I have a Qt Quick Window:
Window{
id: mainWindow
...
}
I want to display a message box before a long blocking operation in QML:
// Set visible=true of 'messageBox' Rectangle{}
messageBox.showWaitMessage("Please wait")
// I want to show it before blocked the screen
mainWindow.requestUpdate()
// Long blocking operation:
compressFile("filepath")
All the objects in the screen are children of mainWindow.
But it is not working. It stills not redrawing the screen before the blocking operation.
Why?
It's because your function which invokes those calls is not finished yet and the requestUpdate() which is queued to be executed by the event loop will actually happen after compressFile.
This is a sign of bad design and it's better to move your compressFile to another thread. If threading is not an option, you may want to call compressFile indirectly like this, which will put that call into the queue. Then the GUI eventloop will repaints the widget before the timer slot being executed. You do not need to update GUI manually.
QTimer::singleShot(0, [=]() { compressFile("filepath") } );
This is only possible for Qt5.4 and above because of QTBUG-26406.
If you are using a lower version of Qt you can do the same thing like:
QTimer *timer = new QTimer(this);
timer->setSingleShot(true);
connect(timer, &QTimer::timeout, [=]() {
compressFile("filepath");
timer->deleteLater();
} );
timer->start(0);
Related
I just want to disable form's close button while doing a task(by QThread), So I connected the thread's signal "started()" and "finished()" to my two slots, for controlling my form's close button.
//...
m_pTestThread = new TestThread();
connect(m_pTestThread, SIGNAL(started()), this, SLOT(onThreadStart()));
connect(m_pTestThread, SIGNAL(finished()), this, SLOT(onThreadFinish()));
m_pTestThread->start();
//...
void QTest::onThreadStart()
{
this->setWindowFlags(this->windowFlags() & (~Qt::WindowCloseButtonHint));
}
void QTest::onThreadFinish()
{
this->setWindowFlags(this->windowFlags() | Qt::WindowCloseButtonHint);
}
After the thread started, my form was hidden... that is strange.
So I call show() after setWindowFlags() function to avoid this problem,
but still don't know why this happened...
Is this the expected behaviour? Should I call show() after setWindowFlags()?
Check the documentation for setWindowFlags here:
Note: This function calls setParent() when changing the flags for a
window, causing the widget to be hidden. You must call show() to make
the widget visible again..
I need to update screen to show how button is moving.
Here is my code:
void mouseReleaseEvent(QMouseEvent *event){
double b=(button->x()*event->y())/(button->x()-1);
double k=(button->y()-b)/button->x();
int time=0;
fnl=false;
if(event->button()==Qt::LeftButton)
{
while(!fnl)
{
int mX=button->x()-1;
int mY=k*(button->x()-1)+b;
button->setText(QString::number(b));
button->move(mX,mY);
QThread::sleep(1);
//here I need to update screen and show button
}
}
}
But it does not update GUI. It simply plays inside the loop.
Never use QThread::sleep() in the GUI thread, It will block the GUI thread from doing anything. Instead, You can use QTimer to schedule something to run at a later point in time. Also, Your slots/functions should be as short and optimized as possible in order to return control to the event loop and be able to handle other events that may happen.
You may want to have a look at this question for a similar problem.
The same technique can be applied here to solve the problem by replacing your while loop with a slot and a QTimer whose interval is set to 0. But Qt can do all that job using the animation framework, Here is an example of a button that gets moved when clicked:
#include <QtWidgets>
int main(int argc, char* argv[]){
QApplication a(argc, argv);
//create and show button
QPushButton button("Animated Button");
button.move(QPoint(100, 100));
button.show();
//create property animator object that works on the position of the button
QPropertyAnimation animation(&button, "pos");
//set duration for the animation process to 500ms
animation.setDuration(500);
//when the button is clicked. . .
QObject::connect(&button, &QPushButton::clicked, [&]{
//set the starting point of the animation to the current position
animation.setStartValue(button.pos());
//set the ending point to (250, 250)
animation.setEndValue(QPoint(250, 250));
//start animation
animation.start();
});
return a.exec();
}
Qt also provides many examples for using the animation framework. . .
A timer is the best option. If you want to use brute force you can call
qApp->processEvents();
inside your loop. Ugly but gets the job done.
