Sample Calculator MVVM in VB.NET

For my work I have developed a small application calculator and now I've decided to share with the community and to show the pattern design MVVM.

First I created the project and have set the folders to the pattern.

I have incorporated the necessary classes to use the pattern are:

DelegateCommand

ViewModelBase

After that incorporates a usercontrol to create the application view

Calc.gif

Public Class CalculatorVM
    Inherits ViewModelBase
    Private _NumberPress As ICommand
    Private _OperatorPress As ICommand
    Private _Display As String = "0.00"
    Private _LastOperator As String
    Private _FirstNumber As Double
 
    Public Property DoubleZero As String
    Public Property Zero As Byte
    Public Property One As Byte
    Public Property Two As Byte
    Public Property Three As Byte
    Public Property Four As Byte
    Public Property Five As Byte
    Public Property Six As Byte
    Public Property Seven As Byte
    Public Property Eight As Byte
    Public Property Nine As Byte
    Public Property LastNumber As Double
    Public Property LastEspecial As String  ' "," or "00"
    Public Result As
Double

 Public Property Display As String
        Get
            Return _Display
        End Get
        Set(ByVal value As String)
            _Display = value
            OnPropertyChanged("Display")
        End Set
    End Property
    Public Property LastOperator As String
        Get
            Return _LastOperator
        End Get
        Set(ByVal value As String)
            _LastOperator = value
            OnPropertyChanged("LastOperator")
        End Set
    End Property
    Public Property FirstNumber As Double
        Get
            Return _FirstNumber
        End Get
        Set(ByVal value As Double)
            _FirstNumber = value
            OnPropertyChanged("FirstNumber")
        End Set
    End Property
 
    Public ReadOnly Property NumberPress As ICommand
        Get
            If _NumberPress Is Nothing Then
                _NumberPress = New MVVM.RelayCommand(AddressOf ExecuteNumberPress)
            End If
            Return _NumberPress
        End Get
    End Property
    Public ReadOnly Property OperatorPress As ICommand
        Get
            If _OperatorPress Is Nothing Then
                _OperatorPress = New MVVM.RelayCommand(AddressOf ExecuteOperatorPress)
            End If
            Return _OperatorPress
        End Get
    End
Property

    Sub ExecuteNumberPress(ByVal Param As Object)
        Select Case Param
            Case Is = ","
                If Display.Contains(CStr(Param)) = False Then
                    LastEspecial = ","
                    Display = Display & LastEspecial
                End If
            Case Is = "00"
                LastEspecial = "00"
                Display = Display & LastEspecial
            Case Is = "CE"
                If String.IsNullOrEmpty(LastOperator) Then
                    FirstNumber = 0
                    Display = 0
                Else
                    LastNumber = 0
                End If
            Case Is = "C"
                LastNumber = 0
                FirstNumber = 0
                Display = 0
                LastOperator = String.Empty
            Case Is = "←"
                If Display.Length <= 1 OrElse CDbl(Display) = 0 Then
                    Display = "0,00"
                Else
                    Display = Left(Display, Display.Length - 1)
                End If
            Case Is = "+/-"
                If CDbl(Display) <> 0 Then
                    Display = CDbl(Display) * -1
                End If
            Case Else
                If String.IsNullOrEmpty(LastOperator) Then
                    If CDbl(Display) = 0 OrElse (FirstNumber = 0 And LastNumber = 0) Then
                        Display = CStr(Param)
                    Else
                        Display = Display & CStr(Param)
                    End If
                    _FirstNumber = CDbl(Display)
                Else
                    If LastNumber <> 0 Then
                        Display = Display & CStr(Param)
                    Else
                        Display = CStr(Param)
                    End If
                    LastNumber = CDbl(Display)
                End If
        End
Select

    End Sub
    Private Sub ExecuteOperatorPress(ByVal Param As Object)
        If String.IsNullOrEmpty(LastOperator) Then
            FirstNumber = CDbl(Display)
            If CStr(Param) <> "=" Then
                LastOperator = CType(Param, String)
            End If
 
            If LastOperator = "√" Then
                Calculate()
            End If
        Else
            LastNumber = CDbl(Display)
            If CStr(Param) <> "=" Then
                LastOperator = CType(Param, String)
            End If
            Calculate()
        End If
 
    End Sub
    Private Sub Calculate()
        Select Case LastOperator
            Case Is = "%"
                Result = FirstNumber * LastNumber / 100
 
            Case Is = "X"
                Result = FirstNumber * LastNumber
 
            Case Is = "/"
                Result = FirstNumber / LastNumber
            Case Is = "+"
                Result = FirstNumber + LastNumber
 
            Case Is = "-"
                Result = FirstNumber - LastNumber
 
            Case Is = "√"
                Result = CDbl(Display)
                Result = Math.Sqrt(Result)
        End Select
        Display = Result
        LastOperator = String.Empty
        FirstNumber = 0
        LastNumber = 0

    End
Sub
End Class 

And it links commands to the buttons on the view like this

<Button Content="-" Height="30" Width="30"  Command="{Binding Path=OperatorPress}" CommandParameter="{Binding Path=Content, RelativeSource={RelativeSource Self}}"/>

And

            <Button Width="45" Height="45" Content="CE" Command="{Binding Path=NumberPress}" CommandParameter="{Binding Path=Content, RelativeSource={RelativeSource Self}}"/>

After, we binds the keypress (this is new  in wpf 4.0)

        <KeyBinding Key="NumPad0" Command="{Binding Path=NumberPress}"  CommandParameter="0"/>
        <KeyBinding Key="Decimal" Command="{Binding Path=NumberPress}"  CommandParameter=","/>

        <KeyBinding Key="Add" Command="{Binding Path=OperatorPress}"  CommandParameter="+"/>

Can download source code from here.