将ObservableCollection(Of T) 数据 绑定到 Canvas(2)

上回说到用ItemsContorl装Canvas的方式，给Canvas绑定集合属性。

还是｛Prism｝的建议，通过AttachProperty给Canvas加一个Helper。

代码

自定义类

  1: Imports System.Collections.ObjectModel

  2: 

  3: Public Class CanvasItemsHelper

  4: 

  5:     Public Shared ReadOnly ItemListProperty As DependencyProperty = _

  6:         DependencyProperty.RegisterAttached("ItemList", GetType(ObservableCollection(Of String)), _

  7:                                             GetType(CanvasItemsHelper), New PropertyMetadata( _

  8:                                                 Nothing, New PropertyChangedCallback(AddressOf OnItemListPropertyChanged)))

  9: 

 10:     Public Shared Sub OnItemListPropertyChanged(ByVal dp As DependencyObject, ByVal e As DependencyPropertyChangedEventArgs)

 11:         Dim can As Canvas = CType(dp, Canvas)

 12:         If can.Children.Count = 0 Then

 13:             For Each s As String In e.NewValue

 14:                 Dim newTextBlock As New TextBlock

 15:                 newTextBlock.Background = Brushes.LightBlue

 16:                 newTextBlock.Text = s

 17:                 can.Children.Add(newTextBlock)

 18:             Next

 19:         End If

 20:     End Sub

 21: 

 22:     Public Shared Sub SetItemList(ByVal e As UIElement, ByVal o As ObservableCollection(Of String))

 23:         e.SetValue(ItemListProperty, o)

 24:     End Sub

 25: 

 26:     Public Shared Function GetItemList(ByVal e As UIElement) As ObservableCollection(Of String)

 27:         Return e.GetValue(ItemListProperty)

 28:     End Function

 29: 

 30:     Public Sub New()

 31: 

 32:     End Sub

 33: End Class

 

通过Attach属性，将Canvas的Children做处理，这里我为了实验，只是简单的将绑定的数据 加入到Canvas中，实际上应该

做更复杂的处理，随着绑定集合的变化，变化内容。那是实际应用当中的事情了。

 

如果希望自定义类可以在Xaml编辑器中给出local：xxx的提示，则需要满足一个条件，存在Setxxx（arg1，arg2）的格式的

Shared 方法，在C#中为Static关键字。

 

Xaml文中 在 Canvas中加入CanvasItemsHelper属性，并进行绑定。

  1: <Window x:Class="MainWindow" x:Name="mainWindow"

  2:     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

  3:     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 

  4:     xmlns:local="clr-namespace:AttachProertyTest"

  5:     Title="MainWindow" Height="350" Width="525">

  6:     <Grid>

  7:         <Canvas local:CanvasItemsHelper.ItemList="{Binding ElementName=mainWindow, Path=NameList}"></Canvas>

  8:     </Grid>

  9: </Window>

 10: 

后台代码

  1: 

  2: Imports System.Collections.ObjectModel

  3: 

  4: Class MainWindow

  5: 

  6:     '

  7:     'NameList As ObservableCollection(Of String)

  8:     '

  9:     Private mNameList As ObservableCollection(Of String)

 10:     Public Property NameList() As ObservableCollection(Of String)

 11:         Get

 12:             Return mNameList

 13:         End Get

 14:         Set(ByVal Value As ObservableCollection(Of String))

 15:             mNameList = Value

 16:         End Set

 17:     End Property

 18: 

 19: 

 20:     Public Sub New()

 21:         NameList = New ObservableCollection(Of String)

 22:         NameList.Add("HelloAttachProerty")

 23:         ' 此调用是设计器所必需的。

 24:         InitializeComponent()

 25: 

 26:         ' 在 InitializeComponent() 调用之后添加任何初始化。

 27: 

 28:     End Sub

 29: End Class

 30: 

 

以上，两篇随笔，描述了如何实现 为Canvas绑定集合元素，再次重申不是为了绑定而绑定。希望给新手一些参考。

再会。