VB.NET Databound Label not updating - vb.net

Question

I am having issues with a label with a databound text value updating. I have a Class that calculates the best throw of an athlete and this is bound to a label in my form. The class is as follows
Imports System.ComponentModel
Imports System.Runtime.CompilerServices
Public Class Competition
Public Sub New()
Competitors = New List(Of Competitor)()
End Sub
Public Property Competitors() As List(Of Competitor)
Get
Return m_Competitors
End Get
Set(value As List(Of Competitor))
m_Competitors = value
End Set
End Property
Private m_Competitors As List(Of Competitor)
Public ReadOnly Property CurrentPlacings() As List(Of Competitor)
Get
Return Competitors.OrderByDescending(Function(c) c.BestThrow).ToList()
End Get
End Property
End Class
Public Class Competitor
Implements System.ComponentModel.INotifyPropertyChanged
Public Event PropertyChanged(sender As Object,
e As System.ComponentModel.PropertyChangedEventArgs) _
Implements System.ComponentModel.INotifyPropertyChanged.PropertyChanged
Public Sub New()
Throws = New List(Of [Throw])()
End Sub
Public Property FirstName() As String
Get
Return m_FirstName
End Get
Set(value As String)
m_FirstName = value
End Set
End Property
Private m_FirstName As String
Public Property LastName() As String
Get
Return m_LastName
End Get
Set(value As String)
m_LastName = value
End Set
End Property
Private m_LastName As String
Public Property compNumber() As String
Get
Return m_compNumb
End Get
Set(value As String)
m_compNumb = value
End Set
End Property
Private m_compNumb As String
Public Property club() As String
Get
Return m_club
End Get
Set(value As String)
m_club = value
End Set
End Property
Private m_club As String
Public Property Throws() As List(Of [Throw])
Get
Return m_Throws
End Get
Set(value As List(Of [Throw]))
m_Throws = value
End Set
End Property
Private m_Throws As List(Of [Throw])
Public ReadOnly Property BestThrow() As Object
Get
Dim bt = Throws.Where(Function(t) t.Status = ThrowStatus.Valid).OrderByDescending(Function(t) t.Distance).First()
If (IsNothing(bt.Distance)) Then
bt.Distance = "0"
End If
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("BestThrow"))
Return bt
End Get
End Property
Public ReadOnly Property getLabel
Get
Return compNumber & " " & LastName & ", " & FirstName & vbCrLf & club
End Get
End Property
End Class
Public Enum ThrowStatus
Valid
Pass
Foul
End Enum
Public Class [Throw]
Implements INotifyPropertyChanged
Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
Public Property Status() As ThrowStatus
Get
Return m_Status
End Get
Set(value As ThrowStatus)
m_Status = value
End Set
End Property
Private m_Status As ThrowStatus
Public Property Distance() As String
Get
If Status = ThrowStatus.Valid Then
If (m_Distance > 0) Then
Return m_Distance
Else
Return Nothing
End If
ElseIf Status = ThrowStatus.Pass Then
Return "PASS"
ElseIf Status = ThrowStatus.Foul Then
Return "FOUL"
Else
Return Nothing
End If
End Get
Set(value As String)
If (value > 0) Then
If (IsNumeric(value)) Then
m_Distance = value
Status = ThrowStatus.Valid
ElseIf (value = "foul") Then
Status = ThrowStatus.Foul
ElseIf (value = "pass") Then
Status = ThrowStatus.Pass
Else
Status = ThrowStatus.Valid
m_Distance = Nothing
End If
Else
m_Distance = Nothing
Status = ThrowStatus.Valid
End If
OnPropertyChanged("Distance")
End Set
End Property
Protected Sub OnPropertyChanged(ByVal name As String)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(name))
End Sub
Private m_Distance As Decimal
Public Property attempt() As Integer
Get
Return m_attempt
End Get
Set(value As Integer)
m_attempt = value
End Set
End Property
Private m_attempt As Integer
End Class
The line that databinds for the Label is as follows:
best.DataBindings.Add(New Binding("text", athlete.BestThrow, "distance", False, DataSourceUpdateMode.OnPropertyChanged))
I can tell that the Property BestThrow is defintely being updated using Watch however for some reason the label seems to only reflect Throw(0).Distance and not BestThrow.Distance
I can change Throw(0) and the label will change, if I add a bigger number to any of the other 5 attempts and Watch the value I can see that the BestThrow is being updated.
Thanks in advance for your assistance.
Mark

Answer 1

I think you have a wrong prespective, property BestThrow is never updated because it has no setter. When you check BestThrow value using watch, it 'recalculated' because you request the value. What you need is to find a way to raise Property Changed event for BestThrow whenever item added or removed from Throws because BestThrow value depends on Throws. After event raised, UI will call BestThrow's getter again looking for updated value.
'You need to execute this code to notify UI that `BestThrow` value has changed
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("BestThrow"))
Raisng the event can be done manually after code for adding/removing item to/from Throws property, or you can make Throws an ObservableCollection of Throw then listen to Collection Changed event. Then in the event handler you can raise BestThrow property changed event.