I would like to abort an application execution (done with Qt) with an error message in case there was a problem regarding it.
with abort(); it was not working with me.
Do you have any suggestions?
The simplest way is to exit the application's event loop with a non-zero result code, and show a message box afterwards. You can either re-spin the event loop manually, or let the messagebox's static method do it for you.
#include <QPushButton>
#include <QMessageBox>
#include <QApplication>
QString globalMessage;
class Failer : public QObject {
Q_OBJECT
public:
Q_SLOT void failure() {
globalMessage = "Houston, we have got a problem.";
qApp->exit(1);
}
};
int main(int argc, char ** argv) {
QApplication app(argc, argv);
QPushButton pb("Fail Me");
Failer failer;
failer.connect(&pb, SIGNAL(clicked()), SLOT(failure()));
pb.show();
int rc = app.exec();
if (rc) {
QMessageBox::critical(NULL, "A problem has occurred...",
globalMessage, QMessageBox::Ok);
}
return rc;
}
#include "main.moc"
Related
I have the following code
#include "dialog.h"
#include <QApplication>
#include <QProgressDialog>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QProgressDialog w;
//w.show();
return a.exec();
}
The execution of this code shows a QProgressDialog UI.
I would like to have the explanation why my QProgressDialog shows up without having an exec()or show() instructions.
I have read the documentation but did not find the explanation on it.
Both constructors of QProgressDialog call QProgressDialogPrivate::init, where forceTimer : QTimer is started:
...
forceTimer = new QTimer(q);
QObject::connect(forceTimer, SIGNAL(timeout()), q, SLOT(forceShow()));
...
forceTimer->start(showTime);
The forceShow() slot in turn looks like this:
void QProgressDialog::forceShow() {
Q_D(QProgressDialog);
d->forceTimer->stop();
if (d->shown_once || d->cancellation_flag)
return;
show();
d->shown_once = true;
}
The show(); statement there is the very reason the QProgressDialog is shown on object creation.
Since it will automatically open after being constructed, follow it with a cancellation.
auto * progressDialog = new QProgressDialog{};
progressDialog.cancel();
I'd like to show and then close a dialog after 5 seconds. The dialog needs to be automatically resized (horizontally and vertically) based on the content of a label. Here is my code:
#include <QApplication>
#include <QDialog>
#include <QLabel>
#include <QTimer>
void notify (int intTime=1000)
{
QDialog notify;
notify.setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
notify.setWindowFlag(Qt::FramelessWindowHint);
QLabel *lbl = new QLabel(¬ify);
lbl->setText("This is a test This is a test This is a test This is a test This is a test This is a test This is a test");
QApplication::processEvents();
notify.adjustSize();
QTimer::singleShot(intTime, ¬ify, SLOT(close()));
notify.exec();
}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
notify(5000);
exit(0);
// return a.exec();
}
It does not not expand the dialog based on the label size. Here is how it looks:
How can I fix it? (Please also let me know if there is better way of doing this.)
I am using Qt5 in Linux.
Since you have not used a QLayout the QLabel will be displayed as large as you can, a possible request is to change the size of QDialog to the recommended size of QLabel with sizeHint():
#include <QApplication>
#include <QDialog>
#include <QLabel>
#include <QTimer>
void notify (int intTime=1000)
{
QDialog notify;
notify.setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
notify.setWindowFlag(Qt::FramelessWindowHint);
QLabel *lbl = new QLabel(¬ify);
lbl->setText("This is a test This is a test This is a test This is a test This is a test This is a test This is a test");
QApplication::processEvents();
notify.resize(lbl->sizeHint());
QTimer::singleShot(intTime, ¬ify, SLOT(close()));
notify.exec();
}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
notify(5000);
exit(0);
// return a.exec();
}
The other possible solution is to use a QLayout:
#include <QApplication>
#include <QDialog>
#include <QLabel>
#include <QTimer>
#include <QVBoxLayout>
void notify (int intTime=1000)
{
QDialog notify;
QVBoxLayout *lay = new QVBoxLayout(¬ify);
//notify.setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
notify.setWindowFlag(Qt::FramelessWindowHint);
QLabel *lbl = new QLabel;
lay->addWidget(lbl);
lbl->setText("This is a test This is a test This is a test This is a test This is a test This is a test This is a test");
QApplication::processEvents();
QTimer::singleShot(intTime, ¬ify, SLOT(close()));
notify.exec();
}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
notify(5000);
exit(0);
// return a.exec();
}
I am using the Urho3D engine with Qt for an application. The problem is that both Urho3D and QApplication require to be ran from main(). For now I am using it in separate processes but IPC makes it complicated.
