In mvvm the view doesn't update

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C#

WPF

MVVM

hi
i am beginner in mvvm concept.so i tried one sample application.it contains two textbox are name and id, one submit button,one label.when i click submit button it combine the two strings from the textbox and display in label.

i can submit the values and in viewmodel the property contain the result.but its not shown in view.why..?

in view contains

<grid>
   <TextBox Grid.Column="1" Grid.Row="1" Text="{Binding name}"  Height="23"  Margin="9" Name="txtname"  Width="120" />
   <TextBox Grid.Column="1" Grid.Row="2" Text="{Binding id}" Height="23"  Margin="9" Name="txtid"  Width="120" />
   <Button Command="{Binding submit}" Content="submit" Grid.Column="2" Grid.Row="2" Height="23"   Name="btnsubmit"  Width="75" />
   <Label Content="{Binding display}" Grid.Row="3" Height="38" HorizontalAlignment="Left"  Name="lbldisplay"  Width="192" />

   </grid>

view.cs code is

public MainWindow()
       {
           InitializeComponent();
           DataContext = new DemoViewModel();
       }

in my viewmodel contains two .cs file

one is DemoViewModelInotify.cs.in this i write the code for inotifypropertychanged.
another one is DemoViewModel.cs.this contain the property and commands.

namespace mvvmdemonixon.ViewModel
   {
   public  class DemoViewModel :DemoViewModelInotify
   {
     public ICommand submit { get; set; }

     public string name { get; set; }
     public string display { get; set; }
     public int id{get;set;}
     public DemoModel model { get; set; }
     public DemoViewModel()
     {

         submit = new DelegateCommand<object>(this.add);

     }

     public void add(object paramter)
     {
       string a=  mvvmdemonixon.Model.DemoModel.addstring(name, id);
       display = a;
     }

   }
   }

my model contains

namespace mvvmdemonixon.Model
   {
   public  class DemoModel
   {
      public static string addstring(string name1, int no1)
      {
          string display = "The Student Name Is " + name1 + "and Id Is" + no1 + ".";
          return display;
      }

   }
   }

in my app.xaml.cs

private void OnStartup(object sender, StartupEventArgs e)
      {
          mvvmdemonixon.MainWindow view = new MainWindow();
          view.DataContext = new mvvmdemonixon.ViewModel.DemoViewModel();
          view.Show();
      }

in my app xaml

<Application x:Class="mvvmdemonixon.App"
   Startup="OnStartup">
   </Application>

advance thanks..