我正在尝试使用VB.Net在Silverlight中实现多重绑定。我在C＃here中找到了一个非常好的实现参考。我花了一些时间尝试使用各种转换器将其迁移到VB.Net但我仍然没有让它正常工作。所以..
我正在寻找一些参考资料来举例说明如何在VB.Net中完成MultiBinding 。
使用Silverlight 5 beta的示例也没问题（我在Stack Overflow上的帖子right here中读到它支持多重绑定）。
答案 0 :(得分：5)
我已将该示例翻译成Silverlight的VB.NET，可以从here下载。对于后代，代码如下所示。请注意，两者仍处于原作者指定的任何许可条款下。
<强> BindingUtil.vb
Imports System.Collections.Generic
Imports System.Net
Imports System.Windows
Imports System.Windows.Controls
Imports System.Windows.Documents
Imports System.Windows.Ink
Imports System.Windows.Input
Imports System.Windows.Media
Imports System.Windows.Media.Animation
Imports System.Windows.Shapes
Imports System.Windows.Data
Imports System.ComponentModel
Namespace SLMultiBinding
''' <summary>
''' Provides a mechanism for attaching a MultiBinding to an element
''' </summary>
Public Class BindingUtil
#Region "DataContextPiggyBack attached property"
''' <summary>
''' DataContextPiggyBack Attached Dependency Property, used as a mechanism for exposing
''' DataContext changed events
''' </summary>
Public Shared ReadOnly DataContextPiggyBackProperty As DependencyProperty = DependencyProperty.RegisterAttached("DataContextPiggyBack", GetType(Object), GetType(BindingUtil), New PropertyMetadata(Nothing, New PropertyChangedCallback(AddressOf OnDataContextPiggyBackChanged)))
Public Shared Function GetDataContextPiggyBack(d As DependencyObject) As Object
Return DirectCast(d.GetValue(DataContextPiggyBackProperty), Object)
End Function
Public Shared Sub SetDataContextPiggyBack(d As DependencyObject, value As Object)
d.SetValue(DataContextPiggyBackProperty, value)
End Sub
''' <summary>
''' Handles changes to the DataContextPiggyBack property.
''' </summary>
Private Shared Sub OnDataContextPiggyBackChanged(d As DependencyObject, e As DependencyPropertyChangedEventArgs)
Dim targetElement As FrameworkElement = TryCast(d, FrameworkElement)
' whenever the targeElement DataContext is changed, copy the updated property
' value to our MultiBinding.
Dim relay As MultiBindings = GetMultiBindings(targetElement)
relay.SetDataContext(targetElement.DataContext)
End Sub
#End Region
#Region "MultiBindings attached property"
Public Shared Function GetMultiBindings(obj As DependencyObject) As MultiBindings
Return DirectCast(obj.GetValue(MultiBindingsProperty), MultiBindings)
End Function
Public Shared Sub SetMultiBindings(obj As DependencyObject, value As MultiBindings)
obj.SetValue(MultiBindingsProperty, value)
End Sub
Public Shared ReadOnly MultiBindingsProperty As DependencyProperty = DependencyProperty.RegisterAttached("MultiBindings", GetType(MultiBindings), GetType(BindingUtil), New PropertyMetadata(Nothing, AddressOf OnMultiBindingsChanged))
''' <summary>
''' Invoked when the MultiBinding property is set on a framework element
''' </summary>
Private Shared Sub OnMultiBindingsChanged(depObj As DependencyObject, e As DependencyPropertyChangedEventArgs)
Dim targetElement As FrameworkElement = TryCast(depObj, FrameworkElement)
' bind the target elements DataContext, to our DataContextPiggyBack property
' this allows us to get property changed events when the targetElement
' DataContext changes
targetElement.SetBinding(DataContextPiggyBackProperty, New Binding())
Dim bindings As MultiBindings = GetMultiBindings(targetElement)
bindings.Initialize(targetElement)
End Sub
#End Region
End Class
End Namespace
<强> IMultiValueConverter.vb
Imports System.Net
Imports System.Windows
Imports System.Windows.Controls
Imports System.Windows.Documents
Imports System.Windows.Ink
Imports System.Windows.Input
Imports System.Windows.Media
Imports System.Windows.Media.Animation
Imports System.Windows.Shapes
Imports System.Globalization
Namespace SLMultiBinding
''' <summary>
''' see: http://msdn.microsoft.com/en-us/library/system.windows.data.imultivalueconverter.aspx
''' </summary>
Public Interface IMultiValueConverter
Function Convert(values As Object(), targetType As Type, parameter As Object, culture As CultureInfo) As Object
Function ConvertBack(value As Object, targetTypes As Type(), parameter As Object, culture As CultureInfo) As Object()
End Interface
End Namespace
<强> MultiBinding.vb
Imports System.Diagnostics
Imports System.Windows
Imports System.Windows.Controls
Imports System.Windows.Data
Imports System.Collections.ObjectModel
Imports System.Windows.Markup
Imports System.ComponentModel
Imports System.Collections.Generic
Imports System.Globalization
Namespace SLMultiBinding
''' <summary>
''' Implements MultiBinding by creating a BindingSlave instance for each of the Bindings.
