#1,067 – Experimenting with Keyboard Focus

A control has keyboard focus if it can accept input from the keyboard.  The sample code below is a working app that lets us experiment with keyboard focus by setting a Label to indicate which control has focus.

XAML includes some controls and defines a GotKeyboardFocus for the top-level Window.

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Keyboard Focus" Width="320" Height="190"
        GotKeyboardFocus="Window_GotKeyboardFocus">

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>

        <StackPanel Orientation="Horizontal">
            <StackPanel Background="AliceBlue" Margin="5">
                <TextBox Name="txtLeft" Margin="5" Width="80"/>
                <Button Name="btnClickMe" Content="Click Me" Margin="5"/>
            </StackPanel>

            <StackPanel Background="PaleGoldenrod" Margin="5">
                <Label Content="I'm a Label"/>
                <TextBox Name="txtRight" Margin="5" Width="80"/>
                <CheckBox Name="chkCheckMe" Margin="5" Content="Check Me"/>
            </StackPanel>
        </StackPanel>

        <Label Grid.Row="1" Margin="5" Content="{Binding WhoHasFocus}"/>
    </Grid>
</Window>

Code-behind uses this code to set property indicating who has focus.

using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Diagnostics;
using System.Drawing;
using System.Threading;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
//using System.Windows.Media;

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window, INotifyPropertyChanged
    {
        public MainWindow()
        {
            InitializeComponent();
            this.DataContext = this;
        }

        // INotifyPropertyChanged
        public event PropertyChangedEventHandler PropertyChanged = delegate { };

        private void RaisePropertyChanged(string propName)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propName));
        }

        private string whoHasFocus;
        public string WhoHasFocus
        {
            get { return whoHasFocus; }
            set {
                if (value != whoHasFocus)
                {
                    whoHasFocus = value;
                    RaisePropertyChanged("WhoHasFocus");
                }
            }
        }

        private void Window_GotKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
        {
            CheckKeyboardFocus();
        }

        private void CheckKeyboardFocus()
        {
            IInputElement elem = Keyboard.FocusedElement;

            if (elem == null)
                WhoHasFocus = "NO FOCUS";
            else
            {
                FrameworkElement felem = elem as FrameworkElement;
                if (felem != null)
                {
                    string identifier = ((felem.Name != null) && (felem.Name.Length > 0)) ?
                        felem.Name :
                        felem.GetType().ToString();
                    WhoHasFocus = string.Format("FrameworkElement [{0}]", identifier);
                }
                else
                {
                    // Maybe a FrameworkContentElement has focus
                    FrameworkContentElement fcelem = elem as FrameworkContentElement;
                    if (fcelem != null)
                    {
                        string identifier = ((fcelem.Name != null) && (fcelem.Name.Length > 0)) ?
                            fcelem.Name :
                            fcelem.GetType().ToString();
                        WhoHasFocus = string.Format("FrameworkContentElement [{0}]", identifier);
                    }
                    else
                    {
                        WhoHasFocus = string.Format("Element of type [{0}] has focus", elem.GetType().ToString());
                    }
                }
            }
        }
    }
}

1067-001

About Sean
Software developer in the Twin Cities area, passionate about .NET technologies. Equally passionate about my own personal projects related to family history and preservation of family stories and photos.

One Response to #1,067 – Experimenting with Keyboard Focus

  1. Pingback: Dew Drop – May 7, 2014 (#1771) | Morning Dew

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