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How to transffer QImage or QPixmap from one window to another using signals and slots

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  • JonBJ JonB

    @swansorter
    You show a connect() but no emit sendImage(...). If you are not getting to the slot, where are you emitting the signal?

    S Offline
    S Offline
    swansorter
    wrote on last edited by
    #10

    @JonB
    QImage img(1024, 150, QImage::Format_RGB888);

           int pixel=0;
           for (int y =  150-1; y>= 0; y--)
           {
              for (int x = 0; x < 1024; x++)
              {
                   img.setPixel(x,y,qRgb(((data[pixel+2]) ),(data[pixel+1]), (data[pixel+0])));
                   pixel+=3;
              }
    
           } 
          emit sendImage(img);
    
    JonBJ 1 Reply Last reply
    0
    • S swansorter

      @JonB
      QImage img(1024, 150, QImage::Format_RGB888);

             int pixel=0;
             for (int y =  150-1; y>= 0; y--)
             {
                for (int x = 0; x < 1024; x++)
                {
                     img.setPixel(x,y,qRgb(((data[pixel+2]) ),(data[pixel+1]), (data[pixel+0])));
                     pixel+=3;
                }
      
             } 
            emit sendImage(img);
      
      JonBJ Offline
      JonBJ Offline
      JonB
      wrote on last edited by
      #11

      @swansorter
      Either you do not hit that code or you have not connected the correct signal instance to the correct slot instance, if you say the slot is not hit. Put a qDebug() << "Slot" as first statement in onGetImage() and see whether it gets printed or not.

      S 1 Reply Last reply
      0
      • JonBJ JonB

        @swansorter
        Either you do not hit that code or you have not connected the correct signal instance to the correct slot instance, if you say the slot is not hit. Put a qDebug() << "Slot" as first statement in onGetImage() and see whether it gets printed or not.

        S Offline
        S Offline
        swansorter
        wrote on last edited by
        #12

        @JonB it is not printing i tried

        JonBJ 1 Reply Last reply
        0
        • S swansorter

          @JonB it is not printing i tried

          JonBJ Offline
          JonBJ Offline
          JonB
          wrote on last edited by JonB
          #13

          @swansorter
          Then as I said

          Either you do not hit that [emit] code or you have not connected the correct signal instance to the correct slot instance

          S 1 Reply Last reply
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          • JonBJ JonB

            @swansorter
            Then as I said

            Either you do not hit that [emit] code or you have not connected the correct signal instance to the correct slot instance

            S Offline
            S Offline
            swansorter
            wrote on last edited by swansorter
            #14

            @JonB i tried qDebug() << "EMIT" near the emit signal. and it is executing

            JonBJ 1 Reply Last reply
            0
            • S swansorter

              @JonB i tried qDebug() << "EMIT" near the emit signal. and it is executing

              JonBJ Offline
              JonBJ Offline
              JonB
              wrote on last edited by JonB
              #15

              @swansorter
              Then

              or you have not connected the correct signal instance to the correct slot instance

              (or, for example, your signal or slot objects have gone out of scope or life-time. I don't know what else to say. You know that signals & slots work, so there is a problem in your code.

              Produce a minimal example. To rule out a problem with transferring a const QImage & as the parameter, temporarily change signal & slot to transfer, say, a QString, and emit sendImage("Hello"); till you get that working....

              S 1 Reply Last reply
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              • JonBJ JonB

                @swansorter
                Then

                or you have not connected the correct signal instance to the correct slot instance

                (or, for example, your signal or slot objects have gone out of scope or life-time. I don't know what else to say. You know that signals & slots work, so there is a problem in your code.

                Produce a minimal example. To rule out a problem with transferring a const QImage & as the parameter, temporarily change signal & slot to transfer, say, a QString, and emit sendImage("Hello"); till you get that working....

