ObservableCollection 类
Private Shared list As New CustomerList Public Shared Function GetList() As CustomerList
Return list
End Function
System.Collections.ObjectModel
Imports System.ComponentModel Public Class CustomerList
Inherits ObservableCollection(Of Customer) Private Shared list As New CustomerList Public Shared Function GetList() As CustomerList
Return list
End Function Private Sub New()
' Make the constructor private, enforcing the "factory" concept
' the only way to create an instance of this class is by calling
' the GetList method.
AddItems()
End Sub Public Shared Sub Reset()
list.ClearItems()
list.AddItems()
End Sub Private Sub AddItems()
Add(New Customer("Maria Anders"))
Add(New Customer("Ana Trujillo"))
Add(New Customer("Antonio Moreno"))
End Sub
End Class
Private Sub AddItems()
Add(New Customer("Maria Anders"))
Add(New Customer("Ana Trujillo"))
Add(New Customer("Antonio Moreno"))
End Sub
Imports System.ComponentModel Public Class Customer
Implements INotifyPropertyChanged Public Event PropertyChanged( _
ByVal sender As Object, _
ByVal e As PropertyChangedEventArgs) _
Implements INotifyPropertyChanged.PropertyChanged Protected Overridable Sub OnPropertyChanged( _
ByVal PropertyName As String) ' Raise the event, and make this procedure
' overridable, should someone want to inherit from
' this class and override this behavior:
RaiseEvent PropertyChanged( _
Me, New PropertyChangedEventArgs(PropertyName))
End Sub Public Sub New(ByVal Name As String)
' Set the backing field so that you don't raise the
' PropertyChanged event when you first create the Customer.
_name = Name
End Sub Private _name As String
Public Property Name() As String
Get
Return _name
End Get
Set(ByVal value As String)
If _name <> value Then
_name = value
OnPropertyChanged("Name")
End If
End Set
End Property
End Class
Public Event PropertyChanged( _
ByVal sender As Object, _
ByVal e As PropertyChangedEventArgs) _
Implements INotifyPropertyChanged.PropertyChanged
Protected Overridable Sub OnPropertyChanged( _
ByVal PropertyName As String) ' Raise the event, and make this procedure
' overridable, should someone want to inherit from
' this class and override this behavior:
RaiseEvent PropertyChanged( _
Me, New PropertyChangedEventArgs(PropertyName))
End Sub
Private _name As String
Public Property Name() As String
Get
Return _name
End Get
Set(ByVal value As String)
If _name <> value Then
_name = value
OnPropertyChanged("Name")
End If
End Set
End Property
<ListBox
DisplayMemberPath="Name"
ItemsSource=
"{Binding ElementName=MainWindow, Path=Data}"
Grid.Column="3" Grid.RowSpan="3" Name="ItemListBox"
Margin="5" />
Public WithEvents Data As CustomerList = CustomerList.GetList()
<Application x:Class="Application"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Startup="Application_Startup"> <Application.Resources> </Application.Resources>
</Application>
Private Sub Application_Startup( _
ByVal sender As System.Object, _
ByVal e As System.Windows.StartupEventArgs) Dim window As New MainWindow
window.Title = "Observable Collection 1"
window.Show() window = New MainWindow
window.Title = "Observable Collection 2"
window.Show()
End Sub
- 在 Visual Studio 2008 中,加载并运行示例应用程序。您会在同一窗口中看到两个实例。
- 单击以打开窗口左侧的组合框。请注意,控件包含 0、1 和 2 这三个数字,分别对应当前的三个用户。选择 1,会选中 Ana Trujillo 并将她的名字复制到文本框。
- 在一个窗口中,单击“删除”。Ana Trujillo 会从两个窗口中消失,因为两个 ListBox 控件都已绑定到同一 ObservableCollection 实例,而绑定使得更新会立即显示出来。再次打开组合框,请注意,现在仅会显示两个用户。在每个窗口中都尝试一下此操作,验证两个实例是否都是最新的。
- 再两次单击“删除”,删除所有用户。单击“重置数据”重新填充两个窗口中的列表。
- 在“添加新项”按钮旁边的文本框中,输入您自己的名字,然后单击“添加新项”。新名字即会显示在两个 ListBox 控件中。单击以打开组合框,并验证组合框现在是否包含 0 到 3 四个数字(每个数字分别对应一个用户)。验证两个窗口中的组合框都已更改,很明显,两个窗口的类都收到了指示集合已更改的事件。
- 在一个窗口的 ListBox 中,选择一个名字。在左侧较低的文本框中,修改名字并单击“更改”。首先,会出现一则警报,指示您已更改了属性,将其关闭后,您会立即看到两个窗口中的名字都已更改(请参见图 4)。
Public WithEvents Data As CustomerList = CustomerList.GetList()
Private Sub Data_CollectionChanged( _
ByVal sender As Object, _
ByVal e As NotifyCollectionChangedEventArgs) _
Handles Data.CollectionChanged ' Because the collection raises this event, you can modify your user
' interface on any window that displays controls bound to the data. On
' both windows, if you add or remove an item, all the controls update
' to indicate the new collection! ' Did you add or remove an item in the collection?
