CODEWITHSUNDEEP
qtqthreadqtimer
user2950911
user2950911

Reputation: 933

QObject::startTimer: Timers can only be used with threads started with QThread

I am trying to start a Timer in a worker thread's event loop, but I get this error: QObject::startTimer: Timers can only be used with threads started with QThread

Whats wrong with this? 

#include <QObject>
#include <QThread>
#include <QTimer>

class A : public QObject
{
    Q_OBJECT
public:
    A();

private:
    QThread m_workerThread;
    QTimer m_myTimer;

};

A::A()
{
    this->moveToThread(&m_workerThread);
    m_myTimer.moveToThread(&m_workerThread);
    m_workerThread.start();
    m_myTimer.start(1000);
}

Upvotes: 11

Views: 38761

Answers (4)

hosh0425
hosh0425

Reputation: 98

Hope this will be helpful:

class ReadYoloResult : public QObject
{
    Q_OBJECT
public:
    ReadYoloResult(QObject *parent = 0);
    void startTimer();
    QThread workerThread;

private:
    QTimer *timer;

public slots:
    void timerSlot();
};

ReadYoloResult::ReadYoloResult(QObject * parent)
{
    this->moveToThread(&workerThread);
    timer = new QTimer();
    connect(timer,SIGNAL(timeout()),this,SLOT(timerSlot()));

    workerThread.start();

    //timer->start(1000);
}

void ReadYoloResult::startTimer(){
    timer->start(100);
}
void ReadYoloResult::timerSlot(){
    qDebug()<<"In timer slot";
}

Upvotes: 0

gabonator
gabonator

Reputation: 391

Initialize your timer anywhere, but start it right when the thread is started (attach it to QThread::started signal): 

class A : public QObject
{
    Q_OBJECT
public:
    A();

private slots:
    void started();
    void timeout();

private:
    QThread m_workerThread;
    QTimer m_myTimer;
};

A::A()
{
    moveToThread(&m_workerThread);

    connect(&m_workerThread, SIGNAL(started()), this, SLOT(started()));
    connect(&m_myTimer, SIGNAL(timeout()), this, SLOT(timeout()));

    m_myTimer.setInterval(1000);
    m_myTimer.moveToThread(&m_workerThread);

    m_workerThread.start();
}

void A::started()
{
    timer.start();
}

void A::timeout()
{
    // timer handler
}

Upvotes: 3

deGoot
deGoot

Reputation: 1006

This approach seems a little dangerous to me. By moving the QObject onto the QThread, you're making the thread responsible for the object's events (signals, slots, messages, etc). When the object is deleted, however, the thread will be deleted before the object itself, which can lead to some unexpected behaviours.

The recommended approach is to instantiate the thread and the object separately.

Upvotes: 0

user2950911
user2950911

Reputation: 933

I Think i figured it out, i tried to start the timer from the GUI thread, after i moved it to the worker thread, this way it seems to work:

class A : public QObject
{
    Q_OBJECT
public:
    A();

private:
    QThread m_workerThread;
    QTimer m_myTimer;

public slots:
    void sl_startTimer();
};

A::A()
{
    this->moveToThread(&m_workerThread);
    m_myTimer.moveToThread(&m_workerThread);
    m_workerThread.start();
    QMetaObject::invokeMethod(this, "sl_startTimer", Qt::QueuedConnection);
}

void A::sl_startTimer()
{
    m_myTimer.start(1000);
}

Upvotes: 1

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