.NET (Core and Framework)

<pre lang="c#">
public class MainViewModel : ViewModelBase
    {
        /// <summary>
        /// Initializes a new instance of the MainViewModel class.
        /// </summary>
        /// 
         IDataAccessService _serviceProxy;

         ObservableCollection<Busta> _Bustas;

         public ObservableCollection<Busta> BustaOservable
         {
             get { return _Bustas; }
             set
             {
                 _Bustas = value;
                 RaisePropertyChanged("BustaOservable");
             }
         }

         ObservableCollection<Negozio> _Negozios;

         public ObservableCollection<Negozio> NegozioObser

         {
             get { return _Negozios; }
             set
             {
                 _Negozios = value;
                 RaisePropertyChanged("Negozio");
             }
         }

        Busta _Busta;
        public Busta Busta
        {
            get { return _Busta; }
            set
            {
                _Busta = value;
                RaisePropertyChanged("Busta");
            }
        }

        Negozio _Negozio;
        public Negozio NegozioSelezionato
        {
            get { return _Negozio; }
            set
            {
                _Negozio = value;
                RaisePropertyChanged("NegozioSelezionato");
            }
        }

        #region Command Object Declarations
       
        public RelayCommand<Busta> SaveCommand { get; set; }

        

       
        #endregion
        public MainViewModel(IDataAccessService servPxy)
        {
            _serviceProxy = servPxy;
            Busta = new Busta();
            NegozioSelezionato = new Negozio();
             
            SaveCommand = new RelayCommand<Busta>(SalvaBusta);
            NegozioObser = new ObservableCollection<Negozio>();
            
        }
//Metodo Per Salvare La Busta
 void SalvaBusta(Busta Bus)
{
    Bus.NegozioID = NegozioSelezionato.NegozioID;
    Busta.BustaID = _serviceProxy.CreateBusta(Bus);
    if (Busta.BustaID != 0)
    {
        BustaOservable.Add(Busta);
        RaisePropertyChanged("Busta");
    }

       
        }
//Metodo Per Caricare I dati Della Combobox
 public void GetNegozio()
 {
     
     foreach (var item in _serviceProxy.GetNegozio())
     {
         NegozioObser.Add(item);
     }
 }
    }
}

<pre lang="HTML"><Window x:Class="Prova1.View.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        DataContext="{Binding Main,Source={StaticResource Locator}}"
        Title="MainWindow" Height="429" Width="615" Loaded="Window_Loaded">


    <Grid>
        <TextBox HorizontalAlignment="Left" Height="23" Margin="327,85,0,0" TextWrapping="Wrap" Text="{Binding Busta.BustaID, Mode=TwoWay }" VerticalAlignment="Top" Width="120"/>
        <Label Content="BustaID" HorizontalAlignment="Left" Margin="238,85,0,0" VerticalAlignment="Top"/>
        <Label Content="NegozioId" HorizontalAlignment="Left" Margin="238,116,0,0" VerticalAlignment="Top"/>
        <TextBox HorizontalAlignment="Left" Height="23" Margin="327,142,0,0" TextWrapping="Wrap" Text="{Binding Busta.NomeCliente, Mode=TwoWay}" VerticalAlignment="Top" Width="120"/>
        <Label Content="NomeCliente" HorizontalAlignment="Left" Margin="238,142,0,0" VerticalAlignment="Top"/>
        <Button Content="Salva" HorizontalAlignment="Left" Margin="215,233,0,0" VerticalAlignment="Top" Width="75"
                Command="{Binding SaveCommand}" CommandParameter="{Binding Busta}"/>
       <!-- <TextBox HorizontalAlignment="Left" Height="23" Margin="327,114,0,0" TextWrapping="Wrap" Text="{Binding Busta.NegozioID, Mode=TwoWay}" VerticalAlignment="Top" Width="120"/>-->
        <ComboBox HorizontalAlignment="Left" Margin="327,116,0,0" VerticalAlignment="Top" Width="120" ItemsSource="{Binding NegozioObser}" SelectedItem="{Binding NegozioSelezionato}">
            <ComboBox.ItemTemplate>
                <DataTemplate>
                    <Grid>
                        <TextBlock Text="{Binding RagioneSociale}"></TextBlock>
                    </Grid>
                </DataTemplate>
            </ComboBox.ItemTemplate>
        </ComboBox> 
    </Grid>

</Window>

System.NullReferenceException verificata
  HResult=-2147467261
  Message=Riferimento a un oggetto non impostato su un'istanza di oggetto.
  Source=Prova1
  StackTrace:
       in Prova1.ViewModel.MainViewModel.SalvaBusta(Busta Bus) in k:\c#\MVVMLight\Prova1\Prova1\ViewModel\MainViewModel.cs:riga 102
  InnerException: 

Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim con As New OleDb.OleDbConnection

        Dim dbProvider As String
        Dim dbSource As String

        Dim ds As New DataSet

        Dim tables As DataTableCollection = ds.Tables

        Dim source1 As New BindingSource()

        Dim da As New OleDb.OleDbDataAdapter

        Dim isFirstColumn As Boolean = True
        Dim author As String = ""
        Dim publisher As String = ""
        Dim yearpublished As String = ""
        Dim genre As String = ""


        Dim aa As String = authorList.Text

        Dim bb As String = publisherList.Text

        Dim cc As String = yearpublishedList.Text

        Dim dd As String = genreList.Text

        Dim astring As String = "SELECT * FROM books "

        If authorList.SelectedIndex > -1 Then
            If isFirstColumn Then
                author = "WHERE author = '" & aa & "' "
            Else
                author = "AND author = '" & aa & "' "
            End If
            isFirstColumn = False
        End If

        If publisherList.SelectedIndex > -1 Then
            If isFirstColumn Then
                publisher = "WHERE publisher = '" & bb & "' " '
            Else
                publisher = "AND publisher = '" & bb & "' "
            End If
            isFirstColumn = False
        End If

        If yearpublishedList.SelectedIndex > -1 Then
            If isFirstColumn Then
                yearpublished = "WHERE yearpublished = '" & cc & "' " '
            Else
                yearpublished = "AND yearpublished = '" & cc & "' "
            End If
            isFirstColumn = False
        End If

        If yearpublishedList.SelectedIndex > -1 Then
            If isFirstColumn Then
                genre = "WHERE genre = '" & dd & "' "
            Else
                genre = "AND genre = '" & dd & "' "
            End If
            isFirstColumn = False
        End If

        dbProvider = "PROVIDER=Microsoft.ACE.OLEDB.12.0;"

        dbSource = "Data Source = C:\Documents and Settings\james\Desktop\authors2.accdb"

        con.ConnectionString = dbProvider & dbSource

        con.Open()



        Dim sql As String = astring & author & publisher & yearpublished & genre

        da = New OleDb.OleDbDataAdapter(sql, con)



        da.Fill(ds, "books")



        Dim view1 As New DataView(tables(0))

        source1.DataSource = view1

        DataGridView1.DataSource = view1

        DataGridView1.Refresh()





<pre lang="vb"><pre lang="vb"><pre lang="vb">

Quote:

Framework:
If I say you to cut a paper of dimension 5m by 5m then surely you would do that. But then I ask you to cut 1000 paper of the same dimension. Then you won't do the measuring for 1000 times, obviously you would make a frame of 5m by 5m and then with the help of it you would be able to cut 1000 papers in less time. So, what you did is you made a framewok which would do that type of task. So, instead of performing same type of task again and again for same type of applications, what you do is you create a framework having all those facilities together in one nice packet and hence providing the abstraction for your application and more importantly many applications.