If e.Action = NotifyCollectionChangedAction.Add Or _
e.Action = NotifyCollectionChangedAction.Remove Then ' Set the list of integers in the combo box:
SetComboDataSource() ' Enable buttons as necessary:
EnableButtons()
End If
End Sub
参数 | 说明 |
---|---|
Action | 检索引发事件的操作的相关信息。此属性包含 NotifyCollectionChangedAction 值,该值可以是 Add、Remove、Replace、Move 或 Reset。 |
NewItems | 检索更改集合时引入的新项目的列表。 |
NewStartingIndex | 检索发生更改的集合的索引。 |
OldItems | 检索受“替换”、“删除”或“移动”操作影响的旧项目列表。 |
OldStartingIndex | 检索执行了“替换”、“删除”或“移动”操作的集合的索引。 |
If e.Action = NotifyCollectionChangedAction.Add Or _
e.Action = NotifyCollectionChangedAction.Remove Then
Private Sub SetComboDataSource()
' Set the list of integers shown in the
' combo box:
ItemComboBox.ItemsSource = _
Enumerable.Range(0, Data.Count)
End Sub
Private Sub HookupChangeEventHandler(ByVal cust As Customer)
' Add a PropertyChanged event handler for
' the specified Customer instance:
AddHandler cust.PropertyChanged, _
AddressOf HandlePropertyChanged
End Sub
Private Sub HookupChangeEventHandlers()
For Each cust As Customer In Data
HookupChangeEventHandler(cust)
Next
End Sub
' From DeleteItemButton_Click Dim index As Integer = ItemComboBox.SelectedIndex
If index >= 0 Then
RemoveHandler Data.Item(index).PropertyChanged, _
AddressOf HandlePropertyChanged Data.RemoveAt(index)
' From NewItemButton_Click cust = New Customer(NewItemTextBox.Text)
HookupChangeEventHandler(cust)
Data.Add(cust)
Private Sub HandlePropertyChanged( _
ByVal sender As Object, _
ByVal e As PropertyChangedEventArgs) ' In this particular application, you only want to bother with this
' code for the first window, although both will run the code. In this
' case, if the event was raised by the window whose title is
' "Observable Collection 1" then process the event:
If Me.Title.EndsWith("1") Then
Dim propName As String = e.PropertyName
Dim myCustomer As Customer = CType(sender, Customer) ' Unfortunately, no one hands you the old property value, or the new
' property value. You can use Reflection to retrieve the new property
' value, given the object that raised the event and the name of the
' property:
Dim propInfo As System.Reflection.PropertyInfo = _
GetType(Customer).GetProperty(propName)
Dim value As Object = _
propInfo.GetValue(myCustomer, Nothing) MessageBox.Show(String.Format( _
"You changed the property '{0}' to '{1}'", _
propName, value))
End If
End Sub
If Me.Title.EndsWith("1") Then
'Code removed here…
End If
Dim propName As String = e.PropertyName
Dim myCustomer As Customer = CType(sender, Customer)
Dim propInfo As System.Reflection.PropertyInfo = _
GetType(Customer).GetProperty(propName)
Dim value As Object = _
propInfo.GetValue(myCustomer, Nothing)
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