luaplus 与官方文档慢慢扯(五)

 

Registering Callbacks(注册lua c函数)

函数原型

int Callback(LuaState* state);  

 

作为一种替代机制 lua stack 是通过LuaStack类提供的

LuaPlus的回调函数使用了一种简单的函数机制  可以让全局函数 静态函数 非虚成员函数 与虚成员函数 成为回调函数

 

下面是一个示例 例子很简单就不注释了 (唯一需要注意的是  LuaStack args(state);)

static int LS_LOG(LuaState* state) { printf("In static function/n"); return 0; } class Logger { public: int LS_LOGMEMBER(LuaState* state) { LuaStack args(state);//需要注意这里哦 printf("In member function. Message: %s/n", args[1].GetString()); return 0; } virtual int LS_LOGVIRTUAL(LuaState* state) { printf("In virtual member function/n"); return 0; } }; LuaObject globalsObj = state->GetGlobals(); globalsObj.Register("LOG", LS_LOG); state->DoString("LOG()"); Logger logger; globalsObj.Register("LOGMEMBER", logger, &Logger::LS_LOGMEMBER); state->DoString("LOGMEMBER('The message')"); globalsObj.Register("LOGVIRTUAL", logger, &Logger::LS_LOGVIRTUAL); state->DoString("LOGVIRTUAL()");  

 

使用 Register() 函数注册回调函数.

LuaObject 提供了几种重载的 Register() 函数:

void Register( const char* funcName, lua_CFunction function, int nupvalues = 0 ); void Register( const char* funcName, int (*func)(LuaState*), int nupvalues = 0 ); void Register( const char* funcName, const Callee& callee, int (Callee::*func)(LuaState*), int nupvalues = 0 );  

 

 

Registering Object Dispatch Functors(注册一个c++类到lua)

虽然Register() 可以注册 c++类成员函数 但是他的第二个参数需要提供一个类对象 

但是内部调用成员函数时候 this指针是一个常量  所以 Register()函数不是适合镜像c++类到lua中

 

this指针的问题  是通过 RegisterObjectFunctor() 函数解决的

官方文档原文

 

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Even though Register() can dispatch to C++ member functions, it uses a 'this' pointer as provided by the second argument passed to the function.  The 'this' pointer is constant, and Register() is not suited for mirroring class hierarchies in Lua.

The solution to the 'this' pointer issue is through RegisterObjectFunctor().  It is a specialized form of Register() where a 'this' pointer isn't provided during the closure registration.  Instead, it is retrieved from either the calling userdata or the calling table's __object member, which must be a full or light userdata.

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下面 是实现2个c++类到lua的例子

class MultiObject { public: MultiObject(int num) : m_num(num) { } int Print(LuaState* state) { printf("%d/n", m_num); return 0; } void Print2(int num) { printf("%d %d/n", m_num, num); } protected: int m_num; }; //注册一个metatable LuaObject metaTableObj = state->GetGlobals().CreateTable("MultiObjectMetaTable"); metaTableObj.SetObject("__index", metaTableObj);//设置metatable是他自己 metaTableObj.RegisterObjectFunctor("Print", &MultiObject::Print);//在table内注册一个 print函数 //现在 我们在lua内实现两个对象 obj1 obj2 MultiObject obj1(10); LuaObject obj1Obj = state->BoxPointer(&obj1); obj1Obj.SetMetaTable(metaTableObj); state->GetGlobals().SetObject("obj1", obj1Obj); MultiObject obj2(20); LuaObject obj2Obj = state->BoxPointer(&obj2); obj2Obj.SetMetaTable(metaTableObj); state->GetGlobals().SetObject("obj2", obj2Obj); //两个c++对象已经设置好了 现在测试下 state->DoString("obj1:Print() ; print(obj1)"); state->DoString("obj2:Print() ; print(obj2)"); // 10 // userdata: 002EB940 // 20 // userdata: 002EB9D0 

 

 

上面的obj1 和 obj2 是作为  userdata 然后设置它的metatables 的方法创建的 

另一种方法是将代表的c++对象的tuserdata作为表的成员 __object

LuaObject table1Obj = state->GetGlobals().CreateTable("table1"); table1Obj.SetLightUserData("__object", &obj1); table1Obj.SetMetaTable(metaTableObj); LuaObject table2Obj = state->GetGlobals().CreateTable("table2"); table2Obj.SetLightUserData("__object", &obj2); table2Obj.SetMetaTable(metaTableObj); state->DoString("table1:Print()"); state->DoString("table2:Print()");  

 

 

Registering Functions Directly(直接注册普通函数)

LuaPlus通过RegisterDirect() 可以直接注册c++函数

float Add(float num1, float num2) { return num1 + num2; } LuaStateOwner state; state->GetGlobals().RegisterDirect("Add", Add); state->DoString("print(Add(10, 5))");  

以这种方式注册的函数  函数可以是任何形式的 内部会自动进行函数参数的类型检查

如果lua调用函数 传入的参数无效 则触发 luaL_argassert  导致调用失败

例如 state->DoString("print(Add(10, 'Hello'))"); 这样就导致失败了

 

全局函数可以这样注册  而成员函数也同样可以这样注册

void LOG(const char* message) { printf("In global function: %s/n", message); } class Logger { public: void LOGMEMBER(const char* message) { printf("In member function: /n", message); } virtual void LOGVIRTUAL(const char* message) { printf("In virtual member function: %s/n", message); } }; LuaObject globalsObj = state->GetGlobals(); globalsObj.RegisterDirect("LOG", LOG); Logger logger; globalsObj.RegisterDirect("LOGMEMBER", logger, &Logger::LOGMEMBER); globalsObj.RegisterDirect("LOGVIRTUAL", logger, &Logger::LOGVIRTUAL); state->DoString("LOG('Hello')"); state->DoString("LOGMEMBER('Hello')"); state->DoString("LOGVIRTUAL('Hello')");  

直接注册的函数在目前版本中最多只支持7个参数

 

 

 

Object Dispatch to Directly Called C++ Member Functions(注册普通c++成员函数)

官方文档原文

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Even though RegisterDirect() can dispatch directly to C++ member functions, it uses a 'this' pointer as provided by the second argument passed to the function.  The 'this' pointer is constant, and RegisterDirect() is not suited for mirroring class hierarchies in Lua.

The solution to the 'this' pointer issue is through RegisterObjectDirect().  It is a specialized form of RegisterDirect() where a 'this' pointer isn't provided during the closure registration.  Instead, it is retrieved from either the calling userdata or the calling table's __object member, which must be a full or light userdata.  The techniques presented in this section mirror closely the RegisterObjectFunctor() description above.

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使用上一个注册c++对象的那个示例  

向metatable内直接注册普通的c++成员函数

metaTableObj.RegisterObjectDirect("Print2", (MultiObject*)0, &MultiObject::Print2);  

测试

state->DoString("obj1:Print2(5)"); state->DoString("obj2:Print2(15)"); state->DoString("table1:Print2(5)"); state->DoString("table2:Print2(15)");  

 

 

Unregistering Callbacks(撤销已经注册到lua内的对象)

注销回调非常简单 只需将其设置为nil

globalsObj.SetNil("LOG");