mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QFileSystemModel>
#include <QThread>
#include <statusdialog.h>
#include <pbt.h>
#include <stdint.h>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private slots:
//void on_treeView_clicked(const QModelIndex &index);
void onCustomContextMenuTV(const QPoint &point);
void dirSize();
void getSelectedTreeItemSize();
void resultHandle(uint64_t);
signals:
void sizeCalculation(uint64_t);
private:
Ui::MainWindow *ui;
QString sPath;
QFileSystemModel *dirmodel;
QFileSystemModel *filemodel;
QAction *dirSizeAct;
statusDialog statusdialog;
};
#endif // MAINWINDOW_H
pbt.h
#ifndef STATUSDIALOG_H
#define STATUSDIALOG_H
#include <QDialog>
#include <stdint.h>
namespace Ui {
class statusDialog;
}
class statusDialog : public QDialog
{
Q_OBJECT
public:
explicit statusDialog(QWidget *parent = 0);
~statusDialog();
void setProgressbarMax(uint64_t);
private slots:
void on_pushButton_clicked();
private:
Ui::statusDialog *ui;
};
#endif // STATUSDIALOG_H
statusdialog.h
#ifndef STATUSDIALOG_H
#define STATUSDIALOG_H
#include <QDialog>
#include <stdint.h>
namespace Ui {
class statusDialog;
}
class statusDialog : public QDialog
{
Q_OBJECT
public:
explicit statusDialog(QWidget *parent = 0);
~statusDialog();
void setProgressbarMax(uint64_t);
private slots:
void on_pushButton_clicked();
private:
Ui::statusDialog *ui;
};
#endif // STATUSDIALOG_H
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
sPath = "C:/";
dirmodel = new QFileSystemModel(this);
dirmodel->setFilter(QDir::NoDotAndDotDot | QDir::AllDirs);
dirmodel->setRootPath(sPath);
ui->treeView->setModel(dirmodel);
ui->treeView->setContextMenuPolicy(Qt::CustomContextMenu);
connect(ui->treeView, SIGNAL(customContextMenuRequested(const QPoint &)), this, SLOT(onCustomContextMenuTV(const QPoint &)));
connect(this,SIGNAL(sizeCalculation(uint64_t)),this,SLOT(resultHandle(uint64_t)));
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::resultHandle(uint64_t t_size)
{
statusdialog.setProgressbarMax(t_size);
}
void MainWindow::onCustomContextMenuTV(const QPoint &point)
{
dirSizeAct = new QAction(tr("Size"), this);
connect(dirSizeAct, SIGNAL(triggered()), this, SLOT(dirSize()));
QMenu contextMenu(this);
contextMenu.addAction(dirSizeAct);
QModelIndex index = ui->treeView->indexAt(point);
if (index.isValid()){
contextMenu.exec(ui->treeView->mapToGlobal(point));
}
}
void MainWindow::dirSize()
{
pBT pbt;
pbt.setFP(this->getSelectedTreeItemSize);
QThread thread1;
connect(&thread1,SIGNAL(started()),&pbt,SLOT(startThreadAction()));//Clone the object and it will not work, becouse it is QWidget
pbt.moveToThread(&thread1);
thread1.start();//Starts in the same thread
statusdialog.setModal(true);
statusdialog.exec();
}
void MainWindow::getSelectedTreeItemSize()
{
QModelIndex index = ui->treeView->selectionModel()->selectedIndexes().takeFirst();
QString dirPath = dirmodel->filePath(index);
QDirIterator it(dirPath, QStringList() << "*.*", QDir::Files, QDirIterator::Subdirectories);
uint64_t t_size = 0;
while (it.hasNext()) {
QFile myFile(it.next());
if (myFile.open(QIODevice::ReadOnly)){
t_size += myFile.size();
myFile.close();
}
}
emit sizeCalculation(t_size);
}
pbt.cpp
#include "pbt.h"
pBT::pBT(QObject *parent) : QObject(parent)
{
}
void pBT::startThreadAction()
{
this->fp1();
}
void pBT::setFP(void (*fp1)())
{
this->fp1 = fp1;
}
statusdialog.cpp
#include "statusdialog.h"
#include "ui_statusdialog.h"
statusDialog::statusDialog(QWidget *parent) :
QDialog(parent),
ui(new Ui::statusDialog)
{
ui->setupUi(this);
}
statusDialog::~statusDialog()
{
delete ui;
}
void statusDialog::on_pushButton_clicked()
{
this->close();
}
void statusDialog::setProgressbarMax(uint64_t size)
{
ui->progressBar->setMaximum(size);
}
main.cpp
