wxWidgets初始化分析-应用定义和初始化
1. 一个wxWidgets的基本结构是：一个App类+一个Frame类，代码如：
class MyApp: public wxApp
{
public:
bool OnInit();
};
IMPLEMENT_APP(MyApp)
2. IMPLEMENT_APP(MyApp) 这个宏包含了入口，抽象了不同平台入口的差异，分析如下:
IMPLEMENT_APP展开如下:
#define IMPLEMENT_APP(appname) \
IMPLEMENT_APP_NO_THEMES(appname) \
IMPLEMENT_WX_THEME_SUPPORT
IMPLEMENT_APP_NO_THEMES展开如下:
#define IMPLEMENT_APP_NO_THEMES(appname) \
IMPLEMENT_APP_NO_MAIN(appname) \
IMPLEMENT_WXWIN_MAIN
IMPLEMENT_APP_NO_MAIN展开如下:
#define IMPLEMENT_APP_NO_MAIN(appname) \
wxAppConsole *wxCreateApp() \
{ \
wxAppConsole::CheckBuildOptions(WX_BUILD_OPTIONS_SIGNATURE, \
"your program"); \
return new appname; \
} \
wxAppInitializer \
wxTheAppInitializer((wxAppInitializerFunction) wxCreateApp); \
DECLARE_APP(appname) \
appname& wxGetApp() { return *wx_static_cast(appname*, wxApp::GetInstance()); }
实际上IMPLEMENT_APP_NO_MAIN定义了wxCreateApp函数new appname创建出应用类的实例.
wxAppInitializer wxTheAppInitializer((wxAppInitializerFunction) wxCreateApp);实际上把创建函数wxCreateApp用接口wxApp::SetInitializerFunction(fn);设置进了系统，都静态变量保存的.
appname& wxGetApp() { return *wx_static_cast(appname*, wxApp::GetInstance()); }这个获取App实例的接口也在此定义.
IMPLEMENT_WXWIN_MAIN展开如下：
#define IMPLEMENT_WXWIN_MAIN \
extern "C" int WINAPI WinMain(HINSTANCE hInstance, \
HINSTANCE hPrevInstance, \
wxCmdLineArgType lpCmdLine, \
int nCmdShow) \
{ \
return wxEntry(hInstance, hPrevInstance, lpCmdLine, nCmdShow); \
} \
IMPLEMENT_WXWIN_MAIN_BORLAND_NONSTANDARD
WinMain是Windows平台Win32应用的入口函数，WinMain包含了C/C++的main函数实现.
多参WXDLLEXPORT int wxEntry(HINSTANCE hInstance,HINSTANCE WXUNUSED(hPrevInstance),wxCmdLineArgType WXUNUSED(pCmdLine),int nCmdShow)，会在最后调用2参的int wxEntry(int& argc, char **argv)，此函数实现有3处，Unicode版本的也是要转换成非Unicode版本的函数调用，最终会调用到wxEntryReal，此接口是真正的库初始化入口：分析如下
wxEntryReal定义如下：
int wxEntryReal(int& argc, wxChar **argv)
{
// library initialization
wxInitializer initializer(argc, argv);
if ( !initializer.IsOk() )
{
#if wxUSE_LOG
// flush any log messages explaining why we failed
delete wxLog::SetActiveTarget(NULL);
#endif
return -1;
}
wxTRY
{
// app initialization
if ( !wxTheApp->CallOnInit() )
{
// don't call OnExit() if OnInit() failed
return -1;
}
// ensure that OnExit() is called if OnInit() had succeeded
class CallOnExit
{
public:
~CallOnExit() { wxTheApp->OnExit(); }
} callOnExit;
WX_SUPPRESS_UNUSED_WARN(callOnExit);
// app execution
return wxTheApp->OnRun();
}
wxCATCH_ALL( wxTheApp->OnUnhandledException(); return -1; )
}
wxInitializer initializer(argc, argv);这句隐含了库的初始化过程，wxInitializer类的构造函数进行了初始化：
wxInitializer(int argc, char **argv) //构造函数
{
m_ok = wxInitialize(argc, argv); //调用了初始化wxInitialize
}
wxInitialize调用了wxEntryStart，此函数也2个版本，unicode的版本也是经过转换调用的非unicode版本，如下：
wxAppPtr app(wxTheApp);
if ( !app.get() )
{
// if not, he might have used IMPLEMENT_APP() to give us a function to
// create it
wxAppInitializerFunction fnCreate = wxApp::GetInitializerFunction(); // 注意此句取得了上边设置的创建App的函数
if ( fnCreate )
{
// he did, try to create the custom wxApp object
app.Set((*fnCreate)()); // 此处构造了应用App类，app变量保存了此指针，这个赋值实际调用wxApp::SetInstance(ptr);赋值了ms_appInstance，
//通过wxTheApp宏访问，上边定义的wxGetApp接口，也是获取此变量.
}
if ( !app.get() )
{
// either IMPLEMENT_APP() was not used at all or it failed -- in any
// case we still need something
app.Set(new wxDummyConsoleApp);
}
// wxApp initialization: this can be customized
// --------------------------------------------
if ( !app->Initialize(argc, argv) ) // 调用app初始化接口，bool wxApp::Initialize(int& argc, wxChar **argv)此接口被调用，进而初始化了系统
{
return false;
}
wxEntryReal调用了系统初始化后，又调用了应用App的OnInit接口，给App初始化的时机：
// app initialization
if ( !wxTheApp->CallOnInit() )
{
// don't call OnExit() if OnInit() failed
return -1;
}
此调用会多态到应用的OnInit接口，应用在此接口中初始化了Frame主窗口之类的窗口组件.wxTheApp宏用的比较多.CallOnInit接口调用了 CallOnInit() { return OnInit(); }接口。
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以上基本完成了库和用户的App初始化过程，在wxEntryReal接口的最后，return wxTheApp->OnRun()；进入:
int wxAppBase::OnRun()
{
// see the comment in ctor: if the initial value hasn't been changed, use
// the default Yes from now on
if ( m_exitOnFrameDelete == Later )
{
m_exitOnFrameDelete = Yes;
}
//else: it has been changed, assume the user knows what he is doing
return MainLoop();
}
//进入了程序主循环，开始了事件接收、分发、处理的过程，指导程序结束.
本文完.
