collection中cell选中状态下分享图片的快照snapshot

总结要点

注意:
1:shouldPerformSegue(withIdentifier:sender:) -> bool 方法控制segue的效能 
2: let index = selectedIcons.index(where:{$0.icon.name == deSelectedIcon.name})
index(where)条件返回index
3:snapshot生成快照
UIGraphicsBeginImageContext(bounds.size)
if let context = UIGraphicsGetCurrentContext(){
self.layer.render(in:context)
image = UIGraphicsGetImageFromCurrentImageContext()
}
UIGraphicsEndImageContext()
return image
4:let indexPaths = collectionView.indexPathsForSelectedItems返回多个索引,所以在单选的情况下,通过indexPaths.first来获取
5:prepare(for:sender:) 与 shouldPerformSegue(withIdentifier identifier: String, sender: Any?) -> Bool连用
6:@IBAction func unwindToHome(segue:UIStoryboardSegue){}//退出exit时link的方法(解除segue)

IconCollectionViewController.swift
IconDetailViewController.swift
IconCollectionViewCell.swift
Icon.swift
UIView+Snapshot.swift

IconCollectionViewController.swift

import UIKit

private let reuseIdentifier = "Cell"

class IconCollectionViewController: UICollectionViewController {

    private var iconSet: [Icon] = [ Icon(name: "Candle icon", imageName: "candle", description: "Halloween icons designed by Tania Raskalova.", price: 3.99, isFeatured: false),
                                    Icon(name: "Cat icon", imageName: "cat", description: "Halloween icon designed by Tania Raskalova.", price: 2.99, isFeatured: true),
                                    Icon(name: "dribbble", imageName: "dribbble", description: "Halloween icon designed by Tania Raskalova.", price: 1.99, isFeatured: false),
                                    Icon(name: "Ghost icon", imageName: "ghost", description: "Halloween icon designed by Tania Raskalova.", price: 4.99, isFeatured: false),
                                    Icon(name: "Hat icon", imageName: "hat", description: "Halloween icon designed by Tania Raskalova.", price: 2.99, isFeatured: false),
                                    Icon(name: "Owl icon", imageName: "owl", description: "Halloween icon designed by Tania Raskalova.", price: 5.99, isFeatured: true),
                                    Icon(name: "Pot icon", imageName: "pot", description: "Halloween icon designed by Tania Raskalova.", price: 1.99, isFeatured: false),
                                    Icon(name: "Pumkin icon", imageName: "pumkin", description: "Halloween icon designed by Tania Raskalova.", price: 0.99, isFeatured: false),
                                    Icon(name: "RIP icon", imageName: "rip", description: "Halloween icon designed by Tania Raskalova.", price: 7.99, isFeatured: false),
                                    Icon(name: "Skull icon", imageName: "skull", description: "Halloween icon designed by Tania Raskalova.", price: 8.99, isFeatured: false),
                                    Icon(name: "Sky icon", imageName: "sky", description: "Halloween icon designed by Tania Raskalova.", price: 0.99, isFeatured: false),
                                    Icon(name: "Toxic icon", imageName: "toxic", description: "Halloween icon designed by Tania Raskalova.", price: 2.99, isFeatured: false),
                                    Icon(name: "Book icon", imageName: "ic_book", description: "Colorful icon designed by Marin Begović.", price: 2.99, isFeatured: false),
                                    Icon(name: "Backpack icon", imageName: "ic_backpack", description: "Colorful icon designed by Marin Begović.", price: 3.99, isFeatured: false),
                                    Icon(name: "Camera icon", imageName: "ic_camera", description: "Colorful camera icon designed by Marin Begović.", price: 4.99, isFeatured: false),
                                    Icon(name: "Coffee icon", imageName: "ic_coffee", description: "Colorful icon designed by Marin Begović.", price: 3.99, isFeatured: true),
                                    Icon(name: "Glasses icon", imageName: "ic_glasses", description: "Colorful icon designed by Marin Begović.", price: 3.99, isFeatured: false),
                                    Icon(name: "Icecream icon", imageName: "ic_ice_cream", description: "Colorful icon designed by Marin Begović.", price: 4.99, isFeatured: false),
                                    Icon(name: "Smoking pipe icon", imageName: "ic_smoking_pipe", description: "Colorful icon designed by Marin Begović.", price: 6.99, isFeatured: false),
                                    Icon(name: "Vespa icon", imageName: "ic_vespa", description: "Colorful icon designed by Marin Begović.", price: 9.99, isFeatured: false)]


    @IBOutlet weak var shareButton: UIBarButtonItem!
    fileprivate var shareEnabled = false
    fileprivate var selectedIcons:[(icon:Icon,snapshot:UIImage)] = []
    override func viewDidLoad() {
        super.viewDidLoad()

    }


    @IBAction func shareButtonTapped(_ sender: Any) {
        guard shareEnabled else {
            // 变更shareEnabled为YES并变更按钮文字为Done
            shareEnabled = true
            collectionView?.allowsMultipleSelection = true
            shareButton.title = "Done"
            shareButton.style = UIBarButtonItemStyle.done
            return
        }
        // 确认是使用者至少有选择一个图片
        guard selectedIcons.count > 0  else {
           let alet = UIAlertController(title: "注意", message: "请选择分享的图片", preferredStyle: .alert)
            self.present(alet, animated: true) {
                alet.dismiss(animated: true, completion: nil)
            }
            return

