day(7) cocos2d::Map

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cocos2d::Map

v3.0 beta加入

定义在"COCOS2DX_ROOT/cocos/base"的"CCMap.h"头文件中。

template <class K, class V>class CC_DLL Map;

cocos2d::Map<K,V>是使用std::unordered_map作为底层结构的关联式容器。而std::unordered_map是一个存储键值对的关联式容器，它可以通过它们的键快速检索对应的值。使用unordered_map，键通常是唯一的，而值则与这个键对应。

在unordered_map内部，元素是无序，它们是根据键的哈希值来存取的，存取的时间复杂度是常量，超级快。

在Cocos2d-x v3.0beta之前，使用的是另外一种顺序式容器cocos2d::CCDictionary,不过它将很快被废弃。

设计者们谨慎地设计了cocos2d::Map<K,V>用来替代cocos2d::CCDictionary，所以应该尽量使用cocos2d::Map而不是cocos2d::CCDictionary

模版参数

cocos2d::Map<K,V>类只包含一个数据成员：

typedef std::unordered_map<K, V> RefMap;RefMap _data;

_data的内存管理是由编译器处理的，当在栈中声明cocos2d::Map<K,V>对象时，无需费心释放它占用的内存。但是如果你是使用new操作来动态分配cocos2d::Map<K,V>的内存的话，就得用delete来释放内存了，new[]操作也一样。

注意：使用现代的c++，本地存储对象比堆存储对象好。所以请不要用new操作来分配cocos2d::Map<K,V>的堆对象，请使用栈对象。

如果真心想动态分配堆cocos2d::Map<K,V>，请将原始指针用智能指针来覆盖。

警告：cocos2d::Map<K,V>并不是cocos2d::Object的子类，所以不要像使用其他cocos2d类一样来用retain/release和引用计数内存管理。

基本用例

警告：cocos2d::Map<K,V>并没有重载[]操作，不要用下标[i]来取cocos2d::Map<K,V>对象中的元素。

为了解更多的用例，你得参考源码和压缩文件中附带的例子。下面是一些简单操作的用例：

//create Map<K, V> with default size and add a sprite into itauto sp0 = Sprite::create();sp0->setTag(0);Map<std::string, Sprite*> map0;std::string mapKey0 = "MAP_KEY_0";map0.insert(mapKey0, sp0);log("The size of map is %zd.",map0.size()); //create a Map<K, V> with capacity equals 5Map<std::string, Sprite*> map1(map0);std::string mapKey1 = "MAP_KEY_1";if(!map1.empty()){    auto spTemp = (Sprite*)map1.at(mapKey0);    log("sprite tag = %d", spTemp->getTag());    auto sp1 = Sprite::create();    sp1->setTag(1);    map1.insert(mapKey1, sp1);          //get all keys,stored in std::vector, that matches the object    std::vector<std::string> mapKeyVec;    mapKeyVec = map1.keys();    for(auto key : mapKeyVec)    {        auto spTag = map1.at(key)->getTag();        log("The Sprite tag = %d, MAP key = %s",spTag,key.c_str());        log("Element with key %s is located in bucket %zd",key.c_str(),map1.bucket(key));    }    log("%zd buckets in the Map container",map1.bucketCount());    log("%zd element in bucket 1",map1.bucketSize(1));      //get a random object if the map isn't empty, otherwise it returns nullptr    log("The random object tag = %d",map1.getRandomObject()->getTag());      //find(const K& key) can be used to search the container for an element with 'key'    //erase(const_iterator position) remove an element with an iterator    log("Before remove sp0, size of map is %zd.",map1.size());    map1.erase(map1.find(mapKey0));    log("After remove sp0, size of map is %zd.",map1.size());}  //create a Map<K, V> with capacity equals 5Map<std::string, Sprite*> map2(5);map2.reserve(10);  //set capacity of the map

结果是：

cocos2d: The size of map is 1.cocos2d: sprite tag = 0cocos2d: The Sprite tag = 1, MAP key = MAP_KEY_1cocos2d: Element with key MAP_KEY_1 is located in bucket 1cocos2d: The Sprite tag = 0, MAP key = MAP_KEY_0cocos2d: Element with key MAP_KEY_0 is located in bucket 0cocos2d: 2 buckets in the Map containercocos2d: 1 element in bucket 1cocos2d: The random object tag = 0cocos2d: Before remove sp0, size of map is 2.cocos2d: After remove sp0, size of map is 1.

最佳用法

将cocos2d::Map<K,V>()作为参数传递时，将它声明为常量引用const cocos2d::Map<K,V>()&
V类型必须为cocos2d::Object的子类指针，不能用其他的类型包括基本类型。

例子：

#include "AtlasLoader.h"AtlasLoader* AtlasLoader::sharedAtlasLoader = nullptr;AtlasLoader* AtlasLoader::getInstance(){if(sharedAtlasLoader == NULL) {sharedAtlasLoader = new AtlasLoader();if(!sharedAtlasLoader->init()){delete sharedAtlasLoader;sharedAtlasLoader = NULL;CCLOG("ERROR: Could not init sharedAtlasLoader");}}return sharedAtlasLoader;}void AtlasLoader::destroyInstance(){    CC_SAFE_DELETE(sharedAtlasLoader);}AtlasLoader::AtlasLoader(){}bool AtlasLoader::init(){return true;}void AtlasLoader::loadAtlas(string filename){auto textureAtlas = Director::getInstance()->getTextureCache()->addImage("atlas.png");this->loadAtlas(filename, textureAtlas);}void AtlasLoader::loadAtlas(string filename, Texture2D *texture) {string data = FileUtils::getInstance()->getStringFromFile(filename);unsigned pos;Atlas atlas;pos = data.find_first_of("\n");string line = data.substr(0, pos);data = data.substr(pos + 1);while(line != ""){sscanf(line.c_str(), "%s %d %d %f %f %f %f", atlas.name, &atlas.width, &atlas.height, &atlas.start.x, &atlas.start.y, &atlas.end.x, &atlas.end.y);atlas.start.x = 1024*atlas.start.x;atlas.start.y = 1024*atlas.start.y;atlas.end.x = 1024*atlas.end.x;atlas.end.y = 1024*atlas.end.y;pos = data.find_first_of("\n");line = data.substr(0, pos);data = data.substr(pos + 1);// use the data to create a sprite frame        // fix 1px edge bug        if(atlas.name == string("land")) {            atlas.start.x += 1;        }Rect rect = Rect(atlas.start.x, atlas.start.y, atlas.width, atlas.height);auto frame = SpriteFrame::createWithTexture(texture, rect);this->_spriteFrames.insert(string(atlas.name), frame);}}SpriteFrame* AtlasLoader::getSpriteFrameByName(string name){return this->_spriteFrames.at(name);}

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