QT分析之QPushButton的初始化

原文地址：http://blog.163.com/net_worm/blog/static/127702419201001003326522/

在简单的QT程序的第二行，声明了一个QPushButton的对象。先简单看看其初始化过程。

QPushButton的类继承关系为：

 QPushButton ：public QAbstractButton ：pubic QWidget ：public QObject, public QPaintDevice

QPushButton的构造：

 QPushButton::QPushButton(const QString &text, QWidget *parent)
     : QAbstractButton(*new QPushButtonPrivate, parent)
 {
     Q_D(QPushButton);  // 声明并获得QPushButtonPrivate函数指针d
     setText(text);    // 设置按钮的名字
     d->init();   // 调用QPushButtonPrivate::init()，其实只是重新设定排布间隔
 }

新生成的QPushButtonPrivate对象传递给QAbstractButton之后，发生了什么事呢？

 QAbstractButton::QAbstractButton(QAbstractButtonPrivate &dd, QWidget *parent)
     : QWidget(dd, parent, )
 {
     Q_D(QAbstractButton);  // 声明并获得QAbstractButtonPrivate函数指针d
     d->init();   // 调用QAbstractButtonPrivate::init()
 }

QAbstractButtonPrivate::init()做了什么呢？其实只是调用了QPushButton的几个设定函数。

继续看QWidget的初始化过程。

 QWidget::QWidget(QWidgetPrivate &dd, QWidget* parent, Qt::WindowFlags f)
     : QObject(dd, ), QPaintDevice()
 {
     d_func()->init(parent, f);
 }

其中d_func()是宏定义Q_DECLARE_PRIVATE(QWidget)中定义的，获取QWidgetPrivate指针的函数。有点奇怪的是，这里怎么没有用Q_D宏定义，与之前的风格有点不同。

QWidgetPrivate::init()里做了什么动作呢？（关键语句用颜色标记）

 void QWidgetPrivate::init(QWidget *parentWidget, Qt::WindowFlags f)
 {
     Q_Q(QWidget);
     if (qApp->type() == QApplication::Tty)
         qFatal("QWidget: Cannot create a QWidget when no GUI is being used");
 
     Q_ASSERT(uncreatedWidgets);
     uncreatedWidgets->insert(q);
 
     QWidget *desktopWidget = ;
     if (parentWidget && parentWidget->windowType() == Qt::Desktop) {
         desktopWidget = parentWidget;
         parentWidget = ;
     }
 
     q->data = &data;
 
     if (!q->parent()) {
         Q_ASSERT_X(q->thread() == qApp->thread(), "QWidget",
                    "Widgets must be created in the GUI thread.");
     }
 
     data.fstrut_dirty = true;
 
     data.winid = ;
     data.widget_attributes = ;
     data.window_flags = f;
     data.window_state = ;
     data.focus_policy = ;
     data.context_menu_policy = Qt::DefaultContextMenu;
     data.window_modality = Qt::NonModal;
 
     data.sizehint_forced = ;
     data.is_closing = ;
     data.in_show = ;
     data.in_set_window_state = ;
     data.in_destructor = false;
 
     // Widgets with Qt::MSWindowsOwnDC (typically QGLWidget) must have a window handle.
     if (f & Qt::MSWindowsOwnDC)
         q->setAttribute(Qt::WA_NativeWindow);
 
     q->setAttribute(Qt::WA_QuitOnClose); // might be cleared in adjustQuitOnCloseAttribute()
     adjustQuitOnCloseAttribute();
 
     q->setAttribute(Qt::WA_WState_Hidden);
 
     //give potential windows a bigger "pre-initial" size; create_sys() will give them a new size later
     data.crect = parentWidget ? QRect(,,,) : QRect(,,,);
 
     focus_next = focus_prev = q;
 
     if ((f & Qt::WindowType_Mask) == Qt::Desktop)
         q->create();  // 调用了QWidget::create()
     else if (parentWidget)
         q->setParent(parentWidget, data.window_flags);
     else {
         adjustFlags(data.window_flags, q);
         resolveLayoutDirection();
         // opaque system background?
         const QBrush &background = q->palette().brush(QPalette::Window);
         setOpaque(q->isWindow() && background.style() != Qt::NoBrush && background.isOpaque());
     }
     data.fnt = QFont(data.fnt, q);
 
     q->setAttribute(Qt::WA_PendingMoveEvent);
     q->setAttribute(Qt::WA_PendingResizeEvent);
 
     if (++QWidgetPrivate::instanceCounter > QWidgetPrivate::maxInstances)
         QWidgetPrivate::maxInstances = QWidgetPrivate::instanceCounter;
 
     if (QApplicationPrivate::app_compile_version < 0x040200
         || QApplicationPrivate::testAttribute(Qt::AA_ImmediateWidgetCreation))
         q->create();
 