                S Offline
                S Offline
                swansorter
                wrote on last edited by swansorter
                #16

                @JonB i changed to Qstring and hello is not displaying. how to rectify this problem

                KroMignonK JonBJ 2 Replies Last reply
                0
                • S swansorter

                  @jsulm Hi i tried

                  I defined onGetImage on Mainwindow.h
                  public slots:
                  void onGetImage(const QImage &img);

                  I defined sendImage on my_qlabel.h
                  signals:
                  void sendImage(const QImage &frame);

                  my_qlabel *test_label=new my_qlabel();
                  connect(test_label,&my_qlabel::sendImage,this,&MainWindow::onGetImage);

                  but it is not displaying the image

                  jsulmJ Offline
                  jsulmJ Offline
                  jsulm
                  Lifetime Qt Champion
                  wrote on last edited by
                  #17

                  @swansorter said in How to transffer QImage or QPixmap from one window to another using signals and slots:

                  my_qlabel *test_label=new my_qlabel();
                  connect(test_label,&my_qlabel::sendImage,this,&MainWindow::onGetImage);

                  Is it possible that you're creating another test_label somewhere and emit the signal there?
                  Without more information (code) we can't treally help.

                  https://forum.qt.io/topic/113070/qt-code-of-conduct

                  1 Reply Last reply
                  0
                  • S swansorter

                    @JonB i changed to Qstring and hello is not displaying. how to rectify this problem

                    KroMignonK Offline
                    KroMignonK Offline
                    KroMignon
                    wrote on last edited by
                    #18

                    @swansorter said in How to transffer QImage or QPixmap from one window to another using signals and slots:

                    i changed to Qstring and hello is not displaying. how to rectify this problem

                    Are you sure the connect() statement was successful?
                    Are you sure to use the right class instance?
                    Can you show my_qlabel class header?

                    It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                    S 1 Reply Last reply
                    0
                    • S swansorter

                      @JonB i changed to Qstring and hello is not displaying. how to rectify this problem

                      JonBJ Offline
                      JonBJ Offline
                      JonB
                      wrote on last edited by
                      #19

                      @swansorter said in How to transffer QImage or QPixmap from one window to another using signals and slots:

                      how to rectify this problem

                      Like I said, produce a minimal example, paste the code, and we will tell you what you are doing wrong.....

                      S 2 Replies Last reply
                      0
                      • JonBJ JonB

                        @swansorter said in How to transffer QImage or QPixmap from one window to another using signals and slots:

                        how to rectify this problem

                        Like I said, produce a minimal example, paste the code, and we will tell you what you are doing wrong.....

                        S Offline
                        S Offline
                        swansorter
                        wrote on last edited by swansorter
                        #20

                        @JonB

                        mainwindow.h file
                        #ifndef MAINWINDOW_H
                        #define MAINWINDOW_H
                        
                        #include <QMainWindow>
                        #include<QRubberBand>
                        #include<my_qlabel.h>
                        namespace Ui {
                        class MainWindow;
                        }
                        
                        class MainWindow : public QMainWindow
                        {
                            Q_OBJECT
                        
                        public:
                            explicit MainWindow(QWidget *parent = 0);
                            ~MainWindow();
                               static QPoint origin;
                               static QPoint Move_test;
                               static QRect f_r;
                         private slots:
                            void onGetImage (QString data);
                        
                        
                        
                        private:
                            Ui::MainWindow *ui;
                            my_qlabel *obj;
                            QPoint origin_x;
                        
                        };
                        
                        #endif // MAINWINDOW_H
                        
                        

                        ``
                        my qlable.h file`
                        #ifndef MY_QLABEL_H
                        #define MY_QLABEL_H

                        #include <QWidget>
                        #include <QLabel>
                        #include <QEvent>
                        #include <QMouseEvent>
                        #include <QDebug>
                        #include<QRubberBand>
                        class my_qlabel : public QLabel
                        {
                        Q_OBJECT
                        public:
                        explicit my_qlabel(QWidget *parent = 0);
                        void mouseMoveEvent(QMouseEvent *ev);
                        void mousePressEvent(QMouseEvent *ev);
                        void mouseReleaseEvent(QMouseEvent *ev);
                        int x,y;
                        signals:
                        void onSendImage(QString data);

                        public slots:
                        private:

                        QRubberBand *rubberBand=0;
                        
                        QPoint origin_x;
                        

                        };

                        #endif // MY_QLABEL_H

                        
                        

                        #include "mainwindow.h"
                        #include "ui_mainwindow.h"
                        QPoint MainWindow::origin;
                        QPoint MainWindow::Move_test;
                        QRect MainWindow::f_r;
                        MainWindow::MainWindow(QWidget *parent) :
                        QMainWindow(parent),
                        ui(new Ui::MainWindow)
                        {
                        ui->setupUi(this);
                        ui->label->setStyleSheet("QLabel{background: yellow;}");
                        obj=new my_qlabel(this);
                        connect(obj,SIGNAL(onSendimage(QString)),this,SLOT(onGetimage(QString)));
                        }

                        MainWindow::~MainWindow()
                        {
                        delete ui;
                        }

                        void MainWindow::onGetimage (QString data)
                        {
                        QPixmap image=data ;
                        ui->label_2->setPixmap(image);
                        }

                        
                        

                        #include "my_qlabel.h"
                        #include<mainwindow.h>
                        my_qlabel::my_qlabel(QWidget *parent) :
                        QLabel(parent)
                        {
                        emit Mouse_Left("image");
                        }

                        void my_qlabel::mouseMoveEvent(QMouseEvent *ev)
                        {
                        this->x = ev->x();
                        this->y = ev->y();
                        rubberBand->setGeometry(QRect(origin_x,ev->pos()).normalized());

                        }

                        void my_qlabel::mousePressEvent(QMouseEvent *ev)
                        {

                        origin_x=ev->pos();
                        if(!rubberBand)
                            rubberBand=new QRubberBand(QRubberBand::Rectangle,this);
                        rubberBand->setGeometry(QRect((origin_x),QSize()));
                        rubberBand->show();
                        

                        }

                        void my_qlabel::mouseReleaseEvent(QMouseEvent *ev)
                        {

                            rubberBand->hide();
                        
                            MainWindow::f_r=rubberBand->geometry();
                            qDebug()<<"f_r"<<MainWindow::f_r;
                            QPixmap  image(rubberBand->geometry().width(),rubberBand->geometry().height());
                            image = grab(rubberBand->geometry()); //copy the selected part
                        
                            emit onSendimage("image");
                        

                        }

                        JonBJ 1 Reply Last reply
                        0
                        • KroMignonK KroMignon

                          @swansorter said in How to transffer QImage or QPixmap from one window to another using signals and slots:

                          i changed to Qstring and hello is not displaying. how to rectify this problem

                          Are you sure the connect() statement was successful?
                          Are you sure to use the right class instance?
                          Can you show my_qlabel class header?

                          S Offline
                          S Offline
                          swansorter
                          wrote on last edited by
                          #21

                          @KroMignon yes i am using right class instance . i have pasted my code

                          KroMignonK jsulmJ 2 Replies Last reply
                          0
                          • S swansorter

                            @KroMignon yes i am using right class instance . i have pasted my code

                            KroMignonK Offline
                            KroMignonK Offline
                            KroMignon
                            wrote on last edited by
                            #22

                            @swansorter said in How to transffer QImage or QPixmap from one window to another using signals and slots:

                            yes i am using right class instance . i have pasted my code

                            Your code seem at little bit confusing to me.
                            Why do you use old connect syntax here:

                            connect(obj,SIGNAL(Mouse_Left(QString)),this,SLOT(Mouse_Left(QString)));
                            

                            and not new syntax?

                            connect(obj,&my_qlabel::Mouse_Left,this, &MainWindow::Mouse_Left);
                            

                            Where did you add obj to the layout?

                            It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                            1 Reply Last reply
                            1
                            • S swansorter

                              @KroMignon yes i am using right class instance . i have pasted my code

                              jsulmJ Offline
                              jsulmJ Offline
                              jsulm
                              Lifetime Qt Champion
                              wrote on last edited by
                              #23

                              @swansorter And please be so kind and format your code properly to make it easier for others to read it...

                              https://forum.qt.io/topic/113070/qt-code-of-conduct

                              S 1 Reply Last reply
                              0
                              • JonBJ JonB

                                @swansorter said in How to transffer QImage or QPixmap from one window to another using signals and slots:

                                how to rectify this problem

                                Like I said, produce a minimal example, paste the code, and we will tell you what you are doing wrong.....

                                S Offline
                                S Offline
                                swansorter
                                wrote on last edited by
                                #24

                                @JonB i resolved issue .by changing this
                                connect(obj,SIGNAL(Mouse_Left(QString)),this,SLOT(Mouse_Left(QString)));
                                to
                                connect(ui.label,SIGNAL(Mouse_Left(QString)),this,SLOT(Mouse_Left(QString)));
                                }

                                1 Reply Last reply
                                0
                                • S swansorter

                                  @JonB

                                  mainwindow.h file
                                  #ifndef MAINWINDOW_H
                                  #define MAINWINDOW_H
                                  
                                  #include <QMainWindow>
                                  #include<QRubberBand>
                                  #include<my_qlabel.h>
                                  namespace Ui {
                                  class MainWindow;
                                  }
                                  
                                  class MainWindow : public QMainWindow
                                  {
                                      Q_OBJECT
                                  
                                  public:
                                      explicit MainWindow(QWidget *parent = 0);
                                      ~MainWindow();
                                         static QPoint origin;
                                         static QPoint Move_test;
                                         static QRect f_r;
                                   private slots:
                                      void onGetImage (QString data);
                                  
                                  
                                  
                                  private:
                                      Ui::MainWindow *ui;
                                      my_qlabel *obj;
                                      QPoint origin_x;
                                  
                                  };
                                  
                                  #endif // MAINWINDOW_H
                                  
                                  

                                  ``
                                  my qlable.h file`
                                  #ifndef MY_QLABEL_H
                                  #define MY_QLABEL_H

                                  #include <QWidget>
                                  #include <QLabel>
                                  #include <QEvent>
                                  #include <QMouseEvent>
                                  #include <QDebug>
                                  #include<QRubberBand>
                                  class my_qlabel : public QLabel
                                  {
                                  Q_OBJECT
                                  public:
                                  explicit my_qlabel(QWidget *parent = 0);
                                  void mouseMoveEvent(QMouseEvent *ev);
                                  void mousePressEvent(QMouseEvent *ev);
                                  void mouseReleaseEvent(QMouseEvent *ev);
                                  int x,y;
                                  signals:
                                  void onSendImage(QString data);

                                  public slots:
                                  private:

                                  QRubberBand *rubberBand=0;
                                  
                                  QPoint origin_x;
                                  

                                  };

                                  #endif // MY_QLABEL_H

                                  
                                  

                                  #include "mainwindow.h"
                                  #include "ui_mainwindow.h"
                                  QPoint MainWindow::origin;
                                  QPoint MainWindow::Move_test;
                                  QRect MainWindow::f_r;
                                  MainWindow::MainWindow(QWidget *parent) :
                                  QMainWindow(parent),
                                  ui(new Ui::MainWindow)
                                  {
                                  ui->setupUi(this);
                                  ui->label->setStyleSheet("QLabel{background: yellow;}");
                                  obj=new my_qlabel(this);
                                  connect(obj,SIGNAL(onSendimage(QString)),this,SLOT(onGetimage(QString)));
                                  }

                                  MainWindow::~MainWindow()
                                  {
                                  delete ui;
                                  }

                                  void MainWindow::onGetimage (QString data)
                                  {
                                  QPixmap image=data ;
                                  ui->label_2->setPixmap(image);
                                  }

                                  
                                  

                                  #include "my_qlabel.h"
                                  #include<mainwindow.h>
                                  my_qlabel::my_qlabel(QWidget *parent) :
                                  QLabel(parent)
                                  {
                                  emit Mouse_Left("image");
                                  }

                                  void my_qlabel::mouseMoveEvent(QMouseEvent *ev)
                                  {
                                  this->x = ev->x();
                                  this->y = ev->y();
                                  rubberBand->setGeometry(QRect(origin_x,ev->pos()).normalized());

                                  }

                                  void my_qlabel::mousePressEvent(QMouseEvent *ev)
                                  {

