problem with combobox in wpf

Put  the combobox in xaml like this

<ComboBox Grid.Row="1"  Height="23" ItemsSource="{Binding}" IsSynchronizedWithCurrentItem="True"   Margin="143,12,185,0" Name="comboBox1" SelectedValue="{Binding Path=id}" DisplayMemberPath="username"  SelectedValuePath="id"  VerticalAlignment="Top" />

And write the code in xaml.cs in windows_loaded event

UserDataSet userdataSet = new UserDataSet();

        UserDataSetTableAdapters.UserTableAdapter userTableAdapter = new UserDataSetTableAdapters.UserTableAdapter();

comboBox1.ItemsSource = userTableAdapter.GetData();

// provide any datasource I am using tableadapter