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How to link a bool variable to a push button in c++ qt?



  • I am working on a project that after clicking on a push button , some labels and lineedits that were hidden before, become unhide. After that, for the second time clicking on the pushbutton, I want to hide the labels again.

    I have written the following code and used a bool variable, but nothing happened.

    Here is my code:

    dialog.h:

    #ifndef DIALOG_H
    #define DIALOG_H
    
    #include <QDialog>
    
    namespace Ui {
    class Dialog;
    }
    
    class Dialog : public QDialog
    {
        Q_OBJECT
    
    public:
        explicit Dialog(QWidget *parent = 0);
        ~Dialog();
    
    private slots:
        void on_pushButton_clicked();
    
        void on_pushButton_2_clicked();
    
    private:
        Ui::Dialog *ui;
        bool bForButton ;
    };
    
    #endif // DIALOG_H
    
    

    dialog.cpp:

    #include "dialog.h"
    #include "ui_dialog.h"
    
    Dialog::Dialog(QWidget *parent) :
        QDialog(parent),
        ui(new Ui::Dialog)
    {
        bForButton = false;
        ui->setupUi(this);
        ui->label->setVisible(false);
        ui->label_2->setVisible(false);
        ui->lineEdit->setVisible(false);
        ui->lineEdit_2->setVisible(false);
        ui->label_3->setVisible(false);
        ui->pushButton_2->setVisible(false);
    }
    
    Dialog::~Dialog()
    {
        delete ui;
    }
    
    void Dialog::on_pushButton_clicked()
    {
        bForButton = !bForButton;
    
        ui->label->setVisible(true);
        ui->label_2->setVisible(true);
        ui->lineEdit->setVisible(true);
        ui->lineEdit_2->setVisible(true);
        ui->label_3->setVisible(true);
        ui->pushButton_2->setVisible(true);
    }
    
    void Dialog::on_pushButton_2_clicked()
    {
    
        double a,b,c;
        a = ui->lineEdit->text().toDouble(); //a=doublevalue of textbar1
        b = ui->lineEdit_2->text().toDouble(); //b = doublevalue of textbar2
    
        c=a*b;
        ui->label_3->setText(QString::number(c));
    }
    


  • @nanor
    You seem to be relying on the names of your slots being auto-connected to signals. Put in debug messages to see whether your slots are being called at all?



  • @JonB Thank you for replying. I don't understand exactly what to do. Do you mean I must run the code in debugging mode and see if there are errors or not?
    I ran the code in debugging mode and there were no errors.



  • @nanor
    Put lines like qDebug() << "Got to this line (1)" (you may need #include <QDebug> at the top of your file) into your on_pushButton_clicked() & on_pushButton_2_clicked() slots. When you run from Qt Creator, do you see output appearing (I think it's in the "Application Output" tab at the bottom)?



  • @JonB I put qDebug() << "1" into on_pushButton_clicked() and qDebug() << "2"; into on_pushButton_2_clicked() . I see outputs when I run the code.
    The code works well (after clicking on the pushButton , the labels become unhide and after clicking the pushButton_2(which is related to the multiply of two numbers) it works well too).
    The only part that does not work, is when I click on the pushButton for the second time to hide the labels again(When I click on the pushButton for the second time, all the labels remain, but my goal is to hide them again, but nothing happens).



  • @nanor said in How to link a bool variable to a push button in c++ qt?:

    When I click on the pushButton for the second time, all the labels remain, but my goal is to hide them again, but nothing happen

    So look at your code in on_pushButton_clicked() where you call setVisible(true) on each widget. So why do you expect them to disappear? What could you write there instead of true there to make it work as you want?



  • @JonB Yes, that's right. But I wrote bForButton = !bForButton; before writing the setvisible(true) for the items in on_pushbutton_clicked(). As in the constructor I wrote bForButton = false, I thought that for the second time clicking on the pushbutton, the boolian value turns into false again and all of the elements become hide again.



  • @nanor but what is using bForButton?

    Actually it is better not to use this flag at all. Can you query the button's current visibility?



  • @nanor said in How to link a bool variable to a push button in c++ qt?:

    But I wrote bForButton = !bForButton

    Think about how/why that then messes things up from then on, because you have changed the value of the bForButton value in doing so. You must not change that variable itself. Hint: it's OK to pass !bForButton as an expression/parameter, but not to go bForButton = !bForButton.... Or, you could choose to go down @Bob64's "current widget visibility" route, though that's more code to write/maintain.



  • @Bob64 Actually I used bForButton to hide and unhide the labels by clicking on push buttons (For the first time clicking on the push_button, I want to unhide the labels, for the second time clicking on the push_button I want to hide them again, for the third time the goal is unhiding them again...).
    I set bForButton=false for hiding and bForButton=!bForButton for unhiding them.



  • @JonB I put setVisible(bForButton) instead of setVisible(true) for the elements into on_pushButton_clicked() slots and my code worked well. Thank you so much. I really appreciate your help.



  • @nanor
    Well done for figuring this for yourself! Hopefully you can see now exactly why that is indeed the right thing to do!



  • @nanor said in How to link a bool variable to a push button in c++ qt?:

    my code worked well

    great, so please don't forget to mark your post as solved!


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