Program closes too soon



  • I have a simple window with 2 textedit inputs, a "go" button and a textedit output. When my C++ function handles the "go" button and sends output to the 3rd textedit field, the whole window closes. I never get to see the output. No errors appear. Using Qt4 Designer on Linux (CentOS 6.6). I would like to use this window to continue to accept pairs of inputs, displaying output until the user asks to exit. How can I do that?


  • Moderators

    @DocDJ Sounds like your app crashes. You should debug it to see where exactly it crashes.
    You can post the code of your "go" function here - maybe we can see what is wrong there.



  • Thanks for the superfast reply. Here's the whole program (stripped down to simplest form that fails).

    #include <QtGui>
    #include "djdialog1.h" // note: no "ui_" prefix here
    #include <sstream>
    #include <string>	
    
    int int1, int2, answer;
    djdialog1::djdialog1(QWidget *parent)
        : QDialog(parent)
    	{
    	    setupUi(this); // initialize my form
    	    connect(int1box, SIGNAL(textChanged(const QString &)),
    	        this, SLOT(on_int1box_textChanged()));
    	    connect(int2box, SIGNAL(textChanged(const QString &)),
    	        this, SLOT(on_int1box_textChanged()));
    	  
    	    connect(GoButton, SIGNAL(clicked()), this, SLOT(accept()));
    	}
    void djdialog1::on_GoButton_clicked()
    	{ 
    	    QString qreply;
    	    qreply=QString::number(answer);
    	    answerbox->append(qreply);
    	}
    void djdialog1::on_int1box_textChanged(const QString &arg)
    	{bool ok;
    	int1 = arg.toInt(&ok,10);
    	}
    void djdialog1::on_int2box_textChanged(const QString &arg)
    	{bool ok;
    	int2 = arg.toInt(&ok,10);}
    


  • at least in the code you posted answer is not initalized and where do you get the pointer to answerbox? shouldn´t this be something like ui->answerbox?


  • Moderators

    @DocDJ To add to @sneubert : did you try to debug? This is the easiest way to find out where the app is crashing.



  • @sneubert Since it compiled without errors or warnings, I wasn't aware it needed a ui->, but I will try it. Thanks for the tip.


  • Qt Champions 2016

    @DocDJ

    Hi , you do not need UI but!

    if you just have
    QTextEdit *int1box; in djdialog1.h, you need to allocate a real objects before use. This is just a definition of a pointer.

    // somewhere else
    int1box = new QTextEdit (this);

    You use use Designer then all Widgets u place on a form is available via
    UI->the_name

    Please notice those are only valid after
    setupUi(this);



  • @jsulm said in program closes too soon:

    @DocDJ To add to @sneubert : did you try to debug? This is the easiest way to find out where the app is crashing.

    Not sure how to proceed with debugging this one, as it gives no clue as to a cause. I assumed that creating the int1box, etc in Designer would create the objects in my header file for my c++ code to use.


  • Moderators

    @DocDJ You said it crashes when your "go" method is called, then put a break point there and debug...


  • Moderators

    @DocDJ If you used designer then you should access your UI objects via ui-> , but you don't.
    If you use designer then you do not add any object pointers to your classes by yourself - this is done for you.
    Instances are created when you call setupUi() and then you can access them via ui->objName.



  • @mrjj said in program closes too soon:

    @DocDJ

    Hi , you do not need UI but!

    if you just have
    QTextEdit *int1box; in djdialog1.h, you need to allocate a real objects before use. This is just a definition of a pointer.

    // somewhere else
    int1box = new QTextEdit (this);

    You use use Designer then all Widgets u place on a form is available via
    UI->the_name

    Please notice those are only valid after
    setupUi(this);

    In "setupui, this line: answerbox = new QTextEdit(djdialog1); creates the object. Adding Ui-> in front of answerbox causes an error.



  • It would appear that setupUi is not being called. Here is my main.cpp:

    #include <QApplication>
    // following 2 lines are initially here to build the "project"
    //#include <QDialog>
    //#include "ui_djdialog1.h"
    // following line replaces the above 2 lines
    #include "djdialog1.h"
    
    int main(int argc, char *argv[])
    {
        QApplication app(argc, argv);
        /** original code before 1st qmake-qt4 my.pro
        Ui::djdialog1 ui;  // define an object named "ui" as being a djdialog1 
        QDialog *mydialog = new QDialog;
        ui.setupUi(mydialog);
        */
        // following line is new (after initial make)
        djdialog1 *mydialog = new djdialog1;
    	mydialog->show();
        return app.exec();
    }
    

    I got this from a Qt tutorial.

    [Added code tags ~kshegunov]


  • Qt Champions 2016

    Hi
    It seems you did already call it the normal place ?
    djdialog1::djdialog1(QWidget *parent)
    : QDialog(parent)
    {
    setupUi(this); // initialize my form <<<<<<<<<<<<<<<<<<<

    In the ctor.
    Outside and in main is very unusual :)



  • @mrjj The call to setupUi in main was commented-out, so it doesn't happen twice. Maybe I need to do it in main, instead of the dialog. I will have read about how to set a breakpoint in Qt4.


  • Qt Champions 2016

    @DocDJ
    Well you can create the default desktop widget application (File -> New Project )
    and see if that includes the setupUi in mainwindow constructor.


  • Moderators

    @DocDJ Sorry, but this is just completely wrong:

    Ui::djdialog1 ui; // define an object named "ui" as being a djdialog1
    QDialog *mydialog = new QDialog;
    ui.setupUi(mydialog);
    

    You call setupUi() in the window/dialog you create. That means djdialog1 calls it in its constructor (what you're already doing). main is not the correct place to call setupUI. You really should learn Qt basics first, what you are doing now is just guessing and is wrong.
    You can create a default widgets project edit the main window, add a dialog and check the generated code.


  • Qt Champions 2016

    @jsulm said in program closes too soon:

    Sorry, but this is just completely wrong:

    Actually it's correct. I often initialize the widgets through forms without deriving. The most typical example being:

    QMainWindow window;
    Ui::MyMainWindowForm ui;
    ui.setupUi(&window);
    
    window.show;
    

    Notice that the initialized widget is a generic one (as with his code).

    PS. And by the way this is commented out.

    Kind regards.


  • Qt Champions 2016

    @DocDJ
    Please use the triple backtick to get the code formatted, so people don't get confused and you don't lose any symbols due to forum markup.


  • Moderators

    @kshegunov You're right - it is not wrong, but it is not how it is usually done (at least what I saw so far).
    Isn't setupUi() called in the constructor already?

    djdialog1::djdialog1(QWidget *parent)
        : QDialog(parent)
    	{
    	    setupUi(this); // initialize my form
    

    @DocDJ "Adding Ui-> in front of answerbox causes an error." - it is ui-> not Ui->


  • Qt Champions 2016

    @jsulm said in program closes too soon:

    but it is not how it is usually done

    True, I'm only remarking it's a valid approach. I actually don't advise its usage for beginners.

    Isn't setupUi() called in the constructor already?

    No, because the object in question is of type QDialog. There's duplication of names - the same name is used for the form and the custom dialog, so I think this is where the confusion stems from.

    @DocDJ
    Please provide the header file for your class as well. I have a strong suspicion you're deriving both from the dialog and the ui form.


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