Question

I need to loop through Components and assign an event handler (for example Dynamically assigning OnClick event for all TButton to

ShowMessage('You clicked on ' + (Sender as TButton).Name);

The problem is that in some cases I already assigned the TButton OnClick event.

Is there a way to solve the problem?

Let’s imagine I have Button1 for which the harcoded onclick event handler is:

ShowMessage('This is Button1');

After my “parsing” I would like that the full event handler for Button1 becomes:

ShowMessage('This is Button1'); // design time event handler code
ShowMessage('You clicked on ' + (Sender as TButton).Name); // runtime added

Note: I am looking for a soliution that allows me to use TButton as it is without inheriting from it.

Answer 1

you could look for an assignment of OnClick before overwriting it, persist this and use it in your new handler – basically chaining the events.

Something like this:

  var original : TNotifyEvent;

  original := Component.OnClick;
  Component.OnClick := NewMethod;

and then in your NewMethod:

  if assigned(original) then original(Sender);

you’ll likely not want a single original variable but instead hold a collection keyed on the component.