Custom signal to slot : The slot requires more arguments than the signal provides.

[Petross404_Petros S]

@mrjj

Hmm, I haven't thought of the old syntax. Thank you, I will test tomorrow morning and report any findings.

[mrjj]

@Petross404_Petros-S
Not the old syntax, the old signal frameChanged.
You would bind it to a private slot and
void MyMovie::FrameChanged() {
emit MynewFrameChanged(this);
}

But please check if move could just be in Dice as its the main user and
should just have the object then.

[Petross404_Petros S]

@mrjj OK before powering off my pc, I thought let's try to declare QMovie* movie as a private member of QtDice.

Afterwards, just before using the movie, I setted the filename movie.setfilename(":/images/etc") but the compiler ranted something about static variable movie but I am quite sleepy to remember.

Perhaps I must also use new somehow on an existing variable to actually create it. I think I found what I will be looking the next day.

All the best, Petros.

[mrjj]

@Petross404_Petros-S
Yes , yes you MUST new it in QtDice constructor before use.
(movie = new QMovie(this) )

and its
movie ->setfilename not the . (dot) syntax :)
(-> for pointers DOt is for non pointers)

[Petross404_Petros S]

Yes , yes you MUST new it in QtDice constructor before use.

Actually, when I new it in QtDice::QtDice I get a segfault when I try to set it's filename in the slot void QtDice::image_update(int) .

The moment I write in the latter, QMovie movie = new QMovie(this) and afterwards set the filename, it works.

Anyway that isn't Qt specific anymore but about my lack of proper C++ understanding. I will keep this for a little longer UNSOLVED and will post any findings to close it. Thank you very much.

[VRonin]

connect(movie, &QMovie::frameChanged, this, std::bind(&QtDice::qmovieFrameChanged,this,movie));

[mrjj]

hi
My guess is that u do the classic error/facepalm
QMovie movie = new QMovie(this) ; // this make a LOCAL variable. not what u want
To use the one from .h
movie = new QMovie(this); // NOTICE No TYPE FIRST. we set the member to something.

[Petross404_Petros S]

@VRonin

Indeed that worked! Compiler didn't warn about anything and as a matter of fact I was thinking of QSignalMapper and std::bind but thought it would be very complex. It's a chance to take a closer look at your code and practice on toy-programs with bind.

Anyway, with your solution I don't need a lambda for this anymore.

@mrjj

In the ctror I wrote movie = new QMovie(this) but there is another problem. Now that I use a private class member movie, the animation doesn't play. The gif is shown, but it's frozen. It doesn't matter if I use std::bind as VRonin proposed or if I use the lambda.

As long as the QMovie is created in the ctor like this :

// In the ctor
movie = new QMovie(this);
movie->setFileName(":/images/rolling_infinite.gif");
...
//In void QtDice::image_update(int image_number)
....
m_ui->label->setMovie(movie);
//Animation works!

But I set the movie's filename inside the function :

// In the ctor
movie = new QMovie(this);
....
// In the void QtDice::image_update(int image_number)
movie->setFileName(":/images/rolling_infinite.gif");
m_ui->label->setMovie(movie);

if(movie->isValid())
{
//again is valid is printed, Qt continues to accept movie as valid.
	qDebug() << "is valid" << '\n';
	movie->start();
}
else...
//Gif is shown, but doesn't animate

I even tried to append this-> infront of movie but of course this wasn't the problem. It can access the variable as there isn't any movie in scope. I can drop the issue here because the custom signal to signal connection is accomplished, but I want to know how to debug the stopped animation problem. GUI isn't unresponsive, I guess it's not a crash...

[mrjj]

Hi
it really should work the same as in ctor.
Must be something else.
In what function is example 2 ?

[Petross404_Petros S]

@mrjj It goes like this :

Ctor connects a pushbutton click with QtDice::reload which in turn calls QtDice::image_update to animate the gif and after it's finished, show an image.

I found out what the problem is. QtDice::image_update is called multiple times and therefore it tries to setFileName every time. So a check if fileName() is empty must be done each time before attempting to setFileName.

void QtDice::image_update(int image_number)
{
	//Make sure we don't constantly re-append a fileName!
	if(movie->fileName() == "" )
	{
		movie->setFileName(":/images/rolling_infinite.gif");
		
		//If it still is empty print error and exit. Not good at all
		//TODO wrap the setFileName in some Qt assert to throw an exception
		if (movie->fileName() == "")
		{
			qDebug() << "Error! Couldn't set a fileName to read for the animation";
			QApplication::quit();
		}
	}
	
	m_ui->label->setMovie(movie);
	.....
}

I don't know exactly why this failed ( I mean I could change the fileName as many times as I like), but I checked and rechecked that with this if (movie->fileName() == "" ).... the animation works.

That could also explain why some (but not all) times the animation played the very first time I push the button (ie called the function) and the second time it stopped. If someone thinks that other reasons come into play, please inform me, I am more than glad to learn.

For any of you, that is curious what is the code and/or want to c&c, this is the QtDice and this is a screenshot

Have a nice afternoon!