BindingGroup.Items Property


Gets the sources that are used by the Binding objects in the BindingGroup.

Namespace:   System.Windows.Data
Assembly:  PresentationFramework (in PresentationFramework.dll)

Public ReadOnly Property Items As IList

Property Value

Type: System.Collections.IList

The sources that are used by the Binding objects in the BindingGroup.

Each object that is used as a source is added into the Items property once, even if the object is used as the source for multiple bindings. Often, there is just one item in Items, which is the object that is the DataContext of the element that uses the BindingGroup. It is possible for a BindingGroup to have multiple sources, however. For example, if Binding objects share the same BindingGroupName but use different source objects, each object that is used as a source is in Items.

There can also be multiple objects in Items if the path of a Binding resolves to a nested property of the source. For example, suppose a TextBox control's binding is a part of a BindingGroup and its DataContext is a Customer object, which has a property of type Address. If the Path of the Binding is the Address.ZipCode property, the Address is added to the Items property.

The following examples are part of an application that checks whether the user has set the properties of two objects to equal values. The first example creates two TextBox controls, each of which are data bound to a different source. The binding of the first TextBox gets its source, object1, from the DataContext of the TextBox control's parent element (the StackPanel). On the second TextBox, the source of the binding is set to object2. The example also creates a Label that displays validation errors.

<StackPanel Name="sp1"
            DataContext="{Binding Source={StaticResource object1}}"
            Validation.ValidationAdornerSite="{Binding ElementName=label1}"

    <BindingGroup Name="bindingGroup">
        <src:BindingGroupValidationRule ValidatesOnTargetUpdated="True" />

  <TextBlock Text="First string" />

  <TextBox Width="150"
           Text="{Binding Path=PropertyA}" />

  <TextBlock Text="Second string" />

  <TextBox Width="150"
           Text="{Binding Source={StaticResource object2}, 
    Path=PropertyB, BindingGroupName=bindingGroup, 
    TargetNullValue=please enter a string}" />

<Label Name="label1"
       Content="{Binding ElementName=sp1, Path=(Validation.Errors)[0].ErrorContent}"
       HorizontalAlignment="Center" />

The following example shows the ValidationRule that the previous example uses. In the Validate method, the example gets each source object from the BindingGroup and checks whether the properties of the objects are equal.

Public Class Type1
    Public Property PropertyA() As String

    Public Sub New()
        PropertyA = "Default Value"
    End Sub
End Class

Public Class Type2
    Public Property PropertyB() As String

    Public Sub New()
    End Sub
End Class

Public Class BindingGroupValidationRule
    Inherits ValidationRule
    Public Overrides Function Validate(ByVal value As Object, ByVal cultureInfo As System.Globalization.CultureInfo) As ValidationResult
        Dim bg As BindingGroup = TryCast(value, BindingGroup)

        Dim object1 As Type1 = Nothing
        Dim object2 As Type2 = Nothing

        For Each item As Object In bg.Items
            If TypeOf item Is Type1 Then
                object1 = TryCast(item, Type1)
            End If

            If TypeOf item Is Type2 Then
                object2 = TryCast(item, Type2)
            End If
        Next item

        If object1 Is Nothing OrElse object2 Is Nothing Then
            Return New ValidationResult(False, "BindingGroup did not find source object.")
        End If

        Dim string1 As String = TryCast(bg.GetValue(object1, "PropertyA"), String)
        Dim string2 As String = TryCast(bg.GetValue(object2, "PropertyB"), String)

        If string1 <> string2 Then
            Return New ValidationResult(False, "The two strings must be identical.")
        End If

        Return ValidationResult.ValidResult

    End Function

End Class

.NET Framework
Available since 3.0
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