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
To see more info of what I am doing you can look this topic(It is all about prograssbar and threaded execution of job). Theoretically I whant to run a member function of mainwindow(which use member variables of mainwindow) into new thread(the function is not static) inside slot dirSize()(also member slot of the same class mainwindow), but it seems with QThread it is necessary to create new class(no matter if I will inherit QThread class or use moveToThread function of QObject) and run that class in new thread. If I use C++ thread.h the function I run must be static, nevermind I have tried to create pBT class in which I have function pointer fp1 and public slot startThreadedAction, but when try to buil this error occures:
C:\Users\niki\Documents\EPsimple\mainwindow.cpp:54: error: C3867:
'MainWindow::getSelectedTreeItemSize': function call missing argument
list; use '&MainWindow::getSelectedTreeItemSize' to create a pointer
to member
I don`t want to create function pointer to static function! How can I fix this?
Related
doit is a Qthread subclass with a signal kif() but the signal emitting is not working I want to show the resualt of gav() on one of my editLines at the same time as its changes inside gav() pls help :((((((( I wasted so much time to find out how I can do it :((((((
main.cpp
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
doit.h
#ifndef DOIT_H
#define DOIT_H
#include <QThread>
class doit : public QThread
{
Q_OBJECT
public:
doit();
int i;
QString z;
void run() ;
void gav(int &i);
signals:
void kif(const QString &text);
};
#endif // DOIT_H
#include "doit.h"
doit::doit()
{
}
void doit::run()
{
gav(i);
}
void doit::gav(int &i)
{
int k=i;
for (int b=0;b<k;b++){
i=b;
z= QString::number(i);
emit kif(z);
}
}
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include "doit.h"
QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = nullptr);
~MainWindow();
doit *dovit=new doit;
private slots:
void checkInput(const QString &text);
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
//QObject::connect(dovit,doit::kif(&QString),this , MainWindow::checkInput(QString)))
connect(dovit,SIGNAL(kif(QString)),this,SLOT(checkInput(QString)));
dovit->start();
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::checkInput(const QString &text)
{
ui->lineEdit_3->setText(text);
}
and Im new in this , so pls tell me exactlly where should I change or add and what tanx alot
Well it finally worked after wasting a lot of my time. For anyone wondering vtables was the problem (as I read its a bug (not sure)) and I should just
right click on the project folder and rebuild and run qmake the project ,
I added Qobject.h too and it worked.
working code:
(it is also a simple and good example of meta signaling in qt if you need it)
doit.h
#define DOIT_H
#include <QThread>
#include <QObject>
class doit : public QThread
{
Q_OBJECT
public:
doit();
void gav();
void run() ;
signals:
void kif(QString text);
};
#endif // DOIT_H
doit.cpp
#include "doit.h"
#include <QDebug>
doit::doit()
{
}
void doit::run()
{
gav();
}
void doit::gav()
{
QString z;
for (int i=0;i<11;i++){
z="mamad";
z = z + QString::number(i);
QThread::sleep(1);
qDebug()<<z;
emit kif(z);
}
}
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include "doit.h"
QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = nullptr);
~MainWindow();
doit *dovit=new doit;
//doit dovit;
private slots:
void on_pushButton_clicked();
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
connect(dovit,SIGNAL(kif(QString)),this->ui->lineEdit_3,SLOT(setText(QString)));
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::on_pushButton_clicked()
{
dovit->start();
}
I created a timer in a thread and in this timer char value counts from 0 to 10.