I have a Qt main window where I call another window, actually a kind of submenu wich contains parameters for the first one; here is a part of this main window :
void Ui_MainWindow::createSignals()
{
connect(actionDisk_galaxy, SIGNAL(triggered()), this, SLOT(ICMenu()));
}
void Ui_MainWindow::ICMenu()
{
qmenu = new QMainWindow;
DiskMenu = new Ui_DiskGalMenu;
DiskMenu->setupUi(qmenu,this);
setInitialDiskMenuPosition(qmenu, this);
qmenu->show();
}
As you can see, I call another QMainwindow ("qmenu"); here's the code of this new window (whose type is "Ui_DiskGalMenu"):
void Ui_DiskGalMenu::createMenuSignals()
{
connect(pushButton_4, SIGNAL(clicked()), this, SLOT(closeMenu()));
}
void Ui_DiskGalMenu::closeMenu()
{
close(true);
}
After setting parameters in this sub-menu, I would like to close it with a pushButton (here "pushButton_4").
My problem is that when I click on "pushButton_4", this window doesn't close.
I have also tried to reimplement closeEvent but without success.
This function call looks like a mistake:
close(true);
QWidget::close() doesn't take any parameters. So what you're doing here, is call the close(int) function of the C library (for closing file descriptors.) bool is implicitly converted to int, so you end up with this call:
::close(1);
Which is (probably) closing stderr.
You can see what's happening if you change the above to:
this->close(true);
You should get a compilation error since no such function exists. So the correct call would have been:
this->close();
However, QWidget::close() is already a slot, so you don't need the Ui_DiskGalMenu::closeMenu() function at all. All you need is connect to the close() slot to begin with:
connect(actionDisk_galaxy, SIGNAL(triggered()), this, SLOT(close()));
If you need to do more stuff when the window closes, you can override closeEvent() which will be called before the window gets closed.
I try to design a gui for an augmented reality application using the kinect. The idea is, to use the hands detected by the kinect skeleton tracking to control an application via gestures.
This question is not about gestures, as this part of my appilcation works fine.
In my application i want to simulate a mouse click whenever a click gesture is performed. To do this, i am sending two events one, mousebuttonpressed, and one mousebuttonreleased, as a normal click is also a series of press and release.
The whole thing works fine on a QWebView. In the browser window, i can "click" on links.
But for some reason i cannot "click" on a QPushButton. The clicked() signal is not emitted.
I have a short example to illustrate my problem:
First the main function:
int main(int argc, char **argv){
QApplication app( argc, argv );
QWebViewButtons mainapp( 0, Qt::Window );
app.setActiveWindow( &mainapp );
mainapp.show();
mainapp.setApplication( &app ); //this is a setter to also get access to the main application in the widget
return app.exec();
}
This is my own widget:
QWebViewButtons::QWebViewButtons(QWidget* parent, Qt::WindowFlags flags ): QWidget(parent, flags ){
this->m_ui.setupUi( this );
QObject::connect( this->m_ui.pushButton, SIGNAL(clicked(bool)), this, SLOT( buttonClicked(bool) ) );
}
void QWebViewButtons::mousePressEvent( QMouseEvent* event ){
printf("mouse click, %d, %d\n", event->pos().x(), event->pos().y() );
}
void QWebViewButtons::buttonClicked( bool clicked ){
printf("slot button clicked\n");
}
void QWebViewButtons::keyPressEvent( QKeyEvent* event ){
printf("Key pressed\n");
QPoint pos( this->width()/2, this->height()/2 );
QPoint global = this->mapToGlobal(pos);
QWidget *w = this->m_app->widgetAt(global);
//printf("widget under point of click: %s", w);
QApplication::sendEvent( w, new QMouseEvent( QEvent::MouseButtonPress, pos, Qt::MouseButton::LeftButton, Qt::MouseButton::LeftButton, Qt::KeyboardModifier::NoModifier ) );
QApplication::sendEvent( w, new QMouseEvent( QEvent::MouseButtonRelease, pos, Qt::MouseButton::LeftButton, Qt::MouseButton::LeftButton, Qt::KeyboardModifier::NoModifier ) );
}
I followed the suggestion here:
Qt Artificial mouse clicks doesnt work properly
and send to send my mouse events directly to the QPushButton. But that didn't help.
