I have a TextBox and a Button in my view.
Now I am checking a condition upon button click and if the condition turns out to be false, displaying the message to the user, and then I have to set the cursor to the TextBox control.
if (companyref == null)
{
    var cs = new Lipper.Nelson.AdminClient.Main.Views.ContactPanels.CompanyAssociation(); 
    MessageBox.Show("Company does not exist.", "Error", MessageBoxButton.OK,
                    MessageBoxImage.Exclamation);
    cs.txtCompanyID.Focusable = true;
    System.Windows.Input.Keyboard.Focus(cs.txtCompanyID);
}
The above code is in the ViewModel.
The CompanyAssociation is the view name.
But the cursor is not getting set in the TextBox.
The xaml is:
<igEditors:XamTextEditor Name="txtCompanyID" 
                         KeyDown="xamTextEditorAllowOnlyNumeric_KeyDown"
                         ValueChanged="txtCompanyID_ValueChanged"
                         Text="{Binding Company.CompanyId,
                                        Mode=TwoWay,
                                        UpdateSourceTrigger=PropertyChanged}"
                         Width="{Binding ActualWidth, ElementName=border}"
                         Grid.Column="1" Grid.Row="0"
                         VerticalAlignment="Top"
                         HorizontalAlignment="Stretch"
                         Margin="0,5,0,0"
                         IsEnabled="{Binding Path=IsEditable}"/>
<Button Template="{StaticResource buttonTemp1}"
        Command="{Binding ContactCommand}"
        CommandParameter="searchCompany"
        Content="Search"
        Width="80"
        Grid.Row="0" Grid.Column="2"
        VerticalAlignment="Top"
        Margin="0"
        HorizontalAlignment="Left"
        IsEnabled="{Binding Path=IsEditable}"/>