（一）初始化

　　1、创建一个layout布局类

UICollectionViewFlowLayout * layout = [[UICollectionViewFlowLayout alloc]init];

     2、设置布局方向为垂直流布局

layout.scrollDirection = UICollectionViewScrollDirectionVertical;

　　3、设置每个item的大小为100*100

layout.itemSize = CGSizeMake(100, 100);

　　4、创建collectionView 通过一个布局策略layout来创建

UICollectionView * collect = [[UICollectionView alloc]initWithFrame:self.view.frame collectionViewLayout:layout];

　　5、代理设置

collect.delegate=self;    collect.dataSource=self;

      6、注册item类型 这里使用系统的类型

[collect registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"cellid"];

　　7、设置白色背景颜色

collect.backgroundColor = [UIColor whiteColor];

　　8、加入视窗

[self.view addSubview:collect];

（二）方法

　　1、返回分区个数

-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView{    return 1;}

　　2、返回每个分区item个数

-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{    return 20;}

　　3、设定cell间上下间距为2

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section{    return 2;}

　　4、设定cell间左右间距为2

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section{    return 2;}

　　5、返回item（设定样式）

-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{    UICollectionViewCell * cell  = [collectionView dequeueReusableCellWithReuseIdentifier:@"cellid" forIndexPath:indexPath];    cell.backgroundColor = [UIColor colorWithRed:arc4random()%255/255.0 green:arc4random()%255/255.0 blue:arc4random()%255/255.0 alpha:1];    //设置图片    NSURL *imageUrl = [NSURL URLWithString:[[_output objectAtIndex:indexPath.row] objectForKey:@"pic"]];    UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:imageUrl]];    UIImageView *orderImage =[[UIImageView alloc]initWithFrame:CGRectMake(0, 0, cell.frame.size.width,cell.frame.size.height)];    orderImage.image = image;    [cell addSubview:orderImage];        //设置名称    UILabel *name=[[UILabel alloc]initWithFrame:CGRectMake(0, cell.frame.size.height-25, 140, 20)];    name.text =[[_output objectAtIndex:indexPath.row] objectForKey:@"username"];    name.textColor = [UIColor whiteColor];    name.font = [UIFont fontWithName:@"Helvetica" size:10];    [cell addSubview:name];           return cell;}