Combobox with dynamically created items for enum type with text coming from Attributes won't support binding of SelectedItem

Question

I have a custom WPF combobox that generates its contents based on an enum type it's told about via a XAML attribute. When that attribute sets the corresponding property, the control calls the function below.
private void OnEnumTypePropChanged(string strNewVal)
{
System.Type typeProposed = System.Type.GetType(strNewVal);

    if(typeProposed == typeOfEnum)
        return;

    if(typeProposed == null || !typeProposed.IsEnum)
        return;

    typeOfEnum = typeProposed;

    foreach(object objCurValInEnumType in typeOfEnum.GetEnumValues())
    {
        System.Windows.Controls.Label labelForCurValInEnumType = new System.Windows.Controls.Label();

        GetEnumDesc(objCurValInEnumType, out string strText, out string strTooltip);

        labelForCurValInEnumType.Content = strText;
        labelForCurValInEnumType.ToolTip = strTooltip;
        labelForCurValInEnumType.Tag = objCurValInEnumType;
        labelForCurValInEnumType.HorizontalAlignment = System.Windows.HorizontalAlignment.Stretch;
        labelForCurValInEnumType.HorizontalContentAlignment = System.Windows.HorizontalAlignment.Center;
        labelForCurValInEnumType.FontFamily = FontFamily;
        labelForCurValInEnumType.FontSize = FontSize;
        labelForCurValInEnumType.FontStretch = FontStretch;
        labelForCurValInEnumType.FontStyle = FontStyle;
        labelForCurValInEnumType.FontWeight = FontWeight;
        labelForCurValInEnumType.UpdateLayout();

        Items.Add(labelForCurValInEnumType);
    }

    UpdateLayout();
}

GetEnumDesc looks up the attributes on each value in the enum type. That then is used to configure the label that's actually shown. But now binding to the selected value doesn't work. Is there a way I can tell the underlying control how to get the value for the label?

Answer 1

Hi,

Welcome to our Microsoft Q&A platform!

You can see my code,use Lable to bind SelectedValue:

Xaml:

<StackPanel>  
        <ComboBox Name="comboBox1" Width="150" ItemsSource="{Binding SelectedTypeDictionary}" DisplayMemberPath="Value" SelectedValuePath="Key" SelectedValue="{Binding ComboBoxSelectedValue}"/>  
          
        <Label Width="150" Content="{Binding ComboBoxSelectedValue}" Margin="30"></Label>  
    </StackPanel>  

C# code:

public partial class MainWindow : Window,INotifyPropertyChanged  
{  
    public event PropertyChangedEventHandler PropertyChanged;  
    public object _comboBoxSelectedValue;  
    public object ComboBoxSelectedValue  
    {  
        get { return _comboBoxSelectedValue; }  
        set { _comboBoxSelectedValue = value; PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("ComboBoxSelectedValue")); }  
    }  
    public Dictionary<Enum_Type, string> SelectedTypeDictionary { get; set; }     
    public MainWindow()  
    {  
        InitializeComponent();  
        SelectedTypeDictionary = new Dictionary<Enum_Type, string>();  
        SelectedTypeDictionary.Add(Enum_Type.SelectedOne, GetDescription(Enum_Type.SelectedOne));  
        SelectedTypeDictionary.Add(Enum_Type.SelectedTwo, GetDescription(Enum_Type.SelectedTwo));  
        SelectedTypeDictionary.Add(Enum_Type.SelectedThree,GetDescription(Enum_Type.SelectedThree));  
  
        this.DataContext = this;  
    }  
  
    public static T GetEnumAttribute<T>(Enum source) where T : Attribute  
    {  
        Type type = source.GetType();  
        var sourceName = Enum.GetName(type, source);  
        FieldInfo field = type.GetField(sourceName);  
        object[] attributes = field.GetCustomAttributes(typeof(T), false);  
        foreach (var o in attributes)  
        {  
            if (o is T)  
                return (T)o;  
        }  
        return null;  
    }  
  
    public static string GetDescription(Enum source)  
    {  
        var str = GetEnumAttribute<DescriptionAttribute>(source);  
        if (str == null)  
            return null;  
        return str.Description;  
    }  
  
  
}  
  
public enum Enum_Type  
{  
    [Description("test1")]  
    SelectedOne,  
    [Description("test2")]  
    SelectedTwo,  
    [Description("test3")]  
    SelectedThree,  
}  

Thanks.