''' PropertyChanged events for the BindingSlae.Value property are handled, and the IMultiValueConveter
''' is used to compute the converted value.
''' </summary>
<ContentProperty("Bindings")> _
Public Class MultiBinding
Inherits Panel
Implements INotifyPropertyChanged
''' <summary>
''' Indicates whether the converted value property is currently being updated
''' as a result of one of the BindingSlave.Value properties changing
''' </summary>
Private _updatingConvertedValue As Boolean
#Region "ConvertedValue dependency property"
Public Shared ReadOnly ConvertedValueProperty As DependencyProperty = DependencyProperty.Register("ConvertedValue", GetType(Object), GetType(MultiBinding), New PropertyMetadata(Nothing, AddressOf OnConvertedValuePropertyChanged))
''' <summary>
''' This dependency property is set to the resulting output of the
''' associated Converter.
''' </summary>
Public Property ConvertedValue() As Object
Get
Return GetValue(ConvertedValueProperty)
End Get
Set(value As Object)
SetValue(ConvertedValueProperty, value)
End Set
End Property
Private Shared Sub OnConvertedValuePropertyChanged(depObj As DependencyObject, e As DependencyPropertyChangedEventArgs)
Dim relay As MultiBinding = TryCast(depObj, MultiBinding)
Debug.Assert(relay IsNot Nothing)
relay.OnConvertedValuePropertyChanged()
End Sub
''' <summary>
''' Handles propety changes for the ConvertedValue property
''' </summary>
Private Sub OnConvertedValuePropertyChanged()
OnPropertyChanged("ConvertedValue")
' if the value is being updated, but not due to one of the multibindings
' then the target property has changed.
If Not _updatingConvertedValue Then
' convert back
Dim convertedValues As Object() = Converter.ConvertBack(ConvertedValue, Nothing, ConverterParameter, CultureInfo.InvariantCulture)
' update all the binding slaves
If Children.Count = convertedValues.Length Then
For index As Integer = 0 To convertedValues.Length - 1
DirectCast(Children(index), BindingSlave).Value = convertedValues(index)
Next
End If
End If
End Sub
#End Region
#Region "CLR properties"
''' <summary>
''' The BindingMode
''' </summary>
Public Property Mode() As BindingMode
Get
Return m_Mode
End Get
Set(value As BindingMode)
m_Mode = value
End Set
End Property
Private m_Mode As BindingMode
''' <summary>
''' The target property on the element which this MultiBinding is assocaited with.
''' </summary>
Public Property TargetProperty() As String
Get
Return m_TargetProperty
End Get
Set(value As String)
m_TargetProperty = value
End Set
End Property
Private m_TargetProperty As String
''' <summary>
''' The Converter which is invoked to compute the result of the multiple bindings
''' </summary>
Public Property Converter() As IMultiValueConverter
Get
Return m_Converter
End Get
Set(value As IMultiValueConverter)
m_Converter = value
End Set
End Property
Private m_Converter As IMultiValueConverter
''' <summary>
''' The configuration parameter supplied to the converter
''' </summary>
Public Property ConverterParameter() As Object
Get
Return m_ConverterParameter
End Get
Set(value As Object)
m_ConverterParameter = value
End Set
End Property
Private m_ConverterParameter As Object
''' <summary>
''' The bindings, the result of which are supplied to the converter.
''' </summary>
Public Property Bindings() As BindingCollection
Get
Return m_Bindings
End Get
Set(value As BindingCollection)
m_Bindings = value
End Set
End Property
Private m_Bindings As BindingCollection
#End Region
Public Sub New()
Bindings = New BindingCollection()
End Sub
''' <summary>
''' Invoked when any of the BindingSlave's Value property changes.
''' </summary>
Private Sub SlavePropertyChanged(sender As Object, e As PropertyChangedEventArgs)
UpdateConvertedValue()
End Sub
''' <summary>
''' Uses the Converter to update the ConvertedValue in order to reflect
''' the current state of the bindings.
