetDisplayRect. The reason seems to be that Temp.Parent is nil so that a call to Temp.Parent.States is impossible.

The version of the VTV is 6.4.1.

[romankassebaum]

Here is the callstack:
exception class : EAccessViolation
exception message : Zugriffsverletzung bei Adresse 00000000025D6EB4 in Modul 'Test.exe'. Lesen von Adresse 000000000000000A.

main thread ($13d4):
025d6eb4 +0f4 Test.exe VirtualTrees 26979 +19 TBaseVirtualTree.GetDisplayRect
025daa25 +045 Test.exe VirtualTrees 29807 +3 TBaseVirtualTree.InvalidateNode
025e7aad +01d Test.exe VirtualTrees 34582 +1 TCustomVirtualStringTree.InvalidateNode
025e588d +02d Test.exe VirtualTrees 33728 +2 TCustomVirtualStringTree.SetText
025e4298 +078 Test.exe VirtualTrees 33206 +6 TStringEditLink.EndEdit
025c6729 +039 Test.exe VirtualTrees 19934 +2 TBaseVirtualTree.DoEndEdit
025e37e7 +127 Test.exe VirtualTrees 32947 +23 TVTEdit.WMKeyDown
00410b3e +03e Test.exe System TObject.Dispatch
0078c913 +383 Test.exe Vcl.Controls TControl.WndProc
007937c2 +8e2 Test.exe Vcl.Controls TWinControl.WndProc
00792a0a +02a Test.exe Vcl.Controls TWinControl.MainWndProc
005e57b3 +023 Test.exe System.Classes StdWndProc
779998bd +000 USER32.dll DispatchMessageW
009317af +12f Test.exe Vcl.Forms TApplication.ProcessMessage
00931823 +013 Test.exe Vcl.Forms TApplication.HandleMessage
00931c8f +0ef Test.exe Vcl.Forms TApplication.Run
03b54e61 +251 Test.exe Test.Run 69 +35 TTestRun.Execute
03b553f5 +015 Test.exe Test 3156 +1 initialization
778759cb +00b kernel32.dll BaseThreadInitThunk

[joachimmarder]

It makes no sense that Temp.Parent is nil without previously Temp having the value of FRoot, which is the exit condition of the loop in GetDisplayRect().

I tested if deleting the node which is currently edited could cause this error, but this worked fine.

We could add another exit condition Assigned(Temp) but this would only cure the symptom and does not fix the root cause, which seems to be some inconsistency in the tree nodes.

[romankassebaum]

The application is working for many years. With moving to Delphi Berlin I updated the VTV. From this time I'm receiving the AV.

Modifying the line

  if not (vsVisible in Temp.States) or not (vsExpanded in Temp.Parent.States) then
    Exit;

to

  if (Temp = nil) or not (vsVisible in Temp.States) or (Temp.Parent = nil) or not (vsExpanded in Temp.Parent.States) then
    Exit;

solved the issue for me.

[joachimmarder]

Without repro steps there is not much else we can do here, so I will use this fix, although it won't fix the root cause.