Question

I am attempting to convert a GUI application that I made in Delphi (actually, its Lazarus) to a library(DLL).

In the GUI application I used a OnDataChange event listener, but I cannot seem to figure out how to do the same thing for the library.

Here is what it looks like in the GUI App:

procedure TForm1.Datasource2DataChange(Sender: TObject; Field: TField);
begin
  ZMakeRankedTable.Close;
  GetNN;
end;  

And in the unit’s LFM file:

object Datasource2: TDatasource
DataSet = ZMakeRankedTable
OnDataChange = Datasource2DataChange
left = 184
top = 95
end       

How do I do the same thing for the library? Where do I initialize the event listener?

Answer 1

What is wrong with creating a new class of your own that will be the delegate, instead of a form:

type
  TDataDelegate = class
  public
    procedure DataChange(Sender: TObject; Field: TField);
    etc...
  end;

procedure TDataDelegate.DataChange(Sender: TObject; Field: TField);
begin
  // Do what you normally would do in your form's event handler
end;

And just be sure to create an instance of the class

DataDelegate := TDataDelegate.Create;
DataSource2.OnDataChange := DataDelegate.DataChange;

etc…

In other words, instead of a form, use a class you wrote to handle the events of the various classes. Like in a form, each of the procedures should have the signature of the event handler. The only difference is that the IDE won’t create these methods for you.

You could also use a TDataModule, I guess, but I am not sure about the implications. The advantage would be IDE support.