TRttiProperty.GetValue(TMemo) for CaretPosition raises 'Invalid class typecast' exception.

[dmitrybv 3]

Hello.

The following code throws an 'Invalid class typecast' exception.

 

procedure TForm1.Button1Click(Sender: TObject);
var
  RttiContext: TRttiContext;
  LType: TRttiType;
  ACaretPositionProp: TRttiProperty;
  Val: TValue;
begin
  RttiContext := TRttiContext.Create;
  LType := RttiContext.GetType(TMemo);
  ACaretPositionProp := LType.GetProperty('CaretPosition');
  Val := ACaretPositionProp.GetValue(Memo1);
end;

 

Although it shouldn't.

 

Place a TMemo and a TButton on a Form and write the Button.OnClick event as described above.

 

Embarcadero® RAD Studio 12 Version 29.0.53571.9782

 Delphi 12 Update 2.

[Rollo62 534]

Try this, untested
 

uses
  System.Rtti, System.SysUtils, Vcl.StdCtrls;

procedure TForm1.Button1Click(Sender: TObject);
var
  RttiContext: TRttiContext;
  LType: TRttiType;
  ACaretPositionProp: TRttiProperty;
  Val: TValue;
  CaretPos: TPoint;
begin
  RttiContext := TRttiContext.Create;
  try
    LType := RttiContext.GetType(TMemo.ClassType);
    ACaretPositionProp := LType.GetProperty('CaretPosition');
    if Assigned(ACaretPositionProp) then
    begin
      Val := ACaretPositionProp.GetValue(Memo1);
      if Val.IsType<TPoint> then // Check if the value is of type TPoint (which is compatible with TCaretPosition)
      begin
        CaretPos := Val.AsType<TPoint>;
        ShowMessage(Format('Caret Position: X=%d, Y=%d', [CaretPos.X, CaretPos.Y]));
      end
      else
        ShowMessage('CaretPosition property is not of type TPoint.');
    end
    else
      ShowMessage('CaretPosition property not found.');
  finally
    RttiContext.Free;
  end;
end;

 

Edited November 7 by Rollo62

[dmitrybv 3]

8 hours ago, Rollo62 said:

Try this, untested
 

uses
  System.Rtti, System.SysUtils, Vcl.StdCtrls;

procedure TForm1.Button1Click(Sender: TObject);
var
  RttiContext: TRttiContext;
  LType: TRttiType;
  ACaretPositionProp: TRttiProperty;
  Val: TValue;
  CaretPos: TPoint;
begin
  RttiContext := TRttiContext.Create;
  try
    LType := RttiContext.GetType(TMemo.ClassType);
    ACaretPositionProp := LType.GetProperty('CaretPosition');
    if Assigned(ACaretPositionProp) then
    begin
      Val := ACaretPositionProp.GetValue(Memo1);
      if Val.IsType<TPoint> then // Check if the value is of type TPoint (which is compatible with TCaretPosition)
      begin
        CaretPos := Val.AsType<TPoint>;
        ShowMessage(Format('Caret Position: X=%d, Y=%d', [CaretPos.X, CaretPos.Y]));
      end
      else
        ShowMessage('CaretPosition property is not of type TPoint.');
    end
    else
      ShowMessage('CaretPosition property not found.');
  finally
    RttiContext.Free;
  end;
end;

 

Exception: Project TestDemo.exe raised exception class EInvalidCast with message 'Invalid class typecast'.

On the line: 

      Val := ACaretPositionProp.GetValue(Memo1);