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I am a beginner with signal & slots in QtCreator.

I would like to know how to connect a signal declared in mainwindow code in a Qwidget LCDNumber include in the mainwindow.

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Because even if my ManWindow signal is diclared correctly (I guess)

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I can't configure the connection between MainWindow signal and LDCNumber Display(int) SLOT it in design mode :

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Would you know how to code the connection of MainWindow SIGNAL declared in MinWindow's Class and LCDNumber include in Mainwindow's SLOT, please?

Here are all the propeties of QLCDNumber class :

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Thanks a lot!!

Nicolas Brx
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  • at first, I want to ask you never to use QT instead of Qt. QT==> QuickTime Qt==> c++ framework in QtCreator there is now no way to connect user defined signal to user defined slot. but you can connect them in c++ code by connect method. something like this : connect(widgetA, SIGNAL(signal()), widgetB, SLOT(slot()); – SajadBlog Jan 25 '21 at 05:17
  • Ok, Qt, got it. I tried a code like `connect(widgetA, SIGNAL(signal()), widgetB, SLOT(slot());` but I have no Widget A to connect only a QObject in my C++ code. I just wanna link my C++ code to the "widget B" LCDNumber widget in the MainWindow. What should I write instead of `widgetB, SLOT(slot())` please? – Nicolas Brx Jan 25 '21 at 06:32
  • I recommend that you read the official document https://doc.qt.io/qt-5/signalsandslots.html in your case you can write the below code : if QMainview object named mainView and LCDNumber named lcd connect(mainView, SIGNAL(Vxx_cost_disp_update(int)), lcd, SLOT(on_Vxx_cost_disp_update(int))); – SajadBlog Jan 25 '21 at 07:35
  • Hello Sajad, thanks for sharing the signals & slots topic. I already read it. I added the propeties of my LCD object in my post above and I tried to code the connection as you suggested : `connect(&Vxx_cost_disp,SIGNAL(TransmitConnectorValue(int)),this,SLOT(on_Vxx_cost_disp_updated(int))); connect(this, SIGNAL(Vxx_cost_disp_update(int)), &lcdNumber, SLOT(display(int)));` But it still say that "lcdNumber" is not declared in that scope. (I also tried to replace "this" by "MainWindow" as you suggested and "&ldcNumber" by "&QLCDNumber") – Nicolas Brx Jan 25 '21 at 12:35
  • @NicolasBrx , use new Signal Slot syntax, it gives better compilet time warnings: https://wiki.qt.io/New_Signal_Slot_Syntax – Roman Pavelka Jan 25 '21 at 12:38
  • Thanks Roman! I tried to decladre the connection the new may but "lcdNumber" is not recognized by connect function... `connect(Vxx_cost_disp,&MainWindowSignal::TransmitConnectorValue(int),lcdNumber,&QLCDNumber::display(int));` (I posed my QLCDNumber object properties above) – Nicolas Brx Jan 25 '21 at 12:56
  • can you share your project or a simple project that demonstrates your problem? note: when any *.ui file send to UIC(what happened in your case) ,a new file was generated that contains all new widgets that inserted in UI file and his name is like ui_classname. finally added all them to base class and declare a ui variable .you have to add "ui->" before call widget.some things like this ==> "ui->lcdnumber" – SajadBlog Jan 25 '21 at 13:51
  • https://estaca-my.sharepoint.com/:u:/g/personal/nicolas_bierinx_estaca_eu/EcMJ4ZOkTxRHi0a9xeyP_gIB2gfCO4SOV5HX7ixARW7-Cw?e=Hfu6UZ Here is a link to my OneDrive. By running the programme you should have a QDebug display each second. Then you will find the issue commented on line 46 of Mainwindow.cpp and it's description on line 43 to 45. This code is compiled on a Raspberry Pi 3B+. – Nicolas Brx Jan 26 '21 at 06:31

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