【发布时间】：2013-10-27 04:51:54
【问题描述】：
WPF/VB.net 新手在这里。
我正在尝试过滤数据网格中的行并玩得很开心。
我已经设法创建了一个对象列表并使用 itemsource 属性来获取要填充的数据网格。
现在我有一个复选框，出于参数考虑，我想单击并仅过滤掉与此条件匹配的那些行。
通过下面的代码，我得到了一般的“对象引用未设置为对象的实例”。错误但有点丢失。我相信 VB 专业人士会看到它。
如果可能的话，我宁愿在代码中做更多的事情，而不是 XAML。
这是我的 XAML：
<Window x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid>
<DataGrid x:Name="displayGrid" HorizontalAlignment="Left" Margin="62,94,0,0" VerticalAlignment="Top" Height="142" Width="360" SelectionChanged="DataGrid_SelectionChanged"/>
<Button Content="Load" HorizontalAlignment="Left" Margin="62,51,0,0" VerticalAlignment="Top" Width="75" Click="Button_Click"/>
<CheckBox x:Name="showOnlyChildren" Content="Show Only Children" HorizontalAlignment="Left" Margin="172,51,0,0" VerticalAlignment="Top" Width="147"/>
</Grid>
</Window>
这是我的代码：
Class MainWindow
Class person
Property name
Property age
End Class
Dim listOfPersons As New List(Of person)
Private filteredList As CollectionViewSource
Private Sub DataGrid_SelectionChanged(sender As Object, e As SelectionChangedEventArgs)
End Sub
Private Sub Button_Click(sender As Object, e As RoutedEventArgs)
Dim aPerson As New person With {
.name = "Fred Smith",
.age = 12}
listOfPersons.Add(aPerson)
Dim bPerson As New person With {
.name = "Tom Jones",
.age = 50}
listOfPersons.Add(bPerson)
displayGrid.ItemsSource = CollectionViewSource.GetDefaultView(listOfPersons)
End Sub
Private Sub ShowOnlyChildrenFilter(ByVal sender As Object, ByVal e As FilterEventArgs)
Dim person As person = TryCast(e.Item, person)
If person IsNot Nothing Then
' Filter out persons with age less than 18
If person.age < 19 Then
e.Accepted = True
Else
e.Accepted = False
End If
End If
End Sub
Private Sub AddFiltering(ByVal sender As Object, ByVal args As RoutedEventArgs) Handles showOnlyChildren.Checked
AddHandler filteredList.Filter, AddressOf ShowOnlyChildrenFilter
End Sub
Private Sub RemoveFiltering(ByVal sender As Object, ByVal args As RoutedEventArgs)
RemoveHandler filteredList.Filter, AddressOf ShowOnlyChildrenFilter
End Sub
End Class
编辑：好的，但肯定会到达那里。我合并了一些我发现 here 的更改，感谢我来到这里的帮助......这就是代码现在的样子：
Imports System.ComponentModel
Class MainWindow
Class person
Property name
Property age
End Class
Dim listOfPersons As New List(Of person)
Private filteredList As CollectionViewSource
Dim view As ICollectionView
Private Sub DataGrid_SelectionChanged(sender As Object, e As SelectionChangedEventArgs)
End Sub
Private Sub Button_Click(sender As Object, e As RoutedEventArgs)
Dim aPerson As New person With {
.name = "Fred Smith",
.age = 12}
listOfPersons.Add(aPerson)
Dim bPerson As New person With {
.name = "Tom Jones",
.age = 50}
listOfPersons.Add(bPerson)
view = CollectionViewSource.GetDefaultView(listOfPersons)
displayGrid.ItemsSource = view
End Sub
Function ShowOnlyChildrenFilter(ByVal param As Object) As Boolean
Dim person As person = TryCast(param, person)
Dim retValue As Boolean
If person IsNot Nothing Then
' Filter out persons with age less than 18
If person.age < 19 Then
retValue = True
Else
retValue = False
End If
End If
Return retValue
End Function
Private Sub showOnlyChildren_Checked(sender As Object, e As RoutedEventArgs) Handles showOnlyChildren.Checked
If showOnlyChildren.IsChecked = True Then
view.Filter = New Predicate(Of Object)(AddressOf ShowOnlyChildrenFilter)
Else
'what goes here?
End If
End Sub
End Class
我唯一缺少的是在未选中复选框时如何刷新数据网格。谢谢大家。我仍然惊讶于这是多么复杂和令人费解，因为我认为这很简单。
【问题讨论】：
-
哪一行给出了错误？
-
@Steve AddHandler filteredList.Filter, AddressOf ShowOnlyChildrenFilter，当我单击复选框时。我在 CollectionViewSource 前面添加了 New 关键字，现在它没有错误。只是没有做我想做的事。
-
我在您发布的代码中没有看到您所指的行？？
-
@steve 它在 Sub AddFiltering 中
-
老实说，我不敢相信您必须通过一些 lambda 函数来获取要过滤的数据网格。是故意复杂的吗？