     // 下面的三行，产生并发送了Create事件
     QEvent e(QEvent::Create);
     QApplication::sendEvent(q, &e);
     QApplication::postEvent(q, new QEvent(QEvent::PolishRequest));
 
     extraPaintEngine = ;
 }

看看QWidget::create()的实现：

 void QWidget::create(WId window, bool initializeWindow, bool destroyOldWindow)
 {
     Q_D(QWidget);
     if (testAttribute(Qt::WA_WState_Created) && window ==  && internalWinId())
         return;
 
     if (d->data.in_destructor)
         return;
 
     Qt::WindowType type = windowType();
     Qt::WindowFlags &flags = data->window_flags;
 
     if ((type == Qt::Widget || type == Qt::SubWindow) && !parentWidget()) {
         type = Qt::Window;
         flags |= Qt::Window;
     }
 
     if (QWidget *parent = parentWidget()) {
         if (type & Qt::Window) {
             if (!parent->testAttribute(Qt::WA_WState_Created))
                 parent->createWinId();
         } else if (testAttribute(Qt::WA_NativeWindow) && !parent->internalWinId()
                    && !testAttribute(Qt::WA_DontCreateNativeAncestors)) {
             // We're about to create a native child widget that doesn't have a native parent;
             // enforce a native handle for the parent unless the Qt::WA_DontCreateNativeAncestors
             // attribute is set.
             d->createWinId(window);
             // Nothing more to do.
             Q_ASSERT(testAttribute(Qt::WA_WState_Created));
             Q_ASSERT(internalWinId());
             return;
         }
     }
 
     static int paintOnScreenEnv = -;
     if (paintOnScreenEnv == -)
         paintOnScreenEnv = qgetenv("QT_ONSCREEN_PAINT").toInt() >  ?  : ;
     if (paintOnScreenEnv == )
         setAttribute(Qt::WA_PaintOnScreen);
 
     if (QApplicationPrivate::testAttribute(Qt::AA_NativeWindows))
         setAttribute(Qt::WA_NativeWindow);
 
 #ifdef ALIEN_DEBUG
     qDebug() << "QWidget::create:" << this << "parent:" << parentWidget()
              << "Alien?" << !testAttribute(Qt::WA_NativeWindow);
 #endif
 
     // Unregister the dropsite (if already registered) before we
     // re-create the widget with a native window.
     if (testAttribute(Qt::WA_WState_Created) && !internalWinId() && testAttribute(Qt::WA_NativeWindow)
             && d->extra && d->extra->dropTarget) {
         d->registerDropSite(false);
     }
 
     d->updateIsOpaque();
 
     setAttribute(Qt::WA_WState_Created);                        // set created flag
     d->create_sys(window, initializeWindow, destroyOldWindow);
 
     // a real toplevel window needs a backing store
     if (isWindow()) {
         delete d->topData()->backingStore;
         // QWidgetBackingStore will check this variable, hence it must be 0
         d->topData()->backingStore = ;
         if (hasBackingStoreSupport())
             d->topData()->backingStore = new QWidgetBackingStore(this);
     }
 
     d->setModal_sys();
 
     if (!isWindow() && parentWidget() && parentWidget()->testAttribute(Qt::WA_DropSiteRegistered))
         setAttribute(Qt::WA_DropSiteRegistered, true);
 
     // need to force the resting of the icon after changing parents
     if (testAttribute(Qt::WA_SetWindowIcon))
         d->setWindowIcon_sys(true);
     if (isWindow() && !d->topData()->iconText.isEmpty())
         d->setWindowIconText_helper(d->topData()->iconText);
     if (windowType() != Qt::Desktop) {
         d->updateSystemBackground();
 
         if (isWindow() && !testAttribute(Qt::WA_SetWindowIcon))
             d->setWindowIcon_sys();
     }
 }

