Using Portable Class Library with Model-View-View Model

.NET Framework 4.5

You can use the .NET Framework Portable Class Library to implement the Model-View-View Model (MVVM) pattern and share assemblies across multiple platforms.

MVVM is an application pattern that isolates the user interface from the underlying business logic. You can implement the model and view model classes in a Portable Class Library project in Visual Studio 2012, and then create views that are customized for different platforms. This approach enables you to write the data model and business logic only once, and use that code from .NET Framework, Silverlight, Windows Phone, and Windows Store apps, as shown in the following illustration.

Portable with MVVM diagram

This topic does not provide general information about the MVVM pattern. It only provides information about how to use Portable Class Library to implement MVVM. For more information about MVVM, see the MVVM Quickstart in the MSDN Library.

To implement MVVM, you typically create both the model and the view model in a Portable Class Library project, because a Portable Class Library project cannot reference a non-portable project. The model and view model can be in the same project or in separate projects. If you use separate projects, add a reference from the view model project to the model project.

After you compile the model and view model projects, you reference those assemblies in the app that contains the view. If the view interacts only with the view model, you only have to reference the assembly that contains the view model.

The following example shows a simplified model class that could reside in a Portable Class Library project.

Namespace SimpleMVVM.Model

    Public Class Customer
        Public Property CustomerID() As Integer 
        Public Property FullName() As String 
        Public Property Phone() As String 
    End Class 
End Namespace

The following example shows a simple way to populate, retrieve, and update the data in a Portable Class Library project. In a real app, you would retrieve the data from a source such as a Windows Communication Foundation (WCF) service.

Namespace SimpleMVVM.Model
    Public Class CustomerRepository
        Private _customers As List(Of Customer)

        Public Sub New()
            _customers = New List(Of Customer) From
            {
                New Customer() With {.CustomerID = 1, .FullName = "Dana Birkby", .Phone = "394-555-0181"},
                New Customer() With {.CustomerID = 2, .FullName = "Adriana Giorgi", .Phone = "117-555-0119"},
                New Customer() With {.CustomerID = 3, .FullName = "Wei Yu", .Phone = "798-555-0118"}
            }
        End Sub 

        Public Function GetCustomers() As List(Of Customer)
            Return _customers
        End Function 

        Public Sub UpdateCustomer(SelectedCustomer As Customer)
            Dim customerToChange = _customers.Single(Function(c) c.CustomerID = SelectedCustomer.CustomerID)
            customerToChange = SelectedCustomer
        End Sub 
    End Class 
End Namespace

A base class for view models is frequently added when implementing the MVVM pattern. The following example shows a base class.

Imports System.ComponentModel

Namespace SimpleMVVM.ViewModel

    Public MustInherit Class ViewModelBase
        Implements INotifyPropertyChanged

        Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged

        Protected Overridable Sub OnPropertyChanged(propname As String)
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propname))
        End Sub 
    End Class 
End Namespace

An implementation of the ICommand interface is frequently used with the MVVM pattern. The following example shows an implementation of the ICommand interface.

Imports System.Windows.Input

Namespace SimpleMVVM.ViewModel

    Public Class RelayCommand
        Implements ICommand

        Private _isEnabled As Boolean 
        Private ReadOnly _handler As Action

        Public Sub New(ByVal hander As Action)
            _handler = hander
        End Sub 

        Public Event CanExecuteChanged As EventHandler Implements ICommand.CanExecuteChanged

        Public Property IsEnabled() As Boolean 
            Get 
                Return _isEnabled
            End Get 
            Set(ByVal value As Boolean)
                If (value <> _isEnabled) Then
                    _isEnabled = value
                    RaiseEvent CanExecuteChanged(Me, EventArgs.Empty)
                End If 
            End Set 
        End Property 

        Public Function CanExecute(parameter As Object) As Boolean Implements ICommand.CanExecute
            Return IsEnabled
        End Function 

        Public Sub Execute(parameter As Object) Implements ICommand.Execute
            _handler()
        End Sub 

    End Class 
End Namespace

The following example shows a simplified view model.

