[Lazarus] how to get Type of Sender or Components[i] in order to Cast?

[Flávio Etrusco]

On Mon, Jul 27, 2015 at 6:37 AM, Mark Morgan Lloyd
<markMLl.lazarus at telemetry.co.uk> wrote:
> JuuS wrote:
>>
>> On 07/27/2015 09:31 AM, Mark Morgan Lloyd wrote:
>>>
>>> Péter Gábor wrote:
>>>>
>>>> Sorry!
>>>> I was "misreading" your mail... you want to know the type of them.
>>>>
>>>> You can compare the type of them:
>>>>
>>>> if Sender = TButton then { do something} ;
>>>
>>> Can this be elegantly put into a case statement?
>>>
>> Hi, I just tried it and no you can't. At least not directly, there may
>> be a way of casting the Sender object to ordinal or string but I'm not
>> sure that is efficient or elegant.
>
>
> I didn't think there was, but thought it worth asking. My use case is this
> sort of thing:
>
>         if MainForm.OutputComponent is TListBox then
>           with MainForm.ListBox1 do begin
>             Font.Name := fontName;
>             Font.Size := fontSize
>           end;
>         if MainForm.OutputComponent is TMemo then
>           with MainForm.Memo1 do begin
>             Font.Name := fontName;
>             Font.Size := fontSize
>           end;
>         ...
>
> Now obviously I could have a separate property holding an enumeration, but
> it's a pity that it's not possible to do something like
>
>         case MainForm.OutputComponent of
>           TListBox: begin end;
>           TMemo:    begin end;
>           ...
>         otherwise
>           // Fatal exception since this is a serious programming error
>         end;
>

If all you need to do is to change the Font you can also just use a
cracker class or use a bogus unchecked to e.g. TMemo (accompanied by
informative comments ;-) , since Font is declared in TControl.

Regards,
Flávio