'QMessageBox::critical' : none of the 4 overloads could convert all the argument types - qt

Question

I want to display an error message whenever my independent thread encounters the word "alert1" in a specific .txt file. But I get the above error inside the monitorForAlerts() inside mythread.cpp file. The line expectedly executes if I were to place it inside dialog.cpp. So I guess this is due to non-inheritance of this object. Can you please advise me how to solve this error for the given code?
Here is the code:
dialog.h
#ifndef DIALOG_H
#define DIALOG_H
#include <QDialog>
#include <QtCore>
#include "mythread.h"
namespace Ui {
class Dialog;
}
class Dialog : public QDialog
{
Q_OBJECT
public:
explicit Dialog(QWidget *parent = 0);
~Dialog();
public slots:
private:
Ui::Dialog *ui;
private slots:
void on_pushButton_clicked();
void on_pushButton_2_clicked();
};
#endif // DIALOG_H
mythread.h
#ifndef MYTHREAD_H
#define MYTHREAD_H
#include <QThread>
#include <QtCore>
#include <QDebug>
#include <QFile>
#include <Windows.h>
#include <QMessageBox>
#include <QTimer>
#define ALERTS_MESSAGE_STORAGE_PATH "E:\\QT1\\simpleGUIThread2\\simpleGUIThread2\\usbAlert.txt"
#define TIMER_VALUE 500
class MyThread : public QThread
{
Q_OBJECT
public:
explicit MyThread(QObject *parent = 0);
void run();
QString name;
void monitorForAlerts();
int exec();
public slots:
signals:
void testSignal(QString message);
public slots:
};
#endif // MYTHREAD_H
dialog.cpp
#include "dialog.h"
#include "ui_dialog.h"
Dialog::Dialog(QWidget *parent) :
QDialog(parent),
ui(new Ui::Dialog)
{
ui->setupUi(this);
}
Dialog::~Dialog()
{
delete ui;
}
void Dialog::on_pushButton_clicked()
{
ui->label->show();
}
void Dialog::on_pushButton_2_clicked()
{
ui->label->hide();
}
mythread.cpp
#include "mythread.h"
#include "dialog.h"
MyThread::MyThread(QObject *parent) :
QThread(parent)
{
}
void MyThread::run()
{
exec();
}
int MyThread::exec()
{
while(1)
{
monitorForAlerts();
emit(testSignal("hello world!!"));
sleep(1);
}
}
void MyThread::monitorForAlerts()
{
QString response = ALERTS_MESSAGE_STORAGE_PATH;
QFile resp(response);
resp.open(QIODevice::WriteOnly);
resp.close();
QFile resp1(response);
char buf[121];
char buf1[] = "alert1";
char buf2[] = "alert2";
resp1.open(QIODevice::ReadOnly);
while(resp1.size() == 0)
{
Sleep(3000);
}
qint64 lineLength = resp1.readLine(buf, sizeof(buf));
resp1.close();
if(strcmp(buf,buf1) == 0)
{
QFile::remove(ALERTS_MESSAGE_STORAGE_PATH);
qDebug()<<"warning 1!!";
QMessageBox::critical(this,tr("ERROR"),tr("Large change in illumination.\nPlease re-capture reference image.\n"));
}
if(strcmp(buf,buf2) == 0)
{
QFile::remove(ALERTS_MESSAGE_STORAGE_PATH);
qDebug()<<"warning 2!!";
QMessageBox::critical(this,tr("ERROR"),tr("The camera position has been moved or an object is obscuring its view.\nPlease check the device.\n"));
}
}
main.cpp
#include "dialog.h"
#include <QApplication>
#include "mythread.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MyThread mThread1;
mThread1.name = "mThread1";
mThread1.start();
Dialog w;
w.show();
return a.exec();
}
LATEST UPDATE*********************************************************************
Hi Zlatomir,
I choose to take your 1st advice. I have created a signal that the thread will emit and connect it to a slot for QDialog. Please let me know if my understanding is correct, because I do not know where to implement the connect(), since the signal is declared in mythread.h and the slot in dialog.h. The connection type argument for connect is Qt::QueuedConnection, so that gui elements from another thread different than main-thread.
are NOT created. Is this statement correct? and where do I place this?
connect( mThread, SIGNAL(alertSignal(QString)), this, SLOT(alertSlot(QString)), Qt::QueuedConnection);
mythread.h
//....
signals:
void alertSignal(QString message);
//....
dialog.h
//....
public slots:
void alertSlot(QString message);
//....
mythread.cpp
//....
if(strcmp(buf,buf1) == 0)
{
QFile::remove(ALERTS_MESSAGE_STORAGE_PATH);
qDebug()<<"warning 1!!";
emit(alertSignal("alert1"));
}
else if(strcmp(buf,buf2) == 0)
{
QFile::remove(ALERTS_MESSAGE_STORAGE_PATH);
qDebug()<<"warning 2!!";
emit(alertSignal("alert2"));
}
dialog.cpp
void Dialog::alertSlot(QString message)
{
if(strcmp(message, "alert1"))
QMessageBox::critical(this,tr("ERROR"),tr("Large change in illumination.\nPlease re-capture reference image.\n"));
else if(strcmp(message, "alert2"))
QMessageBox::critical(this,tr("ERROR"),tr("The camera position has been moved or an object is obscuring its view.\nPlease check the device.\n"));
}
Now if this were correct, how do i implement the connect() and in which file?

Answer 1

The first argument is the problem, in your case this is not a good argument, because there this is a pointer to a MyThread instance, and MyThread is not a QWidget (is not derived from QWidget).
To solve this you can show the QMessageBox::critical from a slot in mainwindow (the Dialog class in your code, there you pass the instance of main-window that is a QWidget) and connect that slot with a signal that you emit from your thread, make sure that the connection type argument for connect is Qt::QueuedConnection, so that you don't try to create gui elements from another thread different than main-thread.
Another option would be to validate the data before you start the second thread and to tell
the user that he needs to provide the right files.
LE: Also check the QThread's documentation for the recommended way to use the class, now it's recommended not to derive from QThread.
LE2 - answer to the update
That connect can be made where ever you can have the two instances that you want to connect, in your case main.cpp is a good place to connect those (don't forget to fully qualify the name for connect: QObject::connect):
//...
MyThread mThread1;
mThread1.name = "mThread1";
mThread1.start();
Dialog w;
QObject::connect( &mThread1, SIGNAL(alertSignal(QString)), &w, SLOT(alertSlot(QString)), Qt::QueuedConnection);
w.show();
//...