Is there any way to solve this issue? Thanks
My platform is Urho3D 1.5, Qt 4.71 and Windows 7 x64 and VS2015 (C++)
I'm new to both c++ and Urho3D, but I've successfully achieved it.
Simple code, haven't had further test:
awidget.h:
#ifndef AWIDGET_H
#define AWIDGET_H
#include <QWidget>
#include <QPushButton>
#include <Urho3D/Engine/Application.h>
class aWidget : public QWidget
{
Q_OBJECT
public:
explicit aWidget(QWidget *parent = 0)
{
QPushButton *button = new QPushButton(this);
connect(button, SIGNAL(clicked()), this, SLOT(pressed()));
}
public slots:
void pressed()
{
Urho3D::Context* context = new Urho3D::Context();
Urho3D::Application *application = new Urho3D::Application(context);
application->Run();
}
};
#endif // AWIDGET_H
main.cpp:
#include <QApplication>
#include <awidget.h>
int main(int argc, char* argv[])
{
QApplication app(argc, argv);
aWidget *widget = new aWidget();
widget->show();
return app.exec();
}
By the way, I'm using Qt 5.9.0
So the answer is quite simple. Instead of running QApplication by calling
app->exec();
it is needed to manually and regularily call this from your main loop:
app->processEvents();
This will take care that all events used by Qt are processed and QApplication will respond accordingly.
Example:
#include <QApplication>
#include <awidget.h>
int main(int argc, char* argv[])
{
QApplication app(argc, argv);
bool shallrun = true;
aWidget *widget = new aWidget();
widget->show();
while (shallrun)
{
app->processEvents();
...
}
...
}
My example:
main.cpp:
QApplication a(argc, argv);
MainWindow w;
w.start();
return a.exec();
w.start():
if (cf.exec()){
this->show();
} else {
qDebug()<<"Need exit";
//here should be exit
}
At comment place, I tried to do: qApp->exit() and qApp->quit() and this->close() (but 'this' not shown and of cource close() is not working). How can I finish app from any place of code?
Whole code:
main.cpp
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.start();
return a.exec();
}
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include "CadrForm.h"
#include "TeacherForm.h"
#include "DepartmentForm.h"
#include "CategoriesForm.h"
#include "PostForm.h"
#include "RanksAndDegreesForm.h"
#include "TeachersRankAndDegreeForm.h"
#include "ConnectionForm.h"
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
void start();
~MainWindow();
signals:
void widgetChanged(QWidget*);
private slots:
void on_actionCadr_triggered();
void resetMainLayout(QWidget* w);
void on_actionTeacher_triggered();
void on_actionDepartment_triggered();
void on_actionPost_triggered();
void on_actionCategories_triggered();
void on_actionRanksAndDegrees_triggered();
void on_actionTeachersRD_triggered();
private:
ConnectionForm cf;
CadrForm *cadrForm;
TeacherForm *teacherForm;
DepartmentForm *departmentForm;
CategoriesForm *categoriesForm;
PostForm *postForm;
RanksAndDegreesForm *ranksAndDegreesForm;
TeachersRankAndDegreeForm *teachersRankAndDegreeForm;
QWidget *current;
Ui::MainWindow *ui;
void addWidgetToMainLayout(QWidget *w);
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
connect(this, SIGNAL(widgetChanged(QWidget*)), this, SLOT(resetMainLayout(QWidget*)));
ui->setupUi(this);
cadrForm = new CadrForm(this);
teacherForm = new TeacherForm(this);
departmentForm = new DepartmentForm(this);
categoriesForm = new CategoriesForm(this);
postForm = new PostForm(this);
ranksAndDegreesForm = new RanksAndDegreesForm(this);
teachersRankAndDegreeForm = new TeachersRankAndDegreeForm(this);
addWidgetToMainLayout(cadrForm);
addWidgetToMainLayout(teacherForm);
addWidgetToMainLayout(departmentForm);
addWidgetToMainLayout(categoriesForm);
addWidgetToMainLayout(postForm);
addWidgetToMainLayout(ranksAndDegreesForm);
addWidgetToMainLayout(teachersRankAndDegreeForm);
}
void MainWindow::start()
{
if (cf.exec()){
this->show();
} else {
qDebug()<<"Need exit";
qApp->quit();
qDebug()<<"still working";
}
}
void MainWindow::addWidgetToMainLayout(QWidget *w)
{
ui->mainLayout->insertWidget(0, w);
ui->mainLayout->itemAt(0)->widget()->hide();
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::resetMainLayout(QWidget *w)
{
int index;
if (current)
{
index = ui->mainLayout->indexOf(current);
ui->mainLayout->itemAt(index)->widget()->hide();
}
index = ui->mainLayout->indexOf(w);
