I am writing a login window in Qt.
When the users clicks on OK, it should close the login window, show a "Connecting to server..." Widget, and open the main window once the connecttoserver method has done its job.
However, the widget appears only when the main window is shown, and disappears immediately (it shouldn't even close!)
How do I solve this issue ?
void LoginWindow::blah()
{
close();
QWidget widget;
widget.show();
//calls to the "connecttoserver method"
Main *main = new Main(student->getInfo()[0], student->getInfo()[1], student->getInfo()[2], view);
main->show();
}
}
QWidget is declared as an automatic on the stack so it is destroyed when the method returns. You want to declare it on the heap instead:
QWidget *widget = new QWidget();
widget->show();
In addition to atomice's answer, make sure you have set your application's quitOnLastWindowClosed to false, or else your application will terminate between closing your login window and opening your main window.
Related
I'm trying to create a C++ Widget Application in QT with multiple windows where you can return to the mainwindow by clicking a Pushbutton.
I'm a complete noobie so I try to follow YouTube tutorial and for opening windows by pushbuttons I watched this one (minute 8:00): https://youtu.be/tP70B-pdTH0
It works when opening secondary windows from the main one but if I try to do the same from a secondary windows to the mainwindow it doesn't. It appears an error "cannot initialize object parameter of type 'Widget' with an expression of type 'MainWindow'"
in the source file I wrote:
void Crediti::on_pushButton_clicked()
{
close();
mainwindow = new MainWindow(this);
mainwindow->show();
}
mainwindow->show(); is the incriminated part
I also included mainwindow in the header of the secondary window and specified the class
MainWindow *mainwindow
in the header so It recognizes mainwindow initially in the source.
I'm doubting if doing this thing is possible at all, and if not so how can I make a pushbutton that, when clicked, can redirect me to the mainwindow?
Please I need this for a school application, thanks
So here you're creating a new main window each time you click on the button. From your description that's not the behaviour you want. I understand you have an application with a main window and other secondary windows and want to bring up the main window when clicking on the button, assuming the main window still exists somewhere and hasn't been deleted.
What I would try is to find the main window when hitting the push button and show / raise it, something along the line of:
#include <QApplication>
#include "MainWindow.h" // Adapt that one to you main window header
// ... some code of your secondary window
void SecondaryWindow::on_pushButton_clicked()
{
for(auto widget : QApplication::topLevelWidgets())
{
// This will return a nullptr if the widget is not the main window
auto mainWindow = dynamic_cast<MainWindow*>(widget);
// skip if not the main window
if(!mainWindow)
continue;
// Show it if hidden
if(mainWindow->isHidden())
mainWindow->show();
// raise it, as in bring it forward, over all other windows
mainWindow->raise();
}
// eventually close the current window if that's what you want
close();
// if you close it and don't need it any more you might also want to delete it
deleteLater();
}
Note that this function won't do anything if the main window has been deleted in the meantime, which might be the case if you closed it and the Qt::WA_DeleteOnClose attribute is set.
Hope that helps.
I have multiple UI windows in my QT project. When a new UI window opens, the previous UI window must be closed, that is, at every point of time only one UI window must be open. How can this be done?
I did that before and i suggest you to not close(delete) UI.
just hide it and when you need it show it again.
check this code:
when user click to see second UI:
void MainApp::on_btnSettings_clicked()
{
this->hide();
settingsManager = new SettingsManager(); // put this line in constructor
settingsManager->show();
}
on second UI on closing form(or back button) emit a signal:
void SettingsManager::closeEvent(QCloseEvent *event)
{
emit settingsBackToMainApp();
}
on main hide second class and show main:
void MainApp::settingsBackToMainApp()
{
settingsManager->hide();
this->show();
}
connect signal to slot:
connect(settingsManager,&SettingsManager::settingsBackToMainApp,this,&MainApp::settingsBackToMainApp); // put this line in constructor
I'm new at Qt. I've created small application and I created second page help.cpp. On MainWindow.cpp I have a button, that switches to help.cpp page.
Function which switches to "help" page:
void MainWindow::on_box1button_clicked()
{
helpwindow = new help(this);
helpwindow->show();
}
This code works properly.
On the "help" page I've got a QButton, which will switch back to mainwindow.cpp. How Can I code that button to actually make this action?
If your intention by "switching" is hiding one window and showing another one, so you can simply pass a reference of the main window to your help window and there when you want to switch back, you can hide/close itself and show the main window.
