Swift - 使用网格（UICollectionView）的自定义布局实现复杂页面

实现自定义布局需要继承UICollectionViewLayout，同时还要重载下面的三个方法：

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// 内容区域总大小，不是可见区域
override var collectionViewContentSize: CGSize {
}

// 所有单元格位置属性
override func layoutAttributesForElements(in rect: CGRect)
    -> [UICollectionViewLayoutAttributes]? {
}

// 这个方法返回每个单元格的位置和大小
override func layoutAttributesForItem(at indexPath: IndexPath)
    -> UICollectionViewLayoutAttributes? {
}

下面实现一个自定义布局的例子，单元格有大小两种。网格从上到下，先是左边一个大单元格右边两个小单元格，接着左边两个小单元格右边一个大单元格，依次同上循环排列。 

效果图如下：

  

--- 自定义布局 CustomLayout.swift ---

（本文样例代码已升级到Swift3）

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import UIKit

/**
 * 这个类只简单定义了一个section的布局
 */
class CustomLayout : UICollectionViewLayout {

    // 内容区域总大小，不是可见区域
    override var collectionViewContentSize: CGSize {
        let width = collectionView!.bounds.size.width - collectionView!.contentInset.left
            - collectionView!.contentInset.right
        let height = CGFloat((collectionView!.numberOfItems(inSection: 0) + 1) / 3)
            * (width / 3 * 2)
        return CGSize(width: width, height: height)
    }

    // 所有单元格位置属性
    override func layoutAttributesForElements(in rect: CGRect)
        -> [UICollectionViewLayoutAttributes]? {
            var attributesArray = [UICollectionViewLayoutAttributes]()
            let cellCount = self.collectionView!.numberOfItems(inSection: 0)
            for i in 0..<cellCount {
                let indexPath =  IndexPath(item:i, section:0)
                let attributes =  self.layoutAttributesForItem(at: indexPath)
                attributesArray.append(attributes!)
            }
            return attributesArray
    }

    // 这个方法返回每个单元格的位置和大小
    override func layoutAttributesForItem(at indexPath: IndexPath)
        -> UICollectionViewLayoutAttributes? {
            //当前单元格布局属性
            let attribute =  UICollectionViewLayoutAttributes(forCellWith:indexPath)

            //单元格边长
            let largeCellSide = collectionViewContentSize.width / 3 * 2
            let smallCellSide = collectionViewContentSize.width / 3

            //当前行数，每行显示3个图片，1大2小
            let line:Int =  indexPath.item / 3
            //当前行的Y坐标
            let lineOriginY =  largeCellSide * CGFloat(line)
            //右侧单元格X坐标，这里按左右对齐，所以中间空隙大
            let rightLargeX = collectionViewContentSize.width - largeCellSide
            let rightSmallX = collectionViewContentSize.width - smallCellSide

            // 每行2个图片，2行循环一次，一共6种位置
            if (indexPath.item % 6 == 0) {
                attribute.frame = CGRect(x:0, y:lineOriginY, width:largeCellSide,
                                         height:largeCellSide)
            } else if (indexPath.item % 6 == 1) {
                attribute.frame = CGRect(x:rightSmallX, y:lineOriginY, width:smallCellSide,
                                         height:smallCellSide)
            } else if (indexPath.item % 6 == 2) {
                attribute.frame = CGRect(x:rightSmallX,
                                         y:lineOriginY + smallCellSide,
                                         width:smallCellSide, height:smallCellSide)
            } else if (indexPath.item % 6 == 3) {
                attribute.frame = CGRect(x:0, y:lineOriginY, width:smallCellSide,
                                         height:smallCellSide )
            } else if (indexPath.item % 6 == 4) {
                attribute.frame = CGRect(x:0,
                                         y:lineOriginY + smallCellSide,
                                         width:smallCellSide, height:smallCellSide)
            } else if (indexPath.item % 6 == 5) {
                attribute.frame = CGRect(x:rightLargeX, y:lineOriginY,
                                         width:largeCellSide,
                                         height:largeCellSide)
            }

            return attribute
    }

    /*
     //如果有页眉、页脚或者背景，可以用下面的方法实现更多效果
     func layoutAttributesForSupplementaryViewOfKind(elementKind: String!,
     atIndexPath indexPath: NSIndexPath!) -> UICollectionViewLayoutAttributes!
     func layoutAttributesForDecorationViewOfKind(elementKind: String!,
     atIndexPath indexPath: NSIndexPath!) -> UICollectionViewLayoutAttributes!
     */
}

--- 主页面 ViewController.swift ---

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import UIKit

class ViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource
{
    var collectionView:UICollectionView!
    //课程名称和图片，每一门课程用字典来表示
    let courses = [
        ["name":"Swift","pic":"swift.png"],
        ["name":"Xcode","pic":"xcode.png"],
        ["name":"Java","pic":"java.png"],
        ["name":"PHP","pic":"php.png"],
        ["name":"JS","pic":"js.png"],
        ["name":"React","pic":"react.png"],
        ["name":"Ruby","pic":"ruby.png"],
        ["name":"HTML","pic":"html.png"],
        ["name":"C#","pic":"c#.png"]
    ]

    override func viewDidLoad() {
        super.viewDidLoad()

        let layout = CustomLayout()
        //let layout = UICollectionViewFlowLayout()
        let frame = CGRect(x:0, y:20, width: view.bounds.size.width,
                           height:view.bounds.height-20)
        self.collectionView = UICollectionView(frame: frame, collectionViewLayout:layout)
        self.collectionView.delegate = self
        self.collectionView.dataSource = self
        // 注册CollectionViewCell
        self.collectionView.register(UICollectionViewCell.self,
                                     forCellWithReuseIdentifier: "ViewCell")
        //默认背景是黑色和label一致
        self.collectionView.backgroundColor = UIColor.white

        //设置collectionView的内边距
        self.collectionView.contentInset = UIEdgeInsetsMake(0, 5, 0, 5)

        self.view.addSubview(collectionView)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }

    // CollectionView行数
    func collectionView(_ collectionView: UICollectionView,
                        numberOfItemsInSection section: Int) -> Int {
        return courses.count;
    }

    // 获取单元格
    func collectionView(_ collectionView: UICollectionView,
                        cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        // storyboard里设计的单元格
        let identify:String = "ViewCell"
        // 获取设计的单元格，不需要再动态添加界面元素
        let cell = self.collectionView.dequeueReusableCell(
            withReuseIdentifier: identify, for: indexPath) as UICollectionViewCell
        //先清空内部原有的元素
        for subview in cell.subviews {
            subview.removeFromSuperview()
        }
        // 添加图片
        let img = UIImageView(image: UIImage(named: courses[indexPath.item]["pic"]!))
        img.frame = cell.bounds
        img.contentMode = .scaleAspectFit
        // 图片上面显示课程名称，居中显示
        let lbl = UILabel(frame:CGRect(x:0, y:0, width:cell.bounds.size.width, height:20))
        lbl.textColor = UIColor.white
        lbl.textAlignment = .center
        lbl.backgroundColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.2)
        lbl.text = courses[indexPath.item]["name"]
        cell.addSubview(img)
        cell.addSubview(lbl)
        return cell
    }

    /* 自定义布局不需要调用
     //单元格大小
     func collectionView(collectionView: UICollectionView!,
     layout collectionViewLayout: UICollectionViewLayout!,
     sizeForItemAtIndexPath indexPath: NSIndexPath!) -> CGSize {
     let size:Float = indexPath.item % 3 == 0 ? 200 : 100
     return CGSize(width:size, height:size)
     }
     */
}