How to communicate between QDialog Window and QMainWindow with Qt C++

Question

I am an application using Qt Creator in C ++. The int main () function is as follows. I am starting a QDialog Window where I am getting the "url" variable content.

How can I get this variable into the mainwindow.cpp file.

QApplication a(argc, argv);
MainWindow *w; //Put it here in case you have several cases where you want to initialize it

QLoginDialog d; //Your login dialog
if(d.exec()==QDialog::Accepted)
{
    if(d.isLogged()) //Check the variable used to validate the login
    {
         w = new MainWindow;
         w->show();
    }
    else
    {
        //Handle bad login
        return -1; //Don't forget to return something here
    }
}
else
{
    //Handle dialog not validated
    return -1; //Don't forget to return something here
}

return a.exec();

mainwindow.cpp

MainWindow::MainWindow(QWidget *parent):
       QMainWindow(parent),
       ui(new Uİ::MainWindow)
{   
    QDialog s;
    s.show();
    s.setmodel(true);

  if(s.exec()==QDialog::Accepted)
  {
    if(s.URL=="true")
    {
      ui.setupUi(this);
    }
  }
}

QDialog.cpp=Start.cpp source code:

#include "start.h"
#include "ui_start.h"

Start::Start(QWidget *parent) :
QDialog(parent),
ui(new Ui::Start)
{
    ui->setupUi(this);
}

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

void Start::on_pushButton_2_clicked()
{
    QString dirName=QFileDialog::getExistingDirectory(
         this,
         tr("Select a Directory"),
         QDir::currentPath());

     if(!dirName.isNull())
         ui->lineEdit_2->setText(dirName);
}

void Start::on_pushButton_3_clicked()
{
    URL=ui->lineEdit->text();
    Directory=ui->lineEdit_2->text();

    if(URL.isEmpty() && Directory.isEmpty())
    {
        QMessageBox::warning(this,tr("Error"),tr("Please, fill in the blanks"));
    }
    else if(URL.isEmpty())
    {
        QMessageBox::warning(this,tr("Error"),tr("is not a valid URL or Path!!"));
    }
    else if(Directory.isEmpty())
    {
         QMessageBox::warning(this,tr("Error"),tr("is not a select directory!!"));
    }



    ControlConfiguration();
}

void Start::ControlConfiguration()
{
    QString configPosition= ui->lineEdit_2->text();

    QString str1="CHECKOUT_HOME";
    QString str2="new_checkout.csh";
    QString str3="setup_prjsvn.csh";

    QMessageBox *msgBox=new QMessageBox(this);
    int sayac=0;
    QDir path(configPosition);

    QStringList files=path.entryList(QDir::Files);
    for(int i=0; i<files.length(); i++)
    {
        if(files[i].compare(str1)==0)
        {
            sayac=sayac+1;
        }
    }
    for(int i=0; i<files.length(); i++)
    {
       if(files[i].compare(str2)==0)
        {
            sayac=sayac+1;
        }
    }
    for(int i=0; i<files.length(); i++)
    {
        if(files[i].compare(str3)==0)
        {
           sayac=sayac+1;
        }
    }

    if(sayac>=3)//Attention Flurent. if true, open QMainWindow
    {
        QMessageBox::information(this,tr(" "),tr("Configuration Directory"));
        //s_path=ui->lineEdit->text();

        this->hide();

        s_path="true";

        URL=ui->lineEdit_2->text();
    }
    else
    {
        msgBox->setInformativeText("Would you like to configure?");
        msgBox->setStandardButtons(QMessageBox::Cancel | QMessageBox::No |   QMessageBox::Yes);
        msgBox->setDefaultButton(QMessageBox::Yes);
        int ret = msgBox->exec();
        switch(ret){
        case QMessageBox::Yes:
           Configuration();
           break;
        case QMessageBox::No:
           //ui->locationEdit->clear();
           break;
        case QMessageBox::Cancel:
           break;

        }

    }
}
void Start::Configuration()
{
    QString projePosition= ui->lineEdit_2->text();  // Proje konumu alınır.
    QProcess* process=new QProcess(this);
    QMessageBox *msgBox=new QMessageBox(this);

    process->setWorkingDirectory(projePosition);

    QString svn_export="svn export       http://atlas/svn/prjsvn/trunk/common/common_bin/istanbul/new_checkout.csh";
    QString s_newcheckout="source new_checkout.csh";
    QString s_prjsvn="source setup_prjsvn.csh";

    process->start("tcsh -c \""+svn_export+";"+s_newcheckout+";"+s_prjsvn+"\"");

    process->waitForBytesWritten();
    process->waitForFi
}

Elcan · Answer 1 · 2016-12-14T10:40:56.763

You should have a proper look at signals and slots, to pass variables between objects. The documentation is here : http://doc.qt.io/qt-4.8/signalsandslots.html

An other way would be to execute the QDialog inside your MainWindow, that would be the best practice. Use controls in the scope where they are useful. You should not have to use dialogs in the main function.

