typedef NS_ENUM(NSInteger, UITableViewCellStyle) {
    UITableViewCellStyleDefault,	// Simple cell with text label and optional image view (behavior of UITableViewCell in iPhoneOS 2.x)
    UITableViewCellStyleValue1,		// Left aligned label on left and right aligned label on right with blue text (Used in Settings)
    UITableViewCellStyleValue2,		// Right aligned label on left with blue text and left aligned label on right (Used in Phone/Contacts)
    UITableViewCellStyleSubtitle	// Left aligned label on top and left aligned label on bottom with gray text (Used in iPod).
};             // available in iPhone OS 3.0

iPhone提供了4种基本的表格视图单元格，在SDK 3.0 之后，每个单元格都有3个属性textLabel，detailTextLabel和imageView。

下面一一介绍这4种基本格式：

1、UITableViewCellStyleDefault

该格式提供了一个简单的左对齐的文本标签textLabel和一个可选的图像imageView。如果显示图像，那么图像将在最左边。

这种格式虽然可以设置detailTextLabel，但是不会显示该标签。

2、UITableViewCellStyleSubtitle

该格式与前一种相比，增加了对detailTextLabel的支持，该标签将会显示在textLabel标签的下面，字体相对较小。

3、UITableViewCellStyleValue1

该格式居左显示textLabel，居右显示detailTextLabel，且字体较小。

4、UITableViewCellStyleValue2

该格式居左现实一个小型蓝色主标签textLabel，在其右边显示一个小型黑色副标题详细标签detailTextLabel。

该格式不支持图像

个人感觉，格式1和2使用较多，如果这两种不能满足我的要求，那么就采用定制UITableViewCell的方式。

from：http://www.cnblogs.com/xuling/archive/2012/02/28/2370692.html

  1)、arc4random() 比较精确不需要生成随即种子

       使用方法 ：

                 通过arc4random() 获取0到x-1之间的整数的代码如下：

                 int value = arc4random() % x; 

                 获取1到x之间的整数的代码如下:

                 int value = (arc4random() % x) + 1; 

       2)、CCRANDOM_0_1() cocos2d中使用 ，范围是[0,1]

       使用方法：

                 float random = CCRANDOM_0_1() * 5; //[0,5]   CCRANDOM_0_1() 取值范围是[0,1]

       3)、random() 需要初始化时设置种子

      使用方法：

         srandom(time(NULL));//初始化时，设置下种子就好了

         int newValue = random() %10;

- (void)updateAssetsLibrary
{
loadImgView.hidden = NO;
[spinner startAnimating];
//selectVideoBtn .userInteractionEnabled = NO;

assetItems = [NSMutableArray arrayWithCapacity:0];
ALAssetsLibrary *assetLibrary = assetsLibrary;

[assetLibrary enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop) 
{
    if (group)
    {
        [group setAssetsFilter:[ALAssetsFilter allVideos]];
        [group enumerateAssetsUsingBlock:^(ALAsset *asset, NSUInteger index, BOOL *stop)
        {
             if (asset)
             {
                 dic = [[NSMutableDictionary alloc] init];
                 ALAssetRepresentation *defaultRepresentation = [asset defaultRepresentation];
                 NSString *uti = [defaultRepresentation UTI];
                 appDelegate.videoURL = [[asset valueForProperty:ALAssetPropertyURLs] valueForKey:uti];

                 mpVideoPlayer = [[MPMoviePlayerController alloc] initWithContentURL:appDelegate.videoURL];

                 NSString *title = [NSString stringWithFormat:@"%@ %i", NSLocalizedString(@"Video", nil), [assetItems count]+1];

                 [self performSelector:@selector(imageFromVideoURL)];
                 [dic setValue:title forKey:kName];
                 [dic setValue:appDelegate.videoURL forKey:kURL];

                 AssetBrowserItem *item = [[AssetBrowserItem alloc] initWithURL:appDelegate.videoURL title:title];
                 [assetItems addObject:item];
                 [appDelegate.videoURLArray addObject:dic];

                 NSLog(@"Video has info:%@",appDelegate.videoURLArray);
             }
             NSLog(@"Values of dictonary==>%@", dic);

             //NSLog(@"assetItems:%@",assetItems);
             NSLog(@"Videos Are:%@",appDelegate.videoURLArray);
        } ];
    }
    // group == nil signals we are done iterating.
    else 
    {
        dispatch_async(dispatch_get_main_queue(), ^{
            //[self updateBrowserItemsAndSignalDelegate:assetItems];
            loadImgView.hidden = NO;
            [spinner stopAnimating];
            [loadImgView removeFromSuperview];
            //selectVideoBtn .userInteractionEnabled = YES;
        });
    }
}
failureBlock:^(NSError *error) 
{
    NSLog(@"error enumerating AssetLibrary groups %@\n", error);
}];
}

- (UIImage *)imageFromVideoURL 
{
// result 
UIImage *image = nil;

// AVAssetImageGenerator
AVAsset *asset = [[AVURLAsset alloc] initWithURL:appDelegate.videoURL options:nil];; 
AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc] initWithAsset:asset];
imageGenerator.appliesPreferredTrackTransform = YES;

// calc midpoint time of video
Float64 durationSeconds = CMTimeGetSeconds([asset duration]);
CMTime midpoint = CMTimeMakeWithSeconds(durationSeconds/2.0, 600); 

// get the image from 
NSError *error = nil; 
CMTime actualTime;
CGImageRef halfWayImage = [imageGenerator copyCGImageAtTime:midpoint actualTime:&actualTime error:&error];

if (halfWayImage != NULL) 
{
    // cgimage to uiimage
    image = [[UIImage alloc] initWithCGImage:halfWayImage];
    [dic setValue:image forKey:kImage];
    NSLog(@"Values of dictonary==>%@", dic);
    NSLog(@"Videos Are:%@",appDelegate.videoURLArray);
    CGImageRelease(halfWayImage);
}
return image;
}

- (void)assetsLibraryDidChange:(NSNotification*)changeNotification
{
[self updateAssetsLibrary];
}

- (void)buildAssetsLibrary
{
assetsLibrary = [[ALAssetsLibrary alloc] init];
ALAssetsLibrary *notificationSender = nil;

NSString *minimumSystemVersion = @"4.1";
NSString *systemVersion = [[UIDevice currentDevice] systemVersion];
if ([systemVersion compare:minimumSystemVersion options:NSNumericSearch] != NSOrderedAscending)
    notificationSender = assetsLibrary;

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(assetsLibraryDidChange:) name:ALAssetsLibraryChangedNotification object:notificationSender];
[self updateAssetsLibrary];
}