Qt4 parent pointer usage - qt

Question

I'm having some problem with understanding usage of parent pointer in QT4.
class firstClass : public QWidget
{
Q_OBJECT
public:
firstClass(QWidget *parent = 0);
~firstClass();
void doSomething();
private:
secondClass * myClass;
};
class secondClass : public QWidget
{
Q_OBJECT
public:
secondClass(QWidget *parent = 0);
void doSomethingElse();
};
I want to call doSomething() method while running doSomethingElse(). Is there any way to do it using parent pointer?
I tried parent->doSomething() but it doesn't work. It seems that Qt Creator is suggesting only methods from QObject class after parent->.
On the other hand I can't write it like secondClass(firstClass *parent = 0); - compilator returns error:
Thanks for any suggestions.

Answer 1

If you are positive that the parent of secondClass is always going to be firstClass then you can do this:
static_cast<firstClass *>(parent)->doSomething();
Alternatively you can use qobject_cast and check to make sure that parent is actually an instance of firstClass:
firstClass *myParent = qobject_cast<firstClass *>(parent);
if(myParent){
myParent->doSomething();
}

Answer 2

The more Qt-ish way to do this would be to use signals and slots, instead of trying to directly call a different function.
class firstClass : public QWidget
{
Q_OBJECT
public:
firstClass(QWidget *parent = 0);
~firstClass();
public slot:
void doSomething();
private:
secondClass * myClass;
};
class secondClass : public QWidget
{
Q_OBJECT
public:
secondClass(QWidget *parent = 0);
void doSomethingElse()
{
// ...
emit ( triggerDoSomething() );
// ...
}
signal:
void triggerDoSomething();
};
firstClass::firstClass(QWidget *parent) :
QWidget(parent), myClass(new secondClass(this))
{
// ...
bool connected = connect(myClass, SIGNAL(triggerDoSomething()),
SLOT(doSomething()));
assert( connected );
}