Cell ControlTemplate binding to AttachedProperty binding to property of view model

问题

Suppose I have a datagrid whose binded objects are of type ObjectVM:

  Public Class ObjectVM
    Implements INotifyPropertyChanged
    Public Event PropertyChanged(sender As Object, e As System.ComponentModel.PropertyChangedEventArgs) Implements System.ComponentModel.INotifyPropertyChanged.PropertyChanged

    Public Property NestedObject As New NestedVM

End Class

And NestedVM is defined as:

 Public Class NestedVM
    Implements INotifyPropertyChanged
    Public Event PropertyChanged(sender As Object, e As System.ComponentModel.PropertyChangedEventArgs) Implements System.ComponentModel.INotifyPropertyChanged.PropertyChanged

    Private _SubValue As Double
    Private _Value As Double

    Public Property Value As Double
        Get
            Return _Value
        End Get
        Set(value As Double)
            _Value = value
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("Value"))
        End Set
    End Property

    Public Property SubValue As Double
        Get
            Return _SubValue
        End Get
        Set(value As Double)
            _SubValue = value
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("SubValue"))
        End Set
    End Property
End Class

I've defined a datagridtextcolumn where the cellstyle's template has been overridden to contain a second TextBlock. I want the main text of the column to bind to the (nested) property Value, and the second TextBlock to bind to the (nested) property SubValue. To accomplish this an attached property NumberSource (of type Double) has been added to GridColumnProperties. Inside the custom controltemplate, the second Textblock is binded to this NumberSource, and the NumberSource is in turn binded to SubValue:

  <DataGridTextColumn Binding="{Binding NestedObject.Value}" local:GridColumnProperties.NumberSource="{Binding NestedObject.SubValue}" >
                <DataGridTextColumn.CellStyle>
                    <Style TargetType="DataGridCell">
                        <Setter Property="Template" Value="{StaticResource NumberTemplate}"/>
                    </Style>
                </DataGridTextColumn.CellStyle>

However this only seems to work if NumberSource is set to a literal value; it fails when NumberSource is binded like above. Here is the current attached property definition:

Public NotInheritable Class GridColumnProperties
Private Sub New()
End Sub
Public Shared ReadOnly NumberSourceProperty As DependencyProperty = DependencyProperty.RegisterAttached("NumberSource", GetType(Double), GetType(GridColumnProperties), New PropertyMetadata())

Public Shared Sub SetNumberSource(obj As DependencyObject, value As Double)
    obj.SetValue(NumberSourceProperty, value)
End Sub

Public Shared Function GetNumberSource(obj As DependencyObject) As Double
    Return CType(obj.GetValue(NumberSourceProperty), Double)
End Function

End Class

How can I get the dependency property to correctly bind to SubValue?

来源：https://stackoverflow.com/questions/17687305/cell-controltemplate-binding-to-attachedproperty-binding-to-property-of-view-mod

标签

wpf

datagrid

attached-properties