GridViewColumnHeader doesn't appear

I have a WPF form with some GridViewColumns in them to display the data. However, even though I set the Header property in each column, the headers never appear.

XAML:

<Window x:Class="MyProject.ViewModel.MyClassView"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="clr-namespace:MyProject.ViewModel"        
        Title="Title" Height="210.4" Width="500" ResizeMode="NoResize" 
        WindowStartupLocation="CenterOwner" WindowStyle="ToolWindow">
    <Window.Resources>
        <DataTemplate x:Key="tempA">
            <TextBlock Text="{Binding Path=dataA}"/>
        </DataTemplate>
        <DataTemplate x:Key="tempB">
            <TextBlock Text="{Binding Path=dataB}"/>
        </DataTemplate>
        <DataTemplate x:Key="tempC">
            <TextBlock Text="{Binding Path=dataC}"/>
        </DataTemplate>
    </Window.Resources>
    <Grid Margin="5,5,5,5">
        <ListView x:Name="MyList" ItemsSource="{Binding MyDataCollection}" MouseDoubleClick="ListView_MouseDoubleClick">
            <ListView.View>
                <GridView>
                    <GridViewColumn x:Name="colA" Header="Name" Width="100" CellTemplate="{StaticResource tempA}"/>
                    <GridViewColumn x:Name="colB" Header="Type" Width="100" CellTemplate="{StaticResource tempB}"/>
                    <GridViewColumn x:Name="colC" Header="Diameter" Width="100" CellTemplate="{StaticResource tempC}"/>
                </GridView>
            </ListView.View>
        </ListView>
    </Grid>
</Window>

Code-behind:

namespace MyProject.ViewModel
{
    public partial class MyClassView : Window
    {
        public object SelectedItem = null;

        public MyClassView()
        {
            InitializeComponent();
        }

        private void ListView_MouseDoubleClick(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            SelectedItem = MyList.SelectedItem;
        }
    }
}

ViewModel:

namespace MyProject.ViewModel
{
    public class MyViewModel : INotifyPropertyChanged
    {
        public string Type { get; set; }
        public object MyDataCollection { get; set; }

        public MyViewModel(object collection, string type)
        {
            Type = type;
            MyDataCollection = collection;
        }

        internal void RaisePropertyChanged(string prop)
        {
            if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(prop)); }
        }
        public event PropertyChangedEventHandler PropertyChanged;
    }
}

The object that is passed into the ViewModel constructor is guaranteed to contain dataA, dataB and dataC among others.

Could someone explain why the headers in my GridView aren't appearing?

Try using a DataGrid instead.

It would look something like this:

<DataGrid ItemsSource="{Binding MyDataCollection}" AutoGenerateColumns="False" >
    <DataGrid.Columns>
        <DataGridTextColumn Header="Name" Binding="{Binding Name}" IsReadOnly="True"/>
        <DataGridComboBoxColumn Header="Type" ItemsSource="{Binding TypeList}" SelectedItemBinding="{Binding Type}"/>
        ...
    </DataGrid.Columns>
</DataGrid>