I am new to Qt. I have downloaded a source from net.
The header file contains the following
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
ainWindow>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private:
Ui::MainWindow *ui; // Need for this line. Any one please help
};
#endif // MAINWINDOW_H
in mainwindow.cpp file ui->setupUI(this) has been called in constructor. Please help what is the need for the creation of ui variable
You need a MainWindow.ui file which is then processed by Qt's UIC mechanism, which is triggered if you run qmake.
If you are using an IDE like Visual Studio with the Qt Plugin or Qt Creator, just create a new Qt GUI class through the wizard and you will have everything you need.
This page discusses usage of UI files in depth.
Related
I am brand new to programming with Qt. I'm trying to do a simple subtraction of some values fed from an epicsQt widget called QELabel, which simply reads the value of an EPICS channel. I want to subtract values from two QELabels and print it to another QELabel. But, I'm getting 'undefined reference to' errors for these ->
MainWindow::on_qeLabel_dbValueChanged(QString const&) MainWindow::on_ShutterOpen_dbValueChanged(QString const&)
Here is the bit of mainwindow.cpp (I followed the example from this youtube video, especially after about the 15 minute mark)
void MainWindow::on_TopShutter_dbValueChanged(const QString &out)
{
double top,bottom,open;
top=ui->TopShutter->text().toDouble();
bottom=ui->BottomShutter->text().toDouble();
open=top-bottom
ui->ShutterOpen->setText(Qstring::number(open));
}
I'm using QTCreator, so I don't have the usual errors that I've been seeing in other forums. I have the slot declared in the header file, and MainWindow set as a Q_Object (this is the whole mainwindow.h file):
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private slots:
void on_qelabel_dbValueChanged(const QString &out);
void on_ShutterOpen_dbValueChanged(const QString &out);
void on_TopShutter_dbValueChanged(const QString &out);
private:
Ui::MainWindow *ui;
};
#endif //MAINWINDOW_H
Because they are short, and for completeness, here is the main.cpp, and then the .pro
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
And the FirstWeatherAlarm.pro:
#-------------------------------------------------
QT += core gui xml
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
TARGET = FirstWeatherAlarm
TEMPLATE = app
SOURCES += main.cpp\
mainwindow.cpp
LIBS += -L/usr/lib64/qt5/plugins/designer -lQEPlugin
INCLUDEPATH += /home/jchavez/epicsqt/3.1.0/framework/include
HEADERS += mainwindow.h
FORMS += mainwindow.ui
Have I got everything declared right at the start of all the files? What is missing so that my slots are not right? I created the slot in the gui, using the "right-click" on my QELabel, and selecting "Go to Slot", so I should think all the formatting would be correct. As I've been editing, I've also run qmake and make clean which are other answers I've seen on forums. But nothing is working.
The problem is with two slots:
MainWindow::on_qeLabel_dbValueChanged(QString const&)
MainWindow::on_ShutterOpen_dbValueChanged(QString const&)
They are declared in MainWindow.h file and used somewhere in your project (otherwise you won't get an error).
But they are not implemented in mainwindow.cpp. You should add implementation to this file and the error will go away.
You have implementation for
void MainWindow::on_TopShutter_dbValueChanged(const QString &out)
in mainwindow.cpp, you can add implementation for two more slots. Think about slot as a function. And read more about signals/slots.
I am using QT (version 5.4 msvc2013_64) with of-course vs2013. The compilation is successful but when running not every thing functions. Before with vs2010 and QT (i think version 5.1 msvc_2010_opengl do not remember exactly) every thing was working but now things are wried which maybe typical with the start of newer versions but need to be resolved. I also got other issues with this but lets get this resolved first as maybe others will be resolved too else I will post another question for the other problems. Of-course If i do not see a solution to this problem with the current QT and vs I will switch to vs2012 (requires downloading and installing); Maybe then everything will work as before. Thanks in advance.
ui_ta7feezquran.h
/********************************************************************************
