I have 2 files Gui.cpp, ReadData.cpp (and headers). I need to access the QComboBox member in the Gui.cpp from ReadData.cpp. When I do this, the code compiles fine but when I run my application, it crashes, saying Access Violation . What am I doing wrong ?
How can I access the QComboBox in Gui.cpp from readdata ?
Gui.h
class Gui : public QObject
{
Q_OBJECT
public:
Gui() {}
~Gui() {}
QComboBox* comboBox;
ReadData* r;
private:
void run();
}
Gui.cpp
void Gui::run()
{
QWidget *w = new QWidget();
comboBox = new QComboBox();
//code...
r = new ReadData();
THROW_IF_FALSE(QObject::connect(loadButton, SIGNAL(clicked()), r, SLOT(read())));
}
readdata.h
class ReadData : public QObject
{
Q_OBJECT
public:
ReadData() {}
~ReadData() {}
public slots :
void read();
private:
void displayResult(QString arg);
};
readdata.cpp
void ReadData::read()
{
Gui cb;
QString str1 = cb.comboBox->currentText();
}
Related
I am try to, by pressing a button in the main QWidget, to create a new QWidget. In that new created QWidget I want to have a button connected to a slot of the main QWidget.
class UI : public QWidget
{
public:
UI(){connection();};
private:
QPushButton* all = new QPushButton{ "ALL" };
void connection(){
QObject::connect(all,QPushButton::clicked,[](){
SmallGUI* s=new SmallGUI{};
s->show();
});
}
void something(){
//something
}
and the second class
class SmallGUI1 :
public QWidget
{
public:
SmallGUI(){connection();};
private:
QPushButton* N =new QPushButton;
void connection(){
//to connect N to something()
}
I want to connect N to something() .
Before we start, there are some other problems with you code.
Note that in your second class, the constructor is not named the same as the class, which will cause some... Problems.
You also forgot to put a parent for your buttons (which may thus cause some unexpected results) AND for your Widgets (which is again not a good idea).
So, that being said, let us get to the main topic.
I tend to only put prototypes and declare the attributes in the .h file to make the code clearer, but you may of course adapt it to your needs or to your own programming convention.
There are several ways to do something like this, but the simplest one should look like this :
SmallGUI1.h :
#include "UI.h" //The file in which the class UI is declared
//OR :
//class UI; //If you need to include this file in UI.h
class SmallGUI1 : public QWidget{
Q_OBJECT //Q_OBJECT macro, check the doc for more explainations about it
public:
explicit SmallGUI1(UI *parent = nullptr); //Explicit means that this constructor cannot be used for implicit casts
~SmallGUI1();//Destructor needed because I only put the constructor above
private:
QPushButton* N; //Not very good looking to initialize attributes in the .h in my opinion, but works fine.
}
SmallGUI1.cpp :
SmallGUI1::SmallGUI1(UI *parent) : QWidget(parent){
N = new QPushButton(tr("Some text on the button") , this); //tr to enable translation on this string
//************* If I understood your question correctly, this is what you are looking for *************
connect(N , &QPushButton::clicked , parent , &UI::doSomething); //Select the signal you want
/*
Some code here
*/
show();
}
SmallGUI1::~SmallGUI1(){qDeleteAll(children());}
UI.h :
class UI : public QWidget{
Q_OBJECT
public:
explicit UI(QWidget *parent = nullptr);
~UI();
private:
QPushButton* all;
private slots :
void createSmallGUI1();
void doSomething();
}
UI.cpp :
#include "SmallGUI1.h"
UI::UI(QWidget *parent) : QWidget(parent){
all = new QPushButton(tr("ALL") , this);
connect(all , &QPushButton::clicked , this , &UI::createSmallGUI1);
/*
Some code here
*/
}
UI::~UI(){qDeleteAll(children());}
void UI::createSmallGUI1(){SmallGUI1 *gui = new SmallGUI1(this);}
void UI::doSomething(){
/*
Clever code here
*/
}
You can define the second widget as a child of the main widget to make things easier:
class UI : public QWidget {
...
private:
SmallGUI* s;
...