MainWindow (this code is fine)
helpwindow = new help(this);
helpwindow->show();
HelpWindow
When you want to switch back to the main window, you can do this:
// Hide the HelpWindow itself
// or this->close()
this->hide()
// Show the MainWindow (i.e. the parent window)
QWidget *parent = this->parentWidget();
parent->show();
Since you are creating a new help(this); on mainwindow it is better to close the help window
Use
this->close();
Let's say I have 2 windows in my application, and two classes responsible for them:
class MainWindow: public QMainWindow and class SomeDialog: public QWidget.
In my Main Window I have a button. When it is clicked, I need to display the second window. I do it this way:
SomeDialog * dlg = new SomeDialog();
dlg.show();
Now, the user does something in the window, and closes it. At this point I want to get some data from that window, and then, I suppose, I will have to delete dlg. But how do I catch the event of that window being closed?
Or is there another way not to have a memory leak? Maybe It would be better to create an instance of each window on startup, and then just Show()/Hide() them?
How do I manage such a case?
It is advised to use show() / exec() and hide() instead of dynamically creating the dialog every time you want to show it. Also use QDialog instead of QWidget.
In the constructor of your main window create it and hide it
MainWindow::MainWindow()
{
// myDialog is class member. No need to delete it in the destructor
// since Qt will handle its deletion when its parent (MainWindow)
// gets destroyed.
myDialog = new SomeDialog(this);
myDialog->hide();
// connect the accepted signal with a slot that will update values in main window
// when the user presses the Ok button of the dialog
connect (myDialog, SIGNAL(accepted()), this, SLOT(myDialogAccepted()));
// remaining constructor code
}
In the slot connected to the buttons's clicked() event simply show it, and if necessary pass some data to the dialog
void myClickedSlot()
{
myDialog->setData(data);
myDialog->show();
}
void myDialogAccepted()
{
// Get values from the dialog when it closes
}
Subclass from QWidget and reimplement
virtual void QWidget::closeEvent ( QCloseEvent * event )
http://doc.qt.io/qt-4.8/qwidget.html#closeEvent
Also it looks like the widget you want to show is a dialog. So consider using QDialog or it's subclasses. QDialog has useful signals you can connect to:
void accepted ()
void finished ( int result )
void rejected ()
I think you are looking for the Qt::WA_DeleteOnClose window flag: http://doc.qt.io/archives/qt-4.7/qt.html#WidgetAttribute-enum
QDialog *dialog = new QDialog(parent);
dialog->setAttribute(Qt::WA_DeleteOnClose)
// set content, do whatever...
dialog->open();
// safely forget about it, it will be destroyed either when parent is gone or when the user closes it.
I´ve beeing programming Java for some time right now...Now that I got into C++ and Qt I am a bit lost about GUI Thread (EDT Thread) and Worker Thread
I am trying to make the main window of my application open only when the configuration window is closed.
I dont want to put the code for creating the main window in the OK button of my configuration window.
I tryed to make them modal but the main window still opens.....
Afther configuration is complete I still have to see if there is an application update...So its something like
EDIT: This is my main:
ConfigurationWindow *cw = new ConfigurationWindow();
//if there is no text file - configuration
cw->show();
//**I need to stop here until user fills the configuration
MainWindow *mw = new MainWindow();
ApplicationUpdateThread *t = new ApplicationUpdateThread();
//connect app update thread with main window and starts it
mw->show();
Try something like this:
#include <QtGui>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QDialog *dialog = new QDialog;
QSlider *slider = new QSlider(dialog);
QHBoxLayout *layout = new QHBoxLayout(dialog);
layout->addWidget(slider);
dialog->setLayout(layout);
dialog->exec();
qDebug() << slider->value(); // prints the slider's value when dialog is closed
QMainWindow mw; // in your version this could be MainWindow mw(slider->value());
w.show();
return a.exec();
}
The idea is that your main window's constructor could accept parameters from the QDialog. In this contrived example I'm just using qDebug() to print the value of the slider in the QDialog when it's closed, not passing it as a parameter, but you get the point.
EDIT: You might also want to "delete" the dialog before creating the main window in order to save memory. In that case you would need to store the parameters for the main window constructor as separate variables before deleting the dialog.
You have to learn about signals and slots. The basic idea is that you would send a signal when you configuration is finished. You put your QMainWindow in a member variable and call mw->show() in a slot of your main programm that is connected with the configurationFinished signal.
If your ConfigurationWindow is a QDialog, you could connect the finished(int) signal to the MainWindow's show() slot (and omit the show() call from main).