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keyPressEvent - how to override?

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  • Christian EhrlicherC Christian Ehrlicher

    @jenya7 said in keyPressEvent - how to override?:

    How do I connect it to my QTextEdit on the MainForm?

    What do you want to connect and why?

    J Offline
    J Offline
    jenya7
    wrote on last edited by
    #3

    @Christian-Ehrlicher said in keyPressEvent - how to override?:

    @jenya7 said in keyPressEvent - how to override?:

    How do I connect it to my QTextEdit on the MainForm?

    What do you want to connect and why?

    I have a text box. When I type in it I want to check what character I type. If it was an Enter - I will take the line and send it serially.

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    • Christian EhrlicherC Offline
      Christian EhrlicherC Offline
      Christian Ehrlicher
      Lifetime Qt Champion
      wrote on last edited by
      #4

      @jenya7 said in keyPressEvent - how to override?:

      I will take the line and send it serially.

      simply emit a signal then, and do whatever you want in your slot: https://doc.qt.io/qt-5/signalsandslots.html

      Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
      Visit the Qt Academy at https://academy.qt.io/catalog

      J 1 Reply Last reply
      1
      • Christian EhrlicherC Christian Ehrlicher

        @jenya7 said in keyPressEvent - how to override?:

        I will take the line and send it serially.

        simply emit a signal then, and do whatever you want in your slot: https://doc.qt.io/qt-5/signalsandslots.html

        J Offline
        J Offline
        jenya7
        wrote on last edited by
        #5

        @Christian-Ehrlicher said in keyPressEvent - how to override?:

        @jenya7 said in keyPressEvent - how to override?:

        I will take the line and send it serially.

        simply emit a signal then, and do whatever you want in your slot: https://doc.qt.io/qt-5/signalsandslots.html
        What slot? I need to check every typed character? how a slot is related to it?
        We have an event especially designed for this purpose - keyPressEvent.

        1 Reply Last reply
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        • Ashok KumarA Offline
          Ashok KumarA Offline
          Ashok Kumar
          wrote on last edited by Ashok Kumar
          #6

          Instead of overriding the keyPressEvent function you can override the eventFilter function.
          bool eventFilter(QObject *obj, QEvent *ev) ;

          and implement as below

          bool eventFilter(QObject *obj, QEvent *event)
          {
          if (obj == MytextEdit)
          {
          if (event->type() == QEvent::KeyPress)
          {
          QKeyEvent keyEvent = static_cast<QKeyEvent>(event);
          qDebug() << keyEvent->key();
          return true;
          }
          else {

                return eventFilter(obj, event);
            }
          

          }

          Now after this you can go to your main form and create the object of Mytextedit and install event filter for the textedit object ...

          J 1 Reply Last reply
          0
          • Ashok KumarA Ashok Kumar

            Instead of overriding the keyPressEvent function you can override the eventFilter function.
            bool eventFilter(QObject *obj, QEvent *ev) ;

            and implement as below

            bool eventFilter(QObject *obj, QEvent *event)
            {
            if (obj == MytextEdit)
            {
            if (event->type() == QEvent::KeyPress)
            {
            QKeyEvent keyEvent = static_cast<QKeyEvent>(event);
            qDebug() << keyEvent->key();
            return true;
            }
            else {

                  return eventFilter(obj, event);
              }
            

            }

            Now after this you can go to your main form and create the object of Mytextedit and install event filter for the textedit object ...

            J Offline
            J Offline
            jenya7
            wrote on last edited by
            #7

            @Ashok-Kumar
            Thank you. How do I install the event filter for the textedit object?

            Ashok KumarA 1 Reply Last reply
            0
            • J jenya7

              @Ashok-Kumar
              Thank you. How do I install the event filter for the textedit object?

