Qt 信号与槽研究：

Qt 信号与槽研究：
author: hjjdebug
date: 2015年 08月 17日 星期一 09:36:31 CST

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先看看简单的源码:
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mainwindow.h, mainwindow.cpp

#ifndef _MAINWINDOW#define _MAINWINDOW#include <QWidget>class QPushButton;class MainWindow : public QWidget{Q_OBJECTpublic:MainWindow(QWidget *parent=0);public slots:void button_click();private:QPushButton *button;};#endif#include <QtGui>#include "mainwindow.h"MainWindow::MainWindow(QWidget *widget) : QWidget(widget){button = new QPushButton(this);button->setText("Push Me");connect(button,SIGNAL(clicked()),this,SLOT(button_click()));}void MainWindow::button_click(){qDebug("button clicked");}

该代码可以实现点击button, 调用显示button_click 信息

下面分析三个方面:
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1. Q_OBJECT 宏
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public: template <typename T> inline  
void qt_check_for_QOBJECT_macro(const T &_q_argument) const  
{
int i = qYouForgotTheQ_OBJECT_Macro(this, &_q_argument);
i = i + 1;  
}
static const QMetaObject staticMetaObject;
virtual const QMetaObject *metaObject() const;
virtual void *qt_metacast(const char *);
static inline QString tr(const char *s, const char *c = 0) { return staticMetaObject.tr(s, c); }
static inline QString trUtf8(const char *s, const char *c = 0) { return staticMetaObject.trUtf8(s, c); }
static inline QString tr(const char *s, const char *c, int n) { return staticMetaObject.tr(s, c, n); }
static inline QString trUtf8(const char *s, const char *c, int n) { return staticMetaObject.trUtf8(s, c, n); }
virtual int qt_metacall(QMetaObject::Call, int, void **);
private:
__attribute__((visibility("hidden"))) static const QMetaObjectExtraData staticMetaObjectExtraData;
__attribute__((visibility("hidden"))) static void qt_static_metacall(QObject *, QMetaObject::Call, int, void **);

注意:
声明了staticMetaObject 对象, 由moc_mainwindow.cpp 根据MainWindow 的信号，槽来实现
声明了staticMetaObjectExtraData , 包含qt_static_metacall 等函数
声明了一些函数接口，公共接口为qt_metacast, qt_metacall, metaObject() 等

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2. moc_mainwindow.cpp
由于声明了Q_OBJECT, 而由工具moc 自动生成对应的moc代码
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内容较多，不便贴出，请参考具体代码，
目的，实现Q_OBJECT 声明的内容， 完成QT 信号与槽对接。

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3. 信号与槽的链接
我们只需要知道，信号经过一个长长的路程，依靠moc 代码，最后找到了它的归宿。
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Breakpoint 2, MainWindow::button_click (this=0x7f4000) at mainwindow.cpp:14
14        qDebug("button clicked");
(gdb) bt
#0  MainWindow::button_click (this=0x7f4000) at mainwindow.cpp:14
#1  0x000000000040292e in MainWindow::qt_static_metacall (_o=0x7f4000, _c=QMetaObject::InvokeMetaMethod, _id=0, _a=0x7fffffffd0e0)
    at moc_mainwindow.cpp:48
#2  0x00007ffff6dd387a in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) ()
   from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#3  0x00007ffff793f0d2 in QAbstractButton::clicked(bool) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#4  0x00007ffff76a29d3 in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#5  0x00007ffff76a3b43 in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#6  0x00007ffff76a3c2c in QAbstractButton::mouseReleaseEvent(QMouseEvent*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#7  0x00007ffff734050a in QWidget::event(QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#8  0x00007ffff72f0e2c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#9  0x00007ffff72f75dd in QApplication::notify(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#10 0x00007ffff6dbf4dd in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#11 0x00007ffff72f6d93 in QApplicationPrivate::sendMouseEvent(QWidget*, QMouseEvent*, QWidget*, QWidget*, QWidget**, QPointer<QWidget>&, bool) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#12 0x00007ffff736b9cb in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#13 0x00007ffff736b269 in QApplication::x11ProcessEvent(_XEvent*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#14 0x00007ffff7392b02 in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#15 0x00007ffff5a31e04 in g_main_context_dispatch () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#16 0x00007ffff5a32048 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#17 0x00007ffff5a320ec in g_main_context_iteration () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#18 0x00007ffff6dec7a1 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
   from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#19 0x00007ffff7392bb6 in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#20 0x00007ffff6dbe0af in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
   from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#21 0x00007ffff6dbe3a5 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#22 0x00007ffff6dc3b79 in QCoreApplication::exec() () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#23 0x00000000004026b7 in main (argc=1, argv=0x7fffffffde48) at main.cpp:9
(gdb)