How can I dynamically inject code into event handlers in Delphi?

Question

For debugging / performance tests I would like to dynamically add logging code to all event handlers of components of a given type at run time.

For example, for all

Answer 1

If the function or procedure in the component you want to 'hook' is declard virtual or dynamic it can be done in the following manner:

Let's assume for arguments sake that you wantto see all AfterOpen's from TDataset. This event handler is called from the virtual method:

procedure TDataSet.DoAfterOpen;

Create a new unit UnitDatasetTester (typed it in manual)

unit UnitDatasetTester;

interface

uses
  DB;

type
  TDataset = class( DB.TDataset )
  protected
    procedure DoAfterOpen; override;
  end;

implementation

uses
  MySpecialLoggingUnit; 

procedure TDataset.DoAfterOpen;
begin
  inherited;
  SpecialLog.Add( 'Hello world' );
end;

If you do not use this unit all works without loggig. If you use this unit as the LASt unit in your uses list (at least AFTER the DB uses) you do have logging for all datasets in that unit.