这里QWidgetPrivate::create_sys()定义在QWidget_win.cpp里。

 void QWidgetPrivate::create_sys(WId window, bool initializeWindow, bool destroyOldWindow)
 {
     Q_Q(QWidget);
     static int sw = -, sh = -;
 
     Qt::WindowType type = q->windowType();
     Qt::WindowFlags flags = data.window_flags;
 
     bool topLevel = (flags & Qt::Window);
     bool popup = (type == Qt::Popup);
     bool dialog = (type == Qt::Dialog
                    || type == Qt::Sheet
                    || (flags & Qt::MSWindowsFixedSizeDialogHint));
     bool desktop = (type == Qt::Desktop);
     bool tool = (type == Qt::Tool || type == Qt::Drawer);
 
     HINSTANCE appinst  = qWinAppInst();
     HWND parentw, destroyw = ;
     WId id;
 
     QString windowClassName = qt_reg_winclass(q);
 
     if (!window)                                // always initialize
         initializeWindow = true;
 
     if (popup)
         flags |= Qt::WindowStaysOnTopHint; // a popup stays on top
 
     if (sw < ) {                                // get the (primary) screen size
         sw = GetSystemMetrics(SM_CXSCREEN);
         sh = GetSystemMetrics(SM_CYSCREEN);
     }
 
     if (desktop && !q->testAttribute(Qt::WA_DontShowOnScreen)) {                                // desktop widget
         popup = false;                                // force this flags off
         if (QSysInfo::WindowsVersion != QSysInfo::WV_NT && QSysInfo::WindowsVersion != QSysInfo::WV_95)
             data.crect.setRect(GetSystemMetrics( /* SM_XVIRTUALSCREEN  */), GetSystemMetrics( /* SM_YVIRTUALSCREEN  */),
                            GetSystemMetrics( /* SM_CXVIRTUALSCREEN */), GetSystemMetrics( /* SM_CYVIRTUALSCREEN */));
         else
             data.crect.setRect(, , GetSystemMetrics(SM_CXSCREEN), GetSystemMetrics(SM_CYSCREEN));
     }
 
     parentw = q->parentWidget() ? q->parentWidget()->effectiveWinId() : ;
 
 #ifdef UNICODE
     QString title;
     const TCHAR *ttitle = ;
 #endif
     QByteArray title95;
     int style = WS_CHILD;
     int exsty = ;
 
     if (window) {
         style = GetWindowLongA(window, GWL_STYLE);
         if (!style)
             qErrnoWarning("QWidget::create: GetWindowLong failed");
         topLevel = false; // #### needed for some IE plugins??
     } else if (popup || (type == Qt::ToolTip) || (type == Qt::SplashScreen)) {
         style = WS_POPUP;
     } else if (topLevel && !desktop) {
         if (flags & Qt::FramelessWindowHint)
             style = WS_POPUP;                // no border
         else if (flags & Qt::WindowTitleHint)
             style = WS_OVERLAPPED;
         else
             style = ;
     }
     if (!desktop) {
         // if (!testAttribute(Qt::WA_PaintUnclipped))
         // ### Commented out for now as it causes some problems, but
         // this should be correct anyway, so dig some more into this
 #ifndef Q_FLATTEN_EXPOSE
         style |= WS_CLIPSIBLINGS | WS_CLIPCHILDREN ;
 #endif
         if (topLevel) {
             if ((type == Qt::Window || dialog || tool)) {
                 if (!(flags & Qt::FramelessWindowHint)) {
                     if (!(flags & Qt::MSWindowsFixedSizeDialogHint)) {
                         style |= WS_THICKFRAME;
                         if(!(flags &
                             ( Qt::WindowSystemMenuHint
                             | Qt::WindowTitleHint
                             | Qt::WindowMinMaxButtonsHint
                             | Qt::WindowCloseButtonHint
                             | Qt::WindowContextHelpButtonHint)))
                             style |= WS_POPUP;
                     } else {
                         style |= WS_POPUP | WS_DLGFRAME;
                     }
                 }
                 if (flags & Qt::WindowTitleHint)
                     style |= WS_CAPTION;
                 if (flags & Qt::WindowSystemMenuHint)
                     style |= WS_SYSMENU;
                 if (flags & Qt::WindowMinimizeButtonHint)
                     style |= WS_MINIMIZEBOX;
                 if (shouldShowMaximizeButton())
                     style |= WS_MAXIMIZEBOX;
                 if (tool)
                     exsty |= WS_EX_TOOLWINDOW;
                 if (flags & Qt::WindowContextHelpButtonHint)
                     exsty |= WS_EX_CONTEXTHELP;
             } else {
                  exsty |= WS_EX_TOOLWINDOW;
             }
         }
     }
 
