C＃LINQ OrderBy on nullable->始终在列表末尾设置空值

问题描述

是否有一种简单的方法，可以通过升序对可空值列表进行排序，并将空值放在列表末尾？就像一个选项之类的

如果没有，那么哪种方法最好：

编写我自己的排序lambda

import Foundation
import UIKit

class MemberProfilePhotosViewController: UIPageViewController {
    
    private let profilePhotoURLs: [URL]
    private let profilePhotoViewControllers: [MemberProfilePhotoViewController]
    private var pageControl: UIPageControl?
    
    // MARK: - Initialization
    
    init(profilePhotoURLs: [URL]) {
        self.profilePhotoURLs = profilePhotoURLs
        profilePhotoViewControllers = profilePhotoURLs.map { (profilePhotoURL) -> MemberProfilePhotoViewController in
            MemberProfilePhotoViewController(profilePhotoURL: profilePhotoURL)
        }
        super.init(transitionStyle: .scroll,navigationorientation: .horizontal,options: nil)
    }
    
    required init?(coder: NSCoder) {
        fatalError()
    }
    
    // MARK: UIViewController
    
    override func loadView() {
        super.loadView()
        pageControl = UIPageControl(frame: CGRect.zero)
        pageControl!.numberOfPages = profilePhotoViewControllers.count
        self.view.addSubview(pageControl!)
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        dataSource = self
        delegate = self
        if let firstViewController = profilePhotoViewControllers.first {
            setViewControllers([firstViewController],direction: .forward,animated: true,completion: nil)
        }
    }
    
    override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()
        if let pageControl = pageControl {
            let pageControlSize = pageControl.size(forNumberOfPages: profilePhotoViewControllers.count)
            pageControl.frame = CGRect(
                origin: CGPoint(x: view.frame.midX - pageControlSize.width / 2,y: view.frame.maxY - pageControlSize.height),size: pageControlSize
            )
        }
    }
    
    // MARK: Private Helpers
    
    private func indexOf(_ viewController: UIViewController) -> Int? {
        return profilePhotoViewControllers.firstIndex(of: viewController as! MemberProfilePhotoViewController)
    }
}

extension MemberProfilePhotosViewController: UIPageViewControllerDelegate {
    func pageViewController(_ pageViewController: UIPageViewController,didFinishAnimating finished: Bool,prevIoUsViewControllers: [UIViewController],transitionCompleted completed: Bool) {
        guard let selectedViewController = pageViewController.viewControllers?.first else { return }
        if let indexOfSelectViewController = indexOf(selectedViewController) {
            pageControl?.currentPage = indexOfSelectViewController
        }
    }
}

extension MemberProfilePhotosViewController: UIPageViewControllerDataSource {
    func pageViewController(_ pageViewController: UIPageViewController,viewControllerBefore viewController: UIViewController) -> UIViewController? {
        guard let viewControllerIndex = profilePhotoViewControllers.firstIndex(of: viewController as! MemberProfilePhotoViewController) else {
            return nil
        }
        let prevIoUsIndex = viewControllerIndex - 1
        guard prevIoUsIndex >= 0 else {
            return nil
        }
        guard profilePhotoViewControllers.count > prevIoUsIndex else {
            return nil
        }
        return profilePhotoViewControllers[prevIoUsIndex]
    }
    
    func pageViewController(_ pageViewController: UIPageViewController,viewControllerAfter viewController: UIViewController) -> UIViewController? {
        guard let viewControllerIndex = profilePhotoViewControllers.firstIndex(of: viewController as! MemberProfilePhotoViewController) else {
            return nil
        }
        let nextIndex = viewControllerIndex + 1
        let profilePhotoViewControllersCount = profilePhotoViewControllers.count
        guard profilePhotoViewControllersCount != nextIndex else {
            return nil
        }
        guard profilePhotoViewControllersCount > nextIndex else {
            return nil
        }
        
        return profilePhotoViewControllers[nextIndex]
    }
}

仅对非null值进行排序，并在其后添加null值

list.sort((v1,v2) => 
{
   if (v1.HasValue && v2.HasValue) return v1.Commpareto(v2);
   else if (!v1.HasValue) return -1;
   else if (!v2.HasValue) return 1;
   else return 0;
})

解决方法

暂无找到可以解决该程序问题的有效方法，小编努力寻找整理中！

如果你已经找到好的解决方法，欢迎将解决方案带上本链接一起发送给小编。

小编邮箱:dio#foxmail.com (将#修改为@）

c#c#linq linq