priyanka.sarkar priyanka.sarkar - 1 month ago 15
C# Question

Set focus on textbox in WPF from view model (C#)

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}"/>

Answer

Let me answer to your question in three parts.

  1. I'm wondering what is "cs.txtCompanyID" in your example? Is it a TextBox control? If yes, then you are on a wrong way. Generally speaking it's not a good idea to have any reference to UI in your ViewModel. You can ask "Why?" but this is another question to post on Stackoverflow :).

  2. The best way to track down issues with Focus is... debugging .Net source code. No kidding. It saved me a lot of time many times. To enable .net source code debugging refer to Shawn Bruke's blog.

  3. Finally, general approach that I use to set focus from ViewModel is Attached Properties. I wrote very simple attached property, which can be set on any UIElement. And it can be bound to ViewModel's property "IsFocused" for example. Here it is:

    public static class FocusExtension
    {
        public static bool GetIsFocused(DependencyObject obj)
        {
            return (bool) obj.GetValue(IsFocusedProperty);
        }
    
        public static void SetIsFocused(DependencyObject obj, bool value)
        {
            obj.SetValue(IsFocusedProperty, value);
        }
    
        public static readonly DependencyProperty IsFocusedProperty =
            DependencyProperty.RegisterAttached(
                "IsFocused", typeof (bool), typeof (FocusExtension),
                new UIPropertyMetadata(false, OnIsFocusedPropertyChanged));
    
        private static void OnIsFocusedPropertyChanged(
            DependencyObject d, 
            DependencyPropertyChangedEventArgs e)
        {
            var uie = (UIElement) d;
            if ((bool) e.NewValue)
            {
                uie.Focus(); // Don't care about false values.
            }
        }
    }
    

    Now in your View (in XAML) you can bind this property to your ViewModel:

    <TextBox local:FocusExtension.IsFocused="{Binding IsUserNameFocused}" />
    

Hope this helps :). If it doesn't refer to the answer #2.

Cheers.

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