可以显示在线图片的CCSprite，使用HttpClient异步请求图片数据，当请求成功时，保存图片数据到本地，然后更新CCSprite的纹理，下载中时显示默认图片（可以设置默认图片）。

OnlineImageSprite.h

#ifndef __ONLINEIMAGESPRITE_H__
#define __ONLINEIMAGESPRITE_H__
 
#include "cocos2d.h"
USING_NS_CC;
#include "cocos-ext.h"
USING_NS_CC_EXT;
 
// 可以显示在线图片的CCSprite
class OnlineImageSprite:public CCSprite{
 
public:
	/*
		创建一个显示在线图片的Sprite
		* defaultImagePath		默认图片路径（当图片加载中时显示）
		* url								图片url
	*/
	static OnlineImageSprite* create(const char* defaultImagePath,const char* url);	
 
	bool init(const char* defaultImagePath,const char* url);
 
	void onDownloadCompleted(CCHttpClient *sender,CCHttpResponse *response);
protected:
	// 下载图片
	void downloadImage(const char* url);
	// 获取图片路径
	std::string getImagePath(const char* url);
	// 图片是否存在
	bool isExist(const char* url);
	// 保存图片
	std::string saveImage(const std::string& data);
private:
	const char* m_url;
};
 
#endif

OnlineImageSprite.cpp

#include "OnlineImageSprite.h"
#include <string>
using namespace std;   
 
string&   replace_all(string&   str,const   string&   old_value,const   string&   new_value)   
{   
	while(true)   {   
		string::size_type   pos(0);   
		if(   (pos=str.find(old_value))!=string::npos   )   
			str.replace(pos,old_value.length(),new_value);   
		else   break;   
	}   
	return   str;   
}   
string&   replace_all_distinct(string&   str,const   string&   new_value)   
{   
	for(string::size_type   pos(0);   pos!=string::npos;   pos+=new_value.length())   {   
		if(   (pos=str.find(old_value,pos))!=string::npos   )   
			str.replace(pos,new_value);   
		else   break;   
	}   
	return   str;   
}   
 
OnlineImageSprite* OnlineImageSprite::create(const char* defaultImagePath,const char* url){
	OnlineImageSprite* pSprite = new OnlineImageSprite();
	if (pSprite && pSprite->init(defaultImagePath,url))
	{
		pSprite->autorelease();
		return pSprite;
	}
	CC_SAFE_DELETE(pSprite);
	return NULL;
}
 
bool OnlineImageSprite::init(const char* defaultImagePath,const char* url){
		
	m_url = url;
	CCTexture2D* pTexture = NULL;
 
	// 图片是否存在，如果不存在使用默认纹理并下载图片
	if (isExist(url))
	{
		const char* path = getImagePath(url).c_str();
		pTexture = CCTextureCache::sharedTextureCache()->addImage(path);
	}else{
		pTexture = CCTextureCache::sharedTextureCache()->addImage(defaultImagePath);
		// 下载图片
		downloadImage(url);
	}
	
	// 初始化
	if (CCSprite::initWithTexture(pTexture))
	{
		return true;
	}	
	return false;
}
 
//判断图片是否已经存在
bool OnlineImageSprite::isExist(const char* url){	
	std::string path = getImagePath(url);
	return CCFileUtils::sharedFileUtils()->isFileExist(path);
}
 
//获取图片全路径
std::string OnlineImageSprite::getImagePath(const char* url){
	std::string urlStr = url;
	replace_all(urlStr,"/","");
	replace_all(urlStr,"\\",":",".","");
	return CCFileUtils::sharedFileUtils()->getWritablePath().append("/").append(urlStr);
}
 
// 下载图片
void OnlineImageSprite::downloadImage(const char* url){
	// 发起http请求，下载图片
	CCHttpRequest* request = new CCHttpRequest();
	request->setUrl(url);
	request->setRequestType(CCHttpRequest::kHttpGet);
	request->setResponseCallback(this,httpresponse_selector(OnlineImageSprite::onDownloadCompleted));	
	CCHttpClient::getInstance()->send(request);
	request->release();	
}
 
// 请求回调
void OnlineImageSprite::onDownloadCompleted(CCHttpClient *sender,CCHttpResponse *response){
	if (!response)
	{
		return;
	}
	// 返回码
	int statusCode = response->getResponseCode();
	char statusString[64] = {};
	sprintf(statusString,"HTTP Status Code: %d",statusCode);	
	CCLog("response code: %d",statusCode);
 
	// 请求失败
	if (!response->isSucceed()) 
	{
		CCLog("response Failed");
		CCLog("error buffer: %s",response->getErrorBuffer());
		return;
	}
 
	// dump data
	std::vector<char> *buffer = response->getResponseData();
	std::string data (buffer->begin(),buffer->end());
	std::string path =saveImage(data);
	//如果保存图片成功，更新纹理
	if (path != "")
	{
		CCTexture2D* pTexture = CCTextureCache::sharedTextureCache()->addImage(path.c_str());
		if (pTexture)
		{
			setTexture(pTexture);
		}		
	}
}
 
// 保存图片
std::string OnlineImageSprite::saveImage(const std::string& data){
	
	std::string path = this->getImagePath(m_url);	
	FILE* file = fopen(path.c_str(),"wb");
	if (file)
	{
		// 1.buff
		// 2.每次写的字节数
		// 3.写多少次结束
		// 4.文件句柄
		fwrite(data.c_str(),1,data.length(),file);
		fclose(file);
		return path;
	}
	return "";
}

//创建OnlineImageSpirte，参数：1.默认图片路径 2.在线图片的url
CCSprite* pSprite = OnlineImageSprite::create("HelloWorld.png","http://cc.cocimg.com/cocos2dx/image/logo.png");
 
//设置位置
pSprite->setPosition(ccp(visibleSize.width/2 + origin.x,visibleSize.height/2 + origin.y));
 
//添加到Layer
this->addChild(pSprite,0);

项目地址：https://coding.net/u/linchaolong/p/OnlineImageSprite/git