C++ QObject：无法为不同线程中的父级创建子级
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QObject: Cannot create children for a parent that is in a different thread
提问by Donotalo
I am using Qt 4.6.0 (32 bit) under Windows 7 Ultimate. Consider the following QThread:
我在 Windows 7 Ultimate 下使用 Qt 4.6.0（32 位）。考虑以下几点QThread：
Interface
界面
class ResultThread : public QThread
{
Q_OBJECT
QString _post_data;
QNetworkAccessManager _net_acc_mgr;
signals:
void onFinished(QNetworkReply* net_reply);
private slots:
void onReplyFinished(QNetworkReply* net_reply);
public:
ResultThread();
void run();
void setPostData(const QString& post_data);
};
Implementation
执行
ResultThread::ResultThread() : _net_acc_mgr(this)
{
connect(&_net_acc_mgr, SIGNAL(finished(QNetworkReply*)),
this, SLOT(onReplyFinished(QNetworkReply*)));
}
void ResultThread::onReplyFinished(QNetworkReply* net_reply)
{
emit onFinished(net_reply);
}
void ResultThread::setPostData(const QString& post_data)
{
_post_data = post_data;
}
void ResultThread::run()
{
_net_acc_mgr.post(QNetworkRequest(QUrl("http://[omitted]")),
QByteArray(_post_data.toStdString().c_str()));
}
Whenever _net_acc_mgr.post()is executed in ResultThread::run(), I got the following Application Output in Qt Creator:
每当_net_acc_mgr.post()在 中执行时ResultThread::run()，我都会在 Qt Creator 中得到以下应用程序输出：
QObject: Cannot create children for a parent that is in a different thread.
(Parent is QNetworkAccessManager(0x22fe58), parent's thread is QThread(0x9284190), current thread is ResultThread(0x22fe48)
QObject：无法为不同线程中的父级创建子级。
(父为QNetworkAccessManager(0x22fe58)，父线程为QThread(0x9284190)，当前线程为ResultThread(0x22fe48)
What does this mean? How to solve it?
这是什么意思？如何解决？
回答by Gunther Piez
The run()member function is executed in a different thread, rather than the thread where QNetworkRequestManagerobject was created.
的运行（）成员函数在不同的线程中执行，而不是其中的线程QNetworkRequestManager被创建的对象。
This kind of different-thread problems happen all the time with Qtwhen you use multiple threads. The canonical way to solve this problem is to use signalsand slots.
当您使用多线程时，这种不同线程的问题在Qt 中一直发生。解决这个问题的规范方法是使用信号和槽。
Create a slotin the object where QNetworkRequestManagerbelongs to, create a signalin ResultThreadand connect both of the somewhere, the constructor of ResultThreadwould be a good place.
在所属的对象中创建一个槽，在ResultThread中QNetworkRequestManager创建一个信号并将两者连接起来，ResultThread的构造函数将是一个好地方。
The code which is currently in ResultThread::run()goes to the new slot, and is replaced by a emit(yourSignal()). If necessary send a pointer to your ResultThreadas a parameter with your emit function to gain access to member functions/variables.
当前在ResultThread::run() 中的代码转到新的slot，并由 a 替换emit(yourSignal())。如有必要，将指向您的ResultThread的指针作为参数与您的发射函数一起发送，以获得对成员函数/变量的访问。
