如何創建包含父項和子項的嵌套串列？

我想創建一個包含父母和孩子的專案串列。我已經在 sqlite 檔案中準備了資料：

所以我想var subjectnames = await db.SubjectNames.ToListAsync();從資料庫中讀取這些資料（我可以讀取類似的資料）并創建一個基于父母和孩子的嵌套串列。每個專案可能有一個或多個孩子，數量未知。

這是我的課：

public class SubjectName
{
    public int Id { get; set; }
    public long SubjectId { get; set; }
    public string Name { get; set; }
    public long ParentId { get; set; }
}

public class ExplorerItem : Observable
{
    public enum ExplorerItemType { Folder, File, CheckMark };
    public string Name { get; set; }
    public ExplorerItem Parent { get; set; }
    public ExplorerItemType Type { get; set; }

    private ObservableCollection<ExplorerItem> m_children;
    public ObservableCollection<ExplorerItem> Children
    {
        get
        {
            if (m_children == null)
            {
                m_children = new ObservableCollection<ExplorerItem>();
            }
            return m_children;
        }
        set
        {
            m_children = value;
        }
    }

    private bool m_isExpanded;
    public bool IsExpanded
    {
        get { return m_isExpanded; }
        set { Set(ref m_isExpanded, value); }
    }
}

我有一個 ExplorerItem 的 ObservableCollection：

var list = new ObservableCollection<ExplorerItem>();

必須將所有資料添加到其中

一旦資料完成，串列應該在TreeView中顯示如下

問題是我不知道如何創建父子關系并將它們添加到串列中。因為它們的數量是未知的，并且它們包括嵌套的父級和子級

uj5u.com熱心網友回復：

public List<ExplorerItem> Subjects = new List<ExplorerItem>();

private async void GetSubjects()
    {
        var rootItems = await db.SubjectNames.Where(x=>x.ParentId == 0).ToListAsync();
        var subjectNames = await db.SubjectNames.ToListAsync();
        var subjects = await db.Subjects.ToListAsync();

        foreach (var root in rootItems)
        {
            var explorerItem = new ExplorerItem
            {
                Id = root.Id,
                SubjectId = root.SubjectId,
                Name = root.Name,
                Type = ExplorerItemType.Folder
            };
            
            var subjectNameChilds = subjectNames.Where(x => x.ParentId == root.SubjectId);

            if (subjectNameChilds.Any())
            {
                var childs = GetChilds(root, subjectNames, subjects, explorerItem);
                explorerItem.Children = new ObservableCollection<ExplorerItem>(childs);
            }
            Subjects.Add(explorerItem);
        }
    }
    public IEnumerable<ExplorerItem> GetChilds(SubjectName subjectName, List<SubjectName> subjectNameList, List<Subjects> subjectList, ExplorerItem parent)
    {
        var subjectNameChilds = subjectNameList.Where(x => x.ParentId == subjectName.SubjectId);

        foreach (var root in subjectNameChilds)
        {
            var explorerItem = new ExplorerItem
            {
                Id = root.Id,
                SubjectId = root.SubjectId,
                Name = root.Name,
                Parent = parent
            };
            if (root.Type == 0)
            {
                explorerItem.Type = ExplorerItemType.Folder;
            }
            else
            {
                var child = subjectList.Where(x => x.SubjectId == root.SubjectId).Any();
                if (child)
                {
                    explorerItem.Type = ExplorerItemType.CheckMark;
                }
                else
                {
                    explorerItem.Type = ExplorerItemType.File;
                }
            }

            var childs = subjectNameList.Where(x => x.ParentId == root.SubjectId);

            if (childs.Any())
            {
                var chils = GetChilds(root, subjectNameList, subjectList, explorerItem);
                explorerItem.Children = new ObservableCollection<ExplorerItem>(chils);
                yield return explorerItem;
            }
            else
            {
                yield return explorerItem;
            }
        }
    }

uj5u.com熱心網友回復：

如果使用 EF 可以更改類并設定配置如下：

public class SubjectName
{
   public int Id { get; set; }
   public long SubjectId { get; set; }
   public string Name { get; set; }
   public long ParentId { get; set; }
   public SubjectName Parent { get; set; }
   public ICollection<SubjectName> Chidren{ get; set; }
}

public class SubjectNameConfig : IEntityTypeConfiguration<SubjectName>
{
    public void Configure(EntityTypeBuilder<SubjectName> builder)
    {
       builder.HasKey(e => e.SubjectId);

       // Relations
        builder.HasOne(d => d.Parent)
            .WithMany(p => p.Children)
            .HasForeignKey(d => d.ParentId)
            .HasPrincipalKey(d => d.SubjectId)
            .OnDelete(DeleteBehavior.Restrict);
    }
}

標籤：C＃ 列表 林克 嵌套的

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