iOS 检测手机总可用存储空间

最近项目中用到视频下载，下载过成中需要检测磁盘空间大小，如果可用储存空间太小就提示终止下载。

   /// 总大小
    float totalsize = 0.0;
    /// 剩余大小
    float freesize = 0.0;
    /// 是否登录
    NSError *error = nil;
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSDictionary *dictionary = [[NSFileManager defaultManager] attributesOfFileSystemForPath:[paths lastObject] error: &error];
    if (dictionary)
    {
        NSNumber *_free = [dictionary objectForKey:NSFileSystemFreeSize];
        freesize = [_free unsignedLongLongValue]*1.0/(1024);
        
        NSNumber *_total = [dictionary objectForKey:NSFileSystemSize];
        totalsize = [_total unsignedLongLongValue]*1.0/(1024);
        
        NSLog(@" totalsize %f G,freesize %f G",totalsize/1024.0/1024.0,freesize/1024.0/1024.0);
    } else
    {
        NSLog(@"Error Obtaining System Memory Info: Domain = %@, Code = %ld", [error domain], (long)[error code]);
    }