Question

我正在尝试创建一个新的线程gpsthread，它应该在后台运行，并存储该值。

class gpsthread: public QThread{
    Q_OBJECT
private:nrega_status_t status2;

public: 
explicit gpsthread(QObject *parent = 0):QThread(parent) {
    // QTimer *t = new QTimer(this);
    // connect(t, SIGNAL(timeout()), this, SLOT(processgps()));
    // t->start(10000);
 }
 void run(){
    qDebug()<<"inside gps thread\n";
    QTimer *t = new QTimer(this);
     connect(t, SIGNAL(timeout()), this, SLOT(processgps()));
     t->start(10000);
    }

public slots:void processgps(){
    int status2;
    status2=gps_management();
}
};

我的主要课程是快速浏览。

int main(int argc, char *argv[])
{

QString file = "qml/main.qml";
QApplication app(argc, argv);
TranslationTest myObj;
QuickView view;
subthread object;
gpsthread obj;
gprsthread gprs;
view.rootContext()->setContextProperty("rootItem", (QObject *)&myObj);

    obj.start();
//from subthread
QObject::connect(&object, SIGNAL(batterytoqml(QVariant,QVariant)),item, SLOT(frombattery(QVariant,QVariant)));
QObject::connect(&gprs, SIGNAL(gprstoqml(QVariant)),item, SLOT(fromgprs(QVariant)));
return app.exec();

}

我也试过这个

class gpsthread: public QThread{
    Q_OBJECT
private:nrega_status_t status2;

public:QTimer* t; 
explicit gpsthread(QObject *parent = 0):QThread(parent) {
    // QTimer *t = new QTimer(this);
    // connect(t, SIGNAL(timeout()), this, SLOT(processgps()));
    // t->start(10000);
 }
 void run(){
    qDebug()<<"inside gps thread\n";
    t = new QTimer(this);
     connect(t, SIGNAL(timeout()), this, SLOT(processgps()));
     t->start(10000);
exec();    
}

public slots:void processgps(){
    int status2;
    status2=gps_management();
}
};

但提出错误

 QObject: Cannot create children for a parent that is in a different thread

如果我在构造函数中创建对象，那么它也会给出相同的错误，因为该对象将在主线程中创建。怎么解决这个？

Answer 1

不推荐使用QThread继承。 QThread是一个运行事件循环的完整类，通常是您需要的。 documentation建议使用从QObject继承并在插槽中工作的worker对象。工人被转移到QThread。发送连接信号时，插槽将以正确的线程运行。

class gpsworker: public QObject
{
Q_OBJECT
public:
    explicit gpsworker(QObject *parent = 0):
    QObject(parent)
    {}

public slots:
    void processgps() {
        qDebug() << "processgps()" << QThread::currentThreadId();
    }
}

void OwnerClass::startWorker() {
    QTimer *timer = new QTimer(this);
    QThread *thread = new QThread(this);
    this->worker = new gpsworker();
    this->worker->moveToThread(thread);
    connect(timer, SIGNAL(timeout()), this->worker, SLOT(processgps()) );
    connect(thread, SIGNAL(finished()), this->worker, SLOT(deleteLater()) );
    thread->start();
    timer->start();
}

如果您希望计时器也在其他线程中，QTimer::start是一个插槽。

Answer 2

QObject: Cannot create children for a parent that is in a different thready

是t = new QTimer(this)中的run()正在子线程中创建一个对象，但this处的gpsthread是在主线程中。一个简单的解决方案是t = new QTimer()没有父级，并删除析构函数中的计时器。这是一个例子：

class gpsthread : public QThread {
    Q_OBJECT
public:
    explicit gpsthread(QObject *parent = 0):
        QThread(parent)
        ,timer(NULL) {
        qDebug() << "Parent thread" << QThread::currentThreadId();
    }
    ~gpsthread() {
        quit();
        wait();
        delete timer;
    }
protected:
    void run() {
        qDebug() << "Inside gps thread" << QThread::currentThreadId();
        timer = new QTimer;  // no parent
        connect(timer, SIGNAL(timeout()), this, SLOT(processgps()));
        timer->start(1000);
        exec();
    }

public slots:
    void processgps() {
        qDebug() << "processgps()" << QThread::currentThreadId();
    }

private:
    QTimer *timer;
};

很快你会发现控制台打印：

Parent thread 0x3b28
inside gps thread 0x3f10
processgps() 0x3b28
processgps() 0x3b28
processgps() 0x3b28
processgps() 0x3b28

这意味着processgps()在您的子线程中无效。这是因为此插槽是gpsthread的成员，它位于主线程中。一个简单的解决方案是直接调用processgps()并使用sleep()作为计时器：

class gpsthread : public QThread
{
    Q_OBJECT
public:
    explicit gpsthread(QObject *parent = 0):
        QThread(parent)
        , abort(false) {
        qDebug() << "Parent thread" << QThread::currentThreadId();
    }
    ~gpsthread() {
        abort = true;
        wait();
    }
protected:
    void run() {
        while(!abort) {
            sleep(1);
            processgps();
        }
    }
public slots:
    void processgps() {
        qDebug() << "processgps()" << QThread::currentThreadId();
    }
private:
    bool abort;
};

这不是一个好的解决方案，推荐的方法是创建一个工作人员完成所有工作，然后使用QObject::moveToThread()中所述的QThread Document

使用Qthread-Qt5创建新线程

2 个答案: