How to use TValue.AsType <TNotifyEvent>?

Question

I am trying to use RTTI to add an event handler to a control that can already have an event handler installed. The code looks something like this:

var
  prop: TRttiProperty;
  val: TValue;
begin
  prop := FContext.GetType(MyControl.ClassInfo).GetProperty('OnChange');
  val := prop.GetValue(MyControl);
  FOldOnChange := val.AsType<TNotifyEvent>;
  prop.SetValue(MyControl, TValue.From<TNotifyEvent>(self.MyOnChange));
end;

I want this to be possible in MyOnChange:

begin
  if assigned(FOldOnChange) then
    FOldOnChange(Sender);
  //additional code here
end;

Unfortunately, the compiler is not like a string FOldOnChange := val.AsType<TNotifyEvent>;. It says:

E2010 Incompatible types: 'procedure, untyped pointer or untyped parameter' and 'TNotifyEvent "

Does anyone know why this is or how to fix it? It seems to me...

Answer 1

FOldOnChange , AsType<TNotifyEvent> - . , . , () , , FOldOnChange.

:

uses SysUtils, Rtti;

type
  TEv = procedure(Sender: TObject) of object;

  TObj = class
  private
    FEv: TEv;
  public
    property Ev: TEv read FEv write FEv;
    class procedure Meth(Sender: TObject);
  end;

class procedure TObj.Meth(Sender: TObject);
begin
end;

procedure P;
var
  ctx: TRttiContext;
  t: TRttiType;
  p: TRttiProperty;
  v: TValue;
  o: TObj;
  e: TEv;
begin
  t := ctx.GetType(TObj);
  p := t.GetProperty('Ev');
  o := TObj.Create;
  try
    // Set value explicitly
    o.Ev := TObj.Meth;
    // Get value via RTTI
    v := p.GetValue(o);
    //e := v.AsType<TEv>; // doesn't work
    e := v.AsType<TEv>(); // works
  finally
    o.Free;
  end;
end;

begin
  try
    P;
  except
    on e: Exception do
      Writeln(e.Message);
  end;
end.

Answer 2

RTTI, 2010 , RTTI TypInfo ( ). TypInfo TMethod. ():

var 
  prop: TRttiProperty;
  val: TValue;
  evt: TNotifyEvent;
begin
  prop := FContext.GetType(MyControl.ClassInfo).GetProperty('OnChange');
  val := prop.GetValue(MyControl);
  TMethod(FOldOnChange) := val.AsType<TMethod>;
  evt := Self.MyOnChange;
  prop.SetValue(MyControl, TValue.From<TMethod>(TMethod(evt));
end;