        }

        // 取得所选图片的快照
        let snapshots = selectedIcons.map { $0.snapshot}
        // 建立分享用的动态视图控制器
        let activityController = UIActivityViewController(activityItems: snapshots, applicationActivities: nil)
        ///typedef void (^UIActivityViewControllerCompletionWithItemsHandler)(UIActivityType activityType, BOOL completed, NSArray *returnedItems, NSError *activityError);
        activityController.completionWithItemsHandler = {(activityType, completed, returnedItems, activityError) in
            // 取消所有选取项目
            if let indexPaths = self.collectionView?.indexPathsForSelectedItems {
                for indexPath in indexPaths {
                    self.collectionView?.deselectItem(at: indexPath, animated: false)
                }
            }
            // selectedIcons阵列中移除所有项目
            self.selectedIcons.removeAll(keepingCapacity: true)
            // 变更分享模式为NO
            self.shareEnabled = false
            self.collectionView?.allowsMultipleSelection = false
            self.shareButton.title = "Share"
            self.shareButton.style = UIBarButtonItemStyle.plain

        }
        present(activityController, animated: true, completion: nil)


    }
    /*很重要,注意点 因为segue是在每一个cell被按下时会被调用,但当app在分享模式下,我们不要触发这个segue,只要在单选模式时才需要触发它,*/
    override func shouldPerformSegue(withIdentifier identifier: String, sender: Any?) -> Bool {
        if identifier == "showIconDetail"{
            if shareEnabled {return false}
        }
        return true
    }

    @IBAction func unwindToHome(segue:UIStoryboardSegue){
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "showIconDetail"{
            if let indexPaths = collectionView?.indexPathsForSelectedItems{
                let destinationController = segue.destination as! IconDetailViewController
                destinationController.icon = iconSet[indexPaths[0].row]
                collectionView?.deselectItem(at: indexPaths[0], animated: false)
            }
        }
    }



    // MARK: UICollectionViewDelegate
    override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        // 检查分享模式是否已经启动,没有的话就离开这个方法
        guard shareEnabled else {return}
        // 使用indexPath来判断所选的项目并带入一个快照
        let selectedIcon = iconSet[indexPath.row]
        if let snapshot = collectionView.cellForItem(at: indexPath)?.snapshot {
            // 增加选中的item到array
            selectedIcons.append((icon: selectedIcon, snapshot: snapshot))
        }
    }

    override func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
        // 检查分享模式是否启动,没有的话就离开这个方法
        guard shareEnabled else {return}
        let deSelectedIcon = iconSet[indexPath.row]
        /* 找到所选图示的索引,这里我们使用索引方法并传递一个闭包.在闭包中
         我们对所选图示的名称与所选图示阵列的所有项目做比较,
         如果名称有符合的话,这个索引方法将会回传其索引值,用这个索引值移除这个item
         */
        if let index = selectedIcons.index(where: {$0.icon.name == deSelectedIcon.name}){
            selectedIcons.remove(at: index)
        }
    }
    // MARK: UICollectionViewDataSource

    override func numberOfSections(in collectionView: UICollectionView) -> Int {
        // Return the number of sections
        return 1
    }


    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        // Return the number of items
        return iconSet.count
    }

    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! IconCollectionViewCell

        // Configure the cell
        let icon = iconSet[indexPath.row]
        cell.iconImageView.image = UIImage(named: icon.imageName)
        cell.iconPriceLabel.text = "$\(icon.price)"
        cell.backgroundView = (icon.isFeatured) ? UIImageView(image: UIImage(named: "feature-bg")) : nil
        cell.selectedBackgroundView = UIImageView(image: UIImage(named: "icon-selected"))
        return cell
    }


}

IconDetailViewController.swift

import UIKit

class IconDetailViewController: UIViewController {

    var icon:Icon?
    @IBOutlet weak var iconImageView: UIImageView!{
        didSet{
            iconImageView.image = UIImage(named: icon?.imageName ?? "")
        }
    }

    @IBOutlet weak var nameLabel: UILabel!{
        didSet{
            nameLabel.text = icon?.name
        }
    }

    @IBOutlet weak var descriptionLabel: UILabel!{
        didSet{
            descriptionLabel.text = icon?.description
            descriptionLabel.numberOfLines = 0
        }
    }

    @IBOutlet weak var priceLabel: UILabel!{
        didSet{
            if let icon = icon {
                priceLabel.text = "$\(icon.price)"
            }
        }
    }

    @IBAction func buyAction(_ sender: UIButton) {
    }
}

IconCollectionViewCell.swift

class IconCollectionViewCell: UICollectionViewCell {
    @IBOutlet var iconImageView: UIImageView!
    @IBOutlet var iconPriceLabel: UILabel!
}

Icon.swift

import Foundation

struct Icon {
    var name: String = ""
    var imageName = ""
    var description = ""
    var price: Double = 0.0
    var isFeatured: Bool = false

    init(name: String, imageName: String, description: String, price: Double, isFeatured: Bool) {
        self.name = name
        self.imageName = imageName
        self.description = description
        self.price = price
        self.isFeatured = isFeatured
    }
}

UIView+Snapshot.swift

import Foundation
import UIKit

extension UIView {
    /*取得视图快照的方式:以视图的大小来建立一个点阵圆为主的图形内容(context),然后我们渲染(render)视图的Neri,并从中取得图片*/
    var snapshot : UIImage? {
    var image:UIImage? = nil
      UIGraphicsBeginImageContext(bounds.size)
        if let context = UIGraphicsGetCurrentContext(){
            self.layer.render(in: context)
            image = UIGraphicsGetImageFromCurrentImageContext()
        }
        UIGraphicsEndImageContext()
        return image
    }
}