Question

我试着从我的datatemplate中调用我的模型类中的方法，但似乎没有编译。给出错误“对象引用未设置为对象的实例。”

在pointerPressed上我想在我的lvitem调用中使用X：bind调用方法“Poke”。

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="*"/>
    </Grid.ColumnDefinitions>
    <ListView Grid.Column="0" ItemsSource="{x:Bind m_ViewModel.ListItems}" >
        <ListView.ItemTemplate>
            <DataTemplate x:DataType="local:lvitem">
                <TextBlock PointerPressed="{x:Bind Poke , Mode=OneWay }"/>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>
    <TextBlock Grid.Column="1" Text="{x:Bind m_ViewModel._Name, Mode=TwoWay}"/>
</Grid>

MyViewModel

Imports Windows.UI
Namespace MyViewModel
Public Class MyViewModel
    Implements INotifyPropertyChanged
    Private Sub NotifyPropertyChanged(Optional propertyName As String = "")
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
    End Sub

    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
    Private Name As String

    Private List_Items As New ObservableCollection(Of lvitem)

    Public Property _Name As String
        Get
            Return Name

        End Get
        Set(value As String)
            Name = value
            NotifyPropertyChanged()
        End Set
    End Property
    Public Sub New()
        Name = "Cater"
        Dim lvi As New lvitem
        Dim lvi2 As New lvitem
        List_Items.Add(lvi)
        List_Items.Add(lvi2)
    End Sub

    Public Property ListItems As ObservableCollection(Of lvitem)
        Get
            Return List_Items
        End Get
        Set(value As ObservableCollection(Of lvitem))
            List_Items = value
        End Set
    End Property
    Public Sub ClickMe()
        _Name = "Clicked"

    End Sub
End Class
End Namespace

CodeBehind

Public NotInheritable Class MainPage
Inherits Page
Public Property ViewModel() As MyViewModel.MyViewModel
    Get
        Return m_ViewModel
    End Get
    Set
        m_ViewModel = Value
    End Set
End Property
Private m_ViewModel As MyViewModel.MyViewModel
Public Sub New()

    Me.InitializeComponent()

    ViewModel = New MyViewModel.MyViewModel
End Sub

Private Sub Rectangle_PointerPressed(sender As Object, e As PointerRoutedEventArgs)

End Sub

Private Sub TextBlock_PointerPressed(sender As Object, e As PointerRoutedEventArgs)

End Sub
End Class

Lvitem Class - Model

Public Class lvitem
Public Sub New()

End Sub
Public Sub Poke(sender As Object, e As Object)
    Dim meint As Integer
    meint = 3
End Sub
End Class

Answer 1

给出错误＆＃34;对象引用未设置为对象的实例。＆＃34;

是的，我们在DataTemplate中找到了x：bind with x：DataType的一些问题。

以下是我们需要注意的几点：

确保Panel包含DataTemplate
中的元素
对于TextBlock控件，如果我们需要使事件x：bind绑定起作用，则Text属性必须设置为x：bind binding。

我简化了您的repro演示并标准化了一些命名问题：

<强> lvitem.vb：

Public Class lvitem
    Public Sub Poke(sender As Object, e As PointerRoutedEventArgs)
        Dim meint As Integer
        meint = 3
    End Sub

    Private _Name As String

    Public Property Name() As String
        Get
            Return _Name
        End Get
        Set(ByVal value As String)
            _Name = value
        End Set
    End Property
End Class

<强> MyViewModel.vb：

Imports Windows.UI

Namespace MyViewModel
  Public Class MyViewModel
    Implements INotifyPropertyChanged
    Private Sub NotifyPropertyChanged(Optional propertyName As String = "")
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
    End Sub

    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
    Private _Name As String

    Public List_Items As New ObservableCollection(Of lvitem)

    Public Property Name As String
        Get
            Return _Name

        End Get
        Set(value As String)
            _Name = value
            NotifyPropertyChanged()
        End Set
    End Property
    Public Sub New()
        Name = "Cater"
        Dim lvi As New lvitem With {.Name = "Item1"}
        Dim lvi2 As New lvitem With {.Name = "Item2"}
        List_Items.Add(lvi)
        List_Items.Add(lvi2)
    End Sub
  End Class
End Namespace

查看：

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"> <Grid.ColumnDefinitions> <ColumnDefinition Width="*"/> <ColumnDefinition Width="*"/> </Grid.ColumnDefinitions> <ListView Margin="0,100,0,0" Grid.Column="0" ItemsSource="{x:Bind m_ViewModel.List_Items}" > <ListView.ItemTemplate> <DataTemplate x:DataType="local:lvitem"> <Grid> <TextBlock PointerPressed="{x:Bind Poke, Mode=OneWay}" Text="{x:Bind Name}"/> </Grid> </DataTemplate> </ListView.ItemTemplate> </ListView> <TextBlock Margin="0,100,0,0" Grid.Column="1" Text="{x:Bind m_ViewModel.Name, Mode=TwoWay}"/> </Grid>

请注意 PointerPressed事件不会被触发，原因在于：Can't fire PointerPressed event from a Listbox in WinRT

X：将datatemplate绑定到事件

1 个答案: