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

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

JonB

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

but it is not displaying the image

What is "not displaying the image"? Your code, as shown, does not do anything about putting the received image into anything on Mainwindow in the slot!

swansorter

@JonB After receiving the image in the main window i am displaying the the image on qlable .there am not able to see the image.

void MainWindow::onGetImage(const QImage dat)
{

ui->label_2->setPixmap(QPixmap::fromImage(dat)); //show "image"
}

SGaist

Hi,

How do you create that image ?
Is it valid ?
Are you sure that your slot is called ?

swansorter

@SGaist Yea its not even going to slot function only y?

swansorter

@swansorter I am receiving the rgb data over tcp client and then after framing the image i am sending it to mainwndow

JonB

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

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);

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.

swansorter

@JonB it is not printing i tried

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

swansorter

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

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....

swansorter

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

jsulm

@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.

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?

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.....

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");

}

swansorter

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

KroMignon

@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?