UICollectionView 簡單的使用和註意事項

UICollectionView 在創建的時候，要給它一個UICollectionViewFlowLayout (不然會崩潰)，就像tableview一樣，也要為它註冊自定義的cell。

 UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc]init];
    [flowLayout setScrollDirection:UICollectionViewScrollDirectionVertical];
    //cell間距
    flowLayout.minimumInteritemSpacing = 10.0f;
    //cell行距
    flowLayout.minimumLineSpacing = 20.0f;
    //1.添加FlowLayout    
    UICollectionView *collectionView = [[UICollectionView alloc]initWithFrame:CGRectMake(0, 64, 320, [UIScreen mainScreen].bounds.size.height - 64) collectionViewLayout:flowLayout];
    
    //2.為collection 註冊cell（自定義的cell）
    [collectionView registerNib:[UINib nibWithNibName:@"CarCollectionViewCell" bundle:nil] forCellWithReuseIdentifier:@"CarCollectionViewCell"];

 還要為它設置代理和實現代理方法：

collectionView.backgroundColor = [UIColor whiteColor];
    self.collectionView = collectionView;
    self.collectionView.delegate = self;
    self.collectionView.dataSource = self;
    [self.view addSubview:self.collectionView];
    

 設置cell的大小：

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    CGSize size = CGSizeMake(80, 100);
    return size;
}

設置整體cell在collection中的上下左右邊距：

- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section{
    return UIEdgeInsetsMake(30, 20, 0, 20);
}

在cellForItemAtIndexPath中使用自定義的cell，註意自定義cell的xib文件時，要加上identifier：

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
    
    CarCollectionViewCell *cell = (CarCollectionViewCell *)[collectionView dequeueReusableCellWithReuseIdentifier:@"CarCollectionViewCell" forIndexPath:indexPath];
 ...
 ...
 ...
return cell;
}