ComboBox not updating display value after change

Question

I have the following ComboBox on a tab:

<ComboBox Name="EmpNoRuleListBox"
          IsReadOnly="True"
          ItemsSource="{Binding AdjustmentSettings.EmpNoRuleCollection}" 
          DisplayMemberPath="Description"
          SelectedItem="{Binding AdjustmentSettings.SelectedEmpNoRule, Mode=TwoWay}" 
          IsSynchronizedWithCurrentItem="True" 
          HorizontalAlignment="Left"
          Width="300" />

And the AdjustmentSettings model is:

public class AdjustmentSettingsModel : ModelBase<AdjustmentSettingsModel>
{
    public String Company { get; set; }
    public Boolean ReloadEmployeeData { get; set; }
    public Boolean SortByName { get; set; }
    public Boolean ApplyJustificationRules { get; set; }
    public Int32 SeedNumber { get; set; }
    public Boolean ScanForMismatchedCodes { get; set; }
    public Boolean ReloadHRTables { get; set; }

    public EmpNoRule SelectedEmpNoRule
    {
        get { return _SelectedEmpNoRule; }
        set
        {
            if (_SelectedEmpNoRule != value)
            {
                _SelectedEmpNoRule = value;
                NotifyPropertyChanged(m => m.SelectedEmpNoRule);
            }
        }
    }
    private EmpNoRule _SelectedEmpNoRule;

    public EmpNoRuleCollection EmpNoRuleCollection { get; set; }
}

public class EmpNoRuleCollection : ObservableCollection<EmpNoRule>, INotifyPropertyChanged
{
      . . . 
}


public class EmpNoRule : ModelBase<EmpNoRule>
{
    #region Initialization & Cleanup

    // Overriding the GetHashCode prevents the Clone operation from marking an 
    // object Dirty when it is first cloned
    public override int GetHashCode()
    {
        return GetHashCode(this);
    }
    private int GetHashCode(object item, params string[] excludeProps)
    {
        int hashCode = 0;
        foreach (var prop in item.GetType().GetProperties())
        {
            if (!excludeProps.Contains(prop.Name))
            {
                object propVal = prop.GetValue(item, null);
                if (propVal != null)
                {
                    hashCode = hashCode ^ propVal.GetHashCode();
                }
            }
        }
        return hashCode;
    }


    public override bool Equals(System.Object obj)
    {
        // If parameter is null return false.
        if (obj == null)
        {
            return false;
        }

        // If parameter cannot be cast to EmpNoRule return false.
        EmpNoRule p = obj as EmpNoRule;
        if ((System.Object)p == null)
        {
            return false;
        }

        // Return true if the fields match:
        return (obj == p);

    }



    public EmpNoRule() { }

    #endregion Initialization & Cleanup

    /// <summary>
    /// Description
    /// </summary>
    [XmlElement("Description")]
    public String Description
    {
        get
        {
            return _Description;
        }
        set
        {
            if (_Description != value)
            {
                this._Description = value;
                NotifyPropertyChanged(m => m.Description);
            }
        }
    }
    private String _Description = "";


    /// <summary>
    /// Formula
    /// </summary>
    [XmlElement("Formula")]
    public String Formula
    {
        get
        {
            return _Formula;
        }
        set
        {
            if (_Formula != value)
            {
                this._Formula = value;
                NotifyPropertyChanged(m => m.Formula);
            }
        }
    }
    private String _Formula = "";
}

Everything works correctly EXCEPT the displayed value in the combobox does not change when I select a different EmpNoRule. The value of SelectedEmpNoRule is correctly set/updated and if I change to another tab and then come back to this one, the drop down value is updated.

Answer 1

Your code does not show how you update EmpNoRuleCollection property, but I assume you simply reassigning a new collection to this property. That will not update the combobox unless you publish a PropertyChanged event on "EmpNoRuleCollection".

I believe the reason why changing tab will update the combobox because the binding pulls the values from your EmpNoRuleCollection collection again when you switch tab.