signal and slots between two classes



  • I have two classes: signin and dialog. When I click a pushbutton on signin I want dialog to perform a slot. I have looked at forums and I believe I did the code correctly and I have no errors. However, when I try click the button nothing happens.

    signin.h

    #define SIGNIN_H
    
    #include <QDialog>
    
    namespace Ui {
    class signin;
    }
    
    class signin : public QDialog
    {
        Q_OBJECT
    
    public:
        explicit signin(QWidget *parent = 0);
        ~signin();
    
    signals:
        void clickedNextSignal();
    
    private:
        Ui::signin *ui;
    };
    
    #endif // SIGNIN_H
    

    signin.cpp

    #include "ui_signin.h"
    
    signin::signin(QWidget *parent) :
        QDialog(parent),
        ui(new Ui::signin)
    {
        ui->setupUi(this);
    
        connect(ui->nextButtonSignin, SIGNAL(clicked()),this,SIGNAL(clickedNextSignal()));
    }
    
    signin::~signin()
    {
        delete ui;
    }
    
    

    dialog.h

    #define DIALOG_H
    
    #include <QDialog>
    #include "signin.h"
    #include "ui_signin.h"
    
    namespace Ui {
    class Dialog;
    }
    
    class Dialog : public QDialog
    {
      Q_OBJECT
    
    public:
      explicit Dialog(QWidget *parent = 0);
      ~Dialog();
    
    public slots:
      void openBox();
    
    private:
      Ui::Dialog *ui;
    
    protected:
      signin *_signin;
    
    };
    
    #endif // DIALOG_H
    

    dialog.cpp

    #include "ui_dialog.h"
    #include <QMessageBox>
    
    Dialog::Dialog(QWidget *parent) :
        QDialog(parent),
        ui(new Ui::Dialog)
    {
        ui->setupUi(this);
    
        _signin = new signin(this);
    
        connect(_signin , SIGNAL(clickedNextSignal()),this,SLOT(openBox()));
    }
    
    void Dialog::openBox()
    {
        QMessageBox::information(this,tr("title"),tr("hi"));
    }
    
    Dialog::~Dialog()
    {
        delete ui;
    }
    

  • Qt Champions 2017

    Hi
    One thing I saw
    connect(ui->nextButtonSignin, SIGNAL(clicked()),this,SIGNAL(clickedNextSignal()));
    should have been SLOT in last.

    If possible, use the new syntax as it has more type checking

    connect( ui->nextButtonSignin, &QPushButton::clicked, this, &Dialog::clickedNextSignal);
    (If nextButtonSignin is QPushbutton)

    Hmm, there is something odd going on:
    signin has signal clickedNextSignal but you never call
    emit clickedNextSignal()
    so in Dialog::Dialog
    when you say
    connect(_signin , SIGNAL(clickedNextSignal()),this,SLOT(openBox()));
    Its correct but since signin do not emit (send) signal then nothing will happen.

    So if you add a slot to sign in, lets cal lit DoNext (bad name:)
    and hook it up to the button
    connect(ui->nextButtonSignin, SIGNAL(clicked()),this,SLOT(DoNext()));
    and in
    void DoNext() {
    emit clickedNextSignal();
    }
    Then the connect in Dialog should be more fun,
    So in short.
    NextButton clicked goes to signin slot that emit clickedNextSignal signal , that is hooked up to Dialog openBox().

    Hope it helps.



  • This post is deleted!

  • Qt Champions 2017

    @marlenet15
    Ok, as far as I know you cannot connect signal to signal but you can
    connect multiple signals to one slot.

    Did you place break point to see if the DoNext is called and
    also check in application output that none of the connets return fail.
    maybe even
    qDebug() << " result:" << connect(ui->nextButtonSignin, SIGNAL(clicked()),this,SLOT(DoNext())); for both connect to see
    if they are successful.



  • @mrjj I read from somewhere that you can have connect with two signals. I did try your recommendation but nothing happens.


  • Qt Champions 2017

    also how does you main.cpp look like ?

    You show the Dialog instead of mainwindow?



  • @mrjj

    #include "dialog.h"
    #include <QApplication>
    
    int main(int argc, char *argv[])
    {
        QApplication a(argc, argv);
        Dialog *w = new Dialog();
        w->showNormal();
    
        return a.exec();
    }``` 
    
    and yes I used Dialog instead of mainwindow

  • Qt Champions 2017

    @marlenet15 said:
    Hi I think the dialog in dialog mess up something.
    Didnt work for me if I new the sign dialog in Start dialog constructor.
    But it does work if I hooked it up outside.
    Have a look at this example
    https://www.dropbox.com/s/bvpps7qd8oovtjf/gonext.zip?dl=0
    Its the same idea but created slightly different.



