计算Objective C（Cocoa）中文件夹内的文件数

I m making an array of images animate like a flicker book animation,i m storing these images inside a folder which intern resides inside Resource folder of my project in xcode.. these images will vary,that is why i have to determine the exact number of images inside the folder so how should i determine this? is there any API in cocoa to achieve this? I m making an array of images animate like a fl