Qt: QTimer和QThread

让QTimer 跑在其他线程. 一般写法如下.

1. 在main thread中为worker thread指定定时器.

	QThread* thread = new QThread(this);
	thread->start();

	QTimer *timer = new QTimer(0);
	timer->setInterval(100);
	timer->moveToThread(thread);
	connect(timer, SIGNAL(timeout()), this, SLOT(onTimeout()), Qt::DirectConnection);
	connect(thread, SIGNAL(started()), timer,SLOT(start()));

需要注意几个地方.

1) QTimer 不能指定parent, 否则 会出现警告 " QObject::moveToThread: Cannot move objects with a parent"

因为moveToThread 无法移动有parent的object.

2) QTimer 需要用moveToThread 来改变线程相关性. 这样emit signal的时候才会在worker线程.

3) connect timeout时, 需要附加参数Qt::DirectConnection,

根据Qt的文档中

Qt::AutoConnection	0	(default) If the signal is emitted from a different thread than the receiving object, the signal is queued, behaving as Qt::QueuedConnection. Otherwise, the slot is invoked directly, behaving as Qt::DirectConnection. The type of connection is determined when the signal is emitted.
Qt::DirectConnection	1	The slot is invoked immediately, when the signal is emitted.
Qt::QueuedConnection	2	The slot is invoked when control returns to the event loop of the receiver‘s thread. The slot is executed in the receiver‘s thread.

connect默认参数为AutoConnection, 所以当slot的object是main线程时, 会自动post 事件到main线程. 指定DirectConnection 才会直接调用slot. 即在worker线程中处理.

4) 如果直接 timer->start(); 的话, 会有警告: QObject::startTimer: Timers can only be used with threads started with QThread

timer 只能在同一个线程中创建和启动. (使用moveToThread 可以修改). 这里写"同一个线程" 似乎描述不太准确. 但大概就是这个意思.

connect(thread, SIGNAL(started()), timer,SLOT(start()));

所以需要这样启动.

其实也可以这样取巧:

	QThread* thread = new QThread(this);
	thread->start();

	QTimer *timer = new QTimer(0);
	timer->setInterval(100);
	connect(timer, SIGNAL(timeout()), this, SLOT(onTimeout()), Qt::DirectConnection);
	//connect(thread, SIGNAL(started()), timer,SLOT(start()));
	timer->start();
	timer->moveToThread(thread);

5)  因为timer 没有指定parent, 所以不会自动销毁.

2. 在worker线程中启动QTimer.

class Worker :public QThread {
	Q_OBJECT
public:
	Worker(MyClass *parent);
	virtual ~Worker(){}
	void run();
	MyClass *timerReceiver;
};

Worker::Worker(MyClass *parent)
	: QThread(parent) {
	timerReceiver = parent;
}

void Worker::run()
{
	QTimer *timer = new QTimer(this);
	timer->setInterval(100);
	connect(timer, SIGNAL(timeout()), timerReceiver, SLOT(onTimeout()), Qt::DirectConnection);
	timer->start();

	exec();
	return;
}

MyClass 是一个UI窗口. 类似如下.

class MyClass : public QMainWindow
{
	Q_OBJECT

public:
	MyClass(QWidget *parent = 0);
	~MyClass();
	public slots:
	void onTimeout(); 

private:
	Ui::MyClassClass ui;
};
MyClass::MyClass(QWidget *parent)
	: QMainWindow(parent)
{
	ui.setupUi(this);
	Worker *thread = new Worker(this);
	//QThread* thread = new QThread(this);
	thread->start();
}

MyClass::~MyClass()
{

}

void MyClass::onTimeout()
{

}

so. 可以看到. 如果timer是在worker 线程中创建的话. 即不需要moveToThread来修改线程相关性.

timer->start()也可以直接调用.

但仍然需要指定 Qt::DirectConnection. 因为timerReceiver 是在main thread中.

如果timerReceiver  也在worker线程中创建, 则不需要指定 Qt::DirectConnection.

void Worker::run()
{
	TestObject *timerReceiver = new TestObject(this);
	QTimer *timer = new QTimer(this);
	timer->setInterval(100);
	connect(timer, SIGNAL(timeout()), timerReceiver, SLOT(onTimeout()));
	timer->start();

	exec();
	return;
}

class TestObject : public QObject {
	Q_OBJECT
public:
	TestObject(QObject *parent) : QObject(parent) {}
	public slots :
		void onTimeout(){}
};

看起来和平时用的一模一样.  →_→