这个问题像this question一样出现了同样的问题,但它涉及到我遇到的另一个问题,因为我使用了绑定。
我添加了一个按钮,用于删除ListBox
中当前选定的项目(以及出现同一问题的DataGrid
的一个项目)。执行此操作的代码通过ICommand
- 对象和Button.Command
属性绑定到按钮:
<Button Command="{Binding DeleteRowCommand}"
CommandParameter="{Binding ElementName=MyListBox, Path=SelectedItem}" />
然而,这意味着点击操作直接汇集到ViewModel中,ViewModel当然不知道视图的ListBox
,因此它无法通知视图或更新任何选择。
在viewmodel 和视图中触发代码隐藏的正确方法是什么?
也许我可以使用命令属性和Handles
语句,但我不确定这是否可行。
答案 0 :(得分:1)
这就是我要做的事。
在ViewModel中创建一个属性,该属性将保存SelectedItem。
private YourTypeHere _SelectedThing;
public YourTypeHere SelectedThing
{
get { return _SelectedThing; }
set
{
_SelectedThing = value;
//Call INotifyPropertyChanged stuff
}
}
现在,将List的SelectedItem绑定到此属性:
<ListBox SelectedItem="{Binding SelectedThing}" ... />
执行这些操作意味着您的SelectedThing
现在是ViewModel的责任,当您调用Delete命令时,您只需将SelectedThing属性更新为列表中的最后一项并且您的ListBox将自动更新。
答案 1 :(得分:0)
XAML:
<ListBox DataContext="{Binding Path=Category, Mode=OneTime}"
ItemsSource="{Binding Path=Fields}"
SelectedItem="{Binding Path=SelectedItem, Mode=OneWay}"
SelectedIndex="{Binding Path=SelectedIndex}" />
CategoryViewModel
中的代码,来自数据上下文的Category
对象的类:
Public ReadOnly Property Fields As ObservableCollection(Of FieldViewModel)
Get
Return m_Fields
End Get
End Property
Private ReadOnly m_Fields As New ObservableCollection(Of FieldViewModel)
Public Property SelectedIndex As Integer
Get
Return m_SelectedIndex
End Get
Set(value As Integer)
m_SelectedIndex = value
ValidateSelectedIndex()
RaisePropertyChanged("SelectedIndex")
RaisePropertyChanged("SelectedItem")
End Set
End Property
Private m_SelectedIndex As Integer = -1
Public ReadOnly Property SelectedItem As FieldViewModel
Get
Return If(m_SelectedIndex = -1, Nothing, m_Fields.Item(m_SelectedIndex))
End Get
End Property
Private Sub ValidateSelectedIndex()
Dim count = m_Fields.Count
Dim newIndex As Integer = m_SelectedIndex
If count = 0 Then
' No Items => no selections
newIndex = -1
ElseIf count <= m_SelectedIndex Then
' Index > max index => correction
newIndex = count - 1
ElseIf m_SelectedIndex < 0 Then
' Index < min index => correction
newIndex = 0
End If
m_SelectedIndex = newIndex
RaisePropertyChanged("SelectedIndex")
RaisePropertyChanged("SelectedItem")
End Sub
Public Sub New(model As Category)
' [...] Initialising of the view model,
' especially the m_Fields collection
' Auto update of SelectedIndex after modification
AddHandler m_Fields.CollectionChanged, Sub() ValidateSelectedIndex()
' Set the SelectedIndex to 0 if there are items
' or -1 if there are none
ValidateSelectedIndex()
End Sub
现在,每当您从m_Fields
集合中删除某个项目时,SelectedItem
都会更改为下一个项目,如果删除了最后一个项目,则会更改为上一个项目,或Nothing
如果最后剩下的项目被删除了。