connect to PushButton in another class: object missing in reference

[homerun4711]

Ok, it works. Thank you for your answer and the explanation.

Is it common, that in such a case the connect-statement appears directly
after the creation of the object? E.g.

AddressBook *customerlist = new AddressBook();
connect(customerlist->addCustomerButton ,SIGNAL(clicked()), this, SLOT(newcustomer()));

AddressBook *customerlist = new AddressBook();
connect(customerlist->addCustomerButton ,SIGNAL(clicked()), this, SLOT(newcustomer()));

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I tried to connect the button in the constructor of MainWindow together with all the
filemenu-toolbar-action-stuff, but the QDialog "AddressBook* newcustomer" is not present at that time,
because it is opened by the user later. So I guess it its not possible to connect it before, in
case if there will be an exiting object, or am I wrong?