VB.net 中的 WPF NumericUpDown 用户控件

Question

我正在 VB 中创建自己的 NumericUpDown 控件。这是我的 XAML：

<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" 
             x:Class="NumericUpDown"
             mc:Ignorable="d" 
             d:DesignHeight="30" d:DesignWidth="100">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="20" />
            <ColumnDefinition Width="20" />
        </Grid.ColumnDefinitions>
        <TextBox x:Name="txtNum" Grid.Column="0" x:FieldModifier="private" TextChanged="txtNum_TextChanged"/>
        <Button x:Name="cmdDown" Grid.Column="1" x:FieldModifier="private" Content="˅" Width="20" Click="cmdDown_Click" />
        <Button x:Name="cmdUp" Grid.Column="2" x:FieldModifier="private" Content="˄" Width="20" Click="cmdUp_Click" />
    </Grid>
</UserControl>

这是它背后的VB代码：

Class NumericUpDown

    Dim _Minimum As Double = 0
    Dim _Maximum As Double = 100

    Private Sub NumericUpDown()
        InitializeComponent()
        txtNum.Text = Numeric
    End Sub

    Public Property Maximum As Double
        Get
            Return _Maximum
        End Get
        Set(value As Double)
            _Maximum = value
        End Set
    End Property

    Public Property Minimum As Double
        Get
            Return _Minimum
        End Get
        Set(value As Double)
            _Minimum = value
        End Set
    End Property

    Public Shared ReadOnly NumericProperty As DependencyProperty = DependencyProperty.Register("Numeric", GetType(String), GetType(NumericUpDown), _
        New PropertyMetadata(""))

    Public Property Numeric As String
        Get
            Return CType(GetValue(NumericProperty), String)
        End Get
        Set(value As String)
            SetValue(NumericProperty, value)
        End Set
    End Property

    Private Sub cmdUp_Click(sender As Object, e As RoutedEventArgs)
        Dim NumValue As Double
        NumValue = Val(txtNum.Text)
        NumValue += 1
        If NumValue > Maximum Then NumValue = Maximum
        txtNum.Text = NumValue.ToString
    End Sub

    Private Sub cmdDown_Click(sender As Object, e As RoutedEventArgs)
        Dim NumValue As Double
        NumValue = Val(txtNum.Text)
        NumValue -= 1
        If NumValue < Minimum Then NumValue = Minimum
        txtNum.Text = NumValue.ToString
    End Sub

    Private Sub txtNum_TextChanged(sender As Object, e As TextChangedEventArgs)
        Numeric = txtNum.Text
    End Sub
End Class

我在我的页面中这样使用它： 把它放在页面定义上：

xmlns:local="clr-namespace:Demo"

并将其放在内容部分：

<local:NumericUpDown Numeric="{Binding Path=score, Mode=TwoWay, NotifyOnValidationError=true, ValidatesOnExceptions=true}"/>

当然，我已经在容器上设置了 DataContext，所有其他数据绑定控件都可以正常工作。但是我的自定义控件中的文本框竟然是空的！它并没有在这里结束。当我在文本框中输入一些内容并使用减少和增加按钮给它一些值时，该值将传输到我的 DataTable；这意味着这个用户控件在某种程度上确实有效。我哪里做错了？为什么Textbox内容不会初始化为起始值？

经过更多测试。看来我的用户控件在“双向”中不起作用。它不从 DataTable 接收数据，它只将值传播给它。我该如何解决？

Answer 1

问题是您没有将txtNum 的Text 属性绑定到您的Numeric 属性。

<TextBox x:Name="txtNum" Grid.Column="0" x:FieldModifier="private"
            Text="{Binding Path=Numeric, RelativeSource={RelativeSource AncestorType={x:Type UserControl}}}"/>

然后您可以删除txtNum_TextChanged，并修改您的上/下点击处理程序以仅更新Numeric 属性，例如：

Private Sub cmdUp_Click(sender As Object, e As RoutedEventArgs)
    If Me.Numeric < Me.Maximum Then
        Me.Numeric += 1
    Else
        Me.Numeric = Me.Maximum
    End If
End Sub

Private Sub cmdDown_Click(sender As Object, e As RoutedEventArgs)
    If Me.Numeric > Me.Minimum Then
        Me.Numeric -= 1
    Else
        Me.Numeric = Me.Minimum
    End If
End Sub

请注意，仍然存在很多问题 - 用户可以输入超出允许范围的值，或者输入非数字数据（这会破坏事情！）等。对于这个特定问题，您可以查看 @ 987654321@，其中有各种up/down controls。