** Form generated from reading UI file 'ta7feezquran.ui'
**
** Created by: Qt User Interface Compiler version 5.4.1
**
** WARNING! All changes made in this file will be lost when recompiling UI file!
********************************************************************************/
#ifndef UI_TA7FEEZQURAN_H
#define UI_TA7FEEZQURAN_H
#include <QtCore/QVariant>
#include <QtWidgets/QAction>
#include <QtWidgets/QApplication>
#include <QtWidgets/QButtonGroup>
#include <QtWidgets/QHeaderView>
#include <QtWidgets/QLabel>
#include <QtWidgets/QMainWindow>
#include <QtWidgets/QMenuBar>
#include <QtWidgets/QToolBar>
#include <QtWidgets/QWidget>
QT_BEGIN_NAMESPACE
class Ui_Ta7feezQuranClass
{
public:
QWidget *centralWidget;
QLabel *a;
QMenuBar *menuBar;
QToolBar *mainToolBar;
void setupUi(QMainWindow *Ta7feezQuranClass)
{
if (Ta7feezQuranClass->objectName().isEmpty())
Ta7feezQuranClass->setObjectName(QStringLiteral("Ta7feezQuranClass"));
Ta7feezQuranClass->resize(572, 485);
centralWidget = new QWidget(Ta7feezQuranClass);
centralWidget->setObjectName(QStringLiteral("centralWidget"));
a = new QLabel(centralWidget);
a->setObjectName(QStringLiteral("a"));
a->setGeometry(QRect(-30, -20, 601, 471));
a->setPixmap(QPixmap(QString::fromUtf8(":/Ta7feezQuran/Resources/Amasjed Alharam.jpg")));
a->setScaledContents(true);
Ta7feezQuranClass->setCentralWidget(centralWidget);
menuBar = new QMenuBar(Ta7feezQuranClass);
menuBar->setObjectName(QStringLiteral("menuBar"));
menuBar->setGeometry(QRect(0, 0, 572, 21));
menuBar->setLayoutDirection(Qt::RightToLeft);
Ta7feezQuranClass->setMenuBar(menuBar);
mainToolBar = new QToolBar(Ta7feezQuranClass);
mainToolBar->setObjectName(QStringLiteral("mainToolBar"));
Ta7feezQuranClass->addToolBar(Qt::TopToolBarArea, mainToolBar);
retranslateUi(Ta7feezQuranClass);
QMetaObject::connectSlotsByName(Ta7feezQuranClass);
} // setupUi
void retranslateUi(QMainWindow *Ta7feezQuranClass)
{
Ta7feezQuranClass->setWindowTitle(QApplication::translate("Ta7feezQuranClass", "Ta7feezQuran", 0));
a->setText(QString());
} // retranslateUi
};
namespace Ui {
class Ta7feezQuranClass: public Ui_Ta7feezQuranClass {};
} // namespace Ui
QT_END_NAMESPACE
#endif // UI_TA7FEEZQURAN_H
ta7feezquran.h
#ifndef TA7FEEZQURAN_H
#define TA7FEEZQURAN_H
#include <QtWidgets/QMainWindow>
#include "ui_ta7feezquran.h"
class Ta7feezQuran : public QMainWindow
{
Q_OBJECT
public:
Ta7feezQuran(QWidget *parent = 0);
~Ta7feezQuran();
private:
Ui::Ta7feezQuranClass ui;
};
#endif // TA7FEEZQURAN_H
ta7feezquran.cpp
#include "ta7feezquran.h"
Ta7feezQuran::Ta7feezQuran(QWidget *parent)
: QMainWindow(parent)
{
ui.setupUi(this);
}
Ta7feezQuran::~Ta7feezQuran()
{
}
main.cpp
#include "ta7feezquran.h"
#include <QtWidgets/QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Ta7feezQuran w;
w.show();
return a.exec();
}
ta7feezquran.qrc
<RCC>
<qresource prefix="/Ta7feezQuran">
<file>Resources/Amasjed Alharam.jpg</file>
</qresource>
</RCC>
Some Application features used, for example images, multimedia, print support, etc., require the use of qt plugins.
The required plugins should be copied to the executable folder (folder where .exe file is included) by copying the plugin folders (with the dlls included) and pasting them inside the executable folder. Every thing else should work as expected.
In this case imageformats folder (with qjpeg.dll included as the file used is jpg) is needed to copied.
I am familiar with Qt4 but we are trying to transition to Qt5 and it's being very difficult. I'm trying to create a very simple application, and I had it working using the Qt PRO file, but we need to base it on cmake to keep the build server happy.
The error I get is "invalid use of incomplete type ‘struct Ui::MainWindow’" in the line in mainwindow.cpp where it constructs "ui(new Ui::MainWindow)".