Answer 2

Well, I thought of building a list of a custom type that would be an intermediary type. So I rewrote my class to look like https://pastebin.com/x7cyaJmu . This doesn't do any better than what I had before. Still won't select. I tried changing entries member to be a HashTable with the key being the value. That caused the labels to be blank. The XAML code in the second sample is required for this to work.

namespace Org.WillPittenger.YouTubeDownloader.Ctrls.ForEnums
{
    public partial class ComboBox : System.Windows.Controls.ComboBox, System.ComponentModel.INotifyPropertyChanged
    {
        #region Constructors & Destructors
            public ComboBox()
            {
                ItemsSource = entries = new System.Collections.Generic.List<OneEntry>();

                InitializeComponent();
            }
        #endregion

        #region Events
            public event System.ComponentModel.PropertyChangedEventHandler PropertyChanged;
        #endregion

        #region Constants
            private static class PropNames
            {
                public const string strEnumType = "EnumType";
            }
        #endregion

        #region Helper Types
            private class OneEntry
            {
                #region Constructors & Deconstructors
                    public OneEntry(object enumVal, string strDisplayText, string strTooltipText)
                    {
                        System.Diagnostics.Debug.Assert(enumVal.GetType().IsEnum);

                        this.enumVal = enumVal;
                        this.strDisplayText = strDisplayText;
                        this.strTooltipText = strTooltipText;
                    }
                #endregion

                #region Members
                    private readonly object enumVal;
                    private readonly string strDisplayText;
                    private readonly string strTooltipText;
                #endregion

                #region Properties
                    public object EnumVal => enumVal;
                    public string DisplayText => strDisplayText;
                    public string TooltipText => strTooltipText;
                #endregion
            }
        #endregion

        #region Members
            #region Dependency Properties
                public static readonly System.Windows.DependencyProperty EnumTypeProperty = System.Windows.DependencyProperty.Register(PropNames.strEnumType,
                    typeof(string), typeof(ComboBox), new System.Windows.PropertyMetadata(OnEnumTypePropChanged));
            #endregion

            private System.Type typeOfEnum = null;

            private System.Collections.Generic.List<OneEntry> entries;
        #endregion

        #region Properties
            [System.ComponentModel.Description("This is the enum type that the items are based on.  Each one must have Org.WillPittenger.AdBlockPlusIniParserWPF.Core.Attr"
                + ".LocalizedDescAttribute applied to it.")]
            [System.ComponentModel.Category("Common")]
            public string EnumType
            {
                get => (string)GetValue(EnumTypeProperty);

                set => SetValue(EnumTypeProperty, value);
            }
        #endregion

        #region Methods
            private void GetEnumDesc(object objEnumValue, out string strDesc, out string strExtendedDesc)
            {
                System.Reflection.FieldInfo fieldInfo = objEnumValue.GetType().GetField(objEnumValue.ToString());

                object[] attribArray = fieldInfo.GetCustomAttributes(typeof(Attr.LocalizedDescAttribute), false);

                if(attribArray.Length == 0)
                {
                    strDesc = objEnumValue.ToString();
                    strExtendedDesc = "";
                }
                else
                {
                    Attr.LocalizedDescAttribute attrib = attribArray[0] as Attr.LocalizedDescAttribute;

                    strDesc = attrib.Desc;
                    strExtendedDesc = attrib.ExtendedDesc;
                }
            }
        #endregion

        #region Event Handlers
            private void OnEnumTypePropChanged(string strNewVal)
            {
                System.Type typeProposed = System.Type.GetType(strNewVal);

                if(typeProposed == typeOfEnum)
                    return;

                if(typeProposed == null || !typeProposed.IsEnum)
                    return;

                typeOfEnum = typeProposed;

                entries.Capacity = typeOfEnum.GetEnumValues().Length;

                foreach(object objCurValInEnumType in typeOfEnum.GetEnumValues())
                {
                    GetEnumDesc(objCurValInEnumType, out string strText, out string strTooltip);

                    entries.Add(new OneEntry(objCurValInEnumType, strText, strTooltip));
                }

                UpdateLayout();
            }

            private static void OnEnumTypePropChanged(System.Windows.DependencyObject ctrlParent, System.Windows.DependencyPropertyChangedEventArgs e) =>
                ((ComboBox)ctrlParent).OnEnumTypePropChanged((string)e.NewValue);

            protected override void OnSelectionChanged(System.Windows.Controls.SelectionChangedEventArgs e) => base.OnSelectionChanged(e);
        #endregion
    }
}

<ComboBox
    x:Class="Org.WillPittenger.YouTubeDownloader.Ctrls.ForEnums.ComboBox"
    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"
    xmlns:local="clr-namespace:Org.WillPittenger.YouTubeDownloader.Ctrls.ForEnums"
    mc:Ignorable="d"
    d:DesignHeight="450"
    d:DesignWidth="800"
    ItemTemplate="{DynamicResource OurItemTemplate}">
    <ComboBox.Resources>
        <DataTemplate x:Key="OurItemTemplate">
            <Label
                Content="{Binding DisplayText}"
                ToolTip="{Binding TooltipText}" />
        </DataTemplate>
    </ComboBox.Resources>
</ComboBox>