绑定问题MVVM

Question

我有一个ListBox，它通过ViewModel和DataTemplate填充，我也有一个绑定。问题是DataTemplate中的绑定不起作用。这是我的代码：

视图模型：

private void NotifyPropertyChanged(string propertyName)
{
    PropertyChangedEventHandler handler = PropertyChanged;

    if (null != handler)
    {
        handler(this, new PropertyChangedEventArgs(propertyName));
    }
}
#endregion

private string strHeaderText;
public string HeaderText
{
    get
    {
        if (null != this.Trips)
        {
            if (null != this._trips.name)
            {
                return this._trips.name;
            }
        }

        return "Trip";
    }
    set
    {
        this.strHeaderText = value;
    }
}

public TripTypeViewModel()
{
    this.TripTypeViewModelDataSource.Clear();

    foreach (TripType tt in TripsResponseTypeViewModelDataSource.FirstOrDefault().Trip)
    {
        this.TripTypeViewModelDataSource.Add(tt);
    }
}
...

private ObservableCollection<TripType> tripTypeViewModelDataSource;
public ObservableCollection<TripType> TripTypeViewModelDataSource
{
    get
    {
        if (null == this.tripTypeViewModelDataSource)
        {
            this.tripTypeViewModelDataSource = new ObservableCollection<TripType>();
        }

        return this.tripTypeViewModelDataSource;
    }
} 

这是我的查看

 <ListBox x:Name="ItemsLB" ItemsSource="{Binding tripTypeViewModel.TripTypeViewModelDataSource}">
        <ListBox.ItemTemplate>
            <DataTemplate>
                <Button Content="{Binding tripTypeViewModel.HeaderText}" Width="Auto" Height="Auto"/>
            </DataTemplate>
        </ListBox.ItemTemplate>
    </ListBox>