              Ashok KumarA Offline
              Ashok KumarA Offline
              Ashok Kumar
              wrote on last edited by
              #8

              @jenya7 you can create textedit object and do

              textedit->installEventFilter(this);

              J 1 Reply Last reply
              0
              • Ashok KumarA Ashok Kumar

                @jenya7 you can create textedit object and do

                textedit->installEventFilter(this);

                J Offline
                J Offline
                jenya7
                wrote on last edited by jenya7
                #9

                @Ashok-Kumar said in keyPressEvent - how to override?:

                @jenya7 you can create textedit object and do

                textedit->installEventFilter(this);

                In mainwindow.cpp I do

                bool eventFilter(QObject *obj, QEvent *event)
                {
                    if (obj == textEditTerminalTx) 
                    {
                        if (event->type() == QEvent::KeyPress) 
                        {
                            QKeyEvent keyEvent = static_cast<QKeyEvent>(event);
                            //qDebug() << keyEvent->key();
                            return true;
                        } 
                        else 
                        {
                            return false;
                        }
                    } 
                    else 
                    {
                        // pass the event on to the parent class
                        return eventFilter(obj, event);
                    }
                }
                

                On this line obj == textEditTerminalTx I get - error: use of undeclared identifier 'textEditTerminalTx'
                On this line QKeyEvent keyEvent = static_cast<QKeyEvent>(event); - I get error: no matching conversion for static_cast from 'QEvent *' to 'QKeyEvent'

                Ashok KumarA 1 Reply Last reply
                0
                • J jenya7

                  @Ashok-Kumar said in keyPressEvent - how to override?:

                  @jenya7 you can create textedit object and do

                  textedit->installEventFilter(this);

                  In mainwindow.cpp I do

                  bool eventFilter(QObject *obj, QEvent *event)
                  {
                      if (obj == textEditTerminalTx) 
                      {
                          if (event->type() == QEvent::KeyPress) 
                          {
                              QKeyEvent keyEvent = static_cast<QKeyEvent>(event);
                              //qDebug() << keyEvent->key();
                              return true;
                          } 
                          else 
                          {
                              return false;
                          }
                      } 
                      else 
                      {
                          // pass the event on to the parent class
                          return eventFilter(obj, event);
                      }
                  }
                  

                  On this line obj == textEditTerminalTx I get - error: use of undeclared identifier 'textEditTerminalTx'
                  On this line QKeyEvent keyEvent = static_cast<QKeyEvent>(event); - I get error: no matching conversion for static_cast from 'QEvent *' to 'QKeyEvent'

                  Ashok KumarA Offline
                  Ashok KumarA Offline
                  Ashok Kumar
                  wrote on last edited by
                  #10

                  @jenya7 instead of doing casting like u did above QKeyEvent keyEvent = static_cast<QKeyEvent>(event);

                  instead u can do like this

                  QKeyEvent keyEvent=(QKeyEvent*)(event);
                  It will work

                  J 1 Reply Last reply
                  0
                  • Ashok KumarA Ashok Kumar

                    @jenya7 instead of doing casting like u did above QKeyEvent keyEvent = static_cast<QKeyEvent>(event);

                    instead u can do like this

                    QKeyEvent keyEvent=(QKeyEvent*)(event);
                    It will work

                    J Offline
                    J Offline
                    jenya7
                    wrote on last edited by jenya7
                    #11

                    @Ashok-Kumar said in keyPressEvent - how to override?:

                    @jenya7 instead of doing casting like u did above QKeyEvent keyEvent = static_cast<QKeyEvent>(event);

                    instead u can do like this

                    QKeyEvent keyEvent=(QKeyEvent*)(event);
                    It will work

                    This way I get - error: no viable conversion from 'QKeyEvent *' to 'QKeyEvent'

                    Ah I see - QKeyEvent keyEvent = (QKeyEvent)(event); - the site editor removes a pointer star.

                    And why the object not visible in the scope - if (obj == textEditTerminalTx) ?
                    I tried if (obj == ui->textEditTerminalTx) but ui also not visible.

                    Say in functions with MainWindow:: ui is visible like
                    void MainWindow::on_ButtonCompileScript_clicked()
                    {
                    QString text = ui->textEditScriptIn->toPlainText();
                    }

                    OK.

