No update of my QGraphicsPixmapItem

SGaist

The wiki page is a bit outdated.

Check the QThread documentation. It has vastly improved and shows both technique with modern syntax.

ademmler

@SGaist thx so much - I try this out

ademmler

Hi there,

now i have modified my minimal app to give threads a try.
I would need help with the new syntax for signal/slots across classes.

I try to connect the signal from the thread with the slot in the main UI app like this:
connect(mThread, &MyThread::signalPaintColor, this, &MainWindow::slotPaintColor);

mainwindow.cpp:20:5: error: no matching member function for call to 'connect'
qobject.h:242:43: note: candidate function [with Func1 = void (MyThread::)(int), Func2 = void (MainWindow::)(int)] not viable: cannot convert from base class pointer 'QThread ' to derived class pointer 'const typename QtPrivate::FunctionPointer<void (MyThread::)(int)>::Object ' (aka 'const MyThread ') for 1st argument
qobject.h:222:36: note: candidate function not viable: no known conversion from 'void (MyThread::)(int)' to 'const char ' for 2nd argument
qobject.h:225:36: note: candidate function not viable: no known conversion from 'void (MyThread::)(int)' to 'const QMetaMethod' for 2nd argument
qobject.h:481:41: note: candidate function not viable: no known conversion from 'void (MyThread::)(int)' to 'const char ' for 2nd argument
qobject.h:283:13: note: candidate template ignored: requirement '!QtPrivate::FunctionPointer<void (MainWindow::)(int)>::IsPointerToMemberFunction' was not satisfied [with Func1 = void (MyThread::)(int), Func2 = void (MainWindow::)(int)]
qobject.h:322:13: note: candidate template ignored: requirement 'QtPrivate::FunctionPointer<void (MainWindow::)(int)>::ArgumentCount == -1' was not satisfied [with Func1 = void (MyThread::)(int), Func2 = void (MainWindow::*)(int)]
qobject.h:274:13: note: candidate function template not viable: requires 3 arguments, but 4 were provided
qobject.h:314:13: note: candidate function template not viable: requires 3 arguments, but 4 were provided

From mythread.h

signals:
    void signalPaintColor(int i);

public slots:
    void slotMeasureColor(int i);

From mainwindow.h

signals:        

private slots:
    void on_startButton_released();
    void slotPaintColor(int i);

JonB

@ademmler
Your error message is not on any of these. It states:

mainwindow.cpp:20:5: error: no matching member function for call to 'connect'
qobject.h:242:43: note: candidate function [with Func1 = void (MyThread::)(int), Func2 = void (MainWindow::)(int)] not viable: cannot convert from base class pointer 'QThread ' to derived class pointer 'const typename QtPrivate::FunctionPointer<void (MyThread::)(int)>::Object ' (aka 'const MyThread ') for 1st argument

So show your corresponding code. It even gives you the line number of the call.

ademmler

@JonB

The code to connect at line 20:
connect(mThread, &MyThread::signalPaintColor, this, &MainWindow::slotPaintColor);

Pls be aware - this is a "minimal for testing and learning - not a rock solid solution.

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

using namespace std;

struct rgb {
    int R;
    int G;
    int B;
    char cn [10];
} colors[6];


MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    connect(mThread, &MyThread::signalPaintColor, this, &MainWindow::slotPaintColor);

    colors[0] = { 255, 255, 255, "white" };
    colors[1] = { 255, 0, 0, "red" };
    colors[2] = { 0, 255, 0, "green" };
    colors[3] = { 0, 0, 255, "blue" };
    colors[4] = { 0, 0, 0, "black" };
    colors[5] = { 128, 128, 128, "grey" };

    scene = new QGraphicsScene(this);
    ui->graphicsView->setScene(scene);
    scene->addItem(&pixmap);
    QPixmap pix(this->width(), this->height());
    pix.fill(QColor(colors[5].R, colors[5].G, colors[5].B));
    pixmap.setPixmap(pix);
}

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

void MainWindow::on_startButton_released() {

    mThread = new MyThread;
    mThread->start();
}

void MainWindow::slotPaintColor(int i){

    ui->statusbar->showMessage("Color: " + QString(colors[i].cn), 0);   

    QPixmap pix(ui->graphicsView->size());
    pix.fill(QColor(colors[i].R, colors[i].G, colors[i].B));
    pixmap.setPixmap(pix);
}

mythread.cpp

#include "mythread.h"

