[SOLVED] QSplashScreen doesn't show unless I run QApplication::processEvents() 1000 times !?

Tory Gaurnier

In my application I have a lot of data loading when it starts, so I want to have a splash screen that says what's loading. The issue I'm having is when I show the splash screen it doesn't show. This is the code I was using originally:
@
QPixmap pixmap(config->getSplashPath());
splash_screen = new SplashScreen(pixmap);
splash_screen->show();
QApplication::processEvents();
@

And this is the only way I can get it to show:
@
QPixmap pixmap(config->getSplashPath());
splash_screen = new SplashScreen(pixmap);
splash_screen->show();
for(int i = 1; i <= 1000; i++) QApplication::processEvents();
@

Later I use this:
@
splash_screen->showMessage("Some text I want to show");
QApplication::processEvents();
@

If I don't have the processEvents() run 1000 times then the splash screen only shows for a second AFTER everything has already be finished. I know I can put my "initialization" code in a second thread, but from what I've been reading I shouldn't need to, the QSplashScreen examples themselves show only using processEvents(), so what's the best way to handle this?

SGaist

Hi,

Since your splash screen is a custom class, are you doing anything unusual in it ?

Tory Gaurnier

No, right now my SplashScreen class is very empty, it's essentially as if I'm directly using QSplashScreen, the only reason I created a class is so I can play with it once I get it working properly.

SGaist

When are you creating this splash screen ? In your main function ?
Can you show the code where you use it ?

Tory Gaurnier

No, it's created in the constructor of my QMainWindow.
I'll post some of my code, sorry about the syntax, I just copied and pasted, my editor is set to about 100 columns.

Here's the constructor:
@
MainWindow::MainWindow() {
// Initialize config singleton
Config::init();

setWindowIcon(QIcon(config->getIconPath()));

// If config is empty, launch first run dialog
if(config->isEmpty()) {
int result = FirstRunDialog::run(this);

// If FirstRunDialog was cancelled then free memory and quit app
if(!result) {
Config::destroy();
// This 'exiting' status needs to be passed back to main() function and then 'return 0'
// Using exit(0) here sometimes results in strange segfault with no real stack trace o_O
exiting = true;
return;
}
}

// Initialize splash screen
SplashScreen::start();

// Initialize global actions
eComics::Actions::init(this);

// Initialize library right after Config and Actions are finished, but before everything else
Library::init();

// Initialize child widgets
status_bar = statusBar();
main_splitter = new QSplitter(this);
MainSidePane::init(main_splitter);
MainView::init(main_splitter); // Must be initialized after MainSidePane
MenuBar::init(this);
main_side_pane->initSelectedList(); // Must happen after MainView is initialized

// Add widgets to window
setCentralWidget(main_splitter);
main_splitter->addWidget(main_side_pane);
main_splitter->addWidget(main_view);
main_splitter->setSizes( {150, 650} );
main_splitter->setCollapsible(1, false);

resize(800, 600);

// Initialize comic info dialog
ComicInfoDialog::init(this);

// Initialize preferences dialog
PreferencesDialog::init(this);

// Connect signals to actions
connect(eComics::actions->statusBar(), SIGNAL(toggled(bool)), this,
SLOT(toggleStatusBar(bool)));
connect(eComics::actions->quit(), SIGNAL(triggered()), qApp, SLOT(quit()));
connect(eComics::actions->fullScreen(), SIGNAL(toggled(bool)), this,
SLOT(toggleFullscreen(bool)));

SplashScreen::finish();
}
@

And here's the implementation of my SplashScreen (it's a singleton):
@
#include "SplashScreen.hpp"

#include <QApplication>

#include "Config.hpp"
#include "MainWindow.hpp"

SplashScreen *splash_screen = nullptr;

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

   SPLASHSCREEN PUBLIC METHODS          *

- - - - */

//THIS IS A STATIC METHOD
void SplashScreen::start() {
if(splash_screen == nullptr) {
//THIS PRINTS RIGHT AWAY NO PROBLEM
qDebug() << config->getSplashPath();
QPixmap pixmap(config->getSplashPath());
splash_screen = new SplashScreen(pixmap);
splash_screen->show();
/for(int i = 1; i <= 1000; i++)/ QApplication::processEvents();
}
}

//THIS IS ALSO STATIC
void SplashScreen::finish() {
splash_screen->QSplashScreen::finish(main_window);
delete splash_screen;
splash_screen = nullptr;
}

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

   SPLASHSCREEN PRIVATE METHODS          *

- - - - */

SplashScreen::SplashScreen(const QPixmap &pixmap, Qt::WindowFlags f) : QSplashScreen(pixmap, f) {
// Don't allow clicking on splash screen to close it
setEnabled(false);
}

SplashScreen::SplashScreen(QWidget *parent, const QPixmap &pixmap, Qt::WindowFlags f) :
QSplashScreen(parent, pixmap, f) {
setEnabled(false);
}

SplashScreen::~SplashScreen() {}
@

Tory Gaurnier

Also, I tried putting it in my main.cpp, but it didn't make a difference.

Tory Gaurnier

Well I figured out the only thing that seems to work, I just have to put all my initialization work in a worker QThread, I was hoping to avoid that using processEvents(), but that doesn't look like it's going to happen.

SGaist

Does it also happen if you use the same code without any modification as the example provided in the documentation ?

By the way, what are you doing in your initialization ? Anything involving the event loop ?

Tory Gaurnier

The initialization code is loading the library from XML, and it scans user selected directories for new content, it is fairly intensive (if they have a lot of content), but there is nothing GUI related (I double checked in case I forgot about something).

Tory Gaurnier

There is use of signals and slots in the initialization, that is separate from the event loop right?

Tory Gaurnier

I should also note that I don't even run app.exec() until after the initialization and the splash screen disappears.

SGaist

Ok, then it's clearer now. The event loop is mandatory for signals and slots to work. That's why it's working if you use a secondary thread: QThread starts it's own event loop.

Anyway, following your description, it sounds that using a secondary thread would be best. QFileSystemModel uses one to populate its data and a signal to let the developer know it's ready to be used.

Tory Gaurnier

OK, awesome, thanks for the info! :D

SGaist

You're welcome !

If that answers your question then please update the thread title prepending [solved] so other forum users may know a solution has been found :)