                                  origin_x=ev->pos();
                                  if(!rubberBand)
                                      rubberBand=new QRubberBand(QRubberBand::Rectangle,this);
                                  rubberBand->setGeometry(QRect((origin_x),QSize()));
                                  rubberBand->show();
                                  

                                  }

                                  void my_qlabel::mouseReleaseEvent(QMouseEvent *ev)
                                  {

                                      rubberBand->hide();
                                  
                                      MainWindow::f_r=rubberBand->geometry();
                                      qDebug()<<"f_r"<<MainWindow::f_r;
                                      QPixmap  image(rubberBand->geometry().width(),rubberBand->geometry().height());
                                      image = grab(rubberBand->geometry()); //copy the selected part
                                  
                                      emit onSendimage("image");
                                  

                                  }

                                  JonBJ Offline
                                  JonBJ Offline
                                  JonB
                                  wrote on last edited by JonB
                                  #25

                                  @swansorter
                                  This is hardly the minimal example I asked for....

                                  Do not use SIGNAL/SLOT macros if you are to have any chance of debugging what is going on. You do not even check your connect()s return result. Use the new syntax only.

                                  You declare Mouse_Left as a signal, yet you provide your own implementation of a method with that name. I don't know that you can do that.

                                  I'm quite mixed up about what are signals and what are slots in main window vs the label.

                                  If you want me to look further: Name your slots differently from your signals, else it's too confusing. Reduce to a minimal example. And enclose blocks of code with the form posts' Code tag.

                                  UPDATE
                                  Crossed with your latest post. Advice: get rid of SIGNAL/SLOT in all your code, only use new style, to help both you and others.

                                  S 1 Reply Last reply
                                  0
                                  • jsulmJ jsulm

                                    @swansorter And please be so kind and format your code properly to make it easier for others to read it...

                                    S Offline
                                    S Offline
                                    swansorter
                                    wrote on last edited by
                                    #26

                                    @jsulm sorry ill do that

                                    1 Reply Last reply
                                    0
                                    • JonBJ JonB

                                      @swansorter
                                      This is hardly the minimal example I asked for....

                                      Do not use SIGNAL/SLOT macros if you are to have any chance of debugging what is going on. You do not even check your connect()s return result. Use the new syntax only.

                                      You declare Mouse_Left as a signal, yet you provide your own implementation of a method with that name. I don't know that you can do that.

                                      I'm quite mixed up about what are signals and what are slots in main window vs the label.

                                      If you want me to look further: Name your slots differently from your signals, else it's too confusing. Reduce to a minimal example. And enclose blocks of code with the form posts' Code tag.

                                      UPDATE
                                      Crossed with your latest post. Advice: get rid of SIGNAL/SLOT in all your code, only use new style, to help both you and others.

                                      S Offline
                                      S Offline
                                      swansorter
                                      wrote on last edited by
                                      #27

                                      @JonB do you have the link for the new style SIGNAL/SLOT Diclaration

                                      jsulmJ JonBJ 2 Replies Last reply
                                      0
                                      • S swansorter

                                        @JonB do you have the link for the new style SIGNAL/SLOT Diclaration

                                        jsulmJ Offline
                                        jsulmJ Offline
                                        jsulm
                                        Lifetime Qt Champion
                                        wrote on last edited by
                                        #28

                                        @swansorter said in How to transffer QImage or QPixmap from one window to another using signals and slots:

                                        do you have the link for the new style SIGNAL/SLOT Diclaration

                                        Easy to find with Google: https://doc.qt.io/qt-5/signalsandslots.html

                                        https://forum.qt.io/topic/113070/qt-code-of-conduct

                                        1 Reply Last reply
                                        0
                                        • S swansorter

                                          @JonB do you have the link for the new style SIGNAL/SLOT Diclaration

                                          JonBJ Offline
                                          JonBJ Offline
                                          JonB
                                          wrote on last edited by
                                          #29

                                          @swansorter
                                          Additionally to @jsulm, you originally had it with your

                                          connect(test_label,&my_qlabel::sendImage,this,&MainWindow::onGetImage);
                                          

                                          You then changed over to SIGNAL/SLOT, for no discernible reason, which may be a clue as to why it went wrong....

                                          1 Reply Last reply
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