AppearanceRule for TreeList to Enable\Disable a property.

Since the TreeListEditor does not support in-place editing, the corresponding appearance customization is not implemented in it. To support the "Enabled" appearance for cells, create a derived list editor as follows:

C#
[ListEditor(typeof(ITreeNode), true)]  
public class TreeListEditorEx : TreeListEditor {  
    public TreeListEditorEx(IModelListView model) : base(model) { }  
    protected override void OnControlsCreated() {  
        base.OnControlsCreated();  
        this.TreeList.ShowingEditor += new System.ComponentModel.CancelEventHandler(control_ShowingEditor);  
    }  
    void control_ShowingEditor(object sender, System.ComponentModel.CancelEventArgs e) {  
        ObjectTreeListNode node  = this.TreeList.FocusedNode as ObjectTreeListNode;  
        if(node == null) return;  
        CustomizeAppearanceEventArgs args = new CustomizeAppearanceEventArgs(this.TreeList.FocusedColumn.FieldName, new CancelEventArgsAppearanceAdapter(e), node.Object);  
        this.OnCustomizeAppearance(args);  
    }  
}  

UPDATE:
Starting from version 12.2.11 use the following controller instead:

C#
public class TreeListAppearanceControllerEx : TreeListAppearanceController {  
    protected override void OnTreeListChanged() {  
        base.OnTreeListChanged();  
        if (base.Active && base.View != null && base.View.Editor != null && base.View.Editor is TreeListEditor && ((TreeListEditor)base.View.Editor).TreeList != null) {  
            ((TreeListEditor)base.View.Editor).TreeList.ShowingEditor += new System.ComponentModel.CancelEventHandler(control_ShowingEditor);  
        }  
    }  
    void control_ShowingEditor(object sender, System.ComponentModel.CancelEventArgs e) {  
        TreeList tl = (TreeList)sender;  
        ObjectTreeListNode node = tl.FocusedNode as ObjectTreeListNode;  
        if (node == null) return;  
        this.OnCustomizeAppearance(new CustomizeAppearanceEventArgs(tl.FocusedColumn.FieldName, "ViewItem", new GridViewCancelEventArgsAppearanceAdapter(null, e), node.Object));  
    }  
}  

UPDATE:
Starting from version 14.2, another CustomizeAppearanceEventArgs shoudl be used:

C#
this.OnCustomizeAppearance(new CustomizeAppearanceEventArgs(tl.FocusedColumn.FieldName, "ViewItem", new GridViewCancelEventArgsAppearanceAdapter(null, e), node.Object, null));