Question

I am walking a form’s control list and when I find a TPicture I want to change a property (image, but anything will do for an example).

How do I code that? It seems like TPciture and TControl are not compatible. Can I cast somehow?

---

Update:
when I add this code

for i:= 0 to Pred(designerForm.ControlCount) do
    if designerForm.Controls[i] is TPicture then
     MessageDlg('Picture : ' + designerForm.Controls[i].name, 
                               mtInformation, [mbOK], 0);

where designerForm is TForm, I go from zero to two errors in D7

[Error] PictureInspEditor.pas(121): Incompatible types: 'TPicture' and 'TControl'
[Fatal Error] E_logger.dpr(22): Could not compile used unit 'PictureInspEditor.pas'

Answer 1

Are you sure when you say TPicture maybe do you really want to say TImage?, anyway in any case first you must check if the current control is of the class which you want evaluate TImage (in this case) then you can cast in this way TImage(Controls[i])

check this sample for a TImage

var
  i  : Integer;
begin
  for i := 0 to ControlCount-1 do
    if Controls[i] is TImage then
     begin
       // do your stuff here 
       TImage(Controls[i]).Picture:=aValue;
     end;
end;

UPDATE
you can’t compare the TPicture class against the TControl using the is operator because the type of the TPicture is unrelated to the TControl.

from the Embarcadero documentation

The is Operator …..If the declared type of object is
unrelated to class – that is, if the
types are distinct and one is not an
ancestor of the other a compilation
error results