on Dialog box show() is not working but exec() is

[rupertrupert]

Whenever I exec() a dialog it works but when I do show() instead, i get this weird seethrough box and it eventually crashes

[JonB]

Do you allow the event loop to be re-entered after the show()? And the dialog instance remains in scope? How does open() behave?

[rupertrupert]

@JonB open() does the exact same thing as show(), and im not sure what you mean about the event loop, but the scope that the dialog is initalized in stays open until someother action happens

[Pl45m4]

@rupertrupert

Show the parts of the code where you open the dialog and what's happening before/after that

Btw: This looks like an assignment for school class or similar?! So do you have some template which you have to use and extend in order to solve some task(s)?

And you are not blocking the event loop after calling show() or open() through any while loop or similar, aren't you?!

[rupertrupert]

@Pl45m4 Yeah I was using while loop with sleep() because I needed a way to update something every second, so im not sure what else to do to implement this

[rupertrupert]

@Pl45m4
Here is what I have right now, allthough update() is never called and I have no idea why
void Object::start(){
ui = new Object2 (nullptr);
ui->open();
QTimer *timer = new QTimer(this);

QObject::connect(timer,SIGNAL(timeout()),this,SLOT(update()));

timer->start(1000);

}

void Object::update(){
qInfo("Hi");
}

[Pl45m4]

@rupertrupert said in on Dialog box show() is not working but exec() is:

update() is never called and I have no idea why

Because your signal calls QWidget::update() and not your Object::update() function.

• https://doc.qt.io/qt-6/qwidget.html#update

Rename your function to something like sayHi() and it should work like expected

Btw: you are leaking memory cause you create a new instance of Object2 every time Object::start() is called. And since your dialog has no valid parent it's not using the auto-cleanup from Qt MetaObject system.

Add Qt::WA_DeleteOnClose as attribute to your dialog or create in just once in your c'tor, then only open/show it when you need it.

[JonB]

@Pl45m4 said in on Dialog box show() is not working but exec() is:

Because your signal calls QWidget::update() and not your Object::update() function.

Although this would explain behaviour, OOI what makes you say QWidget::update() will be called? The slot is on this, which is a Object with its own update(), and what makes you think Object is a QWidget?

Doubtless @Pl45m4 will turn out to be right though I'm not sure why/how he knows. Otherwise what is the scope/lifetime of the Object instance that start() is called on? Or, again, after start() do you allow the event loop to be re-entered?

[Pl45m4]

@JonB said in on Dialog box show() is not working but exec() is:

OOI what makes you say QWidget::update() will be called?

The described behavior by OP

The slot is on this, which is a Object with its own update()

True, but OP uses the String-based connections which are not fully qualified and don't specify a type or class.
From my own experience I'm 99.99% sure ;-)

what makes you think Object is a QWidget?

Must be, otherwise it would have worked ;-)
[Edit: Apparently it's actually a QObject but some other weird stuff is going on. Maybe app quit?!]

Btw:
Using a fully qualified functor will also solve this:

// Object::update(), correct
QObject::connect(timer, &QTimer::timeout, this, &Object::update);
// QWidget::update(), wrong
QObject::connect(timer, SIGNAL(timeout()), this, SLOT(update()));

&Object::update will explicitely pick void Object::update() by function reference, which prints "Hi" in this case.
While the String/Macro based syntax just sends a update() call to this without any checks at runtime, which results in QWidget::update() being called.

[rupertrupert]

@Pl45m4 OK i tried both of the solutions you said and they did not work

[Pl45m4]

@rupertrupert said in on Dialog box show() is not working but exec() is:

OK i tried both of the solutions you said and they did not work

If the below code does not work, you are still blocking the signal with some sleep or while - loop.
You must not have any sleep or blocking loops in your main/GUI thread in your entire program... otherwise it breaks event driven mechanics as used in Qt.

void Object::start()
{
    ui = new Object2(this);
    ui->open();
    QTimer *timer = new QTimer(this);
    QObject::connect(timer, &QTimer::timeout, this, &Object::update);
    timer->start(1000);
}

[rupertrupert]

@Pl45m4 said in on Dialog box show() is not working but exec() is:

QObject::connect(timer, &QTimer::timeout, this, &Object::update);

ok I changed to exactly this and now i dont see my ui or anything and the program just closes when I reach Object::start(), and there is no code after Object::start() is called to be blocking the signal

[Pl45m4]

@rupertrupert said in on Dialog box show() is not working but exec() is:

there is no code after Object::start()

Where do you call start()? In MainWindow? Or in your main.cpp?

How is your Object created and what kind of class is this? As @JonB was also wondering...

[rupertrupert]

@Pl45m4 after my main window is closed, in the signal that closes it, and it is a QObject

[Pl45m4]

@rupertrupert said in on Dialog box show() is not working but exec() is:

after my main window is closed

Usually your program would end at this point...
Post the related code then... this isn't a Q&A game here.
We can't see what your are doing exactly