I want to display this char value on the GUI. I do not get any error but the GUI freeze when I started.
Can you help me on where I am doing wrong please?
main.cpp
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include "mythread.h"
#include <QMainWindow>
QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = nullptr);
~MainWindow();
MyThread *mThread;
private:
Ui::MainWindow *ui;
public slots:
void onNumberChanged(char);
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
mThread = new MyThread(this);
connect(mThread,SIGNAL(NumberChanged(char)), this, SLOT(onNumberChanged(char)));
mThread->start();
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::onNumberChanged(char Number)
{
ui->label->setText(QString::number(Number));
}
mythread.h
#include <QThread>
#include <QTimer>
#include <QObject>
class MyThread : public QThread
{
Q_OBJECT
public:
explicit MyThread(QObject *parent = 0);
void run();
signals:
void NumberChanged(char);
public slots:
void update();
private:
QTimer *timer;
};
mythread.cpp
#include "mythread.h"
#include <QtCore>
char i=45;
QString mystr = "mytext";
MyThread::MyThread(QObject *parent) :
QThread(parent)
{
timer= new QTimer();
connect(timer,SIGNAL(timeout()),this,SLOT(update()));
timer->start(10);
}
void MyThread::update()
{
for( i = 0; i<10; i++){
emit NumberChanged(i);
this->msleep(500);
}
if (i>0)
i=0;
}
void MyThread::run()
{
}
you need to create your timer in the run() function, not in the constructor.
because the constructor is called in GUI thread and each object that is created in this function is in GUI thread. or you can call moveToThread for your timer to move to your thread.
I have a problem. I created two classes in my Qt project. One as the main window, and second as the settings dialog. My idea is to send the values from "Settings" to "MainWindow" (like from one TextEdit to another) but unfortunately, I have no idea how to do it. It's confusing me. I have read similar topics on the internet but none of them gives me a clear answer. Can someone help me understand the way how can I do it via example?
I have no useful code to place it here, so I will put the part of the source code and headers of mine.
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
[...]
}
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include "settings.h"
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = nullptr);
~MainWindow()
[...]
private:
Ui::MainWindow *ui;
[...]
};
#endif // MAINWINDOW_H
settings.cpp
#include "settings.h"
#include "ui_settings.h"
#include "mainwindow.h"
#include "ui_mainwindow.h"
Settings::Settings(QWidget *parent) :
QDialog(parent),
ui(new Ui::Settings)
{
ui->setupUi(this);
}
settings.h
#ifndef SETTINGS_H
#define SETTINGS_H
#include <QDialog>
namespace Ui {
class Settings;
}
class Settings : public QDialog
{
Q_OBJECT
public:
explicit Settings(QWidget *parent = nullptr);
~Settings();
[...]
private:
Ui::Settings *ui;
[...]
};
#endif // SETTINGS_H
main.cpp
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
Use signals/slots mechanism to share values between two QObject.
For example:
The following code allows yout to send the value in a QLineEdit to another widget by clicking on a button:
class Widget1: public QWidget
{
Q_OBJECT
public:
Widget1(): QWidget(),
message(new QLineEdit())
{
QPushButton* button = new QPushButton("Send msg", this);
connect(button, &QPushButton::clicked, this, [=]() { emit this->sendMsg(message->text());}); // When you click on the button, it will emit the signal sendMsg
QVBoxLayout* layout = new QVBoxLayout(this);
layout->addWidget(message);
layout->addWidget(button);
}
private:
QLineEdit* message;
signals:
void sendMsg(QString const& msg);
};
class Widget2: public QWidget
{
Q_OBJECT
public:
Widget2(): QWidget(),
display(new QLabel("Nothing to display", this))
{
QVBoxLayout* layout = new QVBoxLayout(this);
layout->addWidget(display);
}
private:
QLabel* display;
public slots:
void receive(QString const& message)
{
display->setText(message); // When called, display the message in the label
}
};
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QWidget* mainWidget = new QWidget();
QHBoxLayout* layout = new QHBoxLayout(mainWidget);
Widget1* w1 = new Widget1();
Widget2* w2 = new Widget2();
layout->addWidget(w1);
layout->addWidget(w2);
// When the signal sendMsg is emitted, call the slot receive
QObject::connect(w1, &Widget1::sendMsg, w2, &Widget2::receive);
mainWidget->show();
return app.exec();
}
There are multiple ways to achieve this.
