绑定 Silverlight 组合框不显示 EnumBinder 的默认值

Question

我的模型使用枚举来固定多个选择。我正在使用 Dean Chalk 的 EnumBinder，位于 http://deanchalk.me .uk/post/Enumeration-Binding-In-Silverlight.aspx ，绑定到组合框。除了未显示默认值之外，一切似乎都运行良好。选定的索引是-1，我绑定到SelectedItem还是SelectedValue都没关系。否则组合框工作正常。我对任何其他绑定组合框的默认值都没有问题。

enumbindingsupport.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Reflection;

/* All of this was once just part of the RichClient sub-namespace
 * but it has its uses elsewhere, so it has been moved. 
 */

/// <summary>
/// Container for enumeration values.
/// </summary>
/// <remarks>
/// http://deanchalk.me.uk/post/Enumeration-Binding-In-Silverlight.aspx
/// </remarks>
public sealed class EnumContainer
{
    public int EnumValue { get; set; }
    public string EnumDescription { get; set; }
    public object EnumOriginalValue { get; set; }
    public override string ToString() {
        return EnumDescription;
    }

    public override bool Equals(object obj) {
        if (obj == null)
            return false;
        if (obj is EnumContainer)
            return EnumValue.Equals((int)((EnumContainer)obj).EnumValue);
        return EnumValue.Equals((int)obj);
    }

    public override int GetHashCode() {
        return EnumValue.GetHashCode();
    }

}

/// <summary>
/// A collection to store a list of EnumContainers that hold enum values.
/// </summary>
/// <remarks>
/// http://deanchalk.me.uk/post/Enumeration-Binding-In-Silverlight.aspx
/// </remarks>
/// <typeparam name="T"></typeparam>
public class EnumCollection<T> : List<EnumContainer> where T : struct
{
    public EnumCollection() {
        var type = typeof(T);
        if (!type.IsEnum)
            throw new ArgumentException("This class only supports Enum types");
        var fields = typeof(T).GetFields(BindingFlags.Static | BindingFlags.Public);
        foreach (var field in fields) {
            var container = new EnumContainer();
            container.EnumOriginalValue = field.GetValue(null);
            container.EnumValue = (int)field.GetValue(null);
            container.EnumDescription = field.Name;
            var atts = field.GetCustomAttributes(false);
            foreach (var att in atts)
                if (att is DescriptionAttribute) {
                    container.EnumDescription = ((DescriptionAttribute)att).Description;
                    break;
                }
            Add(container);
        }

    }
}

enumvalueconverter.cs

using System;
using System.Globalization;
using System.Windows.Data;

/// <summary>
/// Supports two-way binding of enumerations.
/// </summary>
public class EnumValueConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter,
                            CultureInfo culture) {
        return (int)value;
    }

    public object ConvertBack(object value, Type targetType, object parameter,
                            CultureInfo culture) {
        if (value == null)
            return null;
        if (value.GetType() == targetType)
            return value;
        return ((EnumContainer)value).EnumOriginalValue;
    }
}

使用的枚举：

/// <summary>
/// Describes the available sorting options.
/// </summary>
public enum PeopleSortOptionsEnum
{

    [Display(Order = 10)]
    [Description("First Name, Last Name")]
    FirstNameThenLastName,

    [Display(Order = 20)]
    [Description("Last Name, First Name")]
    LastNameThenFirstName,

    [Display(Order = 30)]
    Grade,

    [Display(Order = 40)]
    Gender,

    [Display(Order = 50)]
    Age
}

我的模型上的属性：

    /// <summary>
    /// This is the list for the enumeration to bind to.
    /// </summary>
    public EnumCollection<PeopleSortOptionsEnum> AvailableSortOptions
    {
        get { return new EnumCollection<PeopleSortOptionsEnum>(); }
    }

XAML 代码片段：

    <ComboBox ItemsSource="{Binding Path=AvailableSortOptions, Mode=OneWay}" SelectedValue="{Binding Path=Preferences.SortOrder, Mode=TwoWay, Converter={StaticResource EnumConverter}}" Grid.Column="1" Grid.Row="2" Height="32" Margin="48,31,0,0" x:Name="cboSort" VerticalAlignment="Top" />

其中 Preferences.SortOrder 的类型为 PeopleSortOptionsEnum，转换器在我的 app.xaml 中作为所有枚举类型的转换器。

任何人都知道为什么它不会将索引设置为当前选定的值？我正要在代码隐藏中添加一些代码，以将 selectedindex 设置为加载时当前选定的值，但一想到它我就觉得很肮脏。

除了这个问题之外，它运行得非常好，所以感谢 Dean！

编辑 添加 Preferences.SortOrder 代码：

public PeopleSortOptionsEnum SortOrder 
{ 
  get { return sortOrder; } 
  set 
  { 
    if (sortOrder != value) 
    { 
      sortOrder = value; 
      PropertyHasChanged("SortOrder"); 
    } 
  } 
}

Answer 1

问题是枚举转换器类上的 Convert 方法：

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

当组合框 SelectedItem 从 SortOrder 获取值时，它会以枚举值返回，该转换器将其转换为 int。但是，组合框项是 EnumContainer 对象的集合，而不是整数。所以无法设置所选项目。

要解决该问题，您必须做两件事。首先更改组合框绑定并设置 SelectedValuePath：

<ComboBox ItemsSource="{Binding Path=AvailableSortOptions}" 
          SelectedValue="{Binding Path=SortOrder, Mode=TwoWay, Converter={StaticResource EnumConverter}}" 
          SelectedValuePath="EnumOriginalValue"/>

其次，您必须稍微修改转换器上的 Convert 方法：

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

一旦我进行了这两项更改，它就开始按预期工作。