Imports System.Collections.Generic
Imports SimpleMVVM.Model

Namespace SimpleMVVM.ViewModel

    Public Class CustomerViewModel
        Inherits ViewModelBase

        Private _customers As List(Of Customer)
        Private _currentCustomer As Customer
        Private _repository As CustomerRepository
        Private _updateCustomerCommand As RelayCommand

        Public Sub New()
            _repository = New CustomerRepository()
            _customers = _repository.GetCustomers()

            WireCommands()
        End Sub 

        Private Sub WireCommands()
            UpdateCustomerCommand = New RelayCommand(AddressOf UpdateCustomer)
        End Sub 

        Public Property UpdateCustomerCommand() As RelayCommand
            Get 
                Return _updateCustomerCommand
            End Get 
            Private Set(value As RelayCommand)
                _updateCustomerCommand = value
            End Set 
        End Property 

        Public Property Customers() As List(Of Customer)
            Get 
                Return _customers
            End Get 
            Set(value As List(Of Customer))
                _customers = value
            End Set 
        End Property 

        Public Property CurrentCustomer() As Customer
            Get 
                Return _currentCustomer
            End Get 
            Set(value As Customer)
                If _currentCustomer.Equals(value) Then
                    _currentCustomer = value
                    OnPropertyChanged("CurrentCustomer")
                    UpdateCustomerCommand.IsEnabled = True 
                End If 
            End Set 
        End Property 

        Public Sub UpdateCustomer()
            _repository.UpdateCustomer(CurrentCustomer)
        End Sub 
    End Class 
End Namespace

From a .NET Framework 4.5 app, Windows Store app, Silverlight-based app, or Windows Phone 7.5 app, you can reference the assembly that contains the model and view model projects. You then create a view that interacts with the view model. The following example shows a simplified Windows Presentation Foundation (WPF) app that retrieves and updates data from the view model. You could create similar views in Silverlight, Windows Phone, or Windows Store apps.

<Window x:Class="SimpleWPF.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:viewModels="clr-namespace:SimpleMVVM.ViewModel;assembly=SimpleMVVM.ViewModel"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <viewModels:MainPageViewModel x:Key="ViewModel" />
    </Window.Resources>
    <Grid DataContext="{Binding Source={StaticResource ViewModel}}">
        <Grid.ColumnDefinitions>
            <ColumnDefinition></ColumnDefinition>
            <ColumnDefinition></ColumnDefinition>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"></RowDefinition>
            <RowDefinition Height="Auto"></RowDefinition>
            <RowDefinition Height="Auto"></RowDefinition>
            <RowDefinition Height="Auto"></RowDefinition>
            <RowDefinition Height="Auto"></RowDefinition>
        </Grid.RowDefinitions>
        <TextBlock Height="23" Margin="5" HorizontalAlignment="Right" Grid.Column="0" Grid.Row="0" Name="textBlock2" 
                   Text="Select a Customer:" VerticalAlignment="Top" />
        <ComboBox Height="23" HorizontalAlignment="Left" Grid.Column="1" Grid.Row="0" Name="CustomersComboBox" VerticalAlignment="Top" Width="173" 
                  DisplayMemberPath="FullName" SelectedItem="{Binding Path=CurrentCustomer, Mode=TwoWay}" ItemsSource="{Binding Path=Customers}" />
        <TextBlock Height="23" Margin="5" HorizontalAlignment="Right" Grid.Column="0" Grid.Row="1" Name="textBlock4" Text="Customer ID" />
        <TextBlock Height="23" Margin="5" HorizontalAlignment="Right" Grid.Column="0" Grid.Row="2" Name="textBlock5" Text="Name" />
        <TextBlock Height="23" Margin="5" HorizontalAlignment="Right" Grid.Column="0" Grid.Row="3" Name="textBlock9" Text="Phone" />
        <TextBlock Height="23" HorizontalAlignment="Left" Grid.Column="1" Grid.Row="1" Name="CustomerIDTextBlock" 
                   Text="{Binding ElementName=CustomersComboBox, Path=SelectedItem.CustomerID}" />
        <TextBox Height="23" HorizontalAlignment="Left" Grid.Column="1" Grid.Row="2" Width="219" 
                 Text="{Binding Path=CurrentCustomer.FullName, Mode=TwoWay}" />
        <TextBox Height="23" HorizontalAlignment="Left" Grid.Column="1" Grid.Row="3" Width="219" 
                 Text="{Binding Path=CurrentCustomer.Phone, Mode=TwoWay}" />
        <Button
            Command="{Binding UpdateCustomerCommand}"
            Content="Update" Height="23" HorizontalAlignment="Right" Grid.Column="0" Grid.Row="4" 
            Name="UpdateButton" VerticalAlignment="Top" Width="75" />
    </Grid>
</Window>
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