''' </summary>
Private Sub UpdateConvertedValue()
Dim values As New List(Of Object)()
For Each slave As BindingSlave In Children
values.Add(slave.Value)
Next
_updatingConvertedValue = True
ConvertedValue = Converter.Convert(values.ToArray(), GetType(Object), ConverterParameter, CultureInfo.CurrentCulture)
_updatingConvertedValue = False
End Sub
''' <summary>
''' Creates a BindingSlave for each Binding and binds the Value
''' accordingly.
''' </summary>
Friend Sub Initialise(targetElement As FrameworkElement)
Children.Clear()
For Each binding As Binding In Bindings
Dim slave As BindingSlave
' create a binding slave instance
If Not String.IsNullOrEmpty(binding.ElementName) Then
' create an element name binding slave, this slave will resolve the
' binding source reference and construct a suitable binding.
slave = New ElementNameBindingSlave(targetElement, binding)
Else
slave = New BindingSlave()
slave.SetBinding(BindingSlave.ValueProperty, binding)
End If
AddHandler slave.PropertyChanged, AddressOf SlavePropertyChanged
Children.Add(slave)
Next
End Sub
#Region "INotifyPropertyChanged Members"
Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
Protected Sub OnPropertyChanged(name As String)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(name))
End Sub
#End Region
End Class
''' <summary>
''' A simple element with a single Value property, used as a 'slave'
''' for a Binding.
''' </summary>
Public Class BindingSlave
Inherits FrameworkElement
Implements INotifyPropertyChanged
#Region "Value"
Public Shared ReadOnly ValueProperty As DependencyProperty = DependencyProperty.Register("Value", GetType(Object), GetType(BindingSlave), New PropertyMetadata(Nothing, AddressOf OnValueChanged))
Public Property Value() As Object
Get
Return GetValue(ValueProperty)
End Get
Set(value As Object)
SetValue(ValueProperty, value)
End Set
End Property
Private Shared Sub OnValueChanged(depObj As DependencyObject, e As DependencyPropertyChangedEventArgs)
Dim slave As BindingSlave = TryCast(depObj, BindingSlave)
Debug.Assert(slave IsNot Nothing)
slave.OnPropertyChanged("Value")
End Sub
#End Region
#Region "INotifyPropertyChanged Members"
Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
Protected Sub OnPropertyChanged(name As String)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(name))
End Sub
#End Region
End Class
''' <summary>
''' A binding slave that performs 'ElementName' binding.
''' </summary>
Public Class ElementNameBindingSlave
Inherits BindingSlave
Private _multiBindingTarget As FrameworkElement
''' <summary>
''' The source element named in the ElementName binding
''' </summary>
Private _elementNameSource As FrameworkElement
Private _binding As Binding
Public Sub New(target As FrameworkElement, binding As Binding)
_multiBindingTarget = target
_binding = binding
' try to locate the named element
ResolveElementNameBinding()
AddHandler _multiBindingTarget.LayoutUpdated, AddressOf MultiBindingTarget_LayoutUpdated
End Sub
''' <summary>
''' Try to locate the named element. If the element can be located, create the required
''' binding.
''' </summary>
Private Sub ResolveElementNameBinding()
_elementNameSource = TryCast(_multiBindingTarget.FindName(_binding.ElementName), FrameworkElement)
If _elementNameSource IsNot Nothing Then
SetBinding(BindingSlave.ValueProperty, New Binding() With { _
.Source = _elementNameSource, _
.Path = _binding.Path, _
.Converter = _binding.Converter, _
.ConverterParameter = _binding.ConverterParameter _
})
End If
End Sub
Private Sub MultiBindingTarget_LayoutUpdated(sender As Object, e As EventArgs)
' try to locate the named element
ResolveElementNameBinding()
End Sub
End Class
Friend Delegate Sub BindingCollectionChangedCallback()
Public Class BindingCollection
Inherits Collection(Of BindingBase)
' Fields
' TODO: Private ReadOnly _collectionChangedCallback As BindingCollectionChangedCallback
Protected Overrides Sub ClearItems()
MyBase.ClearItems()
OnBindingCollectionChanged()
End Sub
Protected Overrides Sub InsertItem(index As Integer, item As BindingBase)
If item Is Nothing Then
Throw New ArgumentNullException("item")
End If
ValidateItem(item)
MyBase.InsertItem(index, item)
OnBindingCollectionChanged()
End Sub
Private Sub OnBindingCollectionChanged()
' TODO: RaiseEvent _collectionChangedCallback()
End Sub
Protected Overrides Sub RemoveItem(index As Integer)
MyBase.RemoveItem(index)