if (index != -1) ui->mainLayout->itemAt(index)->widget()->show();
else {
addWidgetToMainLayout(w);
resetMainLayout(w);
}
current = w;
setWindowTitle(current->windowTitle());
}
void MainWindow::on_actionCadr_triggered()
{
emit widgetChanged(cadrForm);
}
void MainWindow::on_actionTeacher_triggered()
{
emit widgetChanged(teacherForm);
}
void MainWindow::on_actionDepartment_triggered()
{
emit widgetChanged(departmentForm);
}
void MainWindow::on_actionPost_triggered()
{
emit widgetChanged(postForm);
}
void MainWindow::on_actionCategories_triggered()
{
emit widgetChanged(categoriesForm);
}
void MainWindow::on_actionRanksAndDegrees_triggered()
{
emit widgetChanged(ranksAndDegreesForm);
}
void MainWindow::on_actionTeachersRD_triggered()
{
emit widgetChanged(teachersRankAndDegreeForm);
}
And ConnectionForm - it's just a QDialog with some GUI and without any additional code.
It looks like the problem is you're not allowed to call QApplication::quit() or QApplication::exit() until the QApplication event loop has actually started. The event loop gets started by QApplication::exec(), so you're calling quit()/exit() too soon for it to have an effect.
You can fix this either by moving the quit()/exit() call so that it's in the event loop (e.g. by moving your MainWindow::start() code to the QMainWindow::showEvent() slot), or by changing your MainWindow::start() to return a value, inspect that value in main, and exit (without calling QApplication::exec()`) if it's a value that indicates your process should exit early.
Since you start the dialog event loop "early" - which is blocking -, you do not get to the event loop of the application.
If this is an intentional design, you better call exit(3) and remove the application event loop.
If you want to have the application event loop running, then you will need to make sure that it runs before you get to the point of your dialog execution.
The quick fix would be to start a single shot QTimer right just before the application event loop is started and that would trigger your "start" method call.
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.start();
QTimer::singleShot(200, w, SLOT(start()));
return a.exec();
}
and change the start to a slot, respectively.
In the long run, you may wish to consider a button and so on for bringing your dialog up, however.
The idiomatic way of queuing a method call until the event loop gets a chance to run is:
QMetaObject::invokeMethod(&w, "start", Qt::QueuedConnection);
Thus, your main would become:
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
QMetaObject::invokeMethod(&w, "start", Qt::QueuedConnection);
return a.exec();
}
There is a QApplication::lastWindowClosed() signal. The Qt docs say:
This signal is emitted from QApplication::exec()
when the last visible primary window [...] is closed.
However, I used QApplication::processEvents() instead of QApplication::exec() in a loop. See this minimal example. (save as qapp.h, it must end on .h, and run qmake -project && qmake && make)
#include <QApplication>
#include <QDebug>
#include <QObject>
#include <QMainWindow>
int exitprogram = 0;
class MyMainWindow : public QMainWindow
{
Q_OBJECT
public slots:
void request_exit() {
qDebug() << "exit requested";
exitprogram = 1;
}
};
int main(int argc, char** argv)
{
QApplication app(argc, argv);
MyMainWindow w;
QObject::connect(&app, SIGNAL(lastWindowClosed()),
&w, SLOT(request_exit()));
w.show();
while(!exitprogram)
{
app.processEvents(QEventLoop::AllEvents, 20);
}
}
Is there still a good way to find out, or to even get a signal, if the last such window is being closed?
Whatever reason you have for using processEvents in place of exec is wrong. The two are not equivalent. exec() will, for example, process the deferred deletion events, while processEvents will not. As you've just found out, the lastWindowClosed signal is not emitted either. This should be telling you right there that you're doing it wrong.
The idiomatic Qt way of doing something each time the event loop goes for another iteration, is to use a zero-timeout timer. Those are virtual timers that do not use operating system resources, they are an internal Qt construct.
The example below illustrates the following:
Use of a zero-timeout timer within a QObject.
