ios文件读写

//写入缓存文件,缓存目录下
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES);
    NSString *strDocumentsDirectory = paths[0];
    NSString *strCacheDirectoryName = [strDocumentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@_Alarm",@"2000000022"]];

    NSString *strURL = @"http://farm8.static.flickr.com/7443/9493141210_bfda8b9572_s.jpg";
    NSError *error = nil;
    NSData *dataImg = [NSData dataWithContentsOfURL:[NSURL URLWithString:strURL] options:NSDataReadingMappedIfSafe error:&error];
    if ([error code] == 0)
    {
        if([[NSFileManager defaultManager] fileExistsAtPath:strCacheDirectoryName])
        {
            NSLog(@"文件夹存在");
        //创建文件夹路径
        [[NSFileManager defaultManager] createDirectoryAtPath:strCacheDirectoryName withIntermediateDirectories:YES attributes:nil error:nil];

        NSString *imagePath =[strCacheDirectoryName stringByAppendingPathComponent:@"2000000022_01.jpg"];
        //图片写入文件夹
        [UIImagePNGRepresentation([UIImage imageWithData:dataImg]) writeToFile:imagePath atomically:YES];
        }
        else
        {
            NSLog(@"不存在该文件夹");
        }
    }