Question

The Binding on the ComboBox Categories is not updating when a Division is selected.
When a division is selected the ProjectCategories Property does get populated with two results, but the view does not update.

If I send ProjectCategories as a ref through to ProjectCategoriesGetByDivisionId() then the binding does update.

I don’t want to pass references to my model and data classes. How can I have the binding update without changing my model and data classes?

Here is the Divisions ComboBox that changes the value of the binding for the Categories ComboBox.

<ComboBox x:Name="Divisions" ItemsSource="{Binding Divisions}" DisplayMemberPath="Name" SelectedValuePath="DivisionId">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="SelectionChanged">
            <cmd:EventToCommand Command="{Binding DivisionChanged}" CommandParameter="{Binding ElementName=Divisions, Path=SelectedItem}" />
        </i:EventTrigger>
    </i:Interaction.Triggers>
</ComboBox>

The ComboBox that isn’t updating

<ComboBox x:Name="Categories" ItemsSource="{Binding Categories}" DisplayMemberPath="Name" SelectedValuePath="CategoryId" />

The method that gets fired when the Divisions SelectedChanged event is fired.

private void DivisionChanged(Division d)
{
    ProjectCategories = ProjectCategory.GetByDivisionId(d.DivisionId);
}

ViewModel Property the ComboBox is binding to

public ObservableCollection<ProjectCategory> ProjectCategories
{
    get { return projectCategories; }
    set
    {
        projectCategories = value;

        if (base.PropertyChangedHandler != null)
            base.PropertyChangedHandler(this, new PropertyChangedEventArgs("ProjectCategories"));
    }
}

Model Method that is called

public static ObservableCollection<ProjectCategory> GetByDivisionId(int divisionId)
{
    return ProjectData.ProjectCategoriesGetByDivisionId(divisionId);
}

I think the rest is self explanitory.

public static ObservableCollection<ProjectCategory> ProjectCategoriesGetByDivisionId(int divisionId)
{
    ObservableCollection<ProjectCategory> projectCategory = new ObservableCollection<ProjectCategory>();
    SqlConnection conn = null;

    try
    {
        conn = new SqlConnection(connectionString);
        SqlCommand cmd = new SqlCommand("TRK_ProjectCategory_GetByDivisionId", conn);
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Parameters.Add("@DivisionId", SqlDbType.Int).Value = divisionId;
        conn.Open();
        SqlDataReader sdr = cmd.ExecuteReader();

        while (sdr.Read())
            projectCategory.Add(ObjectConstructors.ProjectCategoryConstructor(sdr));
    }
    catch (Exception ex)
    {
        ErrorHandler.EmailLog("MineralsData", "public static ObservableCollection<ProjectCategory> ProjectCategoriesGetByDivisionId(int divisionId)", ex.ToString(), string.Empty);
        throw ex;
    }
    finally
    {
        if (conn != null)
            conn.Close();
        conn = null;
    }

    return projectCategory;
}

public static ProjectCategory ProjectCategoryConstructor(SqlDataReader dr)
{
    ProjectCategory ec = new ProjectCategory();

    ec.CategoryId = dr["CategoryId"].SDR_GetInt();
    ec.Name = dr["Name"].SDR_GetString();
    ec.Description = dr["Description"].SDR_GetString();
    ec.LastModified = dr["LastModified"].SDR_GetDateTime();
    ec.ModifiedBy = dr["ModifiedBy"].SDR_GetString();

    return ec;
}

Thanks for any help.

Answer 1

Your combobox is binding to a property called “categories”. You don’t show any other code for this property. It will only update if you call propertychanged event for categories. Did you mean to bind to “ProjectCategories”?