枚举转换失败的 IValueConverter

Question

我创建了一个 ComboBox 并将系统枚举值绑定到它。并且还为它创建了一个值转换器，以使其更易于阅读。但是当我在 ComboBox 中 select 项目时，它显示错误并且在控制台中转储了一些错误消息知道如何解决这个问题吗？我还尝试为 SelectedItem 设置另一个值转换器，但它也不起作用。

cs文件：

using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO.Ports;
using System.Linq;
using System.Windows;
using System.Windows.Data;

namespace WpfApp1
{
    public partial class MainWindow : Window
    {
        private StopBits _stopBits;

        public StopBits SelectedStopBits
        {
            get { return _stopBits; }
            set { _stopBits = value; }
        }

        public MainWindow()
        {
            InitializeComponent();
            DataContext = this;
        }
    }

    public class DataConvert : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            var tmp = (int[])value;
            var convert = new Dictionary<StopBits, string>()
            {
                {StopBits.None, "none"},
                {StopBits.One, "1 bit"},
                {StopBits.Two, "2 bit"},
                {StopBits.OnePointFive, "1.5 bit"}
            };

            return tmp.Select(item => convert[(StopBits)item]).ToList();
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return value;
        }
    }
}

xaml 文件:

<Window x:Class="WpfApp1.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:WpfApp1"
        xmlns:serialPort="clr-namespace:System.IO.Ports;assembly=System"
        xmlns:provider="clr-namespace:System;assembly=mscorlib"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <ObjectDataProvider x:Key="StopBitsProvider" MethodName="GetValues" ObjectType="{x:Type provider:Enum}">
            <ObjectDataProvider.MethodParameters>
                <x:Type TypeName="serialPort:StopBits"/>
            </ObjectDataProvider.MethodParameters>
        </ObjectDataProvider>
        <local:DataConvert x:Key="DataConverter"/>
    </Window.Resources>
    <StackPanel>
        <TextBlock Text="Stop Bits:"/>
        <ComboBox ItemsSource="{Binding Source={StaticResource StopBitsProvider}, Converter={StaticResource DataConverter}}"
                  SelectedItem="{Binding SelectedStopBits}"/>
    </StackPanel>
</Window>

错误：

System.Windows.Data Error: 7 : ConvertBack cannot convert value '2 bit' (type 'String').
BindingExpression:Path=SelectedStopBits; DataItem='MainWindow' (Name=''); target element is 'ComboBox' (Name='');
target property is 'SelectedItem' (type 'Object') FormatException:'System.FormatException: 2 bit is not valid StopBits value
System.Enum.EnumResult.SetFailure(ParseFailureKind failure, String failureMessageID, Object failureMessageFormatArgument)
System.Enum.TryParseEnum(Type enumType, String value, Boolean ignoreCase, EnumResult& parseResult)
System.Enum.Parse(Type enumType, String value, Boolean ignoreCase)
System.ComponentModel.EnumConverter.ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, Object value)
System.ComponentModel.EnumConverter.ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, Object value)
MS.Internal.Data.DefaultValueConverter.ConvertHelper(Object o, Type destinationType, DependencyObject targetElement, CultureInfo culture, Boolean isForward)
MS.Internal.Data.ObjectTargetConverter.ConvertBack(Object o, Type type, Object parameter, CultureInfo culture)
System.Windows.Data.BindingExpression.ConvertBackHelper(IValueConverter converter, Object value, Type sourceType, Object parameter, CultureInfo culture)'

Answer 1

您需要将 SelectedItem 从 string 转换为 StopBits 值。

因此，您应用于 SelectedItem 绑定的转换器的 ConvertBack 方法应该 return 源属性实际上可以设置为的枚举值：

public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
    StopBits enumValue = default(StopBits);
    if (value != null)
        Enum.TryParse(value.ToString(), out enumValue);

    return enumValue;
}

您无法将 StopBits 属性设置为 string。

编辑： 或者您可以 return 来自转换器的字典：

public class DataConvert : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        var tmp = (int[])value;
        var convert = new Dictionary<StopBits, string>()
        {
            {StopBits.None, "none"},
            {StopBits.One, "1 bit"},
            {StopBits.Two, "2 bit"},
            {StopBits.OnePointFive, "1.5 bit"}
        };

        return convert;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value;
    }
}

...并稍微修改一下 XAML：

<ComboBox ItemsSource="{Binding Source={StaticResource StopBitsProvider}, Converter={StaticResource DataConverter}}"
          SelectedValuePath="Key"
          DisplayMemberPath="Value"
          SelectedValue="{Binding SelectedStopBits}"/>

枚举转换失败的 IValueConverter

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