     if (flags & Qt::WindowTitleHint) {
         QT_WA({
             title = q->isWindow() ? qAppName() : q->objectName();
             ttitle = (TCHAR*)title.utf16();
         } , {
             title95 = q->isWindow() ? qAppName().toLocal8Bit() : q->objectName().toLatin1();
         });
     }
 
     // The Qt::WA_WState_Created flag is checked by translateConfigEvent() in
     // qapplication_win.cpp. We switch it off temporarily to avoid move
     // and resize events during creationt
     q->setAttribute(Qt::WA_WState_Created, false);
 
     if (window) {                                // override the old window
         if (destroyOldWindow)
             destroyw = data.winid;
         id = window;
         setWinId(window);
         LONG res = SetWindowLongA(window, GWL_STYLE, style);
         if (!res)
             qErrnoWarning("QWidget::create: Failed to set window style");
 #ifdef _WIN64
         res = SetWindowLongPtrA( window, GWLP_WNDPROC, (LONG_PTR)QtWndProc );
 #else
         res = SetWindowLongA( window, GWL_WNDPROC, (LONG)QtWndProc );
 #endif
         if (!res)
             qErrnoWarning("QWidget::create: Failed to set window procedure");
     } else if (desktop) {                        // desktop widget
         id = GetDesktopWindow();
 //         QWidget *otherDesktop = QWidget::find(id);        // is there another desktop?
 //         if (otherDesktop && otherDesktop->testWFlags(Qt::WPaintDesktop)) {
 //             otherDesktop->d_func()->setWinId(0);        // remove id from widget mapper
 //             d->setWinId(id);                     // make sure otherDesktop is
 //             otherDesktop->d_func()->setWinId(id);       //   found first
 //         } else {
             setWinId(id);
 //         }
     } else if (topLevel) {                       // create top-level widget
         if (popup)
             parentw = ;
 
         const bool wasMoved = q->testAttribute(Qt::WA_Moved);
         int x = wasMoved ? data.crect.left() : CW_USEDEFAULT;
         int y = wasMoved ? data.crect.top() : CW_USEDEFAULT;
         int w = CW_USEDEFAULT;
         int h = CW_USEDEFAULT;
 
         // Adjust for framestrut when needed
         RECT rect = {,,,};
         bool isVisibleOnScreen = !q->testAttribute(Qt::WA_DontShowOnScreen);
         if (isVisibleOnScreen && AdjustWindowRectEx(&rect, style & ~WS_OVERLAPPED, FALSE, exsty)) {
             QTLWExtra *td = maybeTopData();
             if (wasMoved && (td && !td->posFromMove)) {
                 x = data.crect.x() + rect.left;
                 y = data.crect.y() + rect.top;
             }
 
             if (q->testAttribute(Qt::WA_Resized)) {
                 w = data.crect.width() + (rect.right - rect.left);
                 h = data.crect.height() + (rect.bottom - rect.top);
             }
         }
         //update position & initial size of POPUP window
         if (isVisibleOnScreen && topLevel && initializeWindow && (style & WS_POPUP)) {
             if (!q->testAttribute(Qt::WA_Resized)) {
                 w = sw/;
                 h = *sh/;
             }
             if (!wasMoved) {
                 x = sw/ - w/;
                 y = sh/ - h/;
             }
         }
 
