把游戏截图存储到documents自定义相册！

NSString *path = [[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"] stringByAppendingPathComponent:@"Photos"];    BOOL isCreate = [[NSFileManager defaultManager]createDirectoryAtPath:path withIntermediateDirectories:YES attributes:nil error:nil];    NSAssert(isCreate,@"failed to create!");        NSFileManager *fileManager = [NSFileManager defaultManager];    NSArray *array = [fileManager subpathsAtPath:path];//获取Photos目录下所有的文件名称    NSData *data = UIImageJPEGRepresentation(image,0.0);//将image转换成jpeg格式    NSString *fileName = nil;    if ([array count] ==0) {        fileName = [NSString stringWithString:@"img_0001.jpg"];    }    else    {        NSString *lastObject = [array objectAtIndex:[array count]-1];//获取最后一个图片的名称        NSString *to = [lastObject substringToIndex:8];//获取图片的名称（除去后缀名）        NSString *from = [to substringFromIndex:4];//获取最后一张图片的ID号        int index = [from intValue];        fileName = [NSString stringWithFormat:@"img_%04d.jpg",index+1];    }       NSString *result = [path stringByAppendingPathComponent:fileName];        BOOL isWrite =  [data writeToFile:result atomically:NO];