So, have a look at both solutions. The best, for simple variables, being to execute your dialog inside the class where the value will be used, the second being the use of signals and slots if values have to be passed between complex classes.

main.cpp

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow *w; //Put it here in case you have several cases where you want to initialize it

    QLoginDialog d; //Your login dialog
    if(d.exec()==QDialog::Accepted)
    {
        if(d.isLogged()) //Check the variable used to validate the login
        {
             w = new MainWindow(d.getUrl()); //I guess the URL comes from your login dialog, so make a function that returns it
             w->show();
        }
        else
        {
            //Handle bad login
            return -1; //Don't forget to return something here
        }
    }
    else
    {
        //Handle dialog not validated
        return -1; //Don't forget to return something here
    }

    return a.exec();
}

mainwindow.cpp

//Don't forget to add the "QString sUrl" to your mainwindow.h
MainWindow::MainWindow(QString sUrl, QWidget *parent): QMainWindow(parent), ui(new Uİ::MainWindow)
{   
    ui.setupUi(this);

    qDebug()<<s.URL; //It will be displayed here
}

Your dialog.cpp

//Use this to return the boolean value that represents if the path is valid or not.
bool QDialog::isLogged()
{
    return this->s_path.equals("true");
}

Thank you, but I want to first start QDialogWindow. Because ıt is login panel. Later second start QMainwindow inside QDialogwindow @FlorentUguet — oğuzhan kaynar, Dec 14 '16 at 08:22
Qdialog.cpp----example : if(count>3){QMainwindow *p=new QMainWindow(); p->setAttribute(Qt::WA_DeleteOnClose); p->show}---@FlorentUguet — oğuzhan kaynar, Dec 14 '16 at 08:25
Never start a widget or window from a dialog. Return a value from the dialog and then process what you want. Dialogs are temporary widgets and should not be the parents of windows/widgets. — Elcan, Dec 14 '16 at 08:42
Thank you, I edited main.cpp, it true work. But, I want to get Url variable in Mainwindow.@FlorentUguet — oğuzhan kaynar, Dec 14 '16 at 09:16
Can you show us the code of your dialog ? I don't quite understand how it works, or what you want to achieve. Is your "s" dialog the login dialog ? To help you, we need to see its code, so I can understand where the Url comes from — Elcan, Dec 14 '16 at 09:38

Tom Conijn · Accepted Answer · 2016-12-14T09:35:46.370

A standard generated main file for a qt application contains the following lines:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

The main window is created there.

So in your case you could create the main window before your return. By adding a QString as parameter in the constructor the url would be available in the mainwindow.

so the mainWindow.cpp constructor changes to:

MainWindow::MainWindow(QString url, QWidget *parent) :
    QMainWindow(parent), ui(new Uİ::MainWindow)
{
     ui.setupUi(this);

     //Place your code here that uses the url,
}

so the mainWindow.h constructor changes to:

MainWindow::MainWindow(QString url = "", QWidget *parent = 0);

and the main.cpp changes to:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QString url; //Fill this from your dialog.
    MainWindow w(url);//Pass the url to the main window
    w.show();

    return a.exec();
}

A better practice would be to execute the dialog inside the MainWindow class. It helps keep the code organized since the value is supposed to be used in the MainWindow. — Elcan, Dec 14 '16 at 08:19

score 0 · Answer 3 · answered Dec 14 '16 at 08:28

0

If all you want to do is to ask for an input string, i suggest you to have a look at QInputDialog

Example:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    bool ok;
    QString message = QInputDialog::getText
    (0, "Input","URL:", QLineEdit::Normal,"", &ok);
    qDebug()<<message;
    ui->setupUi(this);
}

answered Dec 14 '16 at 08:28

me_alok

241
2
6

What is this boolflag? I want to first start Qdialogwindow, when start Applicaiton @me_alok – oğuzhan kaynar Dec 14 '16 at 08:35
The &boolflag is a reference to a boolean flag variable, which is replaced by the bool ok in the edit. – me_alok Dec 14 '16 at 08:36
The dialog will appear when the application starts – me_alok Dec 14 '16 at 08:37
Here, only get Url. But I want to control login panel. Later get lineEdit text.@me_alok – oğuzhan kaynar Dec 14 '16 at 08:50
QInputDialog can be used for only one input. If you have multiple inputs, create a QDialog derived class with multiple inputs. – me_alok Dec 14 '16 at 09:01

How to communicate between QDialog Window and QMainWindow with Qt C++

3 Answers3