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gui-cs.Terminal.Gui
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<h1 id="tree-view">Tree View</h1>

<p>TreeView is a control for navigating hierarchical objects. It comes in two forms <code>TreeView</code> and <code>TreeView&lt;T&gt;</code>.</p>
<p><a href="api/Terminal.Gui/Terminal.Gui.TreeView.html">TreeView API Reference</a></p>
<h2 id="using-treeview">Using TreeView</h2>
<p>The basic non generic TreeView class is populated by <code>ITreeNode</code> objects. The simplest tree you can make would look something like:</p>
<pre><code class="lang-csharp">var tree = new TreeView()
{
  X = 0,
  Y = 0,
  Width = 40,
  Height = 20
};

var root1 = new TreeNode(&quot;Root1&quot;);
root1.Children.Add(new TreeNode(&quot;Child1.1&quot;));
root1.Children.Add(new TreeNode(&quot;Child1.2&quot;));

var root2 = new TreeNode(&quot;Root2&quot;);
root2.Children.Add(new TreeNode(&quot;Child2.1&quot;));
root2.Children.Add(new TreeNode(&quot;Child2.2&quot;));

tree.AddObject(root1);
tree.AddObject(root2);
</code></pre><p>Having to create a bunch of TreeNode objects can be a pain especially if you already have your own objects e.g. <code>House</code>, <code>Room</code> etc. There are two ways to use your own classes without having to create nodes manually. Firstly you can implement the <code>ITreeNode</code> interface:</p>
<pre><code class="lang-csharp">// Your data class
private class House : TreeNode {

    // Your properties
    public string Address {get;set;}
    public List&lt;Room&gt; Rooms {get;set;}

    // ITreeNode member:
    public override IList&lt;ITreeNode&gt; Children =&gt; Rooms.Cast&lt;ITreeNode&gt;().ToList();

    public override string Text { get =&gt; Address; set =&gt; Address = value; }
}


// Your other data class
private class Room : TreeNode{

    public string Name {get;set;}

    public override string Text{get=&gt;Name;set{Name=value;}}
}
</code></pre><p>After implementing the interface you can add your objects directly to the tree</p>
<pre><code class="lang-csharp">
var myHouse = new House()
{
    Address = &quot;23 Nowhere Street&quot;,
    Rooms = new List&lt;Room&gt;{
      new Room(){Name = &quot;Ballroom&quot;},
      new Room(){Name = &quot;Bedroom 1&quot;},
      new Room(){Name = &quot;Bedroom 2&quot;}
    }
};

var tree = new TreeView()
{
    X = 0,
    Y = 0,
    Width = 40,
    Height = 20
};

tree.AddObject(myHouse);
</code></pre><p>Alternatively you can simply tell the tree how the objects relate to one another by implementing <code>ITreeBuilder&lt;T&gt;</code>. This is a good option if you don&#39;t have control of the data objects you are working with.</p>
<h2 id="treeviewt"><code>TreeView&lt;T&gt;</code></h2>
<p>The generic <code>Treeview&lt;T&gt;</code> allows you to store any object hierarchy where nodes implement Type T. For example if you are working with <code>DirectoryInfo</code> and <code>FileInfo</code> objects then you could create a <code>TreeView&lt;FileSystemInfo&gt;</code>. If you don&#39;t have a shared interface/base class for all nodes you can still declare a <code>TreeView&lt;object&gt;</code>.</p>
<p>In order to use <code>TreeView&lt;T&gt;</code> you need to tell the tree how objects relate to one another (who are children of who). To do this you must provide an <code>ITreeBuilder&lt;T&gt;</code>.</p>
<h3 id="implementing-itreebuildert"><code>Implementing ITreeBuilder&lt;T&gt;</code></h3>
<p>Consider a simple data model that already exists in your program:</p>
<pre><code class="lang-csharp">private abstract class GameObject
{

}

private class Army : GameObject
{
    public string Designation {get;set;}
    public List&lt;Unit&gt; Units {get;set;}


    public override string ToString ()
    {
        return Designation;
    }
}

private class Unit : GameObject
{
    public string Name {get;set;}
    public override string ToString ()
    {
        return Name;
    }
}
</code></pre><p>An <code>ITreeBuilder&lt;T&gt;</code> for these classes might look like:</p>
<pre><code class="lang-csharp">
private class GameObjectTreeBuilder : ITreeBuilder&lt;GameObject&gt; {
    public bool SupportsCanExpand =&gt; true;

    public bool CanExpand (GameObject model)
    {
        return model is Army;
    }

    public IEnumerable&lt;GameObject&gt; GetChildren (GameObject model)
    {
        if(model is Army a)
            return a.Units;

        return Enumerable.Empty&lt;GameObject&gt;();
    }
}
</code></pre><p>To use the builder in a tree you would use:</p>
<pre><code class="lang-csharp">var army1 = new Army()
{
    Designation = &quot;3rd Infantry&quot;,
    Units = new List&lt;Unit&gt;{
        new Unit(){Name = &quot;Orc&quot;},
        new Unit(){Name = &quot;Troll&quot;},
        new Unit(){Name = &quot;Goblin&quot;},
    }
};

var tree = new TreeView&lt;GameObject&gt;()
{
    X = 0,
    Y = 0,
    Width = 40,
    Height = 20,
    TreeBuilder = new GameObjectTreeBuilder()
};


tree.AddObject(army1);
</code></pre><p>Alternatively you can use <code>DelegateTreeBuilder&lt;T&gt;</code> instead of implementing your own <code>ITreeBuilder&lt;T&gt;</code>. For example:</p>
<pre><code class="lang-csharp">tree.TreeBuilder = new DelegateTreeBuilder&lt;GameObject&gt;(
    (o)=&gt;o is Army a ? a.Units 
      : Enumerable.Empty&lt;GameObject&gt;());
</code></pre><h2 id="node-text-and-tostring">Node Text and ToString</h2>
<p>The default behavior of TreeView is to use the <code>ToString</code> method on the objects for rendering. You can customise this by changing the <code>AspectGetter</code>. For example:</p>
<pre><code class="lang-csharp">treeViewFiles.AspectGetter = (f)=&gt;f.FullName;
</code></pre></article>
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