I have this piece of code. I need to catch the event when my program is about to close, but I cant make that the slot gets called.
QtSingleCoreApplication app(argc, argv);
if(app.isRunning()){
return 0;
}else{
MyClass mainClass;
QObject::connect(&app, SIGNAL(aboutToQuit()),
&mainClass, SLOT(aboutToQuit()));
return app.exec();
}
QtSingleCoreApplication inherits from QCoreApplication
Instead of making MyClass a separate QObject class, why don't you inherit it directly from QtSingleCoreApplication. That way, you can catch the signal before the whole signal/slot mechanism is shut down.
class MyApplication : public QtSingleCoreApplication {
Q_OBJECT
public:
MyApplication(int argc, char **argv) : QtSingleCoreApplication(argc, argv) {
connect(this, &QCoreApplication::aboutToQuit, this, &MyApplication::cleanupApplication);
}
public slots:
void cleanupApplication();
};
void MyApplication::cleanupApplication(){
// do something important
}
void main(int argc, char **argv){
MyApplication app(argc, argv);
return app.isRunning() ? 0 : app.exec();
}
Related
Whenever the application window is minimized or maximized i want to link that signal with a function.
This is the code.
int main(int argc, char *argv[])
{
QApplication application(argc, argv);
Renderer w(model ); // This is QWidget
w.show();
QObject::connect(&w, &QWindow::windowStateChanged, [&](Qt::WindowState state) {
});
// how will i define the QObject::connect
return application.exec();
}
What would be the parameters for the QObject::connect function ?
You cannot use the connect function to connect to different slots based on the given value. You can however simply call the functions based on the value by checking the value in your lambda.
At least, you could if you had the signal. However, your connect suggests that w is - or inherits - a QWindow. You can obviously only connect to signals your class provides. As your Renderer is a QWidget, you have to check that class.
The documentation of QWidget tells us, that there is no windowStateChanged signal, but it states:
When the window state changes, the widget receives a changeEvent() of type QEvent::WindowStateChange.
So therefor we can create our own signal and connect to that. This can look similar to the following working example:
#ifndef RENDERER_H
#define RENDERER_H
#include <QWidget>
#include <QEvent>
class Renderer : public QWidget {
Q_OBJECT
signals:
void stateChanged(bool isMaximized);
protected:
void changeEvent(QEvent *e)
{
if(e->type() == QEvent::WindowStateChange) {
emit stateChanged(windowState() & ~Qt::WindowMaximized);
}
QWidget::changeEvent(e);
}
};
#endif // RENDERER_H
int main(int argc, char *argv[])
{
QApplication application(argc, argv);
Renderer w; // This is QWidget
w.show();
QObject::connect(&w, &Renderer::stateChanged, [&](bool maximized) {
qDebug() << "Maximized?" << maximized;
});
return application.exec();
}
I was able to solve by using QApplication::focusWindow()
int main(int argc, char *argv[])
{
QApplication application(argc, argv);
Renderer w; // This is QWidget
w.show();
QObject::connect(QApplication::focusWindow(), &Renderer::stateChanged, [&](bool maximized) {
qDebug() << "Maximized?" << maximized;
});
return application.exec();
}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QDialog dlg;
dlg.exec();
return a.exec();
}
That's all my code, but when I close the window, The process isn't exit, it seems that drop in the loop a.exec().
Generally speaking, calling any exec is a bad idea, other than QCoreApplication::exec() or QDrag::exec(). The presence of exec() and waitForXxx() methods is an enticing trap for the unwary. Those methods are "easy" to use, but that ease comes at a price of hard to track bugs. Don't use them.
You should simply show the dialog:
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QMessageBox msg;
msg.setText("Hello");
msg.addButton(QMessageBox::Close);
msg.show();
return a.exec();
}
If you wish to wait for the dialog to be accepted or rejected, you should use the dialog's clickedButton slot. QMessageBox has a long-standing bug that makes the accepted and rejected signals useless :(
// https://github.com/KubaO/stackoverflown/tree/master/questions/messagebox-show-25545652
#include <QtGui>
#if QT_VERSION >= QT_VERSION_CHECK(5,0,0)
#include <QtWidgets>
#endif
#include <functional>
[...]