         QT_WA({
             const TCHAR *cname = (TCHAR*)windowClassName.utf16();
             id = CreateWindowEx(exsty, cname, ttitle, style,
                                 x, y, w, h,
                                 parentw, , appinst, );
         } , {
             id = CreateWindowExA(exsty, windowClassName.toLatin1(), title95, style,
                                  x, y, w, h,
                                  parentw, , appinst, );
         });
         if (!id)
             qErrnoWarning("QWidget::create: Failed to create window");
         setWinId(id);
         if ((flags & Qt::WindowStaysOnTopHint) || (type == Qt::ToolTip)) {
             SetWindowPos(id, HWND_TOPMOST, , , , , SWP_NOACTIVATE | SWP_NOMOVE | SWP_NOSIZE);
             if (flags & Qt::WindowStaysOnBottomHint)
                 qWarning() << "QWidget: Incompatible window flags: the window can't be on top and on bottom at the same time";
         } else if (flags & Qt::WindowStaysOnBottomHint)
             SetWindowPos(id, HWND_BOTTOM, , , , , SWP_NOACTIVATE | SWP_NOMOVE | SWP_NOSIZE);
         winUpdateIsOpaque();
     } else if (q->testAttribute(Qt::WA_NativeWindow) || paintOnScreen()) { // create child widget
         QT_WA({
             const TCHAR *cname = (TCHAR*)windowClassName.utf16();
             id = CreateWindowEx(exsty, cname, ttitle, style,
                                 data.crect.left(), data.crect.top(), data.crect.width(), data.crect.height(),
                             parentw, NULL, appinst, NULL);
         } , {
             id = CreateWindowExA(exsty, windowClassName.toLatin1(), title95, style,
                                  data.crect.left(), data.crect.top(), data.crect.width(), data.crect.height(),
                             parentw, NULL, appinst, NULL);
         });
         if (!id)
             qErrnoWarning("QWidget::create: Failed to create window");
         SetWindowPos(id, HWND_TOP, , , , , SWP_NOMOVE | SWP_NOSIZE);
         setWinId(id);
     }
 
     if (desktop) {
         q->setAttribute(Qt::WA_WState_Visible);
     } else if (topLevel && !q->testAttribute(Qt::WA_DontShowOnScreen)) {
         RECT  cr;
         GetClientRect(id, &cr);
         // one cannot trust cr.left and cr.top, use a correction POINT instead
         POINT pt;
         pt.x = ;
         pt.y = ;
         ClientToScreen(id, &pt);
 
         if (data.crect.width() ==  || data.crect.height() == ) {
             data.crect = QRect(pt.x, pt.y, data.crect.width(), data.crect.height());
         } else {
             data.crect = QRect(QPoint(pt.x, pt.y),
                                QPoint(pt.x + cr.right - , pt.y + cr.bottom - ));
         }
 
         if (data.fstrut_dirty) {
             // be nice to activeqt
             updateFrameStrut();
         }
     }
 
     q->setAttribute(Qt::WA_WState_Created);                // accept move/resize events
     hd = ;                                        // no display context
 
     if (window) {                                // got window from outside
         if (IsWindowVisible(window))
             q->setAttribute(Qt::WA_WState_Visible);
         else
             q->setAttribute(Qt::WA_WState_Visible, false);
     }
 
     if (extra && !extra->mask.isEmpty())
         setMask_sys(extra->mask);
 
 #if defined(QT_NON_COMMERCIAL)
     QT_NC_WIDGET_CREATE
 #endif
 
     if (q->hasFocus() && q->testAttribute(Qt::WA_InputMethodEnabled))
         q->inputContext()->setFocusWidget(q);
 
     if (destroyw) {
         DestroyWindow(destroyw);
     }
 
     if (q != qt_tablet_widget && QWidgetPrivate::mapper)
         qt_tablet_init();
 
     if (q->testAttribute(Qt::WA_DropSiteRegistered))
         registerDropSite(true);
 
     if (maybeTopData() && maybeTopData()->opacity != )
         q->setWindowOpacity(maybeTopData()->opacity/.);
 
     if (topLevel && (data.crect.width() ==  || data.crect.height() == )) {
         q->setAttribute(Qt::WA_OutsideWSRange, true);
     }
 
     if (!topLevel && q->testAttribute(Qt::WA_NativeWindow) && q->testAttribute(Qt::WA_Mapped)) {
         Q_ASSERT(q->internalWinId());
         ShowWindow(q->internalWinId(), SW_SHOW);
     }
 }

这里调用了qt_reg_winclass()（在QApplication_win.cpp里定义），查看其代码就是RegisterWindows，把window窗口的消息处理设定为：QtWndProc。QObject的初始化没有什么新意，参看QApplication得初始化。

到目前为止的初始化分析，为下一步我们分析Windows消息传递，也就是QT的事件机制打下了基础。