Here are my files (simplified to shorten this post):
mainwindow.h
#include <QtWidgets/QMainWindow>
namespace Ui { class MainWindow; }
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private:
Ui::MainWindow *ui;
};
mainwindow.cpp
#include "mainwindow.h"
#include "moc_mainwindow.cpp"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{ }
MainWindow::~MainWindow()
{ delete ui; }
cmakelists.txt
CMAKE_MINIMUM_REQUIRED( VERSION 2.8.9 FATAL_ERROR )
PROJECT(Test)
set(CMAKE_AUTOMOC TRUE)
set(CMAKE_INCLUDE_CURRENT_DIR ON)
find_package(Qt5Core REQUIRED)
find_package(Qt5Widgets REQUIRED)
file (GLOB Sources src/*.cpp )
add_executable(Test ${Sources} src/mainwindow.ui )
qt5_use_modules(Test Widgets)
I'm sure I'm missing something obvious, but I've been looking all day and can't figure this one out ...
Looking at the generated moc_mainwindow.cpp (again, some lines truncated to keep this post short):
#include "../src/mainwindow.h"
#include <QtCore/qbytearray.h>
#include <QtCore/qmetatype.h>
QT_BEGIN_MOC_NAMESPACE
void MainWindow::qt_static_metacall(QObject *_o, QMetaObject::Call _c, int _id, void **_a)
{
Q_UNUSED(_o);
Q_UNUSED(_id);
Q_UNUSED(_c);
Q_UNUSED(_a);
}
QT_END_MOC_NAMESPACE
I am guessing that MainWindow::qt_static_metacall() is declared in my mainwindow.h in the Q_OBJECT macro. which means I have no idea where this mystical Ui::MainWindow is coming from. Or not.
UPDATE
The problem seems to be that in my mainwindow.cpp, I should be #including "ui_mainwindow.h" instead of "moc_mainwindow.cpp", but there is no "ui_mainwindow.h" being generated, only moc_mainwindow.cpp.
Turns out my understanding of Qt was completely WRONG. moc doesn't generate those ui files, it's doing other magic to make signals & slots work. The solution is to add this link to CMakeLists.txt:
qt5_wrap_ui(uifiles src/mainwindow.ui)
Is it possible to use a templated class (not based on QObject and doesn't have Q_OBJECT macro) in Qt? I keep getting a linker error when trying to use a templated class. however, when I remove the template from the class, it compiles and links fine. I'm just trying to declare a local variable of type Filter, which uses a template, and I get this linker error:
error: undefined reference to `NumericFilter<int>::NumericFilter(int, int)'
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "filter.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
NumericFilter<int> filter(0, 1);
}
MainWindow::~MainWindow()
{
delete ui;
}
filter.h
template <class T>
class NumericFilter {
public:
NumericFilter (int itemType, int val);
protected:
T m_val;
};
filter.cpp
#include "filter.h"
template <class T>
NumericFilter<T>::NumericFilter (int, int)
{
}
Note that if you remove the template in the declaration and source files and comment out the 'T' member, then it compiles fine.
http://www.parashift.com/c++-faq-lite/separate-template-fn-defn-from-decl.html
If you compile and (try to) link these two .cpp files, most compilers will generate linker errors. There are two solutions for this. The first solution is to physically move the definition of the template function into the .h file, even if it is not an inline function.
This solution may (or may not!) cause significant code bloat, meaning your executable size may increase dramatically (or, if your compiler is smart enough, may not; try it and see).
The other solution is to leave the definition of the template function in the .cpp file and simply add the line template void foo(); to that file:
// File "foo.cpp"
#include <iostream>
#include "foo.h"
template<typename T> void foo()
{
std::cout << "Here I am!\n";
}
template void foo<int>();
So for your case, you would have in your .cpp file:
#include "filter.h"
template <class T>
NumericFilter<T>::NumericFilter(int, int)
{
}
template NumericFilter<int>::NumericFilter<int>(int, int); // added line!!!
Tada! No compile errors!
BTW, parashift's explanations on templates in C++ are the best IMHO.
Hope that helps.
Recently,I use qt creator to develop some demo,but I meet some problems about the qt creator.When I add a class to my project and write the follow codes:
#ifndef BUTTONRECIVER_H
#define BUTTONRECIVER_H
#include <QObject>
#include <iostream>
class ButtonReciver : public QObject
{
Q_OBJECT
public:
explicit ButtonReciver(QObject *parent = 0);
signals:
public slots:
void button_click();
};
#endif // BUTTONRECIVER_H
But I can't make this class become slot(receiver) to receive button click signal,I use the qt creator to choose the receiver,but it does't exist in the list.Please help me.
If your button is called say myButton, then try something like:
ButtonReciver* receiver = new ButtonReciver(this);
connect(ui->myButton, SIGNAL(clicked()), receiver, SLOT(button_click()));
Put this someplace after ui->setupUi(this) in your form's constructor.
Usually, you just right click on the button and click "Go to slot...", and it will create a handler for you.