import <UIKit/UIKit.h>
@interface ViewController : UIViewController<UICollectionViewDataSource,UICollectionViewDelegateFlowLayout>{
}
@property (strong, nonatomic)UICollectionView *collectionView;
@end
ViewController.m
import "ViewController.h"
@interface ViewController ()
@end
@implementation ViewController

(void)viewDidLoad
{
[super viewDidLoad];
//確定是水平滾動，還是垂直滾動
UICollectionViewFlowLayout *flowLayout=[[UICollectionViewFlowLayout alloc] init];
[flowLayout setScrollDirection:UICollectionViewScrollDirectionVertical];
self.collectionView=[[UICollectionView alloc] initWithFrame:CGRectMake(0, 64, 320, 200) collectionViewLayout:flowLayout];
self.collectionView.dataSource=self;
self.collectionView.delegate=self;
[self.collectionView setBackgroundColor:[UIColor clearColor]];
//注冊Cell，必須要有
[self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"UICollectionViewCell"];
[self.view addSubview:self.collectionView];
}


pragma mark -- UICollectionViewDataSource
//定義展示的UICollectionViewCell的個數
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
  return 10;
}
//定義展示的Section的個數
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
  return 2;
}
//每個UICollectionView展示的內容
-(UICollectionViewCell )collectionView:(UICollectionView )collectionView cellForItemAtIndexPath:(NSIndexPath )indexPath
{
  static NSString  CellIdentifier = @"UICollectionViewCell";
  UICollectionViewCell * cell = [collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath];
cell.backgroundColor = [UIColor colorWithRed:((10  indexPath.row) / 255.0) green:((20  indexPath.row)/255.0) blue:((30  indexPath.row)/255.0) alpha:1.0f];
  UILabel label = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 20, 20)];
  label.textColor = [UIColor redColor];
  label.text = [NSString stringWithFormat:@"%d",indexPath.row];
for (id subView in cell.contentView.subviews) {
    [subView removeFromSuperview];
  }
  [cell.contentView addSubview:label];
  return cell;
}
pragma mark --UICollectionViewDelegateFlowLayout
//定義每個Item 的大小

(CGSize)collectionView:(UICollectionView )collectionView layout:(UICollectionViewLayout)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
return CGSizeMake(60, 60);
}

//定義每個UICollectionView 的 margin
-(UIEdgeInsets)collectionView:(UICollectionView )collectionView layout:(UICollectionViewLayout )collectionViewLayout insetForSectionAtIndex:(NSInteger)section
{
  return UIEdgeInsetsMake(5, 5, 5, 5);
}
pragma mark --UICollectionViewDelegate
//UICollectionView被選中時調用的方法
-(void)collectionView:(UICollectionView )collectionView didSelectItemAtIndexPath:(NSIndexPath )indexPath
{
  UICollectionViewCell  cell = (UICollectionViewCell )[collectionView cellForItemAtIndexPath:indexPath];
  //臨時改變個顏色，看好，只是臨時改變的。如果要永久改變，可以先改數據源，然后在cellForItemAtIndexPath中控制。（和UITableView差不多吧！O(∩_∩)O~）
  cell.backgroundColor = [UIColor greenColor];
  NSLog(@"item======%d",indexPath.item);
  NSLog(@"row=======%d",indexPath.row);
  NSLog(@"section===%d",indexPath.section);
}
//返回這個UICollectionView是否可以被選擇
-(BOOL)collectionView:(UICollectionView )collectionView shouldSelectItemAtIndexPath:(NSIndexPath )indexPath
{
  return YES;
}
@end
</pre>