and then initialize it in the UI constructor, along with your all button. You can initially hide the child widget or disable it:
UI() {
all = new QPushButton{"ALL", this};
setWindowTitle("UI"); // just for clarification
s = new SmallGUI(this);
s->hide();
connection();
};
and 'show' it with button clicked signal
connect(all, &QPushButton::clicked, s, &SmallGUI::show);
Doing so gives you the option to connect the clicked signal of your N button to the something function in the parent class
connect(s->N, &QPushButton::clicked, this, &UI::something);
The complete program would be as follows,
#include <QApplication>
#include <QMessageBox>
#include <QPushButton>
#include <QWidget>
class SmallGUI : public QWidget {
public:
SmallGUI(QWidget* parent) : QWidget(parent) {
N = new QPushButton{"btn2", this};
connection();
};
QPushButton* N;
private:
void connection(){};
};
class UI : public QWidget {
public:
UI() {
all = new QPushButton{"ALL", this};
setWindowTitle("UI"); // just for clarification
s = new SmallGUI(this);
s->hide();
connection();
};
private:
SmallGUI* s;
QPushButton* all;
void connection() {
connect(all, &QPushButton::clicked, s, &SmallGUI::show);
connect(s->N, &QPushButton::clicked, this, &UI::something);
}
void something() { QMessageBox::information(this, "Hello", "Hello"); }
};
int main(int argc, char* argv[]) {
QApplication a(argc, argv);
UI w;
w.show();
return a.exec();
}
It is not good idea to connect to parent's slots from "nested" class, since SmallGUI1 will be tied to class UI.
Here is better solution, I think:
class UI : public QWidget
{
public:
UI(){connection();};
private:
QPushButton* all = new QPushButton{ "ALL" };
void connection(){
QObject::connect(all,QPushButton::clicked,[](){
SmallGUI1* s=new SmallGUI1;
connect(s,&USmallGUI1::button_clicked,this,&UI::something);
s->show();
});
}
void something(){
//something
}
And SmallGUI1 class:
class SmallGUI1 :
public QWidget
{
public:
SmallGUI1(){connection();};
signals:
void button_clicked();
private:
QPushButton* N;
void connection(){
//to connect N to something()
N = new QPushButton;
connect(N,&QPushButton::clicked,this,&SmallGUI1::button_clicked)
}
This way, you are connecting QPusButton::clicked signal from SmallGUI1 to the signal SmallGUI1::button_clicked(). Dont need to implement additional slot, just connect signal to signal.
And in UI you are connecting button_clicked() signal to the slot dosomething()
DONT FORGET THE CONSTRUCTOR OF SmallGUI1! In your code, SmallGUI() will be just a method, which will not be called when SmallGUI1 is instantiated, and you have to call it by yourself.
I need some advice to access the field(QString name) variable in QWizardPage from a QThread. I'm building some kind of an installer and I want to do the installing work in a separate Thread.
My purpose:
When reached the commit/install page, I want to execute code to do the "installing" and update the QWizardPage with my progress, until its finished.
The install function is dependent on many field() variables from other QWizardPages. Therefore I tried to execute this install function from a QThread, which is defined in an inner class from my QWizardPage. The problem is, the field()-function i a non-static member and so it's not working. And so I'm out of ideas to run my install-function parallel to my WizardPage.
I tried something like this:
InstallPage.h
class InstallPage : public QWizardPage
{
Q_OBJECT
class WorkerThread : public QThread
{
Q_OBJECT
void run() override;
};
public:
InstallPage(QWidget *parent = 0);
private:
QLabel *lProgress;
WorkerThread *installer;
void install();
};
InstallPage.c
InstallPage::InstallPage(QWidget *parent)
: QWizardPage(parent)
{
...
installer = new WorkerThread(this);
installer->start();
}
void InstallPage::WorkerThread::run()
{
if(field("checkBox1").ToBool())
{
doStuff();
}
}
//QT-Creator says at field("checkBox1"):
//error: call to non-static member function without an object argument
I'm also open for any other idea to make my installer work. Maybe someone knows something I haven't thought of.
