MultiBinding 转换器不显示结果

Question

作为学习在 WPF 中正确使用绑定的一部分，我创建了一个小的转换程序，将温度、长度、分数转换为小数等。温度和分数的一切都很好，因为这些使用简单的绑定和转换器完成。我运行在长度转换方面遇到了问题，因为它需要 MultiBinding 才能运行。

对于控件，我为原始长度和转换后的长度使用了两个文本框。其中每一个都有一个匹配的组合框，用户可以在其中 select 测量单位（即厘米、英寸、毫米等）。

使用断点，我已经确定条目正在进入 Convert 方法，并且该方法中的代码正在正确计算所有内容。 result 变量甚至在方法调用结束时显示正确转换的数字，但该数字没有返回到 lengthResult 文本框。

我已经尝试了所有我能想到的迭代来让它工作，现在用谷歌搜索了大约 3 个小时。我找不到显示足够相似情况的问题或指南，我可以让它适用于这种情况。有人可以仔细查看并找出我犯的 （很可能） 简单错误吗？

注意：我在 C# 代码中有一个 ConvertBack 函数，但其中除了默认的 throw new NotImplementedException 之外什么都没有，所以我把它去掉了。在 Convert 首先工作之后，我会担心这一点。 :)

XAML:

<GroupBox Header="Length" DockPanel.Dock="Top">
        <GroupBox.Resources>
            <local:LengthConverter x:Key="lengthConverter" />
        </GroupBox.Resources>
        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition />
                <ColumnDefinition />
                <ColumnDefinition />
                <ColumnDefinition />
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
            </Grid.RowDefinitions>
            <Label Content="Original Length:" Grid.Column="0" Grid.Row="0" VerticalAlignment="Center" HorizontalAlignment="Right" Margin="10" />
            <Label Content="Destination Length:" Grid.Column="0" Grid.Row="1" VerticalAlignment="Center" HorizontalAlignment="Right" Margin="10" />
            <ComboBox x:Name="originUnitSelect" Grid.Column="2" Grid.Row="0" ItemsSource="{Binding Units}" Height="{Binding ElementName=lengthEntry, Path=ActualHeight}" MinWidth="50" />
            <ComboBox x:Name="destinationUnitSelect" Grid.Column="2" Grid.Row="1" ItemsSource="{Binding Units}" Height="{Binding ElementName=lengthResult, Path=ActualHeight}" MinWidth="50" />
            <TextBox x:Name="lengthEntry" Grid.Column="1" Grid.Row="0" VerticalAlignment="Center" Margin="10" HorizontalContentAlignment="Center" MinWidth="250" />
            <TextBox x:Name="lengthResult" Grid.Column="1" Grid.Row="1" VerticalAlignment="Center" Margin="10" HorizontalContentAlignment="Center" MinWidth="250">
                <TextBox.Text>
                    <MultiBinding Converter="{StaticResource lengthConverter}">
                        <Binding ElementName="lengthEntry" Path="Text" UpdateSourceTrigger="PropertyChanged" />
                        <Binding ElementName="originUnitSelect" Path="SelectedValue" />
                        <Binding ElementName="destinationUnitSelect" Path="SelectedValue" />
                    </MultiBinding>
                </TextBox.Text>
            </TextBox>
            <Button x:Name="convertLength" Grid.Column="1" Grid.Row="2" Content="Convert" VerticalAlignment="Center" HorizontalAlignment="Center" Click="convertLength_Click"  Margin="10"/>
        </Grid>
    </GroupBox>

C#:

public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
        double result = 0.0;
        double cm_to_mm = 10;
        double cm_to_in = 0.3937;
        double cm_to_ft = 0.32808;
        double cm_to_yd = 0.010936;
        double mm_to_cm = 0.10;
        double mm_to_in = mm_to_cm * cm_to_in;
        double mm_to_ft = mm_to_cm * cm_to_ft;
        double mm_to_yd = mm_to_cm * cm_to_yd;
        double in_to_mm = 25.4;
        double in_to_cm = 2.54;
        double in_to_ft = 1 / 12;
        double in_to_yd = 1 / 36;
        double ft_to_yd = 36;
        double ft_to_in = 12;
        double ft_to_cm = ft_to_in * in_to_cm;
        double ft_to_mm = ft_to_in * in_to_mm;
        double yd_to_ft = 3;
        double yd_to_in = 36;
        double yd_to_cm = ft_to_in * in_to_cm;
        double yd_to_mm = ft_to_in * in_to_mm;


        if(values[1] != null && values[2] != null)
        {
            switch(values[1].ToString())
            {
                case "mm":
                    if (double.TryParse(values[0].ToString(), out result))
                    {
                        switch(values[2].ToString())
                        {
                            case "cm":
                                result = result * mm_to_cm;
                                break;
                            case "in":
                                result = result * mm_to_in;
                                break;
                            case "ft":
                                result = result * mm_to_ft;
                                break;
                            case "yd":
                                result = result * mm_to_yd;
                                break;
                        }
                        return result;
                    }
                    break;
                case "cm":
                    if(double.TryParse(values[0].ToString(), out result))
                    {
                        switch(values[2].ToString())
                        {
                            case "mm":
                                result = result * cm_to_mm;
                                break;
                            case "in":
                                result = result * cm_to_in;
                                break;
                            case "ft":
                                result = result * cm_to_ft;
                                break;
                            case "yd":
                                result = result * cm_to_yd;
                                break;
                        }
                        return result;
                    }
                    break;
                case "in":
                    if(double.TryParse(values[0].ToString(), out result))
                    {
                        switch(values[2].ToString())
                        {
                            case "mm":
                                result = result * in_to_mm;
                                break;
                            case "cm":
                                result = result * in_to_cm;
                                break;
                            case "ft":
                                result = result * in_to_ft;
                                break;
                            case "yd":
                                result = result * in_to_yd;
                                break;
                        }
                        return result;
                    }
                    break;
                case "ft":
                    if(double.TryParse(values[0].ToString(), out result))
                    {
                        switch(values[2].ToString())
                        {
                            case "mm":
                                result = result * ft_to_mm;
                                break;
                            case "cm":
                                result = result * ft_to_cm;
                                break;
                            case "in":
                                result = result * ft_to_in;
                                break;
                            case "yd":
                                result = result * ft_to_yd;
                                break;
                        }
                        return result;
                    }
                    break;
                case "yd":
                    if(double.TryParse(values[0].ToString(), out result))
                    {
                        switch(values[2].ToString())
                        {
                            case "mm":
                                result = result * yd_to_mm;
                                break;
                            case "cm":
                                result = result * yd_to_cm;
                                break;
                            case "in":
                                result = result * yd_to_in;
                                break;
                            case "ft":
                                result = result * yd_to_ft;
                                break;
                        }
                    }
                    break;
            }
        }
        return result;

        //throw new NotImplementedException();
    }

Answer 1

textbox 需要字符串，而不是 double。

return result.ToString();

应该可以解决问题。

MultiBinding 转换器不显示结果

MultiBinding Converter Not Displaying Results

c#

data-binding

wpf

converter

multibinding