cannot find Name of DataGridColumn programmatically

I found the Columns collection in my datagrid, and was hoping to iterate through it to find a certain column Name. However, I can't figure out how to address the x:Name attribute of the column. This xaml illustrates my problem with a DataGridTextColumn and a DataGridTemplateColumn:

<t:DataGrid x:Name="dgEmployees" ItemsSource="{Binding Employees}" 
    AutoGenerateColumns="false" Height="300" >
    <t:DataGrid.Columns>
        <t:DataGridTextColumn x:Name="FirstName" Header="FirstName"
Binding="{Binding FirstName}" />
        <t:DataGridTemplateColumn x:Name="LastName" Header="LastName" >
            <t:DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding LastName}" />
                </DataTemplate>
            </t:DataGridTemplateColumn.CellTemplate>
        </t:DataGridTemplateColumn>
    </t:DataGrid.Columns>
</t:DataGrid>

And here is my code:

    DataGrid dg = this.dgEmployees;
    foreach (var column in dg.Columns) 
    {
        System.Console.WriteLine("name: " + (string)column.GetValue(NameProperty));
    }

At runtime, no value is present; column.GetValue doesn't return anything. Using Snoop, I confirmed that there is no Name property on either DataGridTextColumn or DataGridTemplateColumn.

What am I missing?

Solution

WPF has two different, yet similar concepts, x:Name, which is used to create a field which references an element defined in XAML, i.e. connecting your code-behind to your XAML, and FrameworkElement.Name, which uniquely names an element within a namescope.

If an element has a FrameworkElement.Name property, x:Name will set this property to the value given in XAML. However, there are instances where it is useful to link non FrameworkElement elements to fields in code-behind, such as in your example.

See this related question:

In WPF, what are the differences between the x:Name and Name attributes?

As an alternative, you could define your own attached property which can be used to name the columns. The attached property is defined as follows:

public class DataGridUtil
{

    public static string GetName(DependencyObject obj)
    {
        return (string)obj.GetValue(NameProperty);
    }

    public static void SetName(DependencyObject obj, string value)
    {
        obj.SetValue(NameProperty, value);
    }

    public static readonly DependencyProperty NameProperty =
        DependencyProperty.RegisterAttached("Name", typeof(string), typeof(DataGridUtil), new UIPropertyMetadata(""));

}

You can then assign a name to each column ...

xmlns:util="clr-namespace:WPFDataGridExamples"

<t:DataGrid x:Name="dgEmployees" ItemsSource="{Binding Employees}" 
    AutoGenerateColumns="false" Height="300" >
    <t:DataGrid.Columns>
        <t:DataGridTextColumn util:DataGridUtil.Name="FirstName" Header="FirstName"
Binding="{Binding FirstName}" />
        <t:DataGridTemplateColumn util:DataGridUtil.Name="LastName" Header="LastName" >
            <t:DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding LastName}" />
                </DataTemplate>
            </t:DataGridTemplateColumn.CellTemplate>
        </t:DataGridTemplateColumn>
    </t:DataGrid.Columns>
</t:DataGrid>

Then access this name in code as follows:

DataGrid dg = this.dgEmployees;
foreach (var column in dg.Columns) 
{
    System.Console.WriteLine("name: " + DataGridUtil.GetName(column));
}

Hope that helps