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, 0)
{
    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, 0), 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 = 0;
    if (parentWidget && parentWidget->windowType() == Qt::Desktop) {
        desktopWidget = parentWidget;
        parentWidget = 0;
    }

    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 = 0;
    data.widget_attributes = 0;
    data.window_flags = f;
    data.window_state = 0;
    data.focus_policy = 0;
    data.context_menu_policy = Qt::DefaultContextMenu;
    data.window_modality = Qt::NonModal;

    data.sizehint_forced = 0;
    data.is_closing = 0;
    data.in_show = 0;
    data.in_set_window_state = 0;
    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(0,0,100,30) : QRect(0,0,640,480);

    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 = 0;
}

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 == 0 && 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 = -1;
    if (paintOnScreenEnv == -1)
        paintOnScreenEnv = qgetenv("QT_ONSCREEN_PAINT").toInt() > 0 ? 1 : 0;
    if (paintOnScreenEnv == 1)
        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 = 0;
        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 = -1, sh = -1;

    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 = 0;
    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 < 0) {                                // 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(76 /* SM_XVIRTUALSCREEN  */), GetSystemMetrics(77 /* SM_YVIRTUALSCREEN  */),
                           GetSystemMetrics(78 /* SM_CXVIRTUALSCREEN */), GetSystemMetrics(79 /* SM_CYVIRTUALSCREEN */));
        else
            data.crect.setRect(0, 0, GetSystemMetrics(SM_CXSCREEN), GetSystemMetrics(SM_CYSCREEN));
    }

    parentw = q->parentWidget() ? q->parentWidget()->effectiveWinId() : 0;

#ifdef UNICODE
    QString title;
    const TCHAR *ttitle = 0;
#endif
    QByteArray title95;
    int style = WS_CHILD;
    int exsty = 0;

    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 = 0;
    }
    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 = 0;

        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 = {0,0,0,0};
        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/2;
                h = 4*sh/10;
            }
            if (!wasMoved) {
                x = sw/2 - w/2;
                y = sh/2 - h/2;
            }
        }

        QT_WA({
            const TCHAR *cname = (TCHAR*)windowClassName.utf16();
            id = CreateWindowEx(exsty, cname, ttitle, style,
                                x, y, w, h,
                                parentw, 0, appinst, 0);
        } , {
            id = CreateWindowExA(exsty, windowClassName.toLatin1(), title95, style,
                                 x, y, w, h,
                                 parentw, 0, appinst, 0);
        });
        if (!id)
            qErrnoWarning("QWidget::create: Failed to create window");
        setWinId(id);
        if ((flags & Qt::WindowStaysOnTopHint) || (type == Qt::ToolTip)) {
            SetWindowPos(id, HWND_TOPMOST, 0, 0, 0, 0, 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, 0, 0, 0, 0, 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, 0, 0, 0, 0, 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 = 0;
        pt.y = 0;
        ClientToScreen(id, &pt);

        if (data.crect.width() == 0 || data.crect.height() == 0) {
            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 - 1, pt.y + cr.bottom - 1));
        }

        if (data.fstrut_dirty) {
            // be nice to activeqt
            updateFrameStrut();
        }
    }

    q->setAttribute(Qt::WA_WState_Created);                // accept move/resize events
    hd = 0;                                        // 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 != 255)
        q->setWindowOpacity(maybeTopData()->opacity/255.);

    if (topLevel && (data.crect.width() == 0 || data.crect.height() == 0)) {
        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。