How do I pass an event as a function parameter? - delphi

Question

I have a form that has a list of useful procedures that I have created, that I often use in every project. I am adding a procedure that makes it simple to add a click-able image over where would be the TAccessory of a TListBoxItem. The procedure intakes the ListBox currently, but I would also need it to intake which procedure to call for the OnClick Event for the image.. Here is my existing code:
function ListBoxAddClick(ListBox:TListBox{assuming I need to add another parameter here!! but what????}):TListBox;
var
i : Integer;
Box : TListBox;
BoxItem : TListBoxItem;
Click : TImage;
begin
i := 0;
Box := ListBox;
while i <> Box.Items.Count do begin
BoxItem := Box.ListItems[0];
BoxItem.Selectable := False;
Click := Timage.Create(nil);
Click.Parent := BoxItem;
Click.Height := BoxItem.Height;
Click.Width := 50;
Click.Align := TAlignLayout.alRight;
Click.TouchTargetExpansion.Left := -5;
Click.TouchTargetExpansion.Bottom := -5;
Click.TouchTargetExpansion.Right := -5;
Click.TouchTargetExpansion.Top := -5;
Click.OnClick := // this is where I need help
i := +1;
end;
Result := Box;
end;
The desired procedure would be defined in the form that is calling this function.

Answer 1

Since the OnClick event is of type TNotifyEvent you should define a parameter of that type. Look at this (I hope self-explaining) example:
type
TForm1 = class(TForm)
Button1: TButton;
ListBox1: TListBox;
procedure Button1Click(Sender: TObject);
private
procedure TheClickEvent(Sender: TObject);
end;
implementation
procedure ListBoxAddClick(ListBox: TListBox; OnClickMethod: TNotifyEvent);
var
Image: TImage;
begin
Image := TImage.Create(nil);
// here is assigned the passed event method to the OnClick event
Image.OnClick := OnClickMethod;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
// here the TheClickEvent event method is passed
ListBoxAddClick(ListBox1, TheClickEvent);
end;
procedure TForm1.TheClickEvent(Sender: TObject);
begin
// do something here
end;