Custon Control Error Message

Question

Here is the Custom Control:

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:RSComboBox">
    <Style
        TargetType="{x:Type local:CustomComboBox}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate
                    TargetType="{x:Type local:CustomComboBox}">
                    <ComboBox 
                        Height="23"
                        ItemsSource="{Binding Source=SourceItems}"
                        SelectedIndex="{Binding Path=SelectedInteger}" />
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

Public Class CustomComboBox
    Inherits Control
     ....
    Public Property SourceItems As List(Of Integer)
    Public Property SelectedInteger As Integer
End Class

Here is the Project to test it:

<Window
    xmlns:rs="clr-namespace:RSComboBox;assembly=RSComboBox"
    ....
    <rs:CustomComboBox
        SelectedInteger="{Binding Path=MyInteger}"
        SourceItems="{Binding Path=MyList}" />
Window>

Class MainWindow
    Public Sub New(
        InitializeComponent()
        DataContext = Me
    End Sub

    Public ReadOnly Property MyList As List(Of Integer)
        Get
            Return New List(Of Integer) From {1, 2, 3, 4, 5}
        End Get
    End Property

    Private _MyInteger As Integer
    Public Property MyInteger As Integer
        Get
            Return _MyInteger
        End Get
        Set(value As Integer)
            _MyInteger = value
        End Set
     End Property
End Class

When I run the project the ComboBox is not populated properly and generates this error message:

Error: 40 : BindingExpression path error: 'SelectedInteger' property not found on 'object' ''MainWindow' (Name='')'. BindingExpression:Path=SelectedInteger; DataItem='MainWindow' (Name=''); target element is 'ComboBox' (Name=''); target property is 'SelectedIndex' (type 'Int32')

I don't know how to fix this error.

Answer 1

Hi,@ Roger Schlueter. Welcome to Microsoft Q&A. You could set SourceItems and SelectedInteger to Dependency Property. And update MainWindow.vb as follows. MainWindow.xaml.vb:

Imports System.ComponentModel

Public Class MainWindow
    Implements INotifyPropertyChanged

    Public Sub New()
        InitializeComponent()
        DataContext = Me
    End Sub

    Public ReadOnly Property MyList As List(Of Integer)
        Get
            Return New List(Of Integer) From {1, 2, 3, 4, 5}
        End Get
    End Property

    Private _myInteger As Integer
    Public Property MyInteger As Integer
        Get
            Return _myInteger
        End Get
        Set(value As Integer)
            If _myInteger <> value Then
                _myInteger = value
                OnPropertyChanged("MyInteger") ' Notify the UI that the property value has changed
            End If
        End Set
    End Property

    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged

    Protected Sub OnPropertyChanged(propertyName As String)
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
    End Sub
End Class

CustomComboBox.vb:

Public Class CustomComboBox
    Inherits Control
    Public Shared ReadOnly SourceItemsProperty As DependencyProperty = DependencyProperty.Register("SourceItems", GetType(List(Of Integer)), GetType(CustomComboBox), New PropertyMetadata(Nothing))
    Public Property SourceItems As List(Of Integer)
        Get
            Return CType(GetValue(SourceItemsProperty), List(Of Integer))
        End Get
        Set(value As List(Of Integer))
            SetValue(SourceItemsProperty, value)
        End Set
    End Property

    Public Shared ReadOnly SelectedIntegerProperty As DependencyProperty = DependencyProperty.Register("SelectedInteger", GetType(Integer), GetType(CustomComboBox), New PropertyMetadata(0))
    Public Property SelectedInteger As Integer
        Get
            Return CInt(GetValue(SelectedIntegerProperty))
        End Get
        Set(value As Integer)
            SetValue(SelectedIntegerProperty, value)
        End Set
    End Property

    Shared Sub New()
        DefaultStyleKeyProperty.OverrideMetadata(GetType(CustomComboBox), New FrameworkPropertyMetadata(GetType(CustomComboBox)))
    End Sub
End Class

If you still have questions, please feel free to let me know. The problem will be better solved if more details are described (steps, screenshots of error messages, and code to reproduce the problem).

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