如何在集合增删元素时自动计算LeadPerformanceItem的visitorspercentoftotal属性？

当然有办法！这里有几种实用的方案，能帮你实现集合增删元素时自动计算visitorspercentoftotal属性的需求：

方案1：让Item持有所属集合的引用（最直接易懂） #

核心思路是让每个LeadPerformanceItem知道自己属于哪个LeadPerformanceItemCollection，这样它就能随时获取最新的总访客数来计算百分比。

首先修改LeadPerformanceItem类，添加父集合的引用：

public class LeadPerformanceItem { 
    // 持有所属集合的引用，用于获取总访客数
    private LeadPerformanceItemCollection _parentCollection;
    public LeadPerformanceItemCollection ParentCollection {
        get => _parentCollection;
        set => _parentCollection = value;
    }

    public string name { get; set; } 
    public int visitors { get; set; } 
    public decimal visitorspercentoftotal { 
        get { 
            // 避免除以0的运行时错误
            if (ParentCollection?.totalvisitors == 0) return 0;
            // 计算百分比，乘以100转为百分比格式
            return (decimal)visitors / ParentCollection.totalvisitors * 100;
        } 
    } 
}

然后改造LeadPerformanceItemCollection，确保增删元素时自动维护item的父集合引用：

public class LeadPerformanceItemCollection { 
    private List<LeadPerformanceItem> _items = new List<LeadPerformanceItem>();
    public List<LeadPerformanceItem> items {
        get => _items;
        set {
            // 先清空旧item的父引用
            foreach (var item in _items) item.ParentCollection = null;
            _items = value;
            // 给新item绑定父集合
            foreach (var item in _items) item.ParentCollection = this;
        }
    } 

    public int totalvisitors { 
        get { return items.Sum(x => x.visitors); } 
    }

    // 推荐用自定义方法操作集合，代替直接调用List的Add/Remove
    public void AddItem(LeadPerformanceItem item) {
        if (item == null) return;
        item.ParentCollection = this;
        _items.Add(item);
    }

    public void RemoveItem(LeadPerformanceItem item) {
        if (_items.Remove(item)) {
            item.ParentCollection = null;
        }
    }
}

这样，当你通过AddItem/RemoveItem操作集合时，每个item都会自动关联到父集合，visitorspercentoftotal每次被访问时，都会基于最新的总访客数计算出正确结果。

方案2：使用ObservableCollection（适合UI绑定场景） #

如果你的项目是WPF/MAUI这类需要数据绑定自动刷新UI的场景，推荐用ObservableCollection<T>替代List<T>。它会在集合变化时触发CollectionChanged事件，结合INotifyPropertyChanged能让UI自动感知到百分比的更新。

示例代码如下：

using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Runtime.CompilerServices;

public class LeadPerformanceItem : INotifyPropertyChanged { 
    private LeadPerformanceItemCollection _parentCollection;
    public LeadPerformanceItemCollection ParentCollection {
        get => _parentCollection;
        set {
            _parentCollection = value;
            // 通知UI百分比属性已变化
            OnPropertyChanged(nameof(visitorspercentoftotal));
        }
    }

    private string _name;
    public string name { 
        get => _name;
        set {
            _name = value;
            OnPropertyChanged();
        }
    } 

    private int _visitors;
    public int visitors { 
        get => _visitors;
        set {
            _visitors = value;
            OnPropertyChanged();
            // 访客数变化时，百分比也会变，通知UI
            OnPropertyChanged(nameof(visitorspercentoftotal));
        }
    } 

    public decimal visitorspercentoftotal { 
        get { 
            if (ParentCollection?.totalvisitors == 0) return 0;
            return (decimal)visitors / ParentCollection.totalvisitors * 100;
        } 
    } 

    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged([CallerMemberName] string propertyName = null) {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

public class LeadPerformanceItemCollection : INotifyPropertyChanged { 
    private ObservableCollection<LeadPerformanceItem> _items;
    public ObservableCollection<LeadPerformanceItem> items {
        get => _items;
        set {
            if (_items != null) {
                _items.CollectionChanged -= Items_CollectionChanged;
                foreach (var item in _items) item.ParentCollection = null;
            }
            _items = value;
            if (_items != null) {
                _items.CollectionChanged += Items_CollectionChanged;
                foreach (var item in _items) item.ParentCollection = this;
            }
            OnPropertyChanged(nameof(totalvisitors));
        }
    } 

    public int totalvisitors { 
        get { return items.Sum(x => x.visitors); } 
    }

    public LeadPerformanceItemCollection() {
        _items = new ObservableCollection<LeadPerformanceItem>();
        _items.CollectionChanged += Items_CollectionChanged;
    }

    private void Items_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e) {
        // 绑定/解绑新增/移除的item的父集合
        if (e.NewItems != null) {
            foreach (LeadPerformanceItem item in e.NewItems) item.ParentCollection = this;
        }
        if (e.OldItems != null) {
            foreach (LeadPerformanceItem item in e.OldItems) item.ParentCollection = null;
        }
        // 通知总访客数变化，同时触发所有item的百分比更新
        OnPropertyChanged(nameof(totalvisitors));
        foreach (var item in items) {
            item.OnPropertyChanged(nameof(item.visitorspercentoftotal));
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged([CallerMemberName] string propertyName = null) {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

这个方案不仅能自动计算百分比，还能让UI实时刷新最新数据，非常适合可视化场景。

关键注意点 #

• 永远要处理除以0的情况：当总访客数为0时，直接返回0，避免运行时异常。
• 如果一定要直接操作List的Add/Remove方法，记得手动设置item的ParentCollection，否则百分比计算会失效。
• 非UI场景推荐方案1，代码更简洁；UI绑定场景优先方案2，减少手动维护的工作量。

内容的提问来源于stack exchange，提问作者Ben