How to get the returned value?

JonB

@_jao_victor_
As @jsulm says, slots cannot return any value. A lot of people implement your "login" as a modal QDialog, no signals/slots, which can return a result like true/false to caller.

_jao_victor_

@JonBBut my login screen is a QDialog.

JonB

@_jao_victor_
So if it's already a QDialog you are already there! You don't need signals/slots. Just result = theDialog.exec(). Read https://doc.qt.io/qt-5/qdialog.html#exec.

_jao_victor_

@jsulm Aren't signals emitted only when a widget is changed?

_jao_victor_

@JonBSo should it look something like this?

from control.functionslogin import login

app = QtWidgets.QApplication([])

viewlogin = uic.loadUi('./views/ui/login/viewLogin.ui') 
mainview =  uic.loadUi('./views/ui/main/mainview.ui')

result = viewlogin.exec()
viewlogin.button_login.pressed.connect(lambda: login(viewlogin, mainview))


viewlogin.show()
app.exec()

As I understand it, the modal window (QDialog) blocks the interaction with other windows, but how will the window (QDialog) know when to close and send and send the signal?

jsulm

@_jao_victor_ said in How to get the returned value?:

Aren't signals emitted only when a widget is changed?

I was talking about your own custom signals. You emit them whenever needed...

JonB

@_jao_victor_
No. Like I said, no signals/slots/connects. No show. Just:

result = viewlogin.exec()    # Like I said, read https://doc.qt.io/qt-5/qdialog.html#exec
if not result:    # e.g. user clicked `Cancel`
    sys.exit(1)
login = viewlogin.login_login.text()
password = viewlogin.login_password.text()

mainview.show()
sys.exit(app.exec())

Get that working first. Then think about what you want to do if the user presses Cancel, or if the name+password is incorrect. (Hint: you might move the credential validation code into viewlogin when user presses OK, and give an error message and keep him in there till he gets it right or Cancels. There are various possible strategies.) The point initially is to get the dialog working.

jsulm

@_jao_victor_ said in How to get the returned value?:

know when to close and send and send the signal?

It knows that when the user closes the dialog. And if you go for @JonB suggestion there is no need for any signals. Simply check what https://doc.qt.io/qt-5/qdialog.html#exec returns (hint: https://doc.qt.io/qt-5/qdialog.html#DialogCode-enum).

_jao_victor_

@JonB I think my problem is much more due to the design, as @jsulm said. I searched the internet for several tutorials but I couldn't find one that would suit me completely, because at most, they only taught how to create two windows and my system has more than two (1 QMainWindow and 4 QDialog). My login QDialog calls my QMainWindow main and it can call another 3 QDialog.

My problem is that I can't pass the specific variable (session_user) that needs to be passed to the mainview screen and then passed to the other 3 QDialog that can be opened.

I managed to make the variable go to mainview (I think in an unviable way) but I couldn't pass it on to the 3 QDIalog.

Do you know any system that I can get the design?

jsulm

@_jao_victor_ said in How to get the returned value?:

but I couldn't pass it on to the 3 QDIalog

Why not? What stops you from subclassing QDialog and pass that data to the constructor or implement a setter method?

JonB

@_jao_victor_ said in How to get the returned value?:

My login QDialog calls my QMainWindow

Never do this. Use a pattern such as I showed. Nothing should "call" your main window, nor anything in it, other than the Python main program. The main window may "call" dialogs, or access things within them if required, and dialogs may call other dialogs. But keep thing "uni-directional": widgets which open other widgets may pass/access/receive things to/from the sub-widget, but do not make it so the sub-widget accesses or even knows anything about the calling/parent widget.

Follow either of @jsulm's suggestions for passing variables around.

_jao_victor_

@JonB I will reformulate my design based on what you and @jsulm showed me and I return feedback here. Thank you, this problem has been chasing me for a long time.

_jao_victor_

Hello I'm back. Okay, but, how am I going to do so that when the user presses the login button, a verification function is called and returns True (1) to main.py if the login and password are correct, how am I going to do this if I can't use slots or signals?

_jao_victor_

@JonB exec () returns me 0 when I close the window, but how do I return zero when the password and login are not right, for example. I have no control over this returned value.

jsulm

@_jao_victor_ said in How to get the returned value?:

but, how am I going to do so that when the user presses the login button, a verification function is called

@JonB already shown you how to do this, even with code.
Just add additional method to your dialog which returns that information (like loginValid() in this example):

result = viewlogin.exec()    # Like I said, read https://doc.qt.io/qt-5/qdialog.html#exec
if not result or not viewlogin.loginValid():
    sys.exit(1)

JonB

@_jao_victor_ said in How to get the returned value?:

I have no control over this returned value.

Oh, but you do :)

@jsulm suggests you do:

result = viewlogin.exec()    # Like I said, read https://doc.qt.io/qt-5/qdialog.html#exec
if not result or not viewlogin.loginValid():
    sys.exit(1)

This is fine, and I suggest you actually do that to start with as it's simple and you should get that working initially.

However, this will mean that if the user types the wrong credentials and clicks OK you will exit your program; or at best you might create a loop which perhaps gives an error message and shows the logon dialog again. I suggested a hint:

(Hint: you might move the credential validation code into viewlogin when user presses OK, and give an error message and keep him in there till he gets it right or Cancels. There are various possible strategies.)

It might be nicer if the viewlogin dialog checks the credentials before exiting back to the caller, and keeps the user in the dialog until either he types correct credentials and OK or he gives up and clicks Cancel, at which point it's fair enough to exit the program.

For that we will override the virtual void QDialog::accept() in your derived QDialog subclass. [Note: I don't know whether we can do that with your uic.loadUi(). I would suggest you change over to using pyuic at compilation stage to generate compile-time subclasses for your design stuff, instead of loading it dynamically at runtime. Read https://doc.qt.io/qtforpython/tutorials/basictutorial/uifiles.html and follow Option A: Generating a Python class.] Normally clicking OK just calls QDialog::accept(), which exits the dialog and returns non-zero to the caller of QDialog::exec(). You might replace with something like:

/*virtual*/ void ViewDialog::accept() override
{
    if (!loginValid())
    {
        MessageBox("Bad credentials, try again");
        return;
    }
    QDialog::accept();
}

Now so far as the caller of viewLogon::exec() is concerned, it either receives false if the user clicked Cancel, in which case you can exit, or true iff the user clicked OK and the credentials were correct.

_jao_victor_

Ok @jsulm and @JonB, so far I understood correctly, I did the tests and got the expected result, however, what if the buttons are not the ones from QDialog, but one that I implemented myself? The Cancel and OK buttons send the signals automatically when they are pressed, so how do I make my buttons (login and register) send their signals when they are pressed?

a

JonB

@_jao_victor_
Looks OK. Sorry, is there a question here?

_jao_victor_

@JonB yes i rewrote the text to explain it better, sorry.

JonB

@_jao_victor_

connect(loginButton, &QPushButton::clicked, accept);
connect(cancelButton, &QPushButton::clicked, reject);

You'll have to think a bit more carefully about the Register button. It does not do the same thing as the Login button, i.e. it does/should not cause the dialog to exit with "success" back to the main program for the user to continue into the main window.

That's for you to figure out what you want to do.

QDialog does not have to exit with only accept() or reject(). They use void QDialog::done(int r), and you can do the same with as many different r values as you please. That value is the return result when you go int result = dialog.exec().