Question

我是WPF的新手，我对数据绑定的行为方式感到困惑。

我创建了一个具有1个属性（“status”）的类和三个负责更改状态的方法。这个类实现了INotifyPropertyChanged接口，这样我就可以在状态发生变化时通知调用代码。

该课程如下：

Public Class StreetLight
    Implements System.ComponentModel.INotifyPropertyChanged
    Public Event PropertyChanged(ByVal sender As Object, ByVal e As System.ComponentModel.PropertyChangedEventArgs) Implements System.ComponentModel.INotifyPropertyChanged.PropertyChanged

    Private _status As String
    Public Property Status As String
        Get
            Return _status
        End Get
        Set(ByVal value As String)
            _status = value
            RaiseEvent PropertyChanged(Me, New System.ComponentModel.PropertyChangedEventArgs("Satus"))
        End Set
    End Property
    Public Sub New()
        _status = "unknown"
    End Sub
    Public Sub Red()
        Status = "Red"
    End Sub
    Public Sub Yellow()
        Status = "Yellow"
    End Sub
    Public Sub Green()
        Status = "Green"
    End Sub
End Class

我创建了一个WPF用户控件来表示这个类。此用户控件绑定到StreetLight类的实例。它显示StreetLight的状态，并允许用户使用按钮更改状态：

<UserControl x:Class="StreetLightUC"
             x:Name="StreetLightUC"
             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:twpf="clr-namespace:TryingWPF"
             mc:Ignorable="d" 
             d:DesignHeight="30" d:DesignWidth="360">
    <UserControl.Resources>
        <twpf:StreetLight x:Key="theLight" PropertyChanged="theLight_PropertyChanged" />
    </UserControl.Resources>
    <StackPanel x:Name="StreetLightContent" Orientation="Horizontal">
        <Label Width="100" HorizontalAlignment="Left">Street Light _Status</Label>
        <Label x:Name="streetLightValue" Width="120" HorizontalAlignment="Right" Content="{Binding Path=Status, Mode=OneWay}"></Label>
        <Button x:Name="Red" Click="TurnRed" Width="60">Turn Red</Button>
        <Button x:Name="Green" Click="TurnGreen" Width="60">Turn Green</Button>
    </StackPanel>
</UserControl>

我的问题是，即使更改了灯的状态，它也不会在绑定到Status属性的Label中更新，除非我创建一个新的StreetLight并在“StreetLight_PropertyChanged”事件中将DataContext设置为这个新实例处理“theLight”的PropertyChagned事件

像这样：

Public Class StreetLightUC
    Public Sub New()
        InitializeComponent()
    End Sub
    Private Sub TurnRed(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs)
        Dim light As StreetLight= CType(FindResource("theLight"), StreetLight)
        light.Red()
    End Sub

    Private Sub TurnGreen(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs)
        Dim light As StreetLight = CType(FindResource("theLight"), StreetLight)
        light.Unlock()
    End Sub

    Private Sub theLight_PropertyChanged(ByVal sender As System.Object, ByVal e As System.ComponentModel.PropertyChangedEventArgs)
        Dim light As StreetLight = CType(sender, StreetLight )
        Dim newLight As New StreetLight
        newLight.Status = light.Status
        StreetLightContent.DataContext = newLight
    End Sub
End Class

我做错了吗？当这个属性发生变化时，似乎我不应该创建一个新的类实例来显示更新的status-property ....

谢谢，

-Frinny

Answer 1

你有一个拼写错误（"Satus"而不是"Status"）：

RaiseEvent PropertyChanged(Me, New System.ComponentModel.PropertyChangedEventArgs("Satus"))

应该是：

RaiseEvent PropertyChanged(Me, New System.ComponentModel.PropertyChangedEventArgs("Status"))

使用此拼写错误，绑定不会看到“状态”已更改，并且永远不会更新。如果您更正了此问题，PropertyChanged事件将正确反映"Status"已更改。

更改属性时更新UI

1 个答案: