[Lazarus] Newbie, porting class to FPC but get procedure assignment error

Bo Berglund bo.berglund at gmail.com
Fri Jun 19 09:25:56 CEST 2015

I am trying to make a test program in Lazarus to evaluate if I can
port a dongle component in Delphi to a normal class in Lazarus.
So far I had no real problems but now I don't understand what I am
doing wrong. Relevant code below:

TSentinel = class
    FTimer: TTimer;
    procedure OnCheckTimer(Sender: TObject);
    { Public declarations }
    constructor Create;

constructor TSentinel.Create;
  FTimer := TTimer.Create(Application);
  FTimer.Enabled := false;
  FTimer.Interval := 0;
  FTimer.OnTimer := OnCheckTimer(Self); //<= Error here

The timer is used to automatically check the presence of the dongle so
I have to assign the OnTimer procedure to the newly created TTimer
object. This works fine in Delphi...

On compilation I get an error message as follows.

In the Delphi code there was no argument on the assignment of the
OnTimer event procedure, in Lazarus it shows this error:
sentinel.pas(647,21) Error: Wrong number of parameters specified for
call to "OnCheckTimer"

Using argument Self or NIL (like I often do in Delphi):
sentinel.pas(647,39) Error: Incompatible type for arg no. 1: Got
"untyped", expected "<procedure variable type of procedure(TObject) of

Why is this difference Delphi/FPC appearing and what can I do?

Bo Berglund
Developer in Sweden

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