OnBindingCollectionChanged()
End Sub
Protected Overrides Sub SetItem(index As Integer, item As BindingBase)
If item Is Nothing Then
Throw New ArgumentNullException("item")
End If
ValidateItem(item)
MyBase.SetItem(index, item)
OnBindingCollectionChanged()
End Sub
Private Shared Sub ValidateItem(binding As BindingBase)
If Not (TypeOf binding Is Binding) Then
Throw New NotSupportedException("BindingCollectionContainsNonBinding")
End If
End Sub
End Class
End Namespace
<强> MultiBindings.vb
Imports System.Collections.ObjectModel
Imports System.Linq
Imports System.Reflection
Imports System.Windows
Imports System.Windows.Data
Imports System.Windows.Markup
Namespace SLMultiBinding
''' <summary>
''' Manages the construction of multiple MultiBinding instances
''' </summary>
<ContentProperty("Bindings")> _
Public Class MultiBindings
Inherits FrameworkElement
Private _targetElement As FrameworkElement
''' <summary>
''' Gets / sets the collection of MultiBindings
''' </summary>
Public Property Bindings() As ObservableCollection(Of MultiBinding)
Get
Return m_Bindings
End Get
Set(value As ObservableCollection(Of MultiBinding))
m_Bindings = Value
End Set
End Property
Private m_Bindings As ObservableCollection(Of MultiBinding)
Public Sub New()
Bindings = New ObservableCollection(Of MultiBinding)()
End Sub
''' <summary>
''' Sets the DataContext of each of the MultiBinding instances
''' </summary>
Public Sub SetDataContext(dataContext As Object)
For Each relay As MultiBinding In Bindings
relay.DataContext = dataContext
Next
End Sub
''' <summary>
''' Initialises each of the MultiBindings, and binds their ConvertedValue
''' to the given target property.
''' </summary>
Public Sub Initialize(targetElement As FrameworkElement)
_targetElement = targetElement
Const DpFlags As BindingFlags = BindingFlags.[Public] Or BindingFlags.[Static] Or BindingFlags.FlattenHierarchy
For Each relay As MultiBinding In Bindings
relay.Initialise(targetElement)
' find the target dependency property
Dim targetType As Type = Nothing
Dim targetProperty As String = Nothing
' assume it is an attached property if the dot syntax is used.
If relay.TargetProperty.Contains(".") Then
' split to find the type and property name
Dim parts As String() = relay.TargetProperty.Split("."c)
targetType = Type.[GetType]("System.Windows.Controls." & parts(0) & ", System.Windows, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e")
targetProperty = parts(1)
Else
targetType = targetElement.[GetType]()
targetProperty = relay.TargetProperty
End If
Dim sourceFields As FieldInfo() = targetType.GetFields(DpFlags)
Dim targetDependencyPropertyField As FieldInfo = sourceFields.First(Function(i) i.Name = targetProperty & "Property")
Dim targetDependencyProperty As DependencyProperty = TryCast(targetDependencyPropertyField.GetValue(Nothing), DependencyProperty)
' bind the ConvertedValue of our MultiBinding instance to the target property
' of our targetElement
Dim binding As New Binding("ConvertedValue") With { _
.Source = relay, _
.Mode = relay.Mode _
}
targetElement.SetBinding(targetDependencyProperty, Binding)
Next
End Sub
End Class
End Namespace
<强> TitleConverter.vb
Imports System.Net
Imports System.Windows
Imports System.Windows.Controls
Imports System.Windows.Data
Imports System.Windows.Documents
Imports System.Windows.Ink
Imports System.Windows.Input
Imports System.Windows.Media
Imports System.Windows.Media.Animation
Imports System.Windows.Shapes
Namespace SLMultiBinding
Public Class TitleConverter
Implements IMultiValueConverter
#Region "IMultiValueConverter Members"
Public Function Convert(values As Object(), targetType As Type, parameter As Object, culture As System.Globalization.CultureInfo) As Object Implements IMultiValueConverter.Convert
Dim forename As String = TryCast(values(0), String)
Dim surname As String = TryCast(values(1), String)
Return String.Format("{0}, {1}", surname, forename)
End Function
Public Function ConvertBack(value As Object, targetTypes As Type(), parameter As Object, culture As System.Globalization.CultureInfo) As Object() Implements IMultiValueConverter.ConvertBack
Dim source As String = TryCast(value, String)
Dim pos = source.IndexOf(", ")
Dim forename As String = source.Substring(pos + 2)
Dim surname As String = source.Substring(0, pos)
Return New Object() {forename, surname}
End Function
#End Region
End Class
End Namespace