cocos2d TileMap小问题

#include “TmxGame.h”
#include “AboutScene.h”

Scene* TmxGame::createScene()
{

auto scene = Scene::create();

auto layer = TmxGame::create();

scene->addChild(layer);

return scene;

}

bool TmxGame::init()
{
if (!Layer::init())
{
return false;
}
Size visibleSize = Director::getInstance()->getVisibleSize();
Vec2 origin = Director::getInstance()->getVisibleOrigin();

std::string file = "TileMap.tmx";
auto str = String::createWithContentsOfFile(FileUtils::getInstance()->fullPathForFilename(file.c_str()).c_str());
tileMap = TMXTiledMap::createWithXML(str->getCString(), "");
backgroung = tileMap->layerNamed("Background");

this->addChild(tileMap, 1);

}

为什么地图还是没显示出来呢 名字都打对了