Hello,
I'm writing an article about docking in Lazarus.
The first - and most simple - example I tried, failed:
- Drop a panel on a form
- Set dragkind to dkDock
- Set dragmode to dkAutomatic.
- Run application
- Drag panel outside form, and let go.
expected behaviour: a small form should appear, and the panel should be on it.
Actual behaviour: 4 Access violations (fix one to get to the next ;) ).
Attached small patch fixes the 4 access violations, after which the expected behaviour
occurs. They are all checks to see if a object pointer is not-nil.
Better would be to fix the root of the problem:
I think the automatic creation of a dockhost form probably uses createnew(),
which
maybe doesn't correctly allocate all structures (scrollbars/icons). But that is
just
a wild guess, which I currently don't have time to investigate.
Michael.
Index: include/customform.inc
===================================================================
--- include/customform.inc (revision 24391)
+++ include/customform.inc (working copy)
@@ -292,7 +292,7 @@
OldChange: TNotifyEvent;
OldCurrent: Integer;
begin
- if not FIcon.Empty then
+ if Assigned(FIcon) and not FIcon.Empty then
begin
if FBigIconHandle = 0 then
begin
@@ -319,7 +319,7 @@
OldChange: TNotifyEvent;
OldCurrent: Integer;
begin
- if not FIcon.Empty then
+ if Assigned(FIcon) and not FIcon.Empty then
begin
if FSmallIconHandle = 0 then
begin
Index: include/scrollingwincontrol.inc
===================================================================
--- include/scrollingwincontrol.inc (revision 24391)
+++ include/scrollingwincontrol.inc (working copy)
@@ -61,9 +61,9 @@
{if (FHorzScrollBar.Range>Result.Right)
or (FVertScrollBar.Range>Result.Bottom) then
DebugLn(['TScrollingWinControl.GetLogicalClientRect Client=',ClientWidth,'x',ClientHeight,' Ranges=',FHorzScrollBar.Range,'x',FVertScrollBar.Range]);}
- if (FHorzScrollBar.Range > Result.Right) then
+ if Assigned(FHorzScrollBar) and (FHorzScrollBar.Range > Result.Right) then
Result.Right := FHorzScrollBar.Range;
- if (FVertScrollBar.Range > Result.Bottom) then
+ if Assigned(FVertScrollBar) and (FVertScrollBar.Range > Result.Bottom) then
Result.Bottom := FVertScrollBar.Range;
end;
--
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