How to use QTimer

Question

In Qt I m trying to set a QTimer that calls a function called  update  every second  Here is my  cpp file    include  mainwindow h   include  ui mainwindow h   include  lt QTimer gt   include  QDebug   MainWindow  MainWindow QWidget  parent        QMainWindow parent       ui new Ui  MainWindow        ui- gt setupUi this        QTimer  timer   new QTimer this       connect timer  SIGNAL timeout     this  SLOT update          timer- gt start 1000      MainWindow   MainWindow         delete ui     void MainWindow  update         qDebug    lt  lt   update       and the main    include  lt QtGui QApplication gt   include  mainwindow h   int main int argc  char  argv          QApplication a argc  argv       MainWindow w      w show         return a exec        The project is being build  but it doesn t execute update  since the line  update  is not showing anywhere    Does anybody see what I  m doing wrong

User · Answer

mytimer h        ifndef MYTIMER H      define MYTIMER H       include  lt QTimer gt       class MyTimer   public QObject               Q OBJECT     public          MyTimer            QTimer  timer       public slots          void MyTimerSlot                 endif    MYTIME   mytimer cpp    include  mytimer h   include  lt QDebug gt   MyTimer  MyTimer            create a timer     timer   new QTimer this           setup signal and slot     connect timer  SIGNAL timeout               this  SLOT MyTimerSlot              msec     timer- gt start 1000      void MyTimer  MyTimerSlot         qDebug    lt  lt   Timer          main cpp    include  lt QCoreApplication gt   include  mytimer h   int main int argc  char  argv          QCoreApplication a argc  argv           Create MyTimer instance        QTimer object will be created in the MyTimer constructor     MyTimer timer       return a exec        If we run the code   Timer    Timer    Timer    Timer    Timer          resources

User · Answer

It s good practice to give a parent to your QTimer to use Qt s memory management system  update   is a QWidget function - is that what you are trying to call or not  http   qt-project org doc qt-4 8 qwidget html update   If number 2 does not apply  make sure that the function you are trying to trigger is declared as a slot in the header  Finally if none of these are your issue  it would be helpful to know if you are getting any run-time connect errors

User · Answer

Other way is using of built-in method start timer  amp  event TimerEvent   Header    ifndef MAINWINDOW H  define MAINWINDOW H   include  lt QMainWindow gt   namespace Ui   class MainWindow     class MainWindow   public QMainWindow       Q OBJECT  public      explicit MainWindow QWidget  parent   0        MainWindow     private      Ui  MainWindow  ui      int timerId   protected      void timerEvent QTimerEvent  event        endif    MAINWINDOW H   Source    include  mainwindow h   include  ui mainwindow h   include  lt QDebug gt   MainWindow  MainWindow QWidget  parent        QMainWindow parent       ui new Ui  MainWindow        ui- gt setupUi this        timerId   startTimer 1000      MainWindow   MainWindow         killTimer timerId       delete ui     void MainWindow  timerEvent QTimerEvent  event        qDebug    lt  lt   Update

[qt] How to use QTimer

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