I have two textboxes on a wpf window that contain numeric values; call them txt1 and txt2. I want a third textbox (txt3) to show the difference between those two values.
I created a Property in code-behind called Diff defined as:
Diff = Cdec(txt1.Text) - Cdec(txt2.Text)
and bound that value as follows:
txt3.Text={Binding Path=Diff
However, at run-time the Property Diff is not found. How do I make that value available to be bound?
Hi Roger, don't forget:
set DataContext or Source
Notify property changed
check input for invalid decimal numbers
Try following simple demo.
XAML:
<Window x:Class="Window014"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WpfApp1"
mc:Ignorable="d"
Title="Window014" Height="450" Width="800" Loaded="Window_Loaded">
<StackPanel>
<TextBox x:Name="txt1" Margin="5" />
<TextBox x:Name="txt2" Margin="5"/>
<TextBox Text="{Binding Diff}" Margin="5"/>
</StackPanel>
</Window>
CodeBehind:
Imports System.ComponentModel
Imports System.Runtime.CompilerServices
Public Class Window014
Implements INotifyPropertyChanged
Private Sub Window_Loaded(sender As Object, e As RoutedEventArgs)
Me.DataContext = Me
End Sub
Private Sub txt_TextChanged(sender As Object, e As TextChangedEventArgs) Handles txt1.TextChanged, txt2.TextChanged
Dim dec1 As Decimal = 0
Decimal.TryParse(txt1.Text, dec1)
Dim dec2 As Decimal = 0
Decimal.TryParse(txt2.Text, dec2)
Diff = dec1 - dec2
OnPropChanged(NameOf(Diff))
End Sub
Public Property Diff As Decimal
Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
Private Sub OnPropChanged(<CallerMemberName> Optional propName As String = "")
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propName))
End Sub
End Class
I like this approach, Peter, it's clean and simple. Except, as I explained to Alex, I cannot changed the DataContext of the window because so many other controls on the window use a different DataContext.
I tried several ways to modify your approach to see if I could work around the DataContext issue but finally gave up. Now I just compute the value and assign it to the tb3.Text property. Nevertheless, thanks for the help.
Hi Roger, you can set the DataContext only for whole TextBox:
<TextBox x:Name="txt1" Margin="5" />
<TextBox x:Name="txt2" Margin="5"/>
<TextBox x:Name="txt3" Text="{Binding Diff}" Margin="5"/>
Private Sub Window_Loaded(sender As Object, e As RoutedEventArgs)
txt3.DataContext = Me
End Sub
I used your approach to set the DataContext of txt3. I defined Diff as:
Public Property Diff as Decimal
and set the binding of tb3 as:
Text="{Binding Path=Diff, Mode=OneWay}"
and implemented INotifyPropertyChanged on the relevant class but I cannot figure out how to implement the change notification. Using these:
OnPropertyChanged(Diff)
OnPropertyChanged("Diff")
OnPropertyChanged(NameOf(Diff"))
all give compile time errors.
If I am on the right track(?) then how do I implement change notification.
Hi Roger, if you cannot use the DataContext you can use Source und assign binding by code:
<TextBox x:Name="txt1" Margin="5" />
<TextBox x:Name="txt2" Margin="5"/>
<TextBox x:Name="txt3" Margin="5"/>
Private Sub Window_Loaded(sender As Object, e As RoutedEventArgs)
txt3.SetBinding(TextBox.TextProperty, New Binding("Diff") With {.Source = Me})
End Sub
Hi Roger, if your property for binding is located in CodeBehind of Window you can work without DataContext and use only RelativeSoure like this:
<TextBox x:Name="txt1" Margin="5" />
<TextBox x:Name="txt2" Margin="5"/>
<TextBox Text="{Binding Diff, RelativeSource={RelativeSource AncestorType=Window}}" Margin="5"/>
Hi Roger, an another approach without using DataContext is to use MultiValueConverter (see Alex):
<TextBox Margin="5" IsReadOnly="True">
<TextBox.Resources>
<local:Converter x:Key="conv"/>
</TextBox.Resources>
<TextBox.Text>
<MultiBinding Converter="{StaticResource conv}">
<Binding Path="Text" ElementName="txt1"/>
<Binding Path="Text" ElementName="txt2"/>
</MultiBinding>
</TextBox.Text>
</TextBox>
Public Function Convert(values() As Object, targetType As Type, parameter As Object, culture As CultureInfo) As Object Implements IMultiValueConverter.Convert
Dim dec1 As Decimal = 0
Decimal.TryParse(values(0).ToString, dec1)
Dim dec2 As Decimal = 0
Decimal.TryParse(values(1).ToString, dec2)
Return (dec1 - dec2).ToString
Welcome to our Microsoft Q&A platform!