  • @mrjj I followed your example but it is still not working.


  • Qt Champions 2017

    @marlenet15
    ??
    so the getnext example which runs here do no work when you compile it?



  • @mrjj ok it works. I redid my code using only QWidgets and it works. I think I know the problem and I forgot to mention it. I made QDialog a stacked widget and promoted the file signin.


  • Moderators

    @mrjj said:

    Ok, as far as I know you cannot connect signal to signal

    You can. See the documentation:

    You can connect as many signals as you want to a single slot, and a signal can be connected to as many slots as you need. It is even possible to connect a signal directly to another signal. (This will emit the second signal immediately whenever the first is emitted.)


  • Qt Champions 2017

    @JKSH
    Aha, that is news for me. so that is like a chain signal or almost like an alias.

    @marlenet15
    Super. not sure what the real reason was but as long as it works :)



  • @mrjj Before creating the stackedwidget it worked. After adding it, it doesn't work anymore.


  • Qt Champions 2017

    @marlenet15
    Ok. do you promote a qDialog to a stackwidget ?
    Not sure I fully understand.
    At least I have never tried that.



  • @mrjj on the .ui file of the class dialog, I created a stackedwidget and promoted the file signin.h


  • Qt Champions 2017

    @marlenet15
    so the signin dialog was sort of inline to Dialog ?



  • @mrjj can you exaplain what you mean by that? Sorry


  • Qt Champions 2017

    @marlenet15
    Hi np.
    Im not 100% sure what you did.
    If you promote a widget to a dialog.
    the dialog will be sort of inside the parent/widget that contains the
    promoted widget.
    So I wondered if you promoted a stacked widget to the signin dialog ?



  • @mrjj I created a stackedwidget in dialog.ui, in there I promoted signin.h into the stackedwidget.


  • Qt Champions 2017

    ahh that way. Hmm should be the same as using a plain qwidget but seems it was not.

    Can I ask what kind of design u are after ?
    like sort of custom wizard style thing ?



  • @mrjj yes I am. I am doing something simple now in order to understand how it works so that later I can use it so that when i click the button, it goes to the next page.


  • Qt Champions 2017

    @marlenet15
    Ok. but you want it to be standalone Dialogs or pages in a stacked widget ?
    or you want to use UI files that you promote into the stacked widget?



  • @mrjj pages in a stackedwidget. I figured it out how to make it work through code but I am having a difficult time make it work only through Qt Designer/.ui file


  • Qt Champions 2017

    @marlenet15
    Ok. well I think such wizard do need code if not just a Dialog with a stacked widget and the the Next button outside of the stacked.



  • @marlenet15 @mrjj

    You can connect 2 signals.


  • Qt Champions 2017

    @koahnig
    yeah but not sure how it helps ?
    Can you explain more about the setup?



  • @mrjj

    Instead of the SLOT macro you use another SIGNAL macro.

     bool boo = connect (ptrFirst, SIGNAL (mySigFirst() ), this, SIGNAL ( newSignal() ) );
    

    That is useful when you simply have to pass on a signal. It saves you to create a slot in your class which simply is emitting a signal.

    the text in the signal & slot explanatory part below the graph and shortly before the heading Signals is
    You can connect as many signals as you want to a single slot, and a signal can be connected to as many slots as you need. It is even possible to connect a signal directly to another signal. (This will emit the second signal immediately whenever the first is emitted.)

    In the form of the example above I have used it already.


  • Lifetime Qt Champion

    @mrjj It's called signal forwarding. It's used mainly to avoid creating slots that just re-emits the same signal one class upper.


  • Qt Champions 2017

    Thank you :)
    I can see it gives cleaner code if a slot is not really needed.


  • Moderators

    @marlenet15 said:

    @mrjj I created a stackedwidget in dialog.ui, in there I promoted signin.h into the stackedwidget.

    Your code shows that signin inherits QDialog, not QStackedWidget. So, I don't think you can promote a QStackedWidget to a Signin... Did you change your C++ code after you added QStackedWidget?

    so that later I can use it so that when i click the button, it goes to the next page.

    I suggest using QWizard, not a QStackedWidget


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