我正在开发一个发票系统，并且正在使用一个DataGrid项目条目。我希望用户能够以不同的单位（例如英寸、英尺、米）输入数量，并将输入的数量转换为商品的库存单位。我的第一个想法是实现一个IMultiValueConverter，但我从昨天开始就一直在尝试，但无法弄清楚。
我的 Convert 方法确实有效，我实际上已经拿走了身体，将它卡在另一种方法中并测试了它的输出。我的程序在该ConvertBack方法中崩溃，我是 C# 新手，我从未见过有人真正实现该方法，所以我想知道为什么它强迫我实现它（我猜这是因为我的 Quantity 绑定不是oneway），但我实际上需要转换后的值才能返回到源对象的 Quantity 属性。
我在实现该方法时确实没有问题ConvertBack，但是传递给该方法的 value 参数是用户输入的值，而不是转换后的值，这是为什么呢？如果不是转换后的值，因此我无法真正弄清楚如何倒退，因为我只能访问用户输入的内容，而不是该方法中所需的单位。
我意识到我对转换器的理解可能还有很长的路要走，但是如果有人可以帮助我了解我的想法在哪里，我将不胜感激，以及针对我的问题的任何潜在解决方法/解决方案。
提前致谢！
页面/PurchaseInvoicePage.xaml
<DataGrid x:Name="ItemsGrid" Grid.Row="2" Grid.ColumnSpan="3" PreviewKeyDown="ItemsGrid_PreviewKeyDown" ItemsSource="{Binding Items}" FontSize="11" AutoGenerateColumns="False" CanUserAddRows="False" CanUserDeleteRows="False" RowHeaderWidth="0" GridLinesVisibility="None" CanUserResizeRows="False" CanUserResizeColumns="False" CanUserReorderColumns="False">
<DataGrid.Columns>
<DataGridTemplateColumn x:Name="ItemNoColumn" Width="150" Header="Item No." IsReadOnly="True">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<TextBox Cursor="Arrow" Width="130" BorderThickness="0" Background="Transparent" IsReadOnly="True" Text="{Binding Number}" />
<Image Cursor="Hand" MouseDown="ItemSelectionButton_Click" Width="12" Source="/Images/Icons/SearchBlack.png" />
</StackPanel>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
<!-- question relative xaml starts here -->
<DataGridTextColumn x:Name="QuantityColumn" Width="70" Header="Quantity">
<DataGridTextColumn.Binding>
<MultiBinding Converter="{StaticResource unitConverter}">
<Binding Path="Quantity" />
<Binding Path="Units" Mode="OneWay" />
</MultiBinding>
</DataGridTextColumn.Binding>
</DataGridTextColumn>
<!-- question relative xaml ends here -->
<DataGridTextColumn x:Name="OrderColumn" Width="70" Header="Order" Binding="{Binding QuantityOrdered}" />
<DataGridTextColumn x:Name="BackOrderColumn" Width="70" Header="B/O" Binding="{Binding QuantityBackOrdered}" />
<DataGridTextColumn x:Name="UnitsColumn" Width="60" Header="Units" Binding="{Binding Units}" IsReadOnly="True" />
<DataGridTextColumn x:Name="DescriptionColumn" Width="200" Header="Description" Binding="{Binding Description}" />
<DataGridTextColumn x:Name="PriceColumn" Width="90" Header="Price" Binding="{Binding Price}" />
<DataGridComboBoxColumn x:Name="TaxColumn" Width="50" Header="Tax" SelectedValueBinding="{Binding TaxCodeID}" DisplayMemberPath="Code" SelectedValuePath="ID" />
<DataGridTextColumn x:Name="AmountColumn" Width="90" Header="Amount" Binding="{Binding Amount}" IsReadOnly="True" />
<DataGridTextColumn x:Name="LinkedColumn" Width="90" Header="Linked" Binding="{Binding SalesOrderID}" />
</DataGrid.Columns>
</DataGrid>
Fx/IMultiValueConverter.cs
public class UnitConverter : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameters, CultureInfo culture)
{
double num = 0;
// get the quantity value, and try parsing it
string str = values[0].ToString().ToLower();
bool parsed = double.TryParse(str, out num);
// if it parses, no need to convert, return the value
if (parsed)
return num.ToString();
// if it doesnt parse, get the last character in the value
// this character indicates the units being entered
// this will be either "(inches), f(eet), or m(eters)
string suffix = str.Substring(str.Length - 1);
// get the value, without thhe last character
str = str.Substring(0, str.Length - 1);
// try parsing the value now
parsed = double.TryParse(str, out num);
// if it doesn't parse, the formats incorrect, return 0
if (!parsed)
return (0).ToString();
// get the desired units, (the second value in my multibinding)
string units = values[1].ToString().ToLower();
// if either the entry suffix or the desired units are empty, just return
// the number without converting
if (string.IsNullOrEmpty(suffix) || string.IsNullOrEmpty(units))
return num;
// convert from inches to feet
if (suffix == "\"" && units == "feet")
return (num / 12).ToString();
// convert from inches to meters
else if (suffix == "\"" && units == "meters")
return (num * 0.0254).ToString();
// convert from feet to meters
else if (suffix == "f" && units == "meters")
return (num * 0.3048).ToString();
// convert from meters to feet
else if (suffix == "m" && units == "feet")
return (num / 0.3048).ToString();
// if we reachd this far, the user probably entered something random,
// show an error and return 0
MessageBox.Show("Failed to convert between the two units.");
return (0).ToString();
}
public object[] ConvertBack(object value, Type[] targetType, object parameter, CultureInfo culture)
{
// now this is where my program is crashing,
// for some reason I need to actually implement the ConvertBack function
// but when I try to popup the value being passed to this function,
// it is the value the user entered e.g "20f" and not the converted value
// should it not be the converted value? Why do I even need to implement this
// how should i go backwards from here...
string str = value.ToString();
// MessageBox.Show(str);
return new object[] { 0 }; // btw, I'm only returning one value, because the second binding is oneway
}