                    In mainwindow.h I added

                    public:
                        bool eventFilter(QObject *obj, QEvent *event);
                    

                    In mainwindow.cpp

                    MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow)
                    {
                        ui->setupUi(this);
                        ui->textEditTerminalTx->installEventFilter(this);
                    }
                    
                    bool MainWindow::eventFilter(QObject *obj, QEvent *event)
                    {
                        QMessageBox mb;
                        if (obj == ui->textEditTerminalTx)
                        {
                            if (event->type() == QEvent::KeyPress)
                            {
                                QKeyEvent *keyEvent = static_cast<QKeyEvent*>(event);
                                if (keyEvent->key() == Qt::Key_Enter)
                                {
                                    mb.setText("Enter");
                                    mb.exec();
                                }
                                return true;
                            }
                            else
                                return false;
                        }
                        else
                        {
                            // pass the event on to the parent class
                            return eventFilter(obj, event);
                        }
                    }
                    

                    But when I type - no char is typed in the widget and no reaction on Enter key.

                    Ashok KumarA 1 Reply Last reply
                    0
                    • J jenya7

                      @Ashok-Kumar said in keyPressEvent - how to override?:

                      @jenya7 instead of doing casting like u did above QKeyEvent keyEvent = static_cast<QKeyEvent>(event);

                      instead u can do like this

                      QKeyEvent keyEvent=(QKeyEvent*)(event);
                      It will work

                      This way I get - error: no viable conversion from 'QKeyEvent *' to 'QKeyEvent'

                      Ah I see - QKeyEvent keyEvent = (QKeyEvent)(event); - the site editor removes a pointer star.

                      And why the object not visible in the scope - if (obj == textEditTerminalTx) ?
                      I tried if (obj == ui->textEditTerminalTx) but ui also not visible.

                      Say in functions with MainWindow:: ui is visible like
                      void MainWindow::on_ButtonCompileScript_clicked()
                      {
                      QString text = ui->textEditScriptIn->toPlainText();
                      }

                      OK.

                      In mainwindow.h I added

                      public:
                          bool eventFilter(QObject *obj, QEvent *event);
                      

                      In mainwindow.cpp

                      MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow)
                      {
                          ui->setupUi(this);
                          ui->textEditTerminalTx->installEventFilter(this);
                      }
                      
                      bool MainWindow::eventFilter(QObject *obj, QEvent *event)
                      {
                          QMessageBox mb;
                          if (obj == ui->textEditTerminalTx)
                          {
                              if (event->type() == QEvent::KeyPress)
                              {
                                  QKeyEvent *keyEvent = static_cast<QKeyEvent*>(event);
                                  if (keyEvent->key() == Qt::Key_Enter)
                                  {
                                      mb.setText("Enter");
                                      mb.exec();
                                  }
                                  return true;
                              }
                              else
                                  return false;
                          }
                          else
                          {
                              // pass the event on to the parent class
                              return eventFilter(obj, event);
                          }
                      }
                      

                      But when I type - no char is typed in the widget and no reaction on Enter key.

                      Ashok KumarA Offline
                      Ashok KumarA Offline
                      Ashok Kumar
                      wrote on last edited by
                      #12

                      @jenya7 If u r getting no viable conversion from QKeyEvent* to QKeyEvent. include <QKeyEvent> headerfile in the mainwindow class

                      J 1 Reply Last reply
                      0
                      • Ashok KumarA Ashok Kumar

                        @jenya7 If u r getting no viable conversion from QKeyEvent* to QKeyEvent. include <QKeyEvent> headerfile in the mainwindow class

                        J Offline
                        J Offline
                        jenya7
                        wrote on last edited by jenya7
                        #13

                        @Ashok-Kumar said in keyPressEvent - how to override?:

                        @jenya7 If u r getting no viable conversion from QKeyEvent* to QKeyEvent. include <QKeyEvent> headerfile in the mainwindow class

                        I do get the event. To test it I added

                        if (event->type() == QEvent::KeyPress)
                                {
                                    QKeyEvent *keyEvent = static_cast<QKeyEvent*>(event);
                                    if (keyEvent->key() == Qt::Key_Return)
                                    {
                                        mb.setText("Enter");
                                        mb.exec();
                                    }
                                    else
                                    {
                                        term_str += static_cast<char> (keyEvent->key());
                                        ui->textEditTerminalTx->setText(term_str);
                                    }
                                    return true;
                                }
                                else
                                    return false;
                        

                        When I type I get chars in the widget but it types also backspase and delete keys instead of action. And on Key_Return I see the message box.