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QMessageBox msg;
msg.setText("Continue?");
msg.addButton(QMessageBox::Yes);
msg.addButton(QMessageBox::No);
auto onClick = [&msg]() {
auto role = msg.buttonRole(msg.clickedButton());
if (role == QMessageBox::NoRole)
QApplication::quit();
if (role == QMessageBox::YesRole) {
auto label = new QLabel("I'm running");
label->setAttribute(Qt::WA_DeleteOnClose);
label->show();
}
};
#if QT_VERSION >= QT_VERSION_CHECK(5,0,0)
QObject::connect(&msg, &QMessageBox::buttonClicked, onClick);
#else
QObject::connect(&msg, SIGNAL(buttonClicked(QAbstractButton*)),
new FunctorSlot{onClick, &msg}, SLOT(call()));
#endif
msg.show();
return app.exec();
}
#include "main.moc"
For Qt 4, you need the following helper:
// Qt 4 only
struct FunctorSlot : public QObject {
Q_OBJECT
public:
std::function<void()> callable;
template <typename Fun>
FunctorSlot(Fun && fun, QObject * parent = {}) :
QObject{parent}, callable{std::forward<Fun>(fun)} {}
Q_SLOT void call() {
callable();
}
};
Possible solution:
QApplication a(argc, argv);
QDialog dlg;
QTimer::singleShot( &dlg, 0, SLOT(exec()) );
return a.exec();
It will work well. First - application event loop will be started. Then dialog event loop will be executed. After closing of dialog, both dialog and application loop will be finished. Application loop will be terminated automatically (by default), when last window is closed.
But, as noted by #thuga - there are no reason to call exec(). It is enough to call show() method.
I derived an application class from QApplication in order to reimplement some methods.
Here is the code:
class MyApplication : public QApplication
{
Q_OBJECT
private:
public:
//...
virtual ~MyApplication();
};
MyApplication::~MyApplication()
{
qDebug("~MyApp1");
try
{
//some potentially long operations
}
catch(...)
{
qDebug("~MyApp Exception");
}
qDebug("~MyApp2");
}
int main(int argc, char *argv[])
{
int returnValue = 1;
{
MyApplication app(argc, argv);
returnValue = app.exec();
}
return returnValue;
}
The problem is that I tend to get different qDebug outputs. I always get ~MyApp1 printed, but only sometimes ~MyApp2. What could be the reason? It seems, that when the App is closing, Qt does not let the whole destructor to be done. How can I make the program wait till the destructor is finished?
The QApplication Destructor is called properly, it's just that qDebug probably shouldn't/can't be used at such a late state of the application. Try using cout/cin streams directly (iostreams/printf).
Consider a QWidget, normally a child in some Layout.
Supposed I want to make it fullScreen for a while, then have it return to it's old spot.
QWidget::setFullScreen() requires that the widget needs to be an independent window - any ideas how to work it out?
The simplest way I can see is to reparent to 0. Something like this:
#include <QApplication>
#include <QPushButton>
class MyButton : public QPushButton
{
public:
MyButton(QWidget* parent) : QPushButton(parent) {}
void mousePressEvent(QMouseEvent*) {
this->setParent(0);
this->showMaximized();
this->show();
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QWidget mainWidget;
MyButton button(&mainWidget);
mainWidget.show();
return a.exec();
}
I have modified the previous example. The previous example never goes back to normal screen.
Just copy paste the code and it will run.
