CCLuaObjcBridge调Objective-C方法传索引数组报invalid key to 'next'错调试

CCLuaObjcBridge调Objective-C方法传索引数组报invalid key to 'next'错调试

CCLuaObjcBridge是cocos2d-x系列引擎与Objective-C进行交互的“桥梁”，老廖的quick-cocos2d-x在其framework进行了简单了封装，封装到了luaoc类中，大体能够看成：

luaoc.callStaticMethod = CCLuaObjcBridge.callStaticMethod

函数原型例如以下：

--[[

调用Objective-C中的静态方法

@param string className 类名

@param string methodName 方法名

@param table args 參数

]]

function luaoc.callStaticMethod(className, methodName, args)

end

假定有下面Objective-C静态方法：

#import <Foundation/Foundation.h>

@interface SdkApi : NSObject

+ (void)init:(NSDictionary*)dict;

@end

当尝试用下面參数调用时，会报“invalid key to 'next'“错：

luaoc.callStaticMethod("SdkApi", "init", {"platform", true})

非常奇怪的错误，一步一步调试，进到CCLuaObjcBridge.mm，定位到lua_next行代码：

        if (hasArguments)

        {

            NSMutableDictionary *dict = [NSMutableDictionary dictionary];

            lua_pushnil(L);

            while (lua_next(L, -2))

            {

                NSString *key = [NSString stringWithCString:lua_tostring(L, -2) encoding:NSUTF8StringEncoding];

                switch (lua_type(L, -1))

                {

                    case LUA_TNUMBER:

                        [dict setObject:[NSNumber numberWithFloat:lua_tonumber(L, -1)] forKey:key];

                        break;

                    case LUA_TBOOLEAN:

                        [dict setObject:[NSNumber numberWithBool:lua_toboolean(L, -1)] forKey:key];

                        break;

                    case LUA_TSTRING:

                        [dict setObject:[NSString stringWithCString:lua_tostring(L, -1) encoding:NSUTF8StringEncoding]

                                 forKey:key];

                        break;

                    case LUA_TFUNCTION:

                        int functionId = retainLuaFunction(L, -1, NULL);

                        [dict setObject:[NSNumber numberWithInt:functionId] forKey:key];

                        break;

                }

                lua_pop(L, 1);

            }

            [invocation setArgument:&dict atIndex:2];

            [invocation invoke];

        }

        else

        {

            [invocation invoke];

        }

粗略阅读了一下代码，没有发现什么异常，于是去查官方文档，最终有了发现：

int lua_next (lua_State *L, int index);

Pops a key from the stack, and pushes a key–value pair from the table at the given index (the "next" pair after the given key). If there are no more elements in the table, then lua_next returns 0 (and pushes nothing).

A typical traversal looks like this:

     /* table is in the stack at index 't' */

     lua_pushnil(L);  /* first key */

     while (lua_next(L, t) != 0) {

       /* uses 'key' (at index -2) and 'value' (at index -1) */

       printf("%s - %s\n",

              lua_typename(L, lua_type(L, -2)),

              lua_typename(L, lua_type(L, -1)));

       /* removes 'value'; keeps 'key' for next iteration */

       lua_pop(L, 1);

     }

While traversing a table, do not call lua_tolstring directly on a key, unless you know that the key is actually a string. Recall that lua_tolstring may change the value at the given index; this confuses the next call to lua_next.

See function next for the caveats of modifying the table during its traversal. 

大体意思是说在遍历table时，除非你知道key是string类型，否则不要直接对key进行lua_tolstring *** 作，这是由于lua_tolstring *** 作可能改动指定index处的值，从而使下一次调用lua_next混淆。

简言之就是：lua_tolstring可能会破坏table的原有结构，所以不要在遍历的时候对key进行lua_tolstring *** 作。

而lua_tostring终于调用的也是lua_tolstring，所以问题便出在这了。

要避免此错误，不传索引数组便可解决，如：

luaoc.callStaticMethod("SdkApi", "init", {platform = "platform", debug = true})