Added TreeView sample

Features:
* Sort on header click.
* Add, edit, remove value in store (name column).
* Children items.
* Handlers for store events.

Source/Samples/Sections/Widgets/TreeViewSection.cs

@@ -0,0 +1,177 @@
+// This is free and unencumbered software released into the public domain.
+// Happy coding!!! - GtkSharp Team
+
+using System;
+using Gtk;
+
+namespace Samples
+{
+    [Section(ContentType = typeof(TreeView), Category = Category.Widgets)]
+    class TreeViewSection : Box
+    {
+        const int ColumnIndex = 0;
+        const int ColumnName = 1;
+        const int ColumnIcon = 2;
+
+        TreeView tree;
+        TreeStore store;
+        Entry entry;
+        Gdk.Pixbuf icon = new Gdk.Pixbuf(typeof(ImageSection).Assembly, "Testpic", 32, 32);
+
+        public TreeViewSection() : base(Orientation.Vertical, 3)
+        {
+            CreateTreeView();
+
+            var treeScroll = new ScrolledWindow();
+            treeScroll.Expand = true;
+            treeScroll.Add(tree);
+
+            var boxEdit = new Box(Orientation.Horizontal, 3);
+
+            var btn1 = new Button() { Label = "Add" };
+            btn1.Clicked += OnAddClicked;
+
+            var btn2 = new Button() { Label = "Edit" };
+            btn2.Clicked += OnEditClicked;
+
+            var btn3 = new Button() { Label = "Remove" };
+            btn3.Clicked += OnRemoveClicked;
+
+            entry = new Entry();
+
+            boxEdit.PackStart(entry, true, true, 0);
+            boxEdit.PackStart(btn1, false, true, 0);
+            boxEdit.PackStart(btn2, false, true, 0);
+            boxEdit.PackStart(btn3, false, true, 0);
+
+            PackStart(boxEdit, false, true, 0);
+            PackStart(treeScroll, true, true, 0);
+        }
+
+        void CreateTreeView()
+        {
+            store = new TreeStore(typeof(int), typeof(string), typeof(Gdk.Pixbuf));
+            store.RowInserted += OnStoreRowInserted;
+            store.RowDeleted += OnStoreRowDeleted;
+            store.RowChanged += OnStoreRowChanged;
+            store.RowsReordered += OnStoreRowsReordered;
+            store.RowHasChildToggled += OnStoreRowHasChildToggled;
+
+            tree = new TreeView();
+
+            var col = tree.AppendColumn("Index", new CellRendererText(), "text", ColumnIndex);
+            col.Resizable = true;
+            col.SortColumnId = 0;
+            col = tree.AppendColumn("Name", new CellRendererText(), "text", ColumnName);
+            col.Resizable = true;
+            col.Expand = true;
+            col.SortColumnId = 1;
+
+            col = tree.AppendColumn("Icon", new CellRendererPixbuf(), "pixbuf", ColumnIcon);
+            col.Resizable = true;
+            col.Expand = true;
+            col.Alignment = .5f;
+
+            FillTreeView();
+
+            tree.Model = store;
+            tree.Selection.Changed += OnTreeSelectionChanged;
+        }
+
+        void FillTreeView()
+        {
+            int idx = 0;
+
+            TreeIter it = store.InsertWithValues(-1, idx++, "Adam", null);
+            store.InsertWithValues(it, -1, idx++, "Adam child 1", null);
+            store.InsertWithValues(it, -1, idx++, "Adam child 2", icon);
+            store.InsertWithValues(it, -1, idx++, "Adam child 3", null);
+
+            store.InsertWithValues(-1, idx++, "Eve", null);
+            store.InsertWithValues(-1, idx++, "Zack", null);
+            store.InsertWithValues(-1, idx++, "John", icon);
+
+            it = store.InsertWithValues(-1, idx++, "Amy", null);
+            store.InsertWithValues(it, -1, idx++, "Amy child 1", null);
+            store.InsertWithValues(it, -1, idx++, "Amy child 2", null);
+
+            store.InsertWithValues(-1, idx++, "William", null);
+            store.InsertWithValues(-1, idx++, "Evelyn", icon);
+            store.InsertWithValues(-1, idx++, "Wyatt", null);
+        }
+
+        private void OnTreeSelectionChanged(object sender, EventArgs e)
+        {
+            if (!tree.Selection.GetSelected(out TreeIter it))
+                return;
+
+            TreePath path = store.GetPath(it);
+
+            var name = (string)store.GetValue(it, ColumnName);
+            entry.Text = name;
+
+            ApplicationOutput.WriteLine(sender, $"SelectionChanged, path {path}, name {name}");
+        }
+
+        private void OnStoreRowInserted(object sender, RowInsertedArgs args)
+        {
+            var name = (string)store.GetValue(args.Iter, ColumnName);
+            ApplicationOutput.WriteLine(sender, $"RowInserted, path {args.Path}, name {name}");
+        }
+
+        private void OnStoreRowDeleted(object sender, RowDeletedArgs args)
+        {
+            ApplicationOutput.WriteLine(sender, $"RowDeleted, path {args.Path}");
+        }
+
+        private void OnStoreRowChanged(object sender, RowChangedArgs args)
+        {
+            var name = (string)store.GetValue(args.Iter, ColumnName);
+            ApplicationOutput.WriteLine(sender, $"RowChanged, path {args.Path}, name {name}");
+        }
+
+        private void OnStoreRowsReordered(object sender, RowsReorderedArgs args)
+        {
+            ApplicationOutput.WriteLine(sender, $"RowsReordered, path {args.Path}");
+        }
+
+        private void OnStoreRowHasChildToggled(object sender, RowHasChildToggledArgs args)
+        {
+            var name = (string)store.GetValue(args.Iter, ColumnName);
+            ApplicationOutput.WriteLine(sender, $"RowHasChildToggled, path {args.Path}, name {name}");
+        }
+
+        private void OnAddClicked(object sender, EventArgs e)
+        {
+            if (!tree.Selection.GetSelected(out TreeIter it))
+                return;
+
+            string txt = entry.Text.Trim();
+            if (string.IsNullOrEmpty(txt))
+                return;
+
+            int idx = Environment.TickCount % 100;
+            store.InsertWithValues(it, -1, idx, txt, null);
+        }
+
+        private void OnEditClicked(object sender, EventArgs e)
+        {
+            if (!tree.Selection.GetSelected(out TreeIter it))
+                return;
+
+            string txt = entry.Text.Trim();
+            if (string.IsNullOrEmpty(txt))
+                return;
+
+            store.SetValue(it, ColumnName, txt);
+        }
+
+        private void OnRemoveClicked(object sender, EventArgs e)
+        {
+            if (!tree.Selection.GetSelected(out TreeIter it))
+                return;
+
+            store.Remove(ref it);
+        }
+    }
+}