I think you can use MultiBinding:
Imports System.ComponentModel
Imports System.Globalization
Imports System.Runtime.CompilerServices
Class MainWindow
Implements INotifyPropertyChanged
Public Sub New()
' This call is required by the designer.
InitializeComponent()
' Add any initialization after the InitializeComponent() call.
Me.DataContext = Me
End Sub
Private _tb1 As String
Public Property tb1() As String
Get
Return _tb1
End Get
Set(value As String)
_tb1 = value
NotifyPropertyChanged("tb1")
End Set
End Property
Private _tb2 As String
Public Property tb2() As String
Get
Return _tb2
End Get
Set(value As String)
_tb2 = value
NotifyPropertyChanged("tb2")
End Set
End Property
Private _Diff As String
Public Property Diff() As String
Get
Return _Diff
End Get
Set(value As String)
_Diff = value
NotifyPropertyChanged("Diff")
End Set
End Property
Public Event PropertyChanged As PropertyChangedEventHandler _
Implements INotifyPropertyChanged.PropertyChanged
Private Sub NotifyPropertyChanged(ByVal info As String)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(info))
End Sub
End Class
Public Class MultiStringStateConverter
Implements IMultiValueConverter
Private Function IMultiValueConverter_Convert(value() As Object, targetType As Type, parameter As Object, culture As CultureInfo) As Object Implements IMultiValueConverter.Convert
Return (System.Convert.ToInt32(value(0)) - System.Convert.ToInt32(value(1))).ToString()
End Function
Private Function IMultiValueConverter_ConvertBack(value As Object, targetTypes() As Type, parameter As Object, culture As CultureInfo) As Object() Implements IMultiValueConverter.ConvertBack
Throw New NotImplementedException()
End Function
End Class
xaml:
<Window.Resources>
<local:MultiStringStateConverter x:Key="MultiStringStateConverter"/>
</Window.Resources>
<StackPanel>
<TextBox Name="txt1" Text="{Binding tb1,UpdateSourceTrigger=PropertyChanged}"/>
<TextBox Name="txt2" Text="{Binding tb2,UpdateSourceTrigger=PropertyChanged}"/>
<TextBox Name="txt3">
<TextBox.Text>
<MultiBinding UpdateSourceTrigger="PropertyChanged" Converter="{StaticResource MultiStringStateConverter}">
<Binding Path="tb1"/>
<Binding Path="tb2"/>
</MultiBinding>
</TextBox.Text>
</TextBox>
</StackPanel>
That's a good solution but I could not use it directly because I cannot set the DataContext of the window to itsself because many other controls rely on a different window context.
I tried numerous approaches using your idea but finally decided to skip the binding approach and just compute the value and assign it to the tb3.Text property. Nevertheless, thanks for the help.
If you don't want set the DataContent to itself,you can use the following code:
Imports System.ComponentModel
Imports System.Globalization
Imports System.Runtime.CompilerServices
Class MainWindow
Public Sub New()
' This call is required by the designer.
InitializeComponent()
' Add any initialization after the InitializeComponent() call.
Me.DataContext = New MyViewModel()
End Sub
End Class
Public Class MyViewModel
Implements INotifyPropertyChanged
Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
Private Sub NotifyPropertyChanged(ByVal info As String)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(info))
End Sub
Private _tb1 As String = 0
Public Property tb1() As String
Get
Return _tb1
End Get
Set(value As String)
_tb1 = value
NotifyPropertyChanged("tb1")
End Set
End Property
Private _tb2 As String = 0
Public Property tb2() As String
Get
Return _tb2
End Get
Set(value As String)
_tb2 = value
NotifyPropertyChanged("tb2")
End Set
End Property
Private _Diff As String
Public Property Diff() As String
Get
Return _Diff
End Get
Set(value As String)
_Diff = value
NotifyPropertyChanged("Diff")
End Set
End Property
End Class
Public Class MultiStringStateConverter
Implements IMultiValueConverter
Private Function IMultiValueConverter_Convert(value() As Object, targetType As Type, parameter As Object, culture As CultureInfo) As Object Implements IMultiValueConverter.Convert
Return (System.Convert.ToInt32(value(0)) - System.Convert.ToInt32(value(1))).ToString()
End Function
Private Function IMultiValueConverter_ConvertBack(value As Object, targetTypes() As Type, parameter As Object, culture As CultureInfo) As Object() Implements IMultiValueConverter.ConvertBack
Throw New NotImplementedException()
End Function
End Class
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