Class Propert definition

Question

I have a class - Trav with a property Bearing

I am using WinForms VB.Net

I want to enter the string value in a textbox, validate entry and save value as a double so that I can use it in calculations. I want to return the value for display as a formatted string using INotifyPropertyChanged

Can I get some assistance on Property definition eg.

Public Property DisplayBear As String
        Get
            Return mDisplayBear
        End Get
        Set(value As String)
            If String.IsNullOrEmpty(value) Then
                value = "0"
            End If
            If ValidAngle(value) Then
                mDisplayBear = value
                NotifyPropertyChanged()
            Else
                Throw New Exception("Invalid Angle. Enter ddd.mmssss")
            End If

        End Set
    End Property

Thanks

Answer 1

Perhaps use a custom TextBox e.g.

Public Class NumericTextbox
    Inherits TextBox

    Const WM_PASTE As Integer = &H302
    <Browsable(False)>
    Public ReadOnly Property AsDouble As Double
        Get
            If String.IsNullOrWhiteSpace(Text) Then
                Return 0
            Else
                Return CDbl(Text)
            End If
        End Get
    End Property
    Public ReadOnly Property AsDecimal As Decimal
        Get
            If String.IsNullOrWhiteSpace(Text) Then
                Return 0
            Else
                Return CDec(Text)
            End If
        End Get
    End Property
    Public ReadOnly Property AsInteger As Integer
        Get
            If String.IsNullOrWhiteSpace(Text) Then
                Return 0
            Else
                Return CInt(Text)
            End If
        End Get
    End Property
    Public ReadOnly Property IsInteger As Boolean
        Get
            If Integer.TryParse(Text, Nothing) Then
                Return True
            Else
                Return False
            End If
        End Get
    End Property
    Public Sub SetDoubleValue(value As Double)
        Text = value.ToString()
    End Sub
    Public Sub SetInteger(value As Integer)
        Text = value.ToString()
    End Sub
    Public Sub SetDecimal(value As Decimal)
        Text = value.ToString()
    End Sub
    Protected Overrides Sub OnKeyPress(ByVal e As KeyPressEventArgs)
        Dim value As String = Text
        value = value.Remove(SelectionStart, SelectionLength)
        value = value.Insert(SelectionStart, e.KeyChar)

        e.Handled = value.LastIndexOf("-", StringComparison.Ordinal) > 0 Or Not (Char.IsControl(e.KeyChar) OrElse
            Char.IsDigit(e.KeyChar) OrElse (e.KeyChar = "."c And Not Text.Contains(".") Or
            e.KeyChar = "."c And MyBase.SelectedText.Contains(".")) OrElse
            (e.KeyChar = "-"c And SelectionStart = 0))

        MyBase.OnKeyPress(e)

    End Sub
    Protected Overrides Sub WndProc(ByRef m As Message)

        If m.Msg = WM_PASTE Then

            Dim value As String = Text

            value = value.Remove(SelectionStart, SelectionLength)
            value = value.Insert(SelectionStart, Clipboard.GetText)

            Dim result As Decimal = 0
            If Not Decimal.TryParse(value, result) Then
                Return
            End If

        End If

        MyBase.WndProc(m)

    End Sub
End Class

Example class

Note I don't know the rules for validating the angle so I simply did a hard-wired dummy rule.

Public Class Example
    Implements INotifyPropertyChanged

    Private _displayBear As Double

    Public Property DisplayBear As Double
        Get
            Return _displayBear
        End Get
        Set

            If ValidAngle(Value) Then
                Console.WriteLine("Valid")
                _displayBear = Value
                OnPropertyChanged()
            Else
                Console.WriteLine("No valid")
            End If

        End Set
    End Property
    Private Function ValidAngle(value As Double) As Boolean
        If value = 10D Then
            Return True
        Else
            Return False
        End If
    End Function
    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged

    Protected Overridable Sub OnPropertyChanged(<CallerMemberName> Optional ByVal propertyName As String = Nothing)
        PropertyChangedEvent?.Invoke(Me, New PropertyChangedEventArgs(propertyName))
    End Sub
End Class

Here the TextBox above is used.

Usage 1

    Private Sub BearButton_Click(sender As Object, e As EventArgs) Handles Button3.Click
        Dim example As New Example With {.DisplayBear = BearNumericTextbox.AsDouble}
    End Sub

Usage 2

Private _example As New Example
Private Sub BearButton_Click(sender As Object, e As EventArgs) Handles Button3.Click
    _example.DisplayBear = BearNumericTextbox.AsDouble
End Sub

Answer 2

@Karen Payne MVP - many thanks for your reply. I'll try this in my code.