access to ui in a threaded application

[mastupristi]

Hi,

I need to to manage serial port stream, and update my ui consequently.
Reading some post here in the forum I wrote the attached example zufolo.tar.gz, where the thread zotthread simulates serial port management.

here is the screenshot
screenshot.png

the application is very simple.

that are slots in dialog:

void Dialog::ovvaivai(void)
{
    zotThread *zt;
 
    zt = new zotThread;
 
    connect(zt, SIGNAL(lancettasecondi(const QString&)), this, SLOT(cambiatestobottone(const QString&)));
    connect(zt, SIGNAL(uscita()), this, SLOT(chiusura()));
    zt->start();
}
 
void Dialog::cambiatestobottone(const QString &s)
{
    ui->pushButton->setText(s);
}
 
void Dialog::chiusura(void)
{
    close();
}

void Dialog::ovvaivai(void)
{
    zotThread *zt;

    zt = new zotThread;

    connect(zt, SIGNAL(lancettasecondi(const QString&)), this, SLOT(cambiatestobottone(const QString&)));
    connect(zt, SIGNAL(uscita()), this, SLOT(chiusura()));
    zt->start();
}

void Dialog::cambiatestobottone(const QString &s)
{
    ui->pushButton->setText(s);
}

void Dialog::chiusura(void)
{
    close();
}

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and this is the thread taht simulates serial management

void zotThread::run(void)
{
    int i;
    QString s;
    QTimer qt;
    for(i=5;i>0;i--)
    {
        s.setNum(i);
        emit lancettasecondi(s);
        qt.setSingleShot(true);
        qt.start(1000);
        while(qt.isActive()) QCoreApplication::processEvents();
    }
    emit uscita();
}

void zotThread::run(void)
{
    int i;
    QString s;
    QTimer qt;
    for(i=5;i>0;i--)
    {
        s.setNum(i);
        emit lancettasecondi(s);
        qt.setSingleShot(true);
        qt.start(1000);
        while(qt.isActive()) QCoreApplication::processEvents();
    }
    emit uscita();
}

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when clicking the pushbutton ovvaivai(void) is called, so then thread starts. It perform a 5 seconds countdown before close the application.

I wonder if this is the right way to change the ui from a thread.
An also I wonder if is correct to call QCoreApplication::processEvents(); from inside trhead main loop. Without that call timer dosn't walk.

Now I want to read the spin value from thread. How can I perform that action? I don't think through signal/slot.

thanks

[Lesiok]

Better and more elegant will be something like this :

class zotThread : public QThread
{
.
.
private slots :
    void oneStep( void );
private :
    int count_down;
}
 
void zotThread::run(void)
{
    count_down = 5;
    QTimer::singleShot(0,this, SLOT(oneStep()));
    QThread::run();//event loop is starting
}
 
void zotThread::singleStep(void)
(
    if( count_down < 0 )
    {
        quit();//event loop is stopped
        return;
    }
    QString s;
    s.setNum(count_down--);
    emit lancettasecondi(s);
    QTimer::singleShot(1000,this, SLOT(oneStep()));
}

class zotThread : public QThread
{
.
.
private slots :
    void oneStep( void );
private :
    int count_down;
}

void zotThread::run(void)
{
    count_down = 5;
    QTimer::singleShot(0,this, SLOT(oneStep()));
    QThread::run();//event loop is starting
}

void zotThread::singleStep(void)
(
    if( count_down < 0 )
    {
        quit();//event loop is stopped
        return;
    }
    QString s;
    s.setNum(count_down--);
    emit lancettasecondi(s);
    QTimer::singleShot(1000,this, SLOT(oneStep()));
}

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[Lesiok]

Now I want to read the spin value from thread. How can I perform that action? I don't think through signal/slot.

Why not ? Just connect signal QSpinBox::valueChanged ( int i ) to slot in Yours thread and all.

[wysota]

I wonder if this is the right way to change the ui from a thread.

You can't access ui from a thread.

An also I wonder if is correct to call QCoreApplication::processEvents(); from inside trhead main loop.

It's not.

Without that call timer dosn't walk.

Use QThread::exec().