Another approach is to create a worker (QObject) that lives in another thread that performs the heavy task and notifies the status of that task through signals:
#include <QtWidgets>
class InitialPage: public QWizardPage
{
public:
InitialPage(QWidget *parent = nullptr): QWizardPage(parent)
{
QSpinBox *spinbox = new QSpinBox;
QLineEdit *lineedit = new QLineEdit;
QVBoxLayout *lay = new QVBoxLayout(this);
lay->addWidget(spinbox);
lay->addWidget(lineedit);
registerField("value1", spinbox);
registerField("value2", lineedit);
}
};
class InstallWorker: public QObject
{
Q_OBJECT
public:
InstallWorker(QObject *parent=nullptr): QObject(parent)
{
}
public Q_SLOTS:
void install(int param1, const QString & param2)
{
Q_EMIT started();
for(int i=0; i < 100; i++){
qDebug() << __PRETTY_FUNCTION__ << i << param1 << param2;
QThread::msleep(100);
Q_EMIT progressChanged(i);
}
qDebug()<< __PRETTY_FUNCTION__ << "finished";
Q_EMIT finished();
}
Q_SIGNALS:
void started();
void progressChanged(int value);
void finished();
};
class InstallPage: public QWizardPage
{
Q_OBJECT
public:
InstallPage(QWidget *parent = nullptr): QWizardPage(parent),
label(new QLabel), progressbar(new QProgressBar)
{
QVBoxLayout *lay = new QVBoxLayout(this);
lay->addWidget(label);
lay->addWidget(progressbar);
progressbar->setMinimum(0);
progressbar->setMaximum(100);
thread = new QThread(this);
worker.moveToThread(thread);
connect(&worker, &InstallWorker::started, this, &InstallPage::onStarted);
connect(&worker, &InstallWorker::finished, this, &InstallPage::onFinished);
connect(&worker, &InstallWorker::progressChanged, this, &InstallPage::onProgressChanged);
thread->start();
}
~InstallPage(){
thread->quit();
thread->wait();
}
void initializePage(){
start_install();
}
private Q_SLOTS:
void start_install(){
int param1 = field("value1").toInt();;
QString param2 = field("value2").toString();
QMetaObject::invokeMethod(&worker, "install", Qt::QueuedConnection, Q_ARG(int, param1), Q_ARG(QString, param2));
}
void onStarted(){
for(QWizard::WizardButton which: {QWizard::BackButton, QWizard::NextButton, QWizard::CancelButton})
if(QAbstractButton * button = wizard()->button(which))
button->setEnabled(false);
}
void onFinished(){
for(QWizard::WizardButton which: {QWizard::BackButton, QWizard::NextButton, QWizard::CancelButton})
if(QAbstractButton * button = wizard()->button(which))
button->setEnabled(true);
wizard()->next();
}
void onProgressChanged(int value){
progressbar->setValue(value);
label->setNum(value);
}
private:
InstallWorker worker;
QThread *thread;
QLabel *label;
QProgressBar *progressbar;
};
class FinalPage: public QWizardPage
{
public:
FinalPage(QWidget *parent = nullptr): QWizardPage(parent)
{
}
};
#include "main.moc"
int main(int argc, char *argv[]) {
QApplication app(argc, argv);
QWizard wizard;
wizard.addPage(new InitialPage);
wizard.addPage(new InstallPage);
wizard.addPage(new FinalPage);
wizard.show();
return app.exec();
}
This is my Wavefrontrenderer class.
Class WavefrontRenderer : public QMainWindow , private
Ui::WavefrontRendererClass
{
Q_OBJECT
//Q_PROPERTY( QColor m_color READ m_color NOTIFY colorChanged)
public:
WavefrontRenderer(TreeModel* model , QWidget *parent = Q_NULLPTR);
void iterate(const QModelIndex & index, const QAbstractItemModel * model);
void render();
void RenderTreeElement(QModelIndex index);
private:
//Ui::WavefrontRendererClass ui;
TextureManager textureManager;
TextureManagerCubeMap textureManagerCubeMap;
QColor m_color;
void FillComboBox();
private slots:
void PositionXYZ();
};
/////////////////////////////////////////////////////////////////////////////////
WavefrontRenderer::WavefrontRenderer(TreeModel* model , QWidget *parent) :
QMainWindow(parent)
{
setupUi(this);
treeView->setModel(model);
treeView->setDragEnabled(true);
treeView->setAcceptDrops(true);
treeView->installEventFilter(this);
connect(doubleSpinBoxPositionX, SIGNAL(valueChanged(double)), this ,
SLOT(PositionXYZ()));
}
/////////////////////////////////////////////////////////////////////////////////
I am creating controls at runtime from another class to which i pass the Wavefrontrenderer class as a pointer.
void Container::CreateUI(QHBoxLayout* layout)
{
wavefrontrenderer // Pointer defined as a private member
QDoubleSpinBox *PositionXSpinBox = new QDoubleSpinBox;
PositionXSpinBox->setRange(-10000, 10000);
PositionXSpinBox->setSingleStep(.1);
PositionXSpinBox->setValue(x);
layout->addWidget(PositionXSpinBox);
bool ok = QObject::connect(PositionXSpinBox,
SIGNAL(valueChanged(double)), wavefrontrenderer , SLOT(print()));
qDebug() << "The slot is connected =" << ok;
}
I have defined print as a public slot member in Container class.
The issue is that the connect tries to locate print() function in WavefrontRenderer class rather than Container class.
How can i make connect call the print() funtion of the Container class.
I am using Qt and C++, after click on menu item second window appears, and after click on a button in second menu (slot saveData()), I want to change object (obj_map) of class MainMenu. Is it possible, and how to do it the best way? Because I now cannot modify obj_map, because it is in different class. I tried to do something with pointers, but the result was a segmentation fault.
