Qt - 从c ++线程发出一个信号 [英] Qt - emit a signal from a c++ thread

问题描述

我想从Qt中的C ++线程（std :: thread）发出一个信号。

我该怎么办？

$ b $你肯定可以从线程发出一个信号（ QThread ， std :: thread 或甚至 boost :: thread ）。只有你必须小心你的连接函数的第五个参数（ Qt :: ConnectionType ）：

$ c> Qt :: DirectConnection ：当信号被发出时，槽立即被调用（从当前线程）。
如果 Qt :: QueuedConnection ：当控制返回到接收者线程的事件循环时，调用槽。该插槽在接收者的线程中执行。

请参阅 ConnectionType-enum 更多选项。

问题不是真正从哪个线程发出信号，更多从哪个线程调用插槽。例如，我认为 QLabel :: setText 必须从 QLabel 的所有者线程（很可能是主线程） 。所以如果你发出一个信号连接到 QLabel 的 setText 从一个线程，连接必须用 Qt :: AutoConnection ， Qt :: QueuedConnection 或 Qt :: BlockingQueuedConnection 。

I want to emit a signal from a C++ thread (std::thread) in Qt.

How can I do it?

解决方案

You definitely can emit a signal from a thread (QThread, std::thread or even boost::thread). Only you must be careful of your connect function's fifth parameter (Qt::ConnectionType):

If Qt::DirectConnection: The slot is invoked immediately (from the current thread), when the signal is emitted. If Qt::QueuedConnection: 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.

See ConnectionType-enum for more options.

The problem is not really from which thread you emit the signal, it's more from which thread the slot is being invoked. For instance, I think QLabel::setText must be executed from QLabel's owner thread (most likely main thread). So if you emit a signal connected to a QLabel's setText from a thread, connection must be done with Qt::AutoConnection, Qt::QueuedConnection or Qt::BlockingQueuedConnection.

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