Question

我有一个简单的MVVM项目，其中包含设计时数据，主数据和包含每个子项的用户控件的列表框都可以正常工作。但是，当我在运行时实例化类时，主数据显示但子数据不显示（但列表框具有正确的项目数，但它们没有在文本框中显示任何数据）。 / p>

我注意到Sport上的构造函数被调用了很多次，与我期望的相比（例如在运行时，我希望它只被调用两次，但它似乎被称为更多）。

我有班级人员和体育。每个人都喜欢多种运动，并有一个最喜欢的球队。我有一个personViewModel＆amp; sportViewModel，它继承自viewModelBase。

这是我的VB.net代码

Imports System.Collections.ObjectModel

Public Class Person
    Public Property Forename As String
    Public Property Surname As String
    Public Sports As New ObservableCollection(Of Sport)
End Class


Public Class Sport
    Public Sub New()
        Debug.WriteLine("test")
    End Sub

    Public Property SportName As String
    Public Property FavouriteProfessionalTeam As String
End Class


Imports System.Collections.ObjectModel

Namespace ViewModel

    Public Class PersonViewModel
        Inherits ViewModel.ViewModelBase

        Public Property Person1 As Person
        Public Property SportViewModels As New ObservableCollection(Of SportViewModel)

        Public Sub New()
            LoadData()
        End Sub

        ''' <summary> 
        ''' Loads the data for the application. 
        ''' </summary> 
        Private Sub LoadData()
            If IsInDesignModeStatic Then
                LoadDesignData()
            Else

            End If
        End Sub

        ''' <summary> 
        ''' Loads temporary data for use in the designer. 
        ''' </summary> 
        Private Sub LoadDesignData()
            Person1 = New Person
            Person1.Forename = "Mickey Run Time"
            Person1.Surname = "Mouse Run Time"

            Person1.Sports.Add(New Sport With {.FavouriteProfessionalTeam = "Man Utd", .SportName = "Soccer"})
            Person1.Sports.Add(New Sport With {.FavouriteProfessionalTeam = "Barcelona", .SportName = "Spanish Soccer"})
            Person1.Sports.Add(New Sport With {.FavouriteProfessionalTeam = "Ulster", .SportName = "Rugby"})

            For Each sport1 In Person1.Sports
                Dim sportVm As New SportViewModel With {.Sport1 = sport1}
                SportViewModels.Add(sportVm)
            Next

        End Sub

    End Class
End Namespace

Namespace ViewModel
    Public Class SportViewModel
        Inherits ViewModel.ViewModelBase

        Public Property Sport1 As New Sport
        Public Property Person1 As Person

        Public Sub New()
            LoadData()
        End Sub

        ''' <summary> 
        ''' Loads the data for the application. 
        ''' </summary> 
        Private Sub LoadData()
            If IsInDesignModeStatic Then
                LoadDesignData()
            Else
                ' Debug.WriteLine(Sport1.SportName)
                ' Load the student data asynchronously 
                'StudentContextInstance = New StudentContext
                'Dim loadop =
                '  StudentContextInstance.Load(StudentContextInstance.
                '             GetStudentsQuery(),
                '             AddressOf OnStudentsLoaded, Nothing)
            End If
        End Sub

        ''' <summary> 
        ''' Loads temporary data for use in the designer. 
        ''' </summary> 
        Private Sub LoadDesignData()
            Sport1 = New Sport With {.SportName = "Design Time Name", .FavouriteProfessionalTeam = "Design Time Team"}
        End Sub

    End Class
End Namespace

Imports System.ComponentModel

Namespace ViewModel

    Public Class ViewModelBase
        Implements INotifyPropertyChanged
        Public Event PropertyChanged(sender As Object, e As PropertyChangedEventArgs) Implements INotifyPropertyChanged.PropertyChanged

        Private Shared _isInDesignMode As Boolean?
        Public Shared ReadOnly Property IsInDesignModeStatic As Boolean
            Get
                If Not _IsInDesignMode.HasValue Then
                    _IsInDesignMode = DesignerProperties.GetIsInDesignMode(New DependencyObject)
                End If
                Return _IsInDesignMode.Value
            End Get
        End Property


        Protected Sub OnPropertyChanged(ByVal propertyName As String)
            ' Send an event notification that the property changed 
            ' This allows the UI to know when one of the items changes 
            If Not String.IsNullOrEmpty(propertyName) Then
                RaiseEvent PropertyChanged(Me,
                                           New PropertyChangedEventArgs(propertyName))
            End If
        End Sub



    End Class
End Namespace

这是我的wain窗口背后的代码，它设置了用于显示的MVVM Imports System.Collections.ObjectModel 导入WpfApplicationMVVMTest.ViewModel

Class MainWindow
    Public Property Person1 As Person
    Public Property SportViewModels As New ObservableCollection(Of SportViewModel)
    Private Sub Button_Click_1(sender As Object, e As RoutedEventArgs)
        Dim wndPerson As New PersonWindow


