How we can write on C# in Linux: Implementing PanelApplet to Gnome Desktop

using System;

using Gtk;
using GConf;

using WeatherApplet.Model;

namespace WeatherApplet.View
{

	public class TreeView:Window
	{


	Label filterEntry;
	public TreeView ():base("asdasd")
	{
			
		//Create window
		ScrolledWindow sw = new Gtk.ScrolledWindow ();
		this.SetSizeRequest (500,200);
		 
		// Create an Entry used to filter the tree
		filterEntry = new Gtk.Label ();
 
		// Fire off an event when the text in the Entry changes
		//filterEntry.Changed += OnFilterEntryTextChanged;
		
		// Create a nice label describing the Entry
		Gtk.Label filterLabel = new Gtk.Label ("Selected country:");
		
		// Put them both into a little box so they show up side by side
		Gtk.HBox filterBox = new Gtk.HBox ();
			
		filterBox.PackStart (filterLabel, false, false, 5);
		filterBox.PackStart (filterEntry, true, true, 5);
 
		// Create our TreeView
		Gtk.TreeView tree = new Gtk.TreeView ();
 
		// Create a box to hold the Entry and Tree
		Gtk.VBox box = new Gtk.VBox ();
 
		// Add the widgets to the box
		box.PackStart (filterBox, false, false, 5);
		sw.Add (tree);
		box.PackStart (sw, true, true, 5);

		
		//Create column	
		Gtk.TreeViewColumn countriesColumn = new Gtk.TreeViewColumn ();
		countriesColumn.Title = "Countries";
 		Gtk.CellRendererText countriesNameCell = new Gtk.CellRendererText ();
		countriesColumn.PackStart (countriesNameCell, true);
		tree.AppendColumn (countriesColumn);
 		countriesColumn.AddAttribute(countriesNameCell, "text", 0);
			
		//Create list of countries	
		tree.Model = BuildTree();
		
		tree.Selection.Changed += OnSelectionChanged; 	
			
 		this.Add(box);
		this.ShowAll ();
	}
		
		private TreeStore BuildTree()
		{
			Gtk.TreeStore countryListStore = new Gtk.TreeStore(typeof (string));
			
			Gtk.TreeIter europe = countryListStore.AppendValues ("Europe");
		
			SetCountryCities("Belarus", europe, ref countryListStore);
			SetCountryCities("Russia", europe, ref countryListStore);
						
			return countryListStore;
		}
			        
		private void SetCountryCities(string country,TreeIter region, ref TreeStore store)
		{
			TreeIter countryIter = store.AppendNode(region);
			store.SetValue(countryIter,0, country);
		
			foreach(var city in WeatherService.GetCitiesByCountry(country))
				store.AppendValues (countryIter, city);
			
		}
		
		 void OnSelectionChanged (object o, EventArgs args)
        {
			try
			{
                TreeIter iter;
                TreeModel model;
 
                if (((TreeSelection)o).GetSelected (out model, out iter))
                {
					if(model.IterHasChild(iter)) return;
						
						TreeIter parent;
						model.IterParent(out parent, iter);
					
						string state = (string) model.GetValue (parent, 0);
                        string city = (string) model.GetValue (iter, 0);
						filterEntry.Text = String.Format("{0}-{1} was selected", state, city);
						
						SettingsStore.Set("state", state);
						SettingsStore.Set("city", city);
                }
			}
			catch
			{
			}
        }


	}
}