Ako imas instancu mydialog forme onda mozes preko metoda mydialog->findChild(QString name);
Samo moras dati ime objektu textlabel.
Ovo vazi za QT 4.1.

Dokumentacija:

T QObject::findChild ( const QString & name = QString() ) const
Returns the child of this object that can be casted into type T and that is called name, or 0 if there is no such object. An empty string matches all object names. The search is performed recursively.
If there is more than one child matching the search, the most direct ancestor is returned. If there are several direct ancestors, it is undefined which one will be returned. In that case, findChildren() should be used.
This example returns a child QPushButton of parentWidget named "button1":
QPushButton *button = parentWidget->findChild<QPushButton *>("button1");
This example returns a QListWidget child of parentWidget:
QListWidget *list = parentWidget->findChild<QListWidget *>();
Warning: This function is not available with MSVC 6. Use qFindChild() instead if you need to support that version of the compiler.
See also findChildren() and qFindChild().

imao sam problema sa netom u zadnja 3 dana pa nisam mogao da odgovorim...

Ja imam qt 3.3.6, Jel' je jedini nacin da ovo sredim da nabavim qt 4.1?

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Sto se tice pristupanja kontroli u dijalogu, ja sam odavno prestao da ih proglasavam za private, ovo nema mnogo smisla, ne sluzi nicemu, a moze da proizvede probleme u ovakvim situacijama, jer dijalog nije tipicna klasa u kojoj moramo da vodimo racuna o tome koji clan je public, protected ili private.