Example of calling a function to parent?

SGaist

Hi,

The Qt documentation contains quite a lot of examples using signals and slots. You should go through the ones from the widgets module since it's the one you are implementing your application with.

Panoss

@SGaist said in Example of calling a function to parent?:

The Qt documentation contains quite a lot of examples using signals and slots

Didn't find a full working example, only fragments of code I 'm trying to put together.
If you have found a full working example please post it!

SGaist

Here you have the full list of the widgets examples.

Panoss

@SGaist impressive selection of examples, I confess I had not discovered it!
But reading their description I see nothing that suits my needs (two classes (Forms) communicating with Signals and Slots)

Panoss

Ok, let me show you what I tried so far:

In my FormB 's class declaration added:

public slots:
    void setValue(int value);
signals:
    void valueChanged(int newValue);

Am I on the correct way?

SGaist

These lines are to be found in the class declaration.

Panoss

Yes you 're right, I corrected it!

Panoss

And this is the function in my FormB: ()

void FormB::setValue(int value)
{       
        emit valueChanged(value);   
}

Correct?

Panoss

And now this:

QObject::connect(&a, &Counter::valueChanged,
                     &b, &Counter::setValue);

I modified it to (this code is in the constructor of FormB):

connect(&parent, &parent::valueChanged,
                         this, &FormB::setValue);

???
It's wrong...The 'parent' I mean.
The sender is FormB...so..

mpergand

@Panoss
Everything is upside down :)

let's recap, you want the main window (formA) to be inform when a value has changed in second window (formB)

The main window register to receive a signal from the second window.

In formA:

connect(formB, &FormB::valueChanged, this , &FormA::valueChangedInFormB);

Panoss

@mpergand it works!!!
Thank you all!

The actual name of FormA is 'ArticlesWindow' and of FormB 'positionsForm'.
(FormB is the sender)
I post the code in case someone needs it:

articleswindow.h
private slots:    
    void positionChanged();

articleswindow.cpp
void ArticlesWindow::positionChanged(){
    qDebug() << "ArticlesWindow::positionChanged";
}
void ArticlesWindow::openPositionsForm(){    
    class positionsForm *form = new class positionsForm(model, this);
    connect(form, &positionsForm::valueChanged, this , &ArticlesWindow::positionChanged);

And:

positionsform.h
  public slots:
    void setValue(int value);

  signals:
    void valueChanged(int newValue);

positionsform.cpp
 void positionsForm::setValue(int value)
 {          
   emit valueChanged(value);    
 }

Panoss

It works but the message is printed twice, like if function ArticlesWindow::positionChanged is called twice??

mpergand

@Panoss

class positionsForm *form = new class positionsForm(model, this);

What is that ?

You seem to create an new instance each time openPositionsForm() is called ...

Panoss

Why is this wrong?
Every time I want to open the form I create an instance of it 's class.
When I close the form the instance is destroyed, right?

What 's the correct way?

mpergand

@Panoss
Add sender() and look if it's different objects
qDebug() << "ArticlesWindow::positionChanged"<<sender();

jsulm

@Panoss said in Example of calling a function to parent?:

Every time I want to open the form I create an instance of it 's class.

Do you also delete the instance when you do not need it anymore?

mpergand

@jsulm said in Example of calling a function to parent?:

@Panoss said in Example of calling a function to parent?:

Every time I want to open the form I create an instance of it 's class.

Do you also delete the instance when you do not need it anymore?

That's what @Panoss should find out for himself by looking at the sender() on multiple messages.

Panoss

@mpergand said in Example of calling a function to parent?:

@Panoss
Add sender() and look if it's different objects
qDebug() << "ArticlesWindow::positionChanged"<<sender();

This is the output:

updateParent called!!
ArticlesWindow::positionChanged positionsForm(0x5de4a24160, name = "positionsForm")
updateParent called!!
ArticlesWindow::positionChanged positionsForm(0x5de4a24160, name = "positionsForm")

JonB

@Panoss said in Example of calling a function to parent?:

When I close the form the instance is destroyed, right?

No, that depends on what you mean/do by "close". And we don't see that in your shown code?

It works but the message is printed twice, like if function ArticlesWindow::positionChanged is called twice??

Does the "twice" happen from the very first time you create the form or after a second open? Are the number calls equal to the number of times you create the form? If it stays at "twice" always, that alters what i would look for in the code.

Panoss

@jsulm said in Example of calling a function to parent?:

@Panoss said in Example of calling a function to parent?:

Every time I want to open the form I create an instance of it 's class.

Do you also delete the instance when you do not need it anymore?

When I close the form instance (clicking on the close button or with form->close) doesn't it get deleted?

e.g. with this code:

void addArticle::on_cancelButton_clicked()
{
    this->close();
}