For example you can provide the public Getter Methods in your dialog for provide value to the public and use them directly in the MainWindow to read those.
Or you can use Signals/Slots as stated above.
One example with Signal/Slots:
The SettingsWindow emits textEdit(QString) signal if Dialog Accepted, and MainWindow receives this signal via on_textEdit(QString) slot and writes it to its own text field:
SettingsWindow reading text input and emitting signal textEdit(QString):
MainWindow receiving signal via slot on_textEdit(QString):
And this is the code:
maindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = nullptr);
~MainWindow();
private slots:
void on_pushButton_clicked();
void on_textEdited(QString txt);
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "settingsdialog.h"
#include <memory>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::on_pushButton_clicked()
{
auto dlg = new SettingsDialog{this};
connect(dlg, &SettingsDialog::textEdit, this, &MainWindow::on_textEdited);
dlg->setAttribute(Qt::WA_DeleteOnClose);
dlg->show();
}
void MainWindow::on_textEdited(QString txt)
{
ui->textEdit->setText(txt);
}
settingsdialog.h
#ifndef SETTINGSDIALOG_H
#define SETTINGSDIALOG_H
#include <QDialog>
namespace Ui {
class SettingsDialog;
}
class SettingsDialog : public QDialog
{
Q_OBJECT
public:
explicit SettingsDialog(QWidget *parent = nullptr);
~SettingsDialog();
signals:
void textEdit(QString txt);
private slots:
void on_buttonBox_accepted();
private:
Ui::SettingsDialog *ui;
};
#endif // SETTINGSDIALOG_H
settingsdialog.cpp
#include "settingsdialog.h"
#include "ui_settingsdialog.h"
SettingsDialog::SettingsDialog(QWidget *parent) :
QDialog(parent),
ui(new Ui::SettingsDialog)
{
ui->setupUi(this);
}
SettingsDialog::~SettingsDialog()
{
delete ui;
}
void SettingsDialog::on_buttonBox_accepted()
{
emit textEdit(ui->textEdit->toPlainText());
}
More about Signal/Slots
My app, consists in 2 different object (QObject and QMainWIndow), and I am wondering how to communicate between them with SLOT/SIGNAL. Moreover, does existing better approach ?
Can someone make an simple example ? Thank :)
sample
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include "ui_mainwindow.h"
#include "object.h"
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private:
Ui::MainWindow *ui;
private slots:
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "object.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
connect(ui->chkState, SIGNAL(clicked()), this, SLOT(object->chkState();));
}
MainWindow::~MainWindow()
{
delete ui;
}
object.h
#ifndef OBJET_H
#define OBJET_H
#include "mainwindow.h"
#include <QMainWindow>
#include <QObject>
class Object : public QObject
{
Q_OBJECT
public:
explicit Object(QObject *parent = 0);
bool state;
signals:
private slots:
void chkState(Ui::MainWindow *ui);
};
#endif // OBJET_H
objet.cpp
#include "object.h"
#include "mainwindow.h"
Object::Object(QObject *parent) : QObject(parent)
{
}
void Object::chkState(Ui::MainWindow *ui)
{
if (ui->chkState->isChecked())
{
ui->state->setText("true");
state = true;
}
else
{
ui->state->setText("false");
state = false;
}
}
Here is a simple example of how to emit signals and slots.
