CCLuaObjcBridge調Objective-C方法傳索引數組報invalid key to 'next'錯調試

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CCLuaObjcBridge是cocos2d-x系列引擎與Objective-C進行互動的“橋樑”，老廖的quick-cocos2d-x在其framework進行了簡單了封裝，封裝到了luaoc類中，大體能夠看成：

luaoc.callStaticMethod = CCLuaObjcBridge.callStaticMethod

函數原型例如以下：

--[[調用Objective-C中的靜態方法@param string className 類名@param string methodName 方法名@param table args 參數]]function luaoc.callStaticMethod(className, methodName, args)end

假定有下面Objective-C靜態方法：

#import <Foundation/Foundation.h>@interface SdkApi : NSObject+ (void)init:(NSDictionary*)dict;@end

當嘗試用下面參數調用時，會報“invalid key to ‘next‘“錯：

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

非常奇怪的錯誤，一步一步調試，進到CCLuaObjcBridge.mm，定位到lua_next行代碼：

        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];        }

粗略閱讀了一下代碼，沒有發現什麼異常，於是去查官方文檔，最終有了發現：

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. 

大體意思是說在遍曆table時，除非你知道key是string類型，否則不要直接對key進行lua_tolstring操作，這是由於lua_tolstring操作可能改動指定index處的值，從而使下一次調用lua_next混淆。

簡言之就是：lua_tolstring可能會破壞table的原有結構，所以不要在遍曆的時候對key進行lua_tolstring操作。

而lua_tostring終於調用的也是lua_tolstring，所以問題便出在這了。

要避免此錯誤，不傳索引數組便可解決，如：

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

CCLuaObjcBridge調Objective-C方法傳索引數組報invalid key to 'next'錯調試