#include <QApplication>
#include <QPushButton>
class MyButton : public QPushButton
{
public:
MyButton(QWidget* parent) : QPushButton(parent) {
m_pParent = parent;
maxMode = false;
}
QWidget * m_pParent;
bool maxMode;
Qt::WindowFlags m_enOrigWindowFlags;
QSize m_pSize;
void mousePressEvent(QMouseEvent*) {
if (maxMode== false)
{
m_enOrigWindowFlags = this->windowFlags();
m_pSize = this->size();
this->setParent(0);
this->setWindowFlags( Qt::FramelessWindowHint|Qt::WindowStaysOnTopHint);
this->showMaximized();
maxMode = true;
}
else
{
this->setParent(m_pParent);
this ->resize(m_pSize);
this->overrideWindowFlags(m_enOrigWindowFlags);
this->show();
maxMode = false;
}
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QWidget mainWidget;
MyButton button(&mainWidget);
mainWidget.show();
return a.exec();
}
I am trying to make a Collaborative Editor(I have to use Linux networking libraries for all the networking stuff), I have the main widget(custom made class that inherits QWidget) with all the components. In the constructor I create all the Widgets on this main Widget and at the end I try to create a new thread using QFuture(I use QFuture instead of QThread cause it allows me easily to call functions with any type of parameters, like QTextEdit, QTextCursor...) but it gives me this error at compilation:
"QObject: Cannot create children for a parent that is in a different thread.
(Parent is QTextDocument(0x1b064b0), parent's thread is QThread(0x1985750), current thread is QThread(0x1ae7610)".
How to solve the error?
Here is my code:
mainwindow.h:
...//includes
using namespace QtConcurrent;
...
namespace Ui {
class Widget;
class TextEdit;
}
class TextEdit;
class Widget;
class Widget : public QWidget {
Q_OBJECT
public:
Widget(QWidget *parent = 0);
~Widget();
...
QFuture<void> thread;
}
class TextEdit : public QTextEdit {
Q_OBJECT
...
}
static void receiveKeyPress(TextEdit *textedit, QTextCursor *secondUserCursor) {
unsigned long long int Number = NULL;
QMessageBox::information(textedit->parentWidget(), "UI Component", "This makes the thread to throw the error");
while(1) if(connected == 1) {
read(recvFileDescriptor, &Number, sizeof(unsigned long long int));
if( Number != NULL)
if( Number == Qt::Key_Home )
secondUserCursor->movePosition(QTextCursor::StartOfLine);
...
else {
QTextCharFormat backgroundFormat = textedit->textCursor().charFormat();
backgroundFormat.setBackground(QColor("lightGreen"));
//If I don't use QMessageBox up there, it breaks here on the next command
secondUserCursor->setCharFormat(backgroundFormat);
secondUserCursor->setPosition(textedit->textCursor().position());
secondUserCursor->insertText(QString::number(Number));
} //else
}//while
}//the function
And mainwindow.cpp:
#include "mainwindow.h"
Widget::Widget(QWidget *parent) {
...
thread = run(receiveKeyPress, this->edit1, this->edit1->secondUserCursor); //run is from QtConcurrent namespace
}
main.cpp:
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Widget window;
...
window.show();
return a.exec();
}
I've read here on stackoverflow how others use QObject(which I never used and I don't get the idea of it) and QThread(the only combination) but I already tried to use QThread and I wasn't able to pass QTextEdit and QTextCursor to it.
Thanks in advance
Edit:
mainwindow.h
class TextEdit : public QTextEdit {
Q_OBJECT
...
public slots:
void receiveKeyPress(qulonglong);
...
};
mainwindow.cpp
void TextEdit::receiveKeyPress(qulonglong Number) {
if( Number == Qt::Key_Home )
...
}
recv-thread.h - created based on this link http://developer.qt.nokia.com/doc/qt-4.8/thread-basics.html#example-3-clock
#include <QThread>
#include "mainwindow.h" //To get TextEdit in here
class RecvThread : public QThread {
Q_OBJECT
signals:
void transferDataToSlot(qulonglong Data);
protected:
void run();
};
recv-thread.cpp
#include "recv-thread.h"
void RecvThread::run() {
unsigned long long int Number = NULL;
while(1) if(connected == 1) {
read(recvFileDescriptor, &Number, sizeof(unsigned long long int));
if( Number != NULL) {
emit transferDataToSlot(Number);
}
}
}
main.cpp
...
#include "recv-thread.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Widget window;
RecvThread recvThread;
...
QObject::connect(&recvThread, SIGNAL(transferDataToSlot(qulonglong)), window.edit1, SLOT(receiveKeyPress(qulonglong)), Qt::QueuedConnection); //line 38
recvThread.start();
//Displaying the window
window.show();
a.exec();
recvThread.quit();
recvThread.wait();
return 0;
}
Am I doing it right?