I also tried to send the mouse events to "this", or the main app.
Now I am running out of ideas.
What I want to have is, that the buttonClicked() slot is called if i press any key. But i only is called if i click the button with my mouse.
How can i accomplish this? Or is my basic idea completely false?
Thanks for your ideas.
So, do I get that right? When doing your "click-gesture" you come into keyPressEvent? If so, you can check whether the "click" has been done above the button and explicitly call the button's clicked() signal. But that's not what you want?
And what exactly is QWebViewButtons? The area the user does his gestures in?
Have you debugged into the keyPressEvent to see if your sendEvent has the correct widget (w)? I can't see why the widget should not recieve the event...
And remember that when new'ing a QMouseEvent and sending it via sendEvent is is never deleted. When using sendEvent you should create your event on the stack.
Maybe you should have a look at this thread, where a QTestEventList is recommended: Mimicking/faking a Mouse Click and Mouse Wheel using Qt. But I can imagine that you don't want test functions do the trick ;)
Ok, the trick was to really send the click to the EXACT widget at the desired click position. In my application i had some trouble because of semi transparent widgets lying over each other.
So the widgetAt(global) command wouldnt help me.
But you can use childAt(global) instead. Of course you need to know from which widget you want to find the child.
That did the trick for me. :-)
In my MainWindow, I have a push button and a menu bar item whose signals are both connected to the same slot. In the slot function, I have written:
mainWindow->setCursor(QCursor(Qt::WaitCursor));
This works as expected when the slot function is invoked via the button; however, when the same function is invoked from the menu, the wait cursor doesn't appear. Any idea why?
I also considered using QApplication::setOverrideCursor; however, that causes other problems.
Any recommendations? Thanks!
(I am using Qt 4.7 and doing my development on Windows 7 using Qt Creator with the default MinGW compiler.)
Here's more detail.
in MainWindow constructor: this->setCursor(Qt::CrossCursor);
signal/slot connections:
QObject::connect(button, SIGNAL(clicked()), MainWindow, SLOT(showMessageBox()));
QObject::connect(action, SIGNAL(triggered()), MainWindow, SLOT(showMessageBox()));
showMessageBox function:
void MainWindow::showMessageBox()
{
this->setCursor(Qt::WaitCursor);
// display wait cursor briefly before showing message box
for (int i = 0; i < 1<<30; ) {++i;}
QMessageBox msgBox;
msgBox.setText("Hello!");
msgBox.setStandardButtons(QMessageBox::Ok);
msgBox.setCursor(Qt::PointingHandCursor);
msgBox.exec();
this->setCursor(Qt::CrossCursor);
}
When showMessageBox is invoked with 'button', the wait cursor is displayed as expected.
When showMessageBox is invoked through 'action', the wait cursor does not appear; instead the cursor changes from Qt::CrossCursor to a Qt::ArrowCursor as soon as the user selects the 'action' menu item, and then changes to Qt::PointingHandCursor once the message box opens. The wait cursor never appears.
Your code is synchronous and uses a delay loop. When you're in the delay loop, there's no way for any Qt code to execute. A cursor change requires the event loop to be spinning -- so it appears from the symptoms you give.
Here's how to do it correctly -- remember, if you use delays/sleeps and other blocking calls in your GUI code, your users will hate you, and rightly so. Using exec() in message/dialog boxes is also bad style. Your application is asynchronous, code it so. Make sure your slots are declared as such (in the protected slots: section of MainWindow declaration).
void MainWindow::showMessageBox()
{
this->setCursor(Qt::WaitCursor);
QTimer::singleSlot(200, this, SLOT(slot1()); // fire slot1 after 200ms
}
void MainWindow::slot1()
{
QMessageBox * msgBox = new QMessageBox(this);
msgBox->setText("Hello!");
msgBox->setStandardButtons(QMessageBox::Ok);
msgBox->setCursor(Qt::PointingHandCursor);
msgBox->show();
connect(msgBox, buttonClicked(QAbstractButton*), SLOT(slot2(QAbstractButton*)));
}
void MainWindow::slot2(QAbstractButton* button)
{
// a button was clicked on the message box
this->setCursor(Qt::CrossCursor);
}