Qt QThread 使用从工作线程到 gui 的信号/槽时出现问题

发布于 2024-12-11 19:29:41 字数 662 浏览 0 评论 0原文

我有一个使用 Qt Creator 及其附带的 GUI 工具开发的 Qt 应用程序。我有一个主线程 TheGui 和一个由主线程 WorkerThread 创建的工作线程（称为 thread）。

我遇到的问题是，当我在 GUI

public slot:
  void updateTable(string str);

的头文件中使用并在工作线程的头文件中使用信号 void sendList(string str); 创建一个插槽时，插槽永远不会被调用。使用了这两个连接

connect(&thread, SIGNAL(sendList(string str),
        this,    SLOT(updateTable(string str)));

我在 GUI cpp 文件的构造函数中。我做了类似的事情，除了工作线程中的插槽和来自 GUI 的信号之外，它工作得很好。我通过使用调试器知道信号 sendList 确实被调用，只是永远不会进入它。

有什么想法吗？

原文

I have a Qt application that was developed using Qt Creator and the GUI tool that accompanies it. I have a main thread, TheGui and a worker thread that is created by the main thread, WorkerThread (called thread).

The problem I'm having is when I create a slot in the GUI by using

public slot:
  void updateTable(string str);

within the header file of the GUI and signal void sendList(string str); within the header file of the worker thread, the slot never gets called. I connected the two using

connect(&thread, SIGNAL(sendList(string str),
        this,    SLOT(updateTable(string str)));

within the constructor in the GUI cpp file. I did something similar except with the slot in the worker thread and signal from the GUI and it worked fine. I know from using the debugger that the signal sendList is indeed getting called, it is just never going into it.

Any thoughts?

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暗藏城府 2024-12-18 19:29:42

确定确实建立了连接吗？如果 connect 调用有任何问题，cerr 上通常会出现一些有关它的调试输出。

其次，我认为你有一个错字 - 如果你从代码中复制了 connect 调用，那么就知道你在 SIGNAL 周围缺少括号 - 应该是

connect(&thread, SIGNAL(sendList(string)), this, SLOT(updateTable(string)));

第三，你作为信号/槽参数传递的是什么？是 std::string 吗？线程之间的连接必须是排队连接。排队连接只能使用使用 Q_DECLARE_METATYPE 宏声明的类型作为参数，并且已注册 qRegisterMetaType。据我所知，Qt 默认情况下不会为 std::string 声明这些，因为它更喜欢 QString。如果您没有将这些添加到代码中，则可能会导致失败。

Sure that connection is actually made? If there are any problems with connect call, there is usually some debugging output about it on cerr.

Secondly, I think you have a typo - if you copied connect call from your code, then know that you have parenthesis missing around SIGNAL - should be

connect(&thread, SIGNAL(sendList(string)), this, SLOT(updateTable(string)));

Thirdly, what is that you are passing as signal/slot parameter? Is it std::string? Connections between threads must be queued connections. Queued connections can use as parameters only types declared with Q_DECLARE_METATYPE macro, and registered with qRegisterMetaType. As far as I know, Qt by default doesn't declare those for std::string, as it prefers QString. If you didn't add those to your code, it might be the reason for failure.

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半步萧音过轻尘 2024-12-18 19:29:41

由于信号和槽位于不同的线程上，因此它们之间的连接具有 Qt::QueuedConnection 类型。对于排队连接，Qt 必须能够保存信号参数的副本，以便稍后将它们传递到插槽。

因此，要通知 Qt 该类型是可复制的，您必须将其注册到 Qt 的元对象系统（请参阅 QMetaType) 像这样：
```
// 该宏调用应放在您的 .h 文件之一中 
Q_DECLARE_METATYPE(std::string)

// 您应该在任何（排队）之前调用此函数 
// 涉及类型的信号/槽连接
qRegisterMetaType();
```
参数名称不应包含在 QObject::connect 调用中，并且类型名称应与你传递给的人Q_DECLARE_METATYPE：
```
connect(&thread, SIGNAL(sendList(std::string), this, SLOT(updateTable(std::string)));
```

您还可以使用已经注册的QString或QByteArray，而不是std::string，因为这些函数是插槽和信号等已经是 Qt 具体的。

Because the signal and the slot are on distinct threads, the connection between them has the Qt::QueuedConnection type. And for queued connections, Qt has to be able to save a copy of the signal parameters, to pass them later to the slot.

So, to inform Qt that the type is copyable, you have to register it with Qt's meta-object system (see QMetaType) like this:
```
// This macro call should be put in one of your .h files 
Q_DECLARE_METATYPE(std::string)

// You should call this function before any (queued) 
// signal/slot connection involving the type
qRegisterMetaType<std::string>();
```
The parameter name shouldn't be included in the QObject::connect call, and the type names should be exactly the same as the ones you passed to Q_DECLARE_METATYPE:
```
connect(&thread, SIGNAL(sendList(std::string), this, SLOT(updateTable(std::string)));
```

You can also use QString or QByteArray, which are already registered, instead of std::string, since these functions are slots and signals and as such are already Qt specific.

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