MyThread::MyThread(QObject *parent):
    QThread(parent)
{
}

void MyThread::run()
{
    QMutex mutex;
    //Prepare measurment device
    int err = 0;
    m_meas = new Measure(meas_i1d3, &err);


    if (!m_meas){
        qDebug() << "No connection to measurment device";
        return;
    }

    for( int i = 0; i < 5; i++ ) {
      emit signalPaintColor(i);
      slotMeasureColor(i);
    }
    mutex.unlock();
}

void MyThread::slotMeasureColor(int i)
{
    if (int err = m_meas->measure())
    {
        qDebug() << "Could not get correct measurement!";
    }

    char buffer[128];
    sprintf(buffer, "%i, %4.1f %4.1f %4.1f", i, m_meas->meas.xyz.X, m_meas->meas.xyz.Y, m_meas->meas.xyz.Z);
    qDebug() << "Measurment: " << buffer;
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QGraphicsScene>
#include <QGraphicsPixmapItem>
#include <QMessageBox>
#include <QThread>
#include <QDebug>
#include "color/measure.h"
#include "mythread.h"


QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

signals:        

private slots:
    void on_startButton_released();
    void slotPaintColor(int i);

private:
    Ui::MainWindow *ui;       
    QGraphicsScene *scene;
    QGraphicsPixmapItem pixmap;
    Measure *m_meas;
    QThread *mThread;

};
#endif // MAINWINDOW_H

mythread.h

#ifndef MYTHREAD_H
#define MYTHREAD_H
#include <QtCore>
#include <QDebug>
#include "color/measure.h"

class MyThread :public QThread
{
      Q_OBJECT
public:

    explicit MyThread(QObject *parent = 0);
    void run() override;
    QString name;
    bool Stop;
    Measure *m_meas;

signals:
    void signalPaintColor(int i);

public slots:
    void slotMeasureColor(int i);

};

#endif // MYTHREAD_H

JonB

I can't see what's wrong, but then I don't use threads :) While you await an expert who will spot it in 1 second, 10% chance that deleting all files in build output directory and rebuild will work, e.g. if you have added Q_OBJECTs recently.

SGaist

You are declaring a QThread and not a MyThread in your MainWindow class.

Another issue you will have is that your are doing your connection on an ~~initialized~~ uninitialized pointer so you are in fact not connecting anything valid.

You should just start your thread in on_startButton_released. The way it's working now is that it will create a new instance of your MyThread class each time you click on the button which is likely not what you want.

[edit: Fixed typo]

JonB

@SGaist said in No update of my QGraphicsPixmapItem:

You are declaring a QThread and not a MyThread in your MainWindow class.

Dang!

ademmler

@SGaist said in No update of my QGraphicsPixmapItem:

MyThread

Perfect HELP - thank You! The issue with the connect is gone!

Another issue you will have is that your are doing your connection on an initialized pointer so you are in fact not connecting anything valid.

What should I do instead. if I change MyThread *mThread; to MyThread mThread; I get again:
/Users/ademmler/QtTutorials/QtMinimalMeasure/mainwindow.cpp:20: error: no matching member function for call to 'connect'

When I run the code - the measurement works, but the pixmap does not get updated at all - again.

SGaist

@ademmler There was a (now fixed) typo in the sentence: it was "uninitialised" pointer. Which one is the no matching member function ?

JonB

@ademmler said in No update of my QGraphicsPixmapItem:

What should I do instead. if I change MyThread *mThread; to MyThread mThread; I get again:
/Users/ademmler/QtTutorials/QtMinimalMeasure/mainwindow.cpp:20: error: no matching member function for call to 'connect'

If you change from MyThread *mThread to MyThread mThread you must change connect(mThread, ...) to connect(&mThread, ...).

You should do this connect() before you invoke QThread::start(). So if you stick with on_startButton_released() doing a mThread = new MyThread the connect() should come on the next line.

ademmler

Thank you very much to @SGaist and @JonB
I can't set an answer to be the correct one ... missing user rights for that!

In the mean time i did what you and @SGaist has told me to do.

I have put all this to the to after ui->setupUi(this); and now it works as expected :-D

mThread = new MyThread;
connect(mThread, &MyThread::signalPaintColor, this, &MainWindow::slotPaintColor);