Skip to content
  • Categories
  • Recent
  • Tags
  • Popular
  • Users
  • Groups
  • Search
  • Get Qt Extensions
  • Unsolved
Collapse
Brand Logo
  1. Home
  2. Qt Development
  3. General and Desktop
  4. Can you create slots in main.cpp file?
Forum Updated to NodeBB v4.3 + New Features

Can you create slots in main.cpp file?

Scheduled Pinned Locked Moved Solved General and Desktop
threadconnectionslotssignals
20 Posts 5 Posters 5.7k Views 3 Watching
  • Oldest to Newest
  • Newest to Oldest
  • Most Votes
Reply
  • Reply as topic
Log in to reply
This topic has been deleted. Only users with topic management privileges can see it.
  • P ples76

    I have a project that all the widgets are created in the main.cpp file main() function. I have a worker thread that is emitting a signal to the main thread to change the background color of the widget created by main function. Here is an example

    QObject::connect(serialThread, SIGNAL(setReady(QString)), statusWidget, SLOT(setStyleSheet("background-color:gray")));
    

    When running the program I get an error that says the connection could not be made with the above code.

    I have also created connections to change text:

    QObject::connect(serialThread, SIGNAL(setReady(QString)), myStatusText, SLOT(setText(QString)));
    

    Neither of these are working. I do know the signals are probably being emitted because I have other signals fired at the same time which is going to another worker thread and I can see those working. I have tried creating a main.h file and adding slots to that and the main.cpp file and just having the connections fire the SLOTS but the compilers says I can't declare the slots after the main() function in the main.cpp file. Is there any way I can achieve what I am trying to do?

    Pablo J. RoginaP Offline
    Pablo J. RoginaP Offline
    Pablo J. Rogina
    wrote on last edited by
    #9

    @ples76 said in Can you create slots in main.cpp file?:

    I have a project that all the widgets are created in the main.cpp file main() function

    Did you inherit the project with such way of creating Qt widgets, or just you started it that way?

    QObject::connect(serialThread, SIGNAL(setReady()),statusWidget, statusWidget->void{statusWidget->setStyleSheet("background-color:gray;");});

    As @Christian-Ehrlicher already suggested, please use the new syntax for signal & slots...

    Upvote the answer(s) that helped you solve the issue
    Use "Topic Tools" button to mark your post as Solved
    Add screenshots via postimage.org
    Don't ask support requests via chat/PM. Please use the forum so others can benefit from the solution in the future

    1 Reply Last reply
    1
    • P Offline
      P Offline
      ples76
      wrote on last edited by
      #10

      I inherited the base of the project. I am trying to add some functionality.

      As for using the new syntax I was under the understanding that pr QT 5.0 I couldn't use the new syntax. Is my understanding incorrect? I am using QT 4.8.7

      1 Reply Last reply
      0
      • Christian EhrlicherC Online
        Christian EhrlicherC Online
        Christian Ehrlicher
        Lifetime Qt Champion
        wrote on last edited by
        #11

        If you can't use qt5 you have to define a custom slot and call the function with the correct parameter there since you can't mix old style connect and lambdas.

        Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
        Visit the Qt Academy at https://academy.qt.io/catalog

        1 Reply Last reply
        3
        • P Offline
          P Offline
          ples76
          wrote on last edited by
          #12

          Christian,
          I was afraid that was the case. Do you know where I could locate an example of this. The problem I am having is I have found several examples of creating custom slots but they are all in classes outside of main. I have the issue of the widgets being created in the main function. Is it possible to create a custom slot that can be used in main and thus have the widget in scope?
          This is my first project in qt and I am trying to find the easiest solution to this since I am under the gun to get this done asap.

          1 Reply Last reply
          0
          • Christian EhrlicherC Online
            Christian EhrlicherC Online
            Christian Ehrlicher
            Lifetime Qt Champion
            wrote on last edited by
            #13

            A slot must be in a class, you have no other chance.

            Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
            Visit the Qt Academy at https://academy.qt.io/catalog

            1 Reply Last reply
            1
            • P Offline
              P Offline
              ples76
              wrote on last edited by
              #14

              Thank you for your patience with my small amount of knowledge on the subject. I appreciate the help and clarification on my issue. I think my best choice of action is to try and move my code out of main and maybe create a QMainWindow class and see if everything will work that way. Do you think this is my best choice of action or will I possibly run into issues in a QMainWindow class also. I am not speaking about other code in main but specifically about the connections mentioned in this thread. Basically I am asking if am able to move the code to a QMainWindow Class will I then be able to create custom slots to achieve my goal?

              Pablo J. RoginaP 1 Reply Last reply
              0
              • P ples76

                Thank you for your patience with my small amount of knowledge on the subject. I appreciate the help and clarification on my issue. I think my best choice of action is to try and move my code out of main and maybe create a QMainWindow class and see if everything will work that way. Do you think this is my best choice of action or will I possibly run into issues in a QMainWindow class also. I am not speaking about other code in main but specifically about the connections mentioned in this thread. Basically I am asking if am able to move the code to a QMainWindow Class will I then be able to create custom slots to achieve my goal?

                Pablo J. RoginaP Offline
                Pablo J. RoginaP Offline
                Pablo J. Rogina
                wrote on last edited by
                #15

                @ples76 said in Can you create slots in main.cpp file?:

                move my code out of main and maybe create a QMainWindow class

                I was about to suggest something similar, but to subclass QApplication. So to move all the widgets instantiation there, and since your MySuperDuperQApplication class is an QObject you should be able to work with custom slots as suggested.

                I have the issue of the widgets being created in the main function

                Just in case, could it it be possible you show the source code for the main() ?

                Upvote the answer(s) that helped you solve the issue
                Use "Topic Tools" button to mark your post as Solved
                Add screenshots via postimage.org
                Don't ask support requests via chat/PM. Please use the forum so others can benefit from the solution in the future

                1 Reply Last reply
                1
                • P Offline
                  P Offline
                  ples76
                  wrote on last edited by ples76
                  #16
                  This post is deleted!
                  Pablo J. RoginaP 1 Reply Last reply
                  0
                  • Christian EhrlicherC Online
                    Christian EhrlicherC Online
                    Christian Ehrlicher
                    Lifetime Qt Champion
                    wrote on last edited by
                    #17

                    All this stuff should not be in main - this is really bad style. This should all go into the ctor of 'window' since this is the place where this all should happen.

                    Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
                    Visit the Qt Academy at https://academy.qt.io/catalog

                    1 Reply Last reply
                    2
                    • P ples76

                      This post is deleted!

                      Pablo J. RoginaP Offline
                      Pablo J. RoginaP Offline
                      Pablo J. Rogina
                      wrote on last edited by
                      #18

                      @ples76

                      This should all go into the ctor of 'window' since this is the place where this all should happen.

                      Yes, I agree with @Christian-Ehrlicher suggestion. Although you inherit the project that way, it seems there's no reason to continue that bad approach.

                      Your main() code should be reduced to something like this:

                      int main(int argc, char **argv)
                      {
                          QApplication a(argc, argv);
                          QWidget window;
                          window.show();
                          return a.exec();
                      }
                      

                      Upvote the answer(s) that helped you solve the issue
                      Use "Topic Tools" button to mark your post as Solved
                      Add screenshots via postimage.org
                      Don't ask support requests via chat/PM. Please use the forum so others can benefit from the solution in the future

                      1 Reply Last reply
                      2
                      • P Offline
                        P Offline
                        ples76
                        wrote on last edited by ples76
                        #19

                        I have solved the problem with all of your help Specifically LeLev who gave me the final working solution through PM. I created a QWidget class for my statusWidget. I added the following in the StatusWidget.h file:

                        #ifndef STATUSWIDGET_H
                        #define STATUSWIDGET_H
                        
                        #include <QtCore>
                        #include <QWidget>
                        #include <QLabel>
                        
                        
                        
                        
                        class StatusWidget : public QWidget {
                          Q_OBJECT;
                        
                          public:
                            StatusWidget(QWidget *parent = 0);
                            ~StatusWidget();
                        
                          public slots:
                            void setBgColor(QString);
                        };
                        
                        #endif
                        

                        And the StatusWidget.cpp file:

                        #include <ctime>
                        #include <stdint.h>
                        #include "StatusWidget.h"
                        
                        
                        #include <QtCore>
                        #include <QWidget>
                        
                        
                        
