Any ideas on how to make TreeView show changes to the order of items in a List<T>?

[YourRobotOverlord]

I have a Branch class that holds child branches:

class Branch
{
    public string Id;
    public List<Branch>? Branches { get; set; }
    
    public Branch? Parent { get; set; }
}

I have a TreeView that uses the following treebuilder:

_treeView.TreeBuilder = new DelegateTreeBuilder<Branch>(
    branch => branch is not null
        ? branch.Branches
        : []);

I move the selected branch up or down in its List with:

private void ShiftItem(int direction) //-1 for up, 1 for down
{
    var selectedBranch = _treeView.SelectedObject;
    var parent = selectedBranch.Parent;
    var list = parent.Branches;
    
    var currentIndex = list.IndexOf(selectedBranch);
    var newIndex = currentIndex + direction;

    if (!IsValidIndex(list, newIndex)) return;

    list.RemoveAt(currentIndex);
    
    list.Insert(newIndex, selectedBranch);
    _treeView.RefreshObject(parent);
}

private static bool IsValidIndex(List<Branch> list, int index) => (index >= 0 && index < list.Count);

Even after calling RefreshObject on the parent, the items are still displayed in the original order. I've verified that the items in the list have been correctly re-ordered.

I feel like I'm probably doing something wrong or missing something?

I'm using 2.0.0-prealpha.1895 2.0.0-develop.4403

[tznind]

Hmn, I am not at computer at the moment but the first thing to try would be adding Equality members and GetHashCode for your branch class.

Have you tried the true parameter for RefreshObject to rebuild whole hierarchy?

The internal data model for TreeView branches is Dictionary so ordering may somehow have issue... I will need to investigate.

If you simply remove the objects and refresh do they disappear?

[YourRobotOverlord]

Thank you, I will try your suggestions today.

I have tried RefreshObject with startAtTop = true and the result is the same. I also have tried removing an item, and yes it does disappear.

This is the workaround I'm using for the moment:

    private void ShiftBranch(int direction)
    {
        var selectedBranch = _treeView.SelectedObject;
        var parent = selectedBranch.Parent;
        var list = parent.Branches;

        var currentIndex = list.IndexOf(selectedBranch);
        var newIndex = currentIndex + direction;

        if (!IsValidIndex(list, newIndex)) return;

        list.Move(currentIndex, newIndex);

        _treeview.ClearObjects()
        _treeView.AddObject(_rootBranch)

        _treeView.ExpandAll();
        _treeView.SelectedObject = selectedBranch;

        IsDirty = true;
    }

[tznind]

Here is repro, equality wont help. Seems the reordering isnt supported at the moment. After the first state is gotten a branch tracks new and removed children but uses a Dictionary to do so which isn't ordered. Since the objects were there before and still there its probably just adding new ones at the end.

There might be a hacky solution involving having order be part of equality...

using Terminal.Gui;

Application.Init();
var tv = new TreeView<Branch>(new DelegateTreeBuilder<Branch>(
    branch => branch is not null
        ? branch.Branches?.ToArray() ?? []
        : []))
{
    Width= Dim.Fill(),
    Height = Dim.Fill()
};

tv.AddObject(new Branch()
{
    Id = "root",
    Branches = new List<Branch>()
    {
        new Branch(){Id = "A"},
        new Branch(){Id = "B"},
        new Branch(){Id = "C"},
        new Branch(){Id = "D"}
    }
});

Random r = new Random();
tv.ObjectActivated += (sender, e) =>
{
    e.ActivatedObject.Branches = e.ActivatedObject.Branches?.OrderBy(o => r.Next()).ToList();

    // new goes at end even though inserted 0
    e.ActivatedObject.Branches.Insert(0,new Branch(){Id="new"});
    tv.RefreshObject(e.ActivatedObject,true);
};

var w = new Window();
w.Add(tv);

Application.Run(w);
Application.Shutdown();

class Branch
{
    public string Id;
    public List<Branch>? Branches { get; set; }

    public Branch? Parent { get; set; }

    public override string ToString()
    {
        return Id;
    }


    public override bool Equals(object? obj)
    {
        if (obj is Branch other)
        {
            return Id == other.Id;
        }
        return false;
    }

    public override int GetHashCode()
    {
        return Id.GetHashCode();
    }

}

[tznind]

Ok I have a workaround that works:

When you want to re-order:

• Clear the list (store in temp var)
• Refresh
• Set the list you want (from temp var)
• Refresh

The reason is that Branch class in TreeView looks at new and old objects and updates itself accordingly - so that it can keep expanded/collapsed state etc tracked.

tv.ObjectActivated += (sender, e) =>
{
    var newOrder = e.ActivatedObject.Branches?.OrderBy(o => r.Next()).ToList();

    // Clear objects and force refresh
    e.ActivatedObject.Branches = [];
    tv.RefreshObject(e.ActivatedObject);

    // Add objects back and force refresh
    e.ActivatedObject.Branches = newOrder;
    tv.RefreshObject(e.ActivatedObject);
};

[YourRobotOverlord]

This is exactly what I needed. Thank you!

[YourRobotOverlord]

I just noticed that, while it's not obvious with a randomized list, this always redraws the list backwards (i.e. from item 3 to 0) after the refresh. 🤔

Displayed in TreeView

Contents of List

Repro

using Terminal.Gui;

namespace UICatalog.Scenarios;

[ScenarioMetadata ("TreeView Reordering Demo", "Demonstrates reordering of items in a TreeView.")]
[ScenarioCategory ("TreeView")]
public class TreeViewReordering : Scenario
{
    public override void Main ()
    {
        Application.Init ();

        var tv = new TreeView<Branch> (
            new DelegateTreeBuilder<Branch> (
                branch => branch is { }
                  ? branch.Branches?.ToArray () ?? []
                  : []))
        {
            Width = Dim.Fill (),
            Height = Dim.Fill ()
        };

        tv.AddObject (
          new Branch ()
          {
              Id = "root",
              Branches = new List<Branch> ()
              {
                  new Branch () { Id = "A" },
                  new Branch () { Id = "B" },
                  new Branch () { Id = "C" },
                  new Branch () { Id = "D" }
              }
          });

        Random r = new Random ();

        tv.ObjectActivated += (sender, e) =>
          {
              var newOrder = e.ActivatedObject.Branches?.OrderBy (o => r.Next ()).ToList ();

              // Clear objects and force refresh
              e.ActivatedObject.Branches = [];
              tv.RefreshObject (e.ActivatedObject);

              // Add objects back and force refresh
              e.ActivatedObject.Branches = newOrder;
              tv.RefreshObject (e.ActivatedObject);
          };

        var w = new Window ();
        w.Add (tv);

        Application.Run (w);
        w.Dispose ();
        Application.Shutdown ();
    }

    private class Branch
    {
        public string Id;
        public List<Branch>? Branches { get; set; }

        public Branch? Parent { get; set; }

        public override string ToString () { return Id; }

        public override bool Equals (object? obj)
        {
            if (obj is Branch other)
            {
                return Id == other.Id;
            }

            return false;
        }

        public override int GetHashCode () { return Id.GetHashCode (); }
    }
}

[tznind]

I have updated v2 to always respect the order of children provided in: #4015

[tznind]

This has now been merged 🎉 so if you target latest v2 nuget package i.e. 2.0.0-develop.4406 it should work

[YourRobotOverlord]

It's beautiful! Thank you!