Pass variable from mainwindow to another qt c++ forms - c++

Question

I want to pass three strings (cellTitle,cellPoem,cellGroup) from mainwindows to another dialog. I know when i initiate the second form the values become zeros. I read somewhere it's possible with slots but i don't know how.
mainwindows.h
public:
QString cellTitle,cellPoem,cellGroup;
mainwindows.cpp
void MainWindow::on_tableView_pressed(const QModelIndex &index)
{
cellText = ui->tableView->model()->data(index).toString();
QSqlQuery * qry2 = new QSqlQuery(mydb);
qry2->prepare("select * from Poems where Title='"+cellText+"'");
qry2->exec();
while(qry2->next()){
cellTitle = qry2->value(1).toString();
cellPoem = qry2->value(2).toString();
cellGroup = qry2->value(3).toString();
ui->textEdit->setText(qry2->value(2).toString());
}
}
void MainWindow::on_btnUpdate_clicked()
{
frmUpdate frmupdate;
frmupdate.setModal(true);
frmupdate.exec();
}
frmupdate.cpp
#include "frmupdate.h"
#include "ui_frmupdate.h"
#include <mainwindow.h>
frmUpdate::frmUpdate(QWidget *parent) :
QDialog(parent),
ui(new Ui::frmUpdate)
{
ui->setupUi(this);
MainWindow mainwindow;
ui->lineEdit->setText(mainwindow.cellTitle);
ui->lineEdit_2->setText(mainwindow.cellGroup);
ui->textEdit->setText(mainwindow.cellPoem);
}
frmUpdate::~frmUpdate()
{
delete ui;
}
void frmUpdate::on_btnUpdate_clicked()
{
}
void frmUpdate::on_pushButton_2_clicked()
{
this->close();
}

Answer 1

frmUpdate::frmUpdate(QWidget *parent) :
QDialog(parent),
ui(new Ui::frmUpdate)
{
ui->setupUi(this);
MainWindow mainwindow;
You here have created a new, temporary MainWindow instance only with default constructor being called. Of course, this new instance is then created with empty default texts:
ui->lineEdit->setText(mainwindow.cellTitle);
ui->lineEdit_2->setText(mainwindow.cellGroup);
ui->textEdit->setText(mainwindow.cellPoem);
}
Easiest now would be passing the original main window as parameter:
frmUpdate::frmUpdate(QWidget* parent, MainWindow* mainWindow) :
QDialog(parent),
ui(new Ui::frmUpdate)
{
ui->setupUi(this);
ui->lineEdit->setText(mainwindow->cellTitle);
ui->lineEdit_2->setText(mainwindow->cellGroup);
ui->textEdit->setText(mainwindow->cellPoem);
}
If the parent is the main window, you can simply cast:
frmUpdate::frmUpdate(QWidget* parent) :
QDialog(parent),
ui(new Ui::frmUpdate)
{
ui->setupUi(this);
MainWindow* mainWindow = qobject_cast<MainWindow*>(parent);
if(mainWindow)
{
ui->lineEdit->setText(mainwindow->cellTitle);
ui->lineEdit_2->setText(mainwindow->cellGroup);
ui->textEdit->setText(mainwindow->cellPoem);
}
else
{
// appropriate error handling
}
}
You might search the main window from parent as well:
for(;;)
{
MainWindow* mainWindow = qobject_cast<MainWindow*>(parent);
if(mainWindow)
{
ui->lineEdit->setText(mainwindow->cellTitle);
ui->lineEdit_2->setText(mainwindow->cellGroup);
ui->textEdit->setText(mainwindow->cellPoem);
break;
}
parent = parent->parent();
if(!parent)
{
// appropriate error handling
break;
}
}
All above assuming that MainWindow inherits from QObject...