                        Ashok KumarA 1 Reply Last reply
                        0
                        • J jenya7

                          @Ashok-Kumar said in keyPressEvent - how to override?:

                          @jenya7 If u r getting no viable conversion from QKeyEvent* to QKeyEvent. include <QKeyEvent> headerfile in the mainwindow class

                          I do get the event. To test it I added

                          if (event->type() == QEvent::KeyPress)
                                  {
                                      QKeyEvent *keyEvent = static_cast<QKeyEvent*>(event);
                                      if (keyEvent->key() == Qt::Key_Return)
                                      {
                                          mb.setText("Enter");
                                          mb.exec();
                                      }
                                      else
                                      {
                                          term_str += static_cast<char> (keyEvent->key());
                                          ui->textEditTerminalTx->setText(term_str);
                                      }
                                      return true;
                                  }
                                  else
                                      return false;
                          

                          When I type I get chars in the widget but it types also backspase and delete keys instead of action. And on Key_Return I see the message box.

                          Ashok KumarA Offline
                          Ashok KumarA Offline
                          Ashok Kumar
                          wrote on last edited by
                          #14

                          @jenya7
                          if u want only chars in the QTextedit then u can use try this

                          if(keyevent->key()>=Qt::Key_0 && keyevent->key()<=Qt::Key_9)

                          if u want only digits in the QTextedit then u can use try this

                          if(keyevent->key()>=Qt::Key_A && keyevent->key()<=Qt::Key_Z)...

                          If u create the QMessageBox object in the constructor then it will be shown in the beginning itself

                          J 1 Reply Last reply
                          0
                          • Ashok KumarA Ashok Kumar

                            @jenya7
                            if u want only chars in the QTextedit then u can use try this

                            if(keyevent->key()>=Qt::Key_0 && keyevent->key()<=Qt::Key_9)

                            if u want only digits in the QTextedit then u can use try this

                            if(keyevent->key()>=Qt::Key_A && keyevent->key()<=Qt::Key_Z)...

                            If u create the QMessageBox object in the constructor then it will be shown in the beginning itself

                            J Offline
                            J Offline
                            jenya7
                            wrote on last edited by jenya7
                            #15

                            @Ashok-Kumar said in keyPressEvent - how to override?:

                            @jenya7
                            if u want only chars in the QTextedit then u can use try this

                            if(keyevent->key()>=Qt::Key_0 && keyevent->key()<=Qt::Key_9)

                            if u want only digits in the QTextedit then u can use try this

                            if(keyevent->key()>=Qt::Key_A && keyevent->key()<=Qt::Key_Z)...

                            If u create the QMessageBox object in the constructor then it will be shown in the beginning itself

                            to get every possible key I did so

                            if (keyEvent->key() != Qt::Key_Backspace && keyEvent->key() != Qt::Key_Delete)
                             {
                                        term_str += static_cast<char> (keyEvent->key());
                                       ui->textEditTerminalTx->setText(term_str);
                             }
                            

                            but the keys Backspace and Delete don't act as suppose to be - no action - it suppose to delete chars.
                            Also it gets chars only in upper case ignoring CapsLock selection.

                            This way it works

                            bool MainWindow::eventFilter(QObject *obj, QEvent *event)
                            {
                                QMessageBox mb;
                                if (obj == ui->textEditTerminalTx)
                                {
                                    if (event->type() == QEvent::KeyPress)
                                    {
                                        QKeyEvent *keyEvent = static_cast<QKeyEvent*>(event);
                                        if (keyEvent->key() == Qt::Key_Return)
                                        {
                            
                                            mb.setText("Enter");
                                            mb.exec();
                                        }
                                        else
                                        {
                                            //term_str += static_cast<char> (keyEvent->key());
                                            return false;
                                        }
                                    }
                                    else
                                        return false;
                                }
                                else
                                    // pass the event on to the parent class
                                    return MainWindow::eventFilter(obj, event);
                            }
                            
                            Ashok KumarA 1 Reply Last reply
                            0
                            • J jenya7

                              @Ashok-Kumar said in keyPressEvent - how to override?:

                              @jenya7
                              if u want only chars in the QTextedit then u can use try this

                              if(keyevent->key()>=Qt::Key_0 && keyevent->key()<=Qt::Key_9)

                              if u want only digits in the QTextedit then u can use try this

                              if(keyevent->key()>=Qt::Key_A && keyevent->key()<=Qt::Key_Z)...