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include "object.h"
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
signals:
void transmit_to_object(bool value);
private slots:
void receive_from_object(bool value);
void on_checkBox_clicked();
private:
Ui::MainWindow *ui;
object m_object;
};
#endif // MAINWINDOW_H
#ifndef OBJECT_H
#define OBJECT_H
#include <QObject>
class object : public QObject
{
Q_OBJECT
public:
explicit object(QObject * parent = 0);
signals:
void transmit_to_gui(bool value);
private slots:
void receive_from_gui(bool value);
private:
bool state;
};
#endif // OBJECT_H
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
connect(&m_object,SIGNAL(transmit_to_gui(bool)),this,SLOT(receive_from_object(bool)));
connect(this,SIGNAL(transmit_to_object(bool)),&m_object,SLOT(receive_from_gui(bool)));
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::receive_from_object(bool value)
{
if(value)
{
ui->lineEdit->setText("true");
}
else
{
ui->lineEdit->setText("false");
}
}
void MainWindow::on_checkBox_clicked()
{
if(ui->checkBox->isChecked())
{
emit transmit_to_object(true);
}
else
{
emit transmit_to_object(false);
}
}
#include "object.h"
#include "mainwindow.h"
object::object(QObject *parent)
{
}
void object::receive_from_gui(bool value)
{
state = value;
emit transmit_to_gui(state);
}
There are several errors in your code.
First:
connect(ui->chkState, SIGNAL(clicked()), this, SLOT(object->chkState();));
Here you say:
"when we click on the ui->chkState, I want you call a function in this, which is the object->chkState slot". That's definitly not what you want.
What is object ? this object hasn't been created. What you want is :
connect(ui->chkState, SIGNAL(clicked()), myobject, SLOT(chkState()));
with myobject an object of type Object so you need to add in your mainwindow.h a
Object *myobject;
and in your mainwindow.cpp before the connect:
myobject = new Object(this);
Moreover, your function void chkState(Ui::MainWindow *ui); won't work because you cannot get the mainwindow ui in parameter like that.
What I advise you to do, if it's only for tests so you know that parent is the type of MainWindow, you can do:
void Object::chkState()
{
MainWindow* parent = static_cast<MainWindow*>(parent());
if (parent->ui->chkState->isChecked())
{
parent->ui->state->setText("true");
state = true;
}
else
{
parent->ui->state->setText("false");
state = false;
}
}
So the parameter in your slot is removed.
I want to return a QString value from a function that exists in class called DB in my MainWindow class, but it always crashes the application.
db.h
#ifndef DB_H
#define DB_H
#include <QMainWindow>
#include <QtSQl>
#include <QSqlQuery>
#include <QSqlError>
#include <QObject>
#include <QDialog>
class DB : public QMainWindow
{
Q_OBJECT
public:
explicit DB(QWidget *parent = 0);
QString getDriver() const;
void setDriver(const QString &value);
private:
QString Driver="test";
signals:
public slots:
};
#endif // DB_H
and this is db.cpp
#include "db.h"
DB::DB(QWidget *parent) : QMainWindow(parent)
{
}
QString DB::getDriver() const
{
return Driver;
}
void DB::setDriver(const QString &value)
{
Driver = value;
}
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QDebug>
#include <QFileInfo>
#include <QDialog>
#include <QObject>
#include "Db.h"
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
DB *conn;
private slots:
void on_pushButton_clicked();
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::on_pushButton_clicked()
{
QString driverfromdb = conn->getDriver();
qDebug() << driverfromdb;
}
And this what happen when I click the pushbutton: image
You are declaring a pointer to DB class inside your MainWindow class
DB *conn;
but you never initialize it. At the moment it does not point to anything, so if you try to access it:
QString driverfromdb = conn->getDriver(); // boom, conn is somewhere in the void
The solution is simple, you need to create a DB object before using it, e.g.:
void MainWindow::on_pushButton_clicked()
{
conn = new DB();
QString driverfromdb = conn->getDriver();
qDebug() << driverfromdb;
}
or just let conn be a typical variable, not an pointer:
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
DB conn; // conn is created after creating MainWindow object
This way you have not to initialize anything and you will avoid crashes.
or:
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent), conn(new DB),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
}
MainWindow::~MainWindow()
{
delete conn;
delete ui;
}