Auto Update of Values in UI WPF form - wpf

Question

I have a class as follows:
Public Class BillAmounts
Implements INotifyPropertyChanged
Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
Private Sub NotifyPropertyChange(ByVal info As String)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(info))
End Sub
Private _LabourCostValue As Double
Private _TransportPriceValue As Double
Private _ItemsTotalCost_ As Double
Private _FinalPriceValue As Double
Property TransportPrice As Double
Get
Return _TransportPriceValue
End Get
Set(ByVal value As Double)
If Not _TransportPriceValue = value Then
_TransportPriceValue = value
_FinalPriceValue = TransportPrice + LabourCost + ItemsTotalCost_
PriceCalculationNotification()
End If
End Set
End Property
Property LabourCost As Double
Get
Return _LabourCostValue
End Get
Set(ByVal Value As Double)
If Not _LabourCostValue = Value Then
_LabourCostValue = Value
_FinalPriceValue = TransportPrice + LabourCost + ItemsTotalCost_
PriceCalculationNotification()
End If
End Set
End Property
Property ItemsTotalCost_ As Double
Get
Return _ItemsTotalCost_
End Get
Set(ByVal value As Double)
If Not _ItemsTotalCost_ = value Then
_ItemsTotalCost_ = value
FinalPrice = TransportPrice + LabourCost + ItemsTotalCost_
'NotifyPropertyChange("ItemsTotalCost_")
PriceCalculationNotification()
End If
End Set
End Property
ReadOnly Property TotalPrice As Double
Get
Try
Return ItemsTotalCost_ + TransportPrice + LabourCost
Catch ex As Exception
Return 0
End Try
End Get
'Set(ByVal value As Double)
' If Not _TotalpriceValue = value Then
' _TotalpriceValue = value
' NotifyPropertyChange("TotalPrice")
' End If
'End Set
End Property
Property FinalPrice As Double
Get
Return _FinalPriceValue
End Get
Set(ByVal value As Double)
If Not _FinalPriceValue = value Then
_FinalPriceValue = value
PriceCalculationNotification()
End If
End Set
End Property
ReadOnly Property Discount_ As Double
Get
'_Discount_ = FinalPrice - TotalPrice
'Return _Discount_
Return FinalPrice - TotalPrice
End Get
End Property
Public Sub New()
_TransportPriceValue = 0
_LabourCostValue = 0
_ItemsTotalCost_ = 0
_FinalPriceValue = 0
End Sub
Private Sub PriceCalculationNotification()
NotifyPropertyChange("TransportPrice")
NotifyPropertyChange("LabourCost")
NotifyPropertyChange("Discount_")
NotifyPropertyChange("TotalPrice")
NotifyPropertyChange("FinalPrice")
End Sub
End Class
I have the bound the fields as follows:
<StackPanel Name="AmountStack" Orientation="Vertical" >
<Grid Margin="5">
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition />
<ColumnDefinition Width="30"/>
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<TextBlock Text="Transport" Grid.Column="0" Grid.Row="0" VerticalAlignment="Center" />
<TextBox Text="{Binding TransportPrice}" Name="TransportTxtBox" Grid.Column="1" Grid.Row="0" VerticalAlignment="Center" />
<TextBlock Text="Labour" Grid.Column="3" Grid.Row="0" VerticalAlignment="Center" />
<TextBox Text="{Binding LabourCost}" Name="labourTxtBox" Grid.Column="4" Grid.Row="0" VerticalAlignment="Center" />
<TextBlock Text="Total Amount =" VerticalAlignment="Center" Grid.Column="0" Grid.Row="1"/>
<TextBox Text="{Binding TotalPrice}" Name="TotalTextBox" IsReadOnly="True" Grid.Column="1" Grid.Row="1" />
<TextBlock Text="Discount= " VerticalAlignment="Center" Grid.Column="3" Grid.Row="1"/>
<TextBox Text="{Binding Path=Discount_, Mode=OneWay}" IsReadOnly="True" Name="DiscountTextBox" Grid.Column="4" Grid.Row="1" />
</Grid>
<StackPanel Orientation="Horizontal" HorizontalAlignment="Center" Margin="0,5,0,0">
<TextBlock Text="Total Amount = " VerticalAlignment="Center" />
<TextBox Text="{Binding Path=FinalPrice}" Name="FinalTotalTextBox" Width="130" />
</StackPanel>
</StackPanel>
and
AmountStack.DataContext = Bill.Amounts
However, the issue is that TOtalAMount is getting updated automatically but FinalPrice is not getting updated. Any reasons/mistakes I have done. I have tried it a lot in few ways but could not get that working. What i did not understand is that Total amount is getting updated but Final price isn't. Thank you.

Answer 1

Do not use Private _FinalPriceValue to assign value in Setter TransportPrice and LabourCost. Use FinalPrice to raise PriceCalculationNotification() everytime properly.

Answer 2

I do not remember the source but the point is when there is read only property the binding does not work correctly some times and is waiting for a fix in next release, I solved by manually coding for change by text change events.