Main Window:
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
map obj_map;
public Q_SLOTS:
void saveMap();
private:
Ui::MainWindow *ui;
};
Other window which appears after click in on menu item in main window.
namespace Ui
{
class PreferencesWindow;
}
class PreferencesWindow : public QWidget
{
Q_OBJECT
public:
explicit PreferencesWindow(QWidget *parent = 0);
public Q_SLOTS:
void saveData();
private:
Ui::PreferencesWindow *uip;
};
From here I need to change obj_map
void PreferencesWindow::saveData()
{
// FROM HERE I NEED TO CHANGE obj_map
}
Preferences object is created in a slot:
void MainWindow::saveMap()
{
PreferencesWindow *p = new PreferencesWindow();
p->show();
}
You could use signals and slots: when saveData() is called, emit a signal, like emit saveDataClicked() and catch that signal in the MainWindow with a slot called change_obj_map. There, you can do your changes.
So, in MainWindow you can write:
connect (PreferencesWindow, SIGNAL(saveDataClicked()), this, SLOT(change_obj_map());
and then in the slot:
void change_obj_map()
{
// Do your changes here
}
Another way is having a local obj_map in PreferencesWindow that is a pointer to the address of obj_map in MainWindow. So, when you create PreferencesWindow, you can just pass the address of MainWindow's obj_map to the constructor and assign that address to the local variable obj_map.
As PreferencesWindow objects are created by MainWindow, the easiest is to have PreferencesWindow objects store a pointer to MainWindow:
class MainWindow;
class PreferencesWindow : public QWidget
{
Q_OBJECT
public:
explicit PreferencesWindow(MainWindow *parent = 0);
public Q_SLOTS:
void saveData();
private:
Ui::PreferencesWindow *uip;
MainWindow* m_mainwindow;
};
Pass the pointer upon construction:
void MainWindow::saveMap()
{
PreferencesWindow *p = new PreferencesWindow( this );
p->show();
}
Then use it:
PreferencesWindow::PreferencesWindow(MainWindow *parent) :
QWidget( parent ),
m_mainwindow( parent )
{
}
void PreferencesWindow::saveData()
{
// FROM HERE I NEED TO CHANGE obj_map
m_mainwindow->obj_map.....it's accessible!
}
I have two classes, MyClass and Widget. Below is the MyClass class and from my Widget class i want to get the str variable. How is that done?
class MyClass : public QObject
{
Q_OBJECT
public:
MyClass();
void fetch();
public slots:
void replyFinished(QNetworkReply*);
private:
QNetworkAccessManager* m_manager;
};
MyClass::MyClass()
{
m_manager = new QNetworkAccessManager(this);
connect( m_manager, SIGNAL(finished(QNetworkReply*)),
this, SLOT(replyFinished(QNetworkReply*)));
}
void MyClass::fetch()
{
m_manager->get(QNetworkRequest(QUrl("http://stackoverflow.com")));
}
void MyClass::replyFinished(QNetworkReply* pReply)
{
QByteArray data=pReply->readAll();
QString str(data);
//this str should be available in my widget class
}
EDIT: Here is a the important part of the widget
namespace Ui {
class Widget;
}
class Widget : public QWidget
{
Q_OBJECT
public:
explicit Widget(QWidget *parent = 0);
~Widget();
private slots:
void on_pushButton_clicked();
private:
Ui::Widget *ui;
};
Widget::Widget(QWidget *parent) :
QWidget(parent),
ui(new Ui::Widget)
{
ui->setupUi(this);
}
Widget::~Widget()
{
delete ui;
}
void Widget::on_pushButton_clicked()
{
//here str should be accessed
}
If you want the str variable from your function available to classes or other functions, here are two choices:
Return it from the function.
Declare a variable in MyClass to hold the string and set the
variable to the value.
Case 1: Returning from a function
QString MyClass::replyFinished(...)
{
QString str(data);
return data;
}
Case 2: Declare a class member variable
class MyClass
{
public:
QString m_replyStr;
};
//...
void MyClass::replyFinished(...)
{
QByteArray data = pReply->readAll();
m_replyStr = data;
}
Modifying your question with an example of what you want to do would be very helpful.
You can emit a signal with str as argument and connect it to a slot in your widget. Then you can do what you want with it.
This way you will preserve the event oriented design and you have not need to control if str exists. Simply when it's ready the slot will handle it.
class MyClass : public QObject
{
Q_OBJECT
public:
MyClass();
void fetch();
public slots:
void replyFinished(QNetworkReply*);
signals:
void strReplyReady(QString str);
private:
QNetworkAccessManager* m_manager;
};
...
void MyClass::replyFinished(QNetworkReply* pReply)
{
QByteArray data=pReply->readAll();
QString str(data);
emit strReplyRead(str);
}
your Widget
class MyWidget : public QWidget
{
//public members
...
public slots:
void readReply(QString str);
}
void MyWidget::readReply(QString str){
//do what you want with str
}
in the main.cpp you do the connect with the static member of QObject
QObject::connect(myClassPointer,SIGNAL(strReplyReay(QString)) ,
myWidgetPointer,SLOT(readReply(QString)));