Question

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"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:TestMetroChartsVB"        
        xmlns:chart="clr-namespace:GravityApps.Mandelkow.MetroCharts;assembly=GravityApps.Mandelkow.MetroCharts"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Window.DataContext>
        <local:TestPageViewModel/>
    </Window.DataContext>
    <Grid>
        <StackPanel>
            <chart:ClusteredBarChart ChartTitle="Example1 " ChartSubTitle="Test1">
                <chart:ClusteredBarChart.Series>
                    <chart:ChartSeries SeriesTitle="Errors" ItemsSource="{Binding Errors}"
                                       DisplayMember="Category" ValueMember="Number"/>
                </chart:ClusteredBarChart.Series>                    
            </chart:ClusteredBarChart>
            <Button x:Name="btnTest" Height="31" Margin="0,0,405,0" Content="Change Data"/>
        </StackPanel>    
    </Grid>
</Window>

我的观点：

Imports GravityApps.Mandelkow.MetroCharts Class MainWindow

Private Sub btnTest_Click(sender As Object, e As RoutedEventArgs) Handles btnTest.Click
    Dim test As New TestPageViewModel
    test.changeData()
End Sub End Class

我的viewModel：

Imports System.Collections.ObjectModel

Public Class TestPageViewModel

    Public Property Errors() As ObservableCollection(Of TestClass)
        Get
            Return m_Errors
        End Get
        Private Set
            m_Errors = Value
        End Set
    End Property
    Private m_Errors As ObservableCollection(Of TestClass)
    Public Sub New()
        Errors = New ObservableCollection(Of TestClass)
        Errors.Add(New TestClass("Data1", 5))
        Errors.Add(New TestClass("Data2", 10))
        Errors.Add(New TestClass("Data5", 15))
    End Sub

    Public Sub changeData()
        Errors.Clear()
        Errors.Add(New TestClass("DAta9", 10))
    End Sub

End Class

我的模特：

Public Class TestClass
    Public Property Category As String
        Get
            Return m_Category
        End Get
        Set(value As String)
            m_Category = value
        End Set
    End Property
    Private m_Category As String
    Public Property Number As Integer
        Get
            Return m_Number
        End Get
        Set(value As Integer)
            m_Number = value
        End Set
    End Property
    Private m_Number As Integer

    Public Sub New(category As String, number As Integer)
        Me.Category = category
        Me.Number = number
    End Sub End Class

它最初显示的数据如下：

但是当我点击我的＆＃34;更改数据＆＃34;按钮数据不会改变？问题是什么？

Answer 1

您正在更改错误的数据：

Private Sub btnTest_Click(sender As Object, e As RoutedEventArgs) Handles btnTest.Click
    Dim test As New TestPageViewModel
    test.changeData()
End Sub

在按钮的Click事件处理程序中，您可以创建一个新的视图模型对象并在其上调用changeData()。但是，这不是视图正在使用的视图模型对象，也没有做任何事情使其成为视图正在使用的视图模型对象。

最好的方法是获取实际的视图模型并更改它：

Private Sub btnTest_Click(sender As Object, e As RoutedEventArgs) Handles btnTest.Click
    Dim view As Button = CType(sender, Button)
    Dim test As TestPageViewModel = CType(view.DataContext, TestPageViewModel)
    test.changeData()
End Sub

以上假设发送Button事件的Click继承了MainWindow的数据上下文。

当我动态更改数据时，为什么我的MVVM不起作用？

1 个答案: