1，获得沙盒文件夹URL
形式1：
NSURL *pathUrl = [NSURL fileURLWithPath:NSTemporaryDirectory()];
形式2：
NSURL *pathUrl = [NSURL fileURLWithPath:NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)[0]];
形式3：
NSURL *pathUrl = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] firstObject];