Use of the State Machine Framework to manage the state of the application. We have three states:
sWindows is the state when the application windows are still shown. The application is set not to quit on the last window being closed.
sSetup is the state reached when the last of the windows was closed. In this state we ask our Object to send its notification signal with the number of times it executed the zero-timeout timer. This will set the proper count in the message label (C++11 code) or in the count label (legacy code). The state machine automatically transitions to the following state.
sMessage is the state when the message labels are shown, and the application is set to quit upon the last window being closed.
The use of a state machine leads to declarative code: you tell the state machine how to behave, without implementing all of the behavior. You only have to implement the behaviors that are specific to your application and not already provided by Qt. The objects that the state machine manages can be very much decoupled, and the code that declares the behavior of the machine is cohesive - it can be all in one function, instead of being spread around. This is considered to be good software design.
Do note that the zero-timeout timer is very diligent: it will force your handler code to execute constantly whenever the event loop is empty. This will force 100% CPU consumption on the core where the GUI thread happens to be executing. If you have nothing to do, you should stop() the timer.
Qt 5 C++11 Code
// https://github.com/KubaO/stackoverflown/tree/master/questions/close-process-19343325
#include <QtWidgets>
int main(int argc, char** argv)
{
QApplication app{argc, argv};
QLabel widget{"Close me :)"};
QLabel message{"Last window was closed"};
int counter = 0;
auto worker = [&]{
counter++;
};
QTimer workerTimer;
QObject::connect(&workerTimer, &QTimer::timeout, worker);
workerTimer.start(0);
QStateMachine machine;
QState sWindows{&machine};
QState sSetup {&machine};
QState sMessage{&machine};
sWindows.assignProperty(qApp, "quitOnLastWindowClosed", false);
sWindows.addTransition(qApp, &QGuiApplication::lastWindowClosed, &sSetup);
QObject::connect(&sSetup, &QState::entered, [&]{
workerTimer.stop();
message.setText(QString("Last window was closed. Count was %1.").arg(counter));
});
sSetup.addTransition(&sMessage);
sMessage.assignProperty(&message, "visible", true);
sMessage.assignProperty(qApp, "quitOnLastWindowClosed", true);
machine.setInitialState(&sWindows);
machine.start();
widget.show();
return app.exec();
}
Qt 4/5 C++11 Code
#include <QApplication>
#include <QLabel>
#include <QStateMachine>
#include <QBasicTimer>
class Object : public QObject {
Q_OBJECT
QBasicTimer m_timer;
int m_counter = 0;
protected:
void timerEvent(QTimerEvent * ev) {
if (ev->timerId() == m_timer.timerId())
m_counter ++;
}
public:
Object(QObject * parent = 0) : QObject{parent} {
m_timer.start(0, this);
}
Q_SLOT void stop() const {
m_timer.stop();
emit countedTo(m_counter);
}
Q_SIGNAL void countedTo(int) const;
};
int main(int argc, char** argv)
{
QApplication app{argc, argv};
Object object;
QLabel widget{"Close me :)"};
QLabel message{"Last window was closed"};
QLabel count;
QStateMachine machine;
QState sWindows{&machine};
QState sSetup{&machine};
QState sMessage{&machine};
sWindows.assignProperty(qApp, "quitOnLastWindowClosed", false);
sWindows.addTransition(qApp, "lastWindowClosed()", &sSetup);
object.connect(&sSetup, SIGNAL(entered()), SLOT(stop()));
count.connect(&object, SIGNAL(countedTo(int)), SLOT(setNum(int)));
sSetup.addTransition(&sMessage);
sMessage.assignProperty(&message, "visible", true);
sMessage.assignProperty(&count, "visible", true);
sMessage.assignProperty(qApp, "quitOnLastWindowClosed", true);
machine.setInitialState(&sWindows);
machine.start();
widget.show();
return app.exec();
}
#include "main.moc"
I modified your code and now it works. I override closeEvent
==> test.cpp <==
#include "windows.hpp"
int exitprogram = 0;
int main(int argc, char** argv)
{
QApplication app(argc, argv);
MyMainWindow w;
w.show();
while(!exitprogram)
{
app.processEvents(QEventLoop::AllEvents, 20);
}
}
==> test.pro <==
TEMPLATE = app
TARGET = test
QT += widgets
INCLUDEPATH += .
HEADERS += windows.hpp
# Input
SOURCES += test.cpp
==> windows.hpp <==
#include <QApplication>
#include <QDebug>
#include <QObject>
#include <QMainWindow>
#include <QCloseEvent>
extern int exitprogram;
class MyMainWindow : public QMainWindow
{
Q_OBJECT
public slots:
void closeEvent(QCloseEvent *event) override {
exitprogram = 1;
event->accept();
}
};