Binding comobox to cells in datagrid and adding rows dynamically.

 I have a filter kind of interface which takes 3 fields. The filter and operator contains combobox list while value is a textbox. 

So i want to bind the same list to comboboxes in all the rows and when a user clicks on add button a row is added with comoboxes and text block .
 

I have reached upto this point only and it is not working the way it should . Here is the code :-

It does not display the list and how do i create rows dynamically with comobobox entites?

<DataGrid x:Name="filtergrid" Grid.Column="1" Grid.Row="0" Margin="19,0,0,45" CanUserAddRows="True" ItemsSource="{Binding}"><DataGrid.Columns><DataGridComboBoxColumn x:Name="filter1" Header="Filter"  TextBinding="{Binding filter }"></DataGridComboBoxColumn><DataGridComboBoxColumn x:Name="filter2" Header="Operator" ItemsSource="{Binding oper}" /><DataGridTextColumn x:Name="filter3" Header="Value"/></DataGrid.Columns> </DataGrid>