Convert received keys in PreviewKeyDown to a string

Question

I am using PreviewKeyDown event on a window to receive all the keys from a barcode scanner. The KeyEventArgs is an enumeration and does not given me the actual string. I dont want to use TextInput as some of the keys may get handled by the control itself and may not bubble up to the TextInput event.

I am looking for a way to convert the the Keys that I get in PreviewKeyDown to actual string. I looked at the InputManager, TextCompositionManager etc but I am not finding a way where I give the list of keys and it comes back with a string. TextCompositionManager or something must be converting these Keys to a string which is what is available in TextInput.

score 2 · Accepted Answer · answered Oct 01 '09 at 18:18

Here is the event that I am using. The KeyDown gets the keys and the PreviewTextInput gets the actual text. So somewhere in between the keys are getting converted to text.

 public Window1()
            {
                InitializeComponent();
                TextCompositionManager.AddPreviewTextInputStartHandler(this, new TextCompositionEventHandler(Window_PreviewTextInput));
                this.AddHandler(Window.KeyDownEvent, new System.Windows.Input.KeyEventHandler(Window_KeyDown), true);
            }

    private void Window_PreviewTextInput(object sender, TextCompositionEventArgs e)
            {
            }

    private void Window_KeyDown(object sender, System.Windows.Input.KeyEventArgs e)
            {
            }

That the .NET framework returns the raw scan codes on KeyUp/KeyDown events is simply "impossible" (as in "too shocking to be true"). So what do we do? Use the `PreviewTextInput` event instead. We get the string representation of the key pressed like this: `void KeyboardNavigation(object sender, TextCompositionEventArgs e) { string typedChar = e.Text; }` — Helge Klein, Sep 25 '10 at 21:39

score 1 · Answer 2 · answered Oct 05 '09 at 10:52

Key -> Text conversion is much more complicated than you think, there is actually no way to map a single key stroke to a single character because in some languages and some cases you need multiple keystrokes to compose a single character.

Since you are interested in input from a barcode scanner (that I assume will only generate a small subset of what windows can handle, maybe only ASCII maybe even less) you can build the conversion table yourself and hard code it into your program - it's much easier then to handle all the craziness that Windows text handling does (for fun, lookup "dead keys").

Convert received keys in PreviewKeyDown to a string

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