原创收藏QT开发相关问题

 2011-10-19 17:34  1118 1 1 分类: 软件与OS

解决Qt信号与槽的一个问题：QObject::connect: Cannot queue arguments of type 'QUuid'

2009-07-03 02:14

程序能编译运行，但出现这个提示：
QObject::connect: Cannot queue arguments of type 'QUuid'
(Make sure 'QUuid' is registed using qRegisterMetaType().)

意思是说，信号槽队列中的数据类型必须是系统能识别的元类型，不然得用qRegisterMetaType()进行注册。参考如下链接和Qt的帮助文档即可解决这个问题:
http://blog.ayoy.net/2009/2/15/registering-custom-types

http://www.qtcentre.org/forum/f-qt-programming-2/t-qobjectconnect-cannot-queue-arguments-of-type-qmodelindex-8926.html

enum Qt::ConnectionType

This enum describes the types of connection that can be used between signals and slots. In particular, it determines whether a particular signal is delivered to a slot immediately or queued for delivery at a later time.

Constant	Value	Description
`Qt::DirectConnection`	`1`	When emitted, the signal is immediately delivered to the slot.
`Qt::QueuedConnection`	`2`	When emitted, the signal is queued until the event loop is able to deliver it to the slot.
`Qt::BlockingQueuedConnection`	`4`	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 deadlocks in your application.
`Qt::AutoConnection`	`0`	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.

With queued connections, the parameters must be of types that are known to Qt's meta-object system, because Qt needs to copy the arguments to store them in an event behind the scenes. If you try to use a queued connection and get the error message

QObject::connect: Cannot queue arguments of type 'MyType'

call qRegisterMetaType() to register the data type before you establish the connection.

注意上面紫色的内容。

connect的第五个参数用于指定反应速度:

若将：
connect(cm, SIGNAL(sendLog(QUuid, QByteArray, bool)),
this,SLOT(sendRes(QUuid,QByteArray,bool)));
改为：
connect(cm, SIGNAL(sendLog(QUuid, QByteArray, bool)),
this,SLOT(sendRes(QUuid,QByteArray,bool)), Qt::DirectConnection);

可解决因信号没有及时发送，致使connect的接收方的槽不能作进一步处理，如上表中绿色部分内容所述。