#311 – Giving Focus to a Control, Part II

June 1, 2011 Leave a comment

You can give focus to a specific control at run-time using the Keyboard.Focus static method.  You can also give focus to any control that inherits from UIElement using the control’s Focus method.

		public MainWindow()
		{
			this.InitializeComponent();

            this.Loaded += new RoutedEventHandler(MainWindow_Loaded);

		}

        void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
            // On startup, set focus to first TextBox in window
            txtFirst.Focus();
        }

The difference between these two methods is:

  • Keyboard.Focus just sets keyboard focus
  • UIElement.Focus tries to set keyboard focus.  If the control fails to get keyboard focus, the method sets logical focus to the control

Filed under Controls Tagged with , , , ,

#310 – Give a Control Logical Focus

May 31, 2011 2 Comments

You can give a control the keyboard focus using the static Keyboard.Focus method.  If you want to instead give a control the logical focus, you can use the FocusManager.SetFocusedElement static method.  (In the System.Windows.Input namespace).

                // Give logical focus to txtFirst TextBox
                DependencyObject focusScope = FocusManager.GetFocusScope(txtFirst);
                FocusManager.SetFocusedElement(focusScope, txtFirst);

If you do this in an application with multiple windows and you set logical focus for a control in the inactive window, you’ll see that it does not get keyboard focus.  You can continue entering text in a control in the active window.  But when you switch back to the inactive window, you’ll see that the control does get keyboard focus.

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#309 – Keyboard Focus vs. Logical Focus

May 27, 2011 Leave a comment

In WPF, there are two types of focus–keyboard focus and logical focus.

If an element has keyboard focus, it is the element that can currently receive input from the keyboard.  Only a single element in an entire application can have keyboard at any given time.

An element has logical focus if it is the element within a focus scope that has focus.  The idea is that WPF keeps track of one or more groups of controls, each of which makes up a focus scope.  Within each focus scope, a single control can have logical focus.  This allows WPF to remember the control that last had focus in a group of controls and give the keyboard focus back to the proper control when a group of controls becomes active again.

An element that has keyboard focus always has logical focus.  An element that has logical focus may not have keyboard focus.

Filed under Controls Tagged with , , , ,

#308 – Checking to See Which Control Has Keyboard Focus

May 26, 2011 Leave a comment

You can use the Keyboard.FocusedElement static property (in System.Windows.Input namespace) to determine which control currently has focus.

Here’s an example:

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

            if (elem == null)
                Debug.WriteLine("Nobody has focus");
            else
            {
                FrameworkElement felem = elem as FrameworkElement;
                if (felem != null)
                {
                    string identifier = ((felem.Name != null) && (felem.Name.Length > 0)) ?
                        felem.Name :
                        felem.GetType().ToString();
                    Debug.WriteLine(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();
                        Debug.WriteLine(string.Format("FrameworkContentElement - {0}", identifier));
                    }
                    else
                    {
                        Debug.WriteLine(string.Format("Element of type {0} has focus", elem.GetType().ToString()));
                    }
                }
            }
        }

Filed under Controls Tagged with , , ,

#307 – Giving Focus to a Control When an Application Starts

May 25, 2011 1 Comment

A WPF application does not automatically gives keyboard focus to any single control when the application starts.  You can force a control to get focus at application startup by using the Keyboard.Focus static method (in the System.Windows.Input namespace).

Here’s an example that sets focus to one of the TextBox controls in the main window.

        public MainWindow()
        {
   	        this.InitializeComponent();

            this.Loaded += new RoutedEventHandler(MainWindow_Loaded);
        }

        void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
            // On startup, set focus to my first TextBox
            Keyboard.Focus(txtFirst);
        }

Filed under Controls Tagged with , , ,

#306 – Keyboard Focus

May 24, 2011 1 Comment

In WPF, as in other Windows applications, a control or user interface element has focus if it can receive keyboard input.  Specifically, we say that the control has keyboard focus.

By default, when a WPF application start up, no control has focus.  You can give a control focus by pressing the TAB key–which cycles through all of the controls that are able to receive focus.  You can also give a control focus by clicking on the control.

Not all controls are able to receive focus.  In general, only controls that can accept user input can get focus.

Most controls will give some visual indication that the control currently has keyboard focus.  Many controls will display a dashed line around the control to indicate that it has focus.  The TextBox will display a light blue border to show that it has focus and also contain an editing carat.

Filed under Controls Tagged with , ,

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