Question

I’m effectively trying to deserialize a form.

One of the objects on the serialized form has a method which takes a series of events as parameters.

Now since I don’t have the class type of the object when I’m deserializing, I have a method on the object doing the deserialization called AddMethod which is declared like this:

procedure TMyDeserializer.AddMethod(ControlName, EventName: String;
  MethodAddr: Pointer);
var
    TargetControl : TControl;
    Method : TMethod;
begin
    if Not Assigned(TempForm) then
        Exit;
    if TempForm.Name = ControlName then
        TargetControl := TempForm
    else
        TargetControl := TempForm.FindChildControl(ControlName);

    if Assigned(TargetControl) then
    begin
        Method.Code := MethodAddr;
        Method.Data := TargetControl;
        SetMethodProp(TargetControl, EventName, Method);
    end;
end;

So that I can poke subroutines into the various controls as I deserialize them, The problem is I need to add events as a list of parameters (not to a control). e.g.

SetUpEvents(EventHandler1:TNotifyEvent;EventHandler2:TNotifyEvent);

Where EventHandler1 and EventHandler2 are defined somewhere in code as

Procedure EventHandler1(Sender:TNotifyEvent);  
begin
    // Do something
end;

These are not methods but stand alone subroutines.

When I’m assigning these to objects the subroutine doesn’t need to be part of an object as the AddMethod procedure handles it with a call like

MyDeserializerInstance.AddMethod('Button1','OnClick',@EventHandler1);

This works for standard event handlers, such as Button1.OnClick but not if I want to do

Procedure SetUpButton1Click(Method: TNotifyEvent)
begin
    TButton(MyDeserializerInstance.TempForm.FindChildControl('Button1')).OnClick = Method;
end;

The problem is I can’t pass the subroutine as a method to the example Set Up Procedure.

The form being created isn’t declared in an interface and is entirely defined by the file it is read from as well as a few stand alone routines in code.

So I suppose the question is how do turn a subroutine into a method at run time (after creating the object it is supposed to be part of), and if I can’t do that how do I pass the subroutines in code as parameters in another method?

So far I’ve tried casting a TMethod as the correct event type and filling in the .Data as the TempForm. It called the correct method but it scrambled the parameters.

Delphi version is 2007

Answer 1

Non-static class methods have a hidden Self input parameter that is filled in when the method is called. That is what the TMethod.Data field corresponds to. In order to use a standalone procedure as a handler for an event that expects a class method, the procedure must have an extra parameter defined to represent the Self parameter so the value of TMethod.Data has somewhere to go, ie:

procedure Button1ClickHandler(Self: Pointer; Sender: TObject);
begin 
  // Do something 
end; 

MyDeserializerInstance.AddMethod('Button1', 'OnClick', @Button1ClickHandler);

Your AddMethod() implementation is assigning the TargetControl as the TMethod.Data value, so the Self and Sender parameters above will end up pointing at the same object at runtime, but that is OK.

Without the explicit Self parameter defined, that explains why your parameters are getting “scrambled” when the procedure called at runtime. The hidden Self value is being assigned to the Sender parameter, and the real Sender value is being ignored.