                        StatusWidget::StatusWidget(QWidget *parent) : QWidget(parent)
                        {
                        }
                        StatusWidget::~StatusWidget()
                        {
                        }
                        
                        
                        void StatusWidget::setBgColor(QString color) {
                          this->setStyleSheet("background-color:" + color + ";");
                        }
                        

                        I then changed my connections to the following:

                        QObject::connect(serialThread, SIGNAL(setReady(QString)),statusWidget, SLOT(setBgColor(QString)));
                        QObject::connect(serialThread, SIGNAL(setReading(QString)), statusWidget, SLOT(setBgColor(QString)));
                        QObject::connect(serialThread, SIGNAL(setReReading(QString)), statusWidget, SLOT(setBgColor(QString)));
                        QObject::connect(serialThread, SIGNAL(setPass(QString)), statusWidget, SLOT(setBgColor(QString)));
                        QObject::connect(serialThread, SIGNAL(setFail(QString)), statusWidget, SLOT(setBgColor(QString)));
                        

                        I can now change my background color accordingly. Thank you all for your help!!!

                        Pablo J. RoginaP 1 Reply Last reply
                        0
                        • P ples76

                          I have solved the problem with all of your help Specifically LeLev who gave me the final working solution through PM. I created a QWidget class for my statusWidget. I added the following in the StatusWidget.h file:

                          #ifndef STATUSWIDGET_H
                          #define STATUSWIDGET_H
                          
                          #include <QtCore>
                          #include <QWidget>
                          #include <QLabel>
                          
                          
                          
                          
                          class StatusWidget : public QWidget {
                            Q_OBJECT;
                          
                            public:
                              StatusWidget(QWidget *parent = 0);
                              ~StatusWidget();
                          
                            public slots:
                              void setBgColor(QString);
                          };
                          
                          #endif
                          

                          And the StatusWidget.cpp file:

                          #include <ctime>
                          #include <stdint.h>
                          #include "StatusWidget.h"
                          
                          
                          #include <QtCore>
                          #include <QWidget>
                          
                          
                          
                          StatusWidget::StatusWidget(QWidget *parent) : QWidget(parent)
                          {
                          }
                          StatusWidget::~StatusWidget()
                          {
                          }
                          
                          
                          void StatusWidget::setBgColor(QString color) {
                            this->setStyleSheet("background-color:" + color + ";");
                          }
                          

                          I then changed my connections to the following:

                          QObject::connect(serialThread, SIGNAL(setReady(QString)),statusWidget, SLOT(setBgColor(QString)));
                          QObject::connect(serialThread, SIGNAL(setReading(QString)), statusWidget, SLOT(setBgColor(QString)));
                          QObject::connect(serialThread, SIGNAL(setReReading(QString)), statusWidget, SLOT(setBgColor(QString)));
                          QObject::connect(serialThread, SIGNAL(setPass(QString)), statusWidget, SLOT(setBgColor(QString)));
                          QObject::connect(serialThread, SIGNAL(setFail(QString)), statusWidget, SLOT(setBgColor(QString)));
                          

                          I can now change my background color accordingly. Thank you all for your help!!!

                          Pablo J. RoginaP Offline
                          Pablo J. RoginaP Offline
                          Pablo J. Rogina
                          wrote on last edited by
                          #20

                          @ples76 said in Can you create slots in main.cpp file?:

                          I have solved the problem with all of your help

                          Great, so please don't forget to mark your post as solved!

                          I am trying to find the easiest solution to this since I am under the gun to get this done asap

                          Although you find a solution now, you may want to take into account that having such a main() function is not a good idea as @Christian-Ehrlicher pointed out.
                          So time (and stakeholders) permitting, you might want to look at refactoring your code...

                          Upvote the answer(s) that helped you solve the issue
                          Use "Topic Tools" button to mark your post as Solved
                          Add screenshots via postimage.org
                          Don't ask support requests via chat/PM. Please use the forum so others can benefit from the solution in the future

                          1 Reply Last reply
                          2

                          • Login

                          • Login or register to search.
                          • First post
                            Last post
                          0
                          • Categories
                          • Recent
                          • Tags
                          • Popular
                          • Users
                          • Groups
                          • Search
                          • Get Qt Extensions
                          • Unsolved