WPF itemscontrol binding problems - wpf

Question

<ItemsControl ItemsSource="{Binding ExportFormat, UpdateSourceTrigger=PropertyChanged}" Grid.Column="1">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<Button Content="{Binding}" Margin="5" Height="50" Width="70" Command="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}, Path=DataContext.setExportFormat, UpdateSourceTrigger=PropertyChanged}" CommandParameter="{Binding}"></Button>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
So i have that code in my xaml and the button gets filed with a list of string. Depending on what the users chooses on previous Usercontrol that item will be filed with differents items. The problem is if the user select one option at the first run the button will be filled correctly but if the user go back and select the other option the control doenst update and shows the same as before..
My english is not the best but i think i could made me understand! Any idea?!
PS: the bindind on Button is to a readOnly property so i cant define it to Mode="TwoWay".. i took a look on the debug and the property ExportFormat gets updates with the new items but the usercontrol still displays the first option!!
Sincerely Rui Nunes

Answer 1

You didn't provide code-behind so I'm gonna take a few shots in the dark here:
The ExportFormatcollection is not an ObservableCollection (or more generally, doesn't implement INotifyCollectionChanged).
If it actually is an ObservableCollection, you assign it directly, instead of clearing its items and adding the new ones. example:
ExportFormat = MyNewObsCollection; //Bad
ExportFormat.Clear();
foreach(var newItem in myNewObsCollection)
{
ExportFormat.Add(newItem); //Good
}
Side note: ExportFormat should be readonly

Answer 2

Thanks to #Baboon for giving me some lights on this problem. So the Solution to my problem is:
So my ExportFormat Property was defined as:
Private _ExportFormat As New List(Of String)
Public Property ExportFormat As List(Of String)
Get
Return _ExportFormat
End Get
Set(value As List(Of String))
_ExportFormat = value
NotifyPropertyChanged("ExportFormat")
End Set
End Property
and i just had to change the List(of String) to ObjectModel.ObservableCollection(Of String)..
Private _ExportFormat As New ObjectModel.ObservableCollection(Of String)
Public Property ExportFormat As ObjectModel.ObservableCollection(Of String)
Get
Return _ExportFormat
End Get
Set(value As ObjectModel.ObservableCollection(Of String))
_ExportFormat = value
NotifyPropertyChanged("ExportFormat")
End Set
End Property
And my problems got solved.. Thanks once again!