Hi all, I have a custom component that I've created and I get an AV anytime I try to change/set a string property within the IDE. Setting these properties at runtime doesn't produce the AV.

Also, the message that I get is simply "Access Violation". No more information other than that.

I'm using Lazarus 0.9.24.

Thanks,

Also, I'm having another problem with this component. It's a TShape descendant and I have hooked up mousedown and mouseup events to change Pen.color and Brush.Color properties to different values in order to indicate visual feedback.

If I create the component at runtime, the values work. IE: If I mouse down on the component the colors changes as expected. If I create the component at design time, then there is no change.

I suspect there are some subtle difference in streaming or something between the way Delphi does it and Lazarus, but am at a loss as to what those could be.

Thanks again,

Setting Mode to Delphi fixed it, but I'm curious as to how to get this to work in FPC mode.

Thanks,

Start the IDE with gdb and create a breaktrace.

http://wiki.lazarus.freepascal.org/Creating_a_Backtrace_with_GDB

Mattias

MousDown and MouseUp events are handled by the IDE (designer).

Maybe this helps:
http://www.freepascal.org/docs-html/prog/progap4.html#progse62.html

Mattias

Sorry Mattias, I wasn't clear enough. When I site the component at *design time*, the mouse down events do not fire at *runtime*. In the create event, I have this:

constructor TPOSButton.Create(AOwner: TComponent);
begin
   inherited Create(AOwner);
   Self.OnMouseDown := HandleMouseDown;  // <== handlers with correct signatures.
   self.OnMouseUp := HandleMouseUp;
end;

I'll take a look. Thank you.

Hi,

In FPC mode, your event assignments should prefix with '@' like this:

constructor TPOSButton.Create(AOwner: TComponent);
begin
   inherited Create(AOwner);
   Self.OnMouseDown := @HandleMouseDown;  // <== handlers with correct signatures.
   self.OnMouseUp := @HandleMouseUp;
end;

HTH,
Funky Beast

They were, but I had to change the mode to Delphi to get the String properties from throwing an AV when I tried to set them at design time.

Thanks,

Then you forgot the {$H+} switch to enable ansistrings.

Every lazarus unit begins with:
{$mode ObjFPC}{$H+}

Mattias

Components should not set their own events, but instead override the methods. For example

  protected
    procedure MouseDown(Button: TMouseButton; Shift: TShiftState; X,
           Y: Integer); override;
procedure TPOSButton.MouseDown(Button: TMouseButton; Shift:
TShiftState; X, Y: Integer);
begin
  inherited MouseDown(Button, Shift, X, Y);
end;

Mattias

That was it, Mattias. Thank you, I am learning quite a bit about component writing which is a new endeavor for me.

I have just one more problem with this component which is centering the text vertically. I had posted a separate thread above concerning this and once I figure out how to get the text to center vertically, I should this component right where I want it :)

Thanks again, everyone's help is most appreciated.