                              If u create the QMessageBox object in the constructor then it will be shown in the beginning itself

                              to get every possible key I did so

                              if (keyEvent->key() != Qt::Key_Backspace && keyEvent->key() != Qt::Key_Delete)
                               {
                                          term_str += static_cast<char> (keyEvent->key());
                                         ui->textEditTerminalTx->setText(term_str);
                               }
                              

                              but the keys Backspace and Delete don't act as suppose to be - no action - it suppose to delete chars.
                              Also it gets chars only in upper case ignoring CapsLock selection.

                              This way it works

                              bool MainWindow::eventFilter(QObject *obj, QEvent *event)
                              {
                                  QMessageBox mb;
                                  if (obj == ui->textEditTerminalTx)
                                  {
                                      if (event->type() == QEvent::KeyPress)
                                      {
                                          QKeyEvent *keyEvent = static_cast<QKeyEvent*>(event);
                                          if (keyEvent->key() == Qt::Key_Return)
                                          {
                              
                                              mb.setText("Enter");
                                              mb.exec();
                                          }
                                          else
                                          {
                                              //term_str += static_cast<char> (keyEvent->key());
                                              return false;
                                          }
                                      }
                                      else
                                          return false;
                                  }
                                  else
                                      // pass the event on to the parent class
                                      return MainWindow::eventFilter(obj, event);
                              }
                              
                              Ashok KumarA Offline
                              Ashok KumarA Offline
                              Ashok Kumar
                              wrote on last edited by
                              #16

                              @jenya7 What exactly is your problem. Which keys do you need to use in textedit . can u elaborate it .

                              J 1 Reply Last reply
                              0
                              • Ashok KumarA Ashok Kumar

                                @jenya7 What exactly is your problem. Which keys do you need to use in textedit . can u elaborate it .

                                J Offline
                                J Offline
                                jenya7
                                wrote on last edited by jenya7
                                #17

                                @Ashok-Kumar said in keyPressEvent - how to override?:

                                @jenya7 What exactly is your problem. Which keys do you need to use in textedit . can u elaborate it .

                                The last function's version solves the problem - I get all the chars and keys Backspase and Delete work.
                                Now - on Enter key - I'd like to take the line before the Enter key and send it. Looking how to get the line before the Enter key. Trivial things so difficult in Qt... :)

                                Ashok KumarA 1 Reply Last reply
                                0
                                • J jenya7

                                  @Ashok-Kumar said in keyPressEvent - how to override?:

                                  @jenya7 What exactly is your problem. Which keys do you need to use in textedit . can u elaborate it .

                                  The last function's version solves the problem - I get all the chars and keys Backspase and Delete work.
                                  Now - on Enter key - I'd like to take the line before the Enter key and send it. Looking how to get the line before the Enter key. Trivial things so difficult in Qt... :)

                                  Ashok KumarA Offline
                                  Ashok KumarA Offline
                                  Ashok Kumar
                                  wrote on last edited by
                                  #18

                                  @jenya7 If u want the text before the enter key then you have to emit signal with parameter as string and write a particular slot for that and there u can get that text...

                                  signal:
                                  void textBeforeEnter(QString);

                                  slot :
                                  void getText(QString);

                                  connect(this,SIGNAL(textBeforeEnter(QString)),this,SLOT(getText(QString)));
                                  emit textBeforeEnter(textedit.text);

                                  void getText(QString text)
                                  {
                                  qDebug()<<"The text in textedit before pressing enter key is "<<text<<endl;
                                  }

                                  1 Reply Last reply
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