Accessing objects in different forms

[Lebowski]

Hello. I have a very basic question.

Let's say I created 2 forms in designer: FormA and FormB. I've added push button named Button into FormA and set it to disbale by default. Now I would like to enable it from FormB. How do I do that? If it was in same form it would be simply Button->setEnabled (TRUE);
How do I do it if it's in different form?

Thanx in advance.

[munna]

you should be using signal and slot for this.

connect(formAButton,SIGNAL(pressed()),formB,SLOT(enableButton()));

connect(formAButton,SIGNAL(pressed()),formB,SLOT(enableButton()));

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[Lebowski]

But I don't want to make another button just to change one property. Is there any other way?

[munna]

In that case u need to have a reference of your formA in formB and then call a function in formB from formA which will actually enable the button.

Example:

In formB

formA->enableButton()

formA->enableButton()

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In formA

void FormA::enableButton()
{
     button->setEnabled(true);
}

void FormA::enableButton()
{
     button->setEnabled(true);
}

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[wysota]

It doesn't have to be a button. It has to be a signal

For example:

class SomeClass : public QObject{
Q_OBJECT
public:
  SomeClass(QObject *p=0) : QObject(p){}
  void someMethod(){ if(something>10) emit someButtonEnableStateChanged(something==20); }
signals:
  void someButtonEnableStateChanged(bool);
};
//...
SomeClass *sc = new SomeClass(this);
connect(sc, SIGNAL(someButtonEnableStateChanged(bool)), someotherForm->button78, SLOT(setEnabled(bool)));

class SomeClass : public QObject{
Q_OBJECT
public:
  SomeClass(QObject *p=0) : QObject(p){}
  void someMethod(){ if(something>10) emit someButtonEnableStateChanged(something==20); }
signals:
  void someButtonEnableStateChanged(bool);
};
//...
SomeClass *sc = new SomeClass(this);
connect(sc, SIGNAL(someButtonEnableStateChanged(bool)), someotherForm->button78, SLOT(setEnabled(bool)));

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Better yet, that class which owns the button should have some slot which will handle those changes and the "source" class should just emit signals like "myStateChanged" and not "pleaseChangeTheStateOfSomeOfTheButtonsOfYours ".

Of course another way is to ignore signals and slots and store a pointer to that button in the class which is to manipulate it.

[Lebowski]

For this code

formA->enableButton()

formA->enableButton()

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I'm getiing "error: expected unqualified-id before ‘->’ token"

[munna]

I suggest you use the method wysota has suggested. I think it a cleaner way to accomplish your task.

If you still want to use the other way and know what the error is, can you please show us your code ?

[Lebowski]

In povezava.ui.h I have:

void Povezava::Connect_clicked()
{
      .
      .
      .
      GlavnoO->enable_lista_tabel();
      close();
 
    };

void Povezava::Connect_clicked()
{
      .
      .
      .
      GlavnoO->enable_lista_tabel();
      close();
	
    };

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In GlavnoO.ui.h I have:

void GlavnoO::enable_lista_tabel()
    {
    lista_tabel->setEnabled(true);
    };

void GlavnoO::enable_lista_tabel()
    {
    lista_tabel->setEnabled(true);
    };

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[Lebowski]

I think I know where the problem is: GlavnoO is class while I would need to call object of that class. The problem is that I have that object defined in main.cpp and I don't know how to include it.

[jacek]

The problem is that I have that object defined in main.cpp and I don't know how to include it.

You can use signals and slots mechanism to connect those two objects.

[Lebowski]

I already have a slot defined:

void GlavnoO::enable_lista_tabel()
          {
          lista_tabel->setEnabled(true);
          };

void GlavnoO::enable_lista_tabel()
          {
          lista_tabel->setEnabled(true);
          };

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How do I create signal in designer? Just adding it in Object Explorer doesn't generate anything really. And adding it to .h file in ".ui/" folder won't work cause all changes there are being ignored.

[jacek]

How do I create signal in designer? Just adding it in Object Explorer doesn't generate anything really.

You don't implement signals --- it's enough to declare them within class definition (the rest will be handled by moc).

Then just write:

emit someSignal( someParameter );

emit someSignal( someParameter );

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And adding it to .h file in ".ui/" folder won't work cause all changes there are being ignored.

Then try the subclassing approach: http://doc.trolltech.com/3.3/designer-manual-6.html

[Lebowski]

You don't implement signals --- it's enough to declare them within class definition (the rest will be handled by moc).

Then just write:

emit someSignal( someParameter );

emit someSignal( someParameter );

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Is it enough to just write that line of code in (for example) my povezava.ui.h file within some function (slot)?

[jacek]

Is it enough to just write that line of code in (for example) my povezava.ui.h file within some function (slot)?

Yes, if you have declared that signal in the Designer. Of course you will also have to make the connection.

[Lebowski]

Signal and slot are now working ok. Thanx for help.

Where do I make connection though? In main.cpp? Cause QT Designer's wizard only allows creation of connections within same form.

[jacek]

Where do I make connection though? In main.cpp? Cause QT Designer's wizard only allows creation of connections within same form.

You will have to create the connection by hand. The best place to do it is the one where you have an easy access to both objects, in your case this might be the main() function.

[Lebowski]

It works!!! Thanx a lot
Btw in connect I had to use '&' character in front of object names. What does that mean? Does it mean memory address of that object maybe?

[wysota]

Yes. Connect needs pointers.