Qt将所有GUI相关的处理都限制在主线程中,这么做有助于防止意想不到的访问冲突产生,但也限制了线程中某些简单的UI交互的实现,比如QMessageBox。
因为QMessageBox必须在主线程中打开,为了使用它,便不得不自己动手实现一些信号和槽,从而增加了自己代码的复杂度。为降低使用QMessageBox时的设计负担,本文从QThread类继承一个新类MsgBoxThread,将这些实现细节封装为MsgBoxThread的成员函数about、aboutQt、critical、information、question、warning,分别与QMessageBox的静态成员about、aboutQt、critical、information、question、warning对应,使用时可从该类继承子类,并在run函数中使用这些函数:
#include <QThread> #include <QMessageBox> class MsgBoxThread : public QThread { Q_OBJECT typedef enum { mbt_about = 0, mbt_aboutqt = 1, mbt_critical = 2, mbt_information = 3, mbt_question = 4, mbt_warning = 5 } MSGBOXTYPE; protected: int m_btnres; void about(QWidget * parent, const QString &title, const QString &text) { emit msgbox_sig(mbt_about, parent, title, text, QMessageBox::NoButton, QMessageBox::NoButton); } void aboutQt(QWidget *parent, const QString &title = QString()) { emit msgbox_sig(mbt_aboutqt, parent, title, tr(""), QMessageBox::NoButton, QMessageBox::NoButton); } int critical(QWidget * parent, const QString &title, const QString &text, QMessageBox::StandardButtons buttons = QMessageBox::Ok, QMessageBox::StandardButtons defaultButton = QMessageBox::NoButton) { emit msgbox_sig(mbt_critical, parent, title, text, buttons, defaultButton); return m_btnres; } int information(QWidget * parent, const QString &title, const QString &text, QMessageBox::StandardButtons buttons = QMessageBox::Ok, QMessageBox::StandardButtons defaultButton = QMessageBox::NoButton) { emit msgbox_sig(mbt_information, parent, title, text, buttons, defaultButton); return m_btnres; } int question(QWidget * parent, const QString &title, const QString &text, QMessageBox::StandardButtons buttons = QMessageBox::StandardButtons(QMessageBox::Yes | QMessageBox::No), QMessageBox::StandardButtons defaultButton = QMessageBox::NoButton) { emit msgbox_sig(mbt_question, parent, title, text, buttons, defaultButton); return m_btnres; } int warning(QWidget * parent, const QString &title, const QString &text, QMessageBox::StandardButtons buttons = QMessageBox::Ok, QMessageBox::StandardButtons defaultButton = QMessageBox::NoButton) { emit msgbox_sig(mbt_warning, parent, title, text, buttons, defaultButton); return m_btnres; } public: MsgBoxThread(QObject * parent = 0) :QThread(parent), m_btnres(QMessageBox::NoButton) { qRegisterMetaType<QMessageBox::StandardButtons>("QMessageBox::StandardButtons"); connect(this, SIGNAL(msgbox_sig(MSGBOXTYPE, QWidget *, const QString, const QString, QMessageBox::StandardButtons, QMessageBox::StandardButtons)), SLOT(on_information(MSGBOXTYPE, QWidget *, const QString , const QString, QMessageBox::StandardButtons , QMessageBox::StandardButtons )), Qt::BlockingQueuedConnection); } signals: void msgbox_sig(MSGBOXTYPE type, QWidget * parent, const QString &title, const QString &text, QMessageBox::StandardButtons buttons, QMessageBox::StandardButtons defaultButton); private slots: void on_msgbox(MSGBOXTYPE type, QWidget * parent, const QString &title, const QString &text, QMessageBox::StandardButtons buttons, QMessageBox::StandardButtons defaultButton) { switch(type) { case mbt_about: QMessageBox::about(parent,title,text); break; case mbt_aboutqt: QMessageBox::aboutQt(parent, title); break; case mbt_critical: m_btnres = QMessageBox::critical(parent, title, text, buttons, defaultButton); break; case mbt_information: m_btnres = QMessageBox::information(parent, title, text, buttons, defaultButton); break; case mbt_question: m_btnres = QMessageBox::question(parent, title, text, buttons, defaultButton); break; case mbt_warning: m_btnres = QMessageBox::warning(parent, title, text, buttons, defaultButton); break; default: Q_ASSERT_X(false,"QMessageBox in thread","invalid box type specified."); } } };
原理:
自定义的MsgBoxThread类继承自QThread类,其中声明了可在子线程中发射的信号msgbox_sig,并在MsgBoxThread的构造函数中将该信号以阻塞模式(Qt::BlockingQueuedConnection)连接到私有槽函数on_msgbox。因为槽函数的父对象在主线程中创建,这保证了信号msgbox_sig在主线程的事件循环中执行;又由于槽函数on_msgbox采用组色模式连接,使得子线程在调用了这些封装函数(about、aboutQt、information、critical、warning)后会等待主线程的槽函数执行并返回后才会继续执行;综上,即可保证使用QMessageBox实现简单的UI交互,又不违反Qt的GUI相关处理必须在主线程中的限制。
参考:http://blog.csdn.net/johnyork/article/details/46419185