        Person1 = New Person
        Person1.Forename = "Donald"
        Person1.Surname = "Duck"

        Person1.Sports.Add(New Sport With {.FavouriteProfessionalTeam = "Man Utd", .SportName = "Soccer"})
        Person1.Sports.Add(New Sport With {.FavouriteProfessionalTeam = "Barcelona", .SportName = "Spanish Soccer"})

        For Each sport1 In Person1.Sports
            Dim sportVm As New SportViewModel With {.Sport1 = sport1}
            SportViewModels.Add(sportVm)
        Next




        Dim vm As New ViewModel.PersonViewModel
        vm.SportViewModels = SportViewModels
        vm.Person1 = Person1
        wndPerson.DataContext = vm
        wndPerson.Show()
    End Sub
End Class

这是XAML代码

<Window
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:ViewModel="clr-namespace:WpfApplicationMVVMTest.ViewModel"
    xmlns:View="clr-namespace:WpfApplicationMVVMTest" mc:Ignorable="d" x:Class="PersonWindow"
    Title="PersonWindow" Height="1114.8" Width="542">
    <Window.Resources></Window.Resources>
    <Window.DataContext>
        <ViewModel:PersonViewModel />
    </Window.DataContext>

    <Grid>
        <Grid x:Name="Grid1" HorizontalAlignment="Left" Margin="41,39,0,0" VerticalAlignment="Top">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="Auto"/>
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition Height="Auto"/>
            </Grid.RowDefinitions>
            <Label Content="Forename:" Grid.Column="0" HorizontalAlignment="Left" Margin="3" Grid.Row="0" VerticalAlignment="Center"/>
            <TextBox x:Name="ForenameTextBox" Grid.Column="1" HorizontalAlignment="Left" Height="23" Margin="3" Grid.Row="0" Text="{Binding Person1.Forename, Mode=TwoWay, NotifyOnValidationError=true, ValidatesOnExceptions=true}" VerticalAlignment="Center" Width="120"/>
            <Label Content="Surname:" Grid.Column="0" HorizontalAlignment="Left" Margin="3" Grid.Row="1" VerticalAlignment="Center"/>
            <TextBox x:Name="SurnameTextBox" Grid.Column="1" HorizontalAlignment="Left" Height="23" Margin="3" Grid.Row="1" Text="{Binding Person1.Surname, Mode=TwoWay, NotifyOnValidationError=true, ValidatesOnExceptions=true}" VerticalAlignment="Center" Width="120"/>
        </Grid>
        <ListBox Margin="41,108,59,753" ItemsSource="{Binding Path=SportViewModels}"  >
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <View:SportUserControl DataContext="{Binding}"  Margin="5"/>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</Window>

<UserControl
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:ViewModel="clr-namespace:WpfApplicationMVVMTest.ViewModel" x:Class="SportUserControl" 
             mc:Ignorable="d" 
             d:DesignHeight="600" d:DesignWidth="600">
    <UserControl.Resources></UserControl.Resources>
    <UserControl.DataContext>
        <ViewModel:SportViewModel />
    </UserControl.DataContext>


    <Grid>
        <Grid x:Name="Grid1" HorizontalAlignment="Left" Margin="31,26,0,0" VerticalAlignment="Top">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="Auto"/>
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition Height="Auto"/>
            </Grid.RowDefinitions>
            <Label Content="Favourite Professional Team:" Grid.Column="0" HorizontalAlignment="Left" Margin="3" Grid.Row="0" VerticalAlignment="Center"/>
            <TextBox x:Name="FavouriteProfessionalTeamTextBox" Grid.Column="1" HorizontalAlignment="Left" Height="23" Margin="3" Grid.Row="0" Text="{Binding Sport1.FavouriteProfessionalTeam, Mode=TwoWay, NotifyOnValidationError=true, ValidatesOnExceptions=true}" VerticalAlignment="Center" Width="120"/>
            <Label Content="Sport Name:" Grid.Column="0" HorizontalAlignment="Left" Margin="3" Grid.Row="1" VerticalAlignment="Center"/>
            <TextBox x:Name="SportNameTextBox" Grid.Column="1" HorizontalAlignment="Left" Height="23" Margin="3" Grid.Row="1" Text="{Binding Sport1.SportName, Mode=TwoWay, NotifyOnValidationError=true, ValidatesOnExceptions=true}" VerticalAlignment="Center" Width="120"/>
        </Grid>

    </Grid>
</UserControl>

这是我的设计时间图像显示3运动（根据我的负载设计时间数据）。 enter image description here

这是我的运行时间窗口，显示2个体育项目（尽管它们没有数据 - 这是问题）。 enter image description here

Answer 1

您正在标记和代码中设置Datacontexts ...删除标记并坚持使用一种模式

与设计时数据的MVVM绑定在设计时正常工作，但在运行时不能正常工作

1 个答案: