Qt实现多线程下的信号与槽通讯

初学QT，前期因为信号与槽只能在QT界面上面方便的使用，没有想到只要继承QObject便能使用且支持多线程操作。

为了能够让后台自定义类能够使用信号与槽，首先在自定义类继承QObject

1.DayouTraderSpi.h

#include "qobject.h"
class DayouTraderSpi : public QObject,public CThostFtdcTraderSpi
{

//宏必须申明
    Q_OBJECT
public:
    DayouTraderSpi(CThostFtdcTraderApi* api) :pUserApi(api){};
    ~DayouTraderSpi();
signals:
//自定义的信号   
 void signal_add_int(QString);
 };

2.DayouTraderSpi.cpp

DayouTraderSpi::~DayouTraderSpi()
{
    //析构函数必须申明
}

//自定义函数中触发信号
void DayouTraderSpi::ReqQryTradingAccount()
{
   emit signal_add_int("ok");
}

然后在界面定义槽函数及链接信号与槽
1.DayouOption.h

class DayouOption : public QMainWindow
{
    Q_OBJECT
public:
    DayouOption(QWidget *parent = 0);
    ~DayouOption();
private slots:

    void set_lineEdit_text(QString);//自定义槽函数
};

2.DayouOption.cpp

DayouOption::DayouOption(QWidget *parent)
: QMainWindow(parent),
ui(new Ui::DayouOptionClass)
{
    ui->setupUi(this);
                    MdApi = CThostFtdcMdApi::CreateFtdcMdApi();
    dayouMDSpi = new DayouMDSpi(MdApi);//创建回调处理类对象
    TraderApi = CThostFtdcTraderApi::CreateFtdcTraderApi();
    dayouTraderSpi = new DayouTraderSpi(TraderApi);
//链接信号与槽 dayouTraderSpi指针必须是QObject类型，所以dayouTraderSpi必须继承QObject。Qt::QueuedConnection是链接方式的一种。
    connect(dayouTraderSpi, SIGNAL(signal_add_int(QString)), this, SLOT(set_lineEdit_text(QString)), Qt::QueuedConnection);
    
}

DayouOption::~DayouOption()
{
    delete ui;
    
}
//槽函数实现
void DayouOption::set_lineEdit_text(QString str)
{
    QMessageBox::warning(this, "查询成功", str);
}

传递消息的方式有四个取值：

Qt::DirectConnection When emitted, the signal is immediately delivered to the slot. 假设当前有4个slot连接到QPushButton::clicked(bool)，当按钮被按下时，QT就把这4个slot按连接的时间顺序调用一遍。显然这种方式不能跨线程（传递消息）。

Qt::QueuedConnection When emitted, the signal is queued until the event loop is able to deliver it to the slot. 假设当前有4个slot连接到QPushButton::clicked(bool)，当按钮被按下时，QT就把这个signal包装成一个 QEvent，放到消息队列里。QApplication::exec()或者线程的QThread::exec()会从消息队列里取消息，然后调用 signal关联的几个slot。这种方式既可以在线程内传递消息，也可以跨线程传递消息。

Qt::BlockingQueuedConnection Same as QueuedConnection, except that the current thread blocks until the slot has been delivered. This connection type should only be used for receivers in a different thread. Note that misuse of this type can lead to dead locks in your application. 与Qt::QueuedConnection类似，但是会阻塞等到关联的slot都被执行。这里出现了阻塞这个词，说明它是专门用来多线程间传递消息的。

Qt::AutoConnection If the signal is emitted from the thread in which the receiving object lives, the slot is invoked directly, as with Qt::DirectConnection; otherwise the signal is queued, as with Qt::QueuedConnection. 这种连接类型根据signal和slot是否在同一个线程里自动选择Qt::DirectConnection或Qt::QueuedConnection