I'm building a form in a C# WinRT app, and I'd like to restrict the characters in one of the TextBox components to numerals only. (This TextBox would be for a user to enter a year into.)
I've searched for a while, but haven't been able to figure this one out without setting up an event listener on the TextChanged event, and inspecting the text property on every key press. Is there a way to simply say that a user can only enter specific characters into a TextBox?
The simplest thing that could possibly work is to bind to the OnTextChanged event and modify the text according to your rules.
<TextBox x:Name="TheText" TextChanged="OnTextChanged" MaxLength="4"/> private void OnTextChanged(object sender, TextChangedEventArgs e) { if (TheText.Text.Length == 0) return; var text = TheText.Text; int result; var isValid = int.TryParse(text, out result); if (isValid) return; TheText.Text = text.Remove(text.Length - 1); TheText.SelectionStart = text.Length; } However, I'd shy away from this approach since the mantra of Metro is touch first UI and you can easy do it in a touch first manner with a FlipView control.
Try setting TextBox.InputScope property to InputScopeNameValue.Number, as mentioned in Guidelines and checklist for text input in MSDN.
Valid Year
DateTime newDate; var validYear = DateTime.TryParseExact("2012", "yyyy", CultureInfo.InvariantCulture, DateTimeStyles.None, out newDate); //valid Invalid Year
var validYear = DateTime.TryParseExact("0000", "yyyy", CultureInfo.InvariantCulture, DateTimeStyles.None, out newDate); //invalid This seems to work for me:
private void TextBox_KeyDown(object sender, KeyRoutedEventArgs e) { if ((e.Key < VirtualKey.Number0) || (e.Key > VirtualKey.Number9)) { // If it's not a numeric character, prevent the TextBox from handling the keystroke e.Handled = true; } } See the documentation for the VirtualKey enumeration for all the values.
Based on a posting at link, adding the tab to allow navigation.
private void decimalTextBox_KeyDown(object sender, KeyRoutedEventArgs e) { bool isGoodData; // flag to make the flow clearer. TextBox theTextBox = (TextBox)sender; // the sender is a textbox if (e.Key>= Windows.System.VirtualKey.Number0 && e.Key <= Windows.System.VirtualKey.Number9) // allow digits isGoodData = true; else if (e.Key == Windows.System.VirtualKey.Tab) isGoodData = true; else if (e.Key >= Windows.System.VirtualKey.NumberPad0 && e.Key <= Windows.System.VirtualKey.NumberPad9) // allow digits isGoodData = true; else if (e.Key == Windows.System.VirtualKey.Decimal || (int)e.Key == 190) // character is a decimal point, 190 is the keyboard period code // which is not in the VirtualKey enumeration { if (theTextBox.Text.Contains(".")) // search for a current point isGoodData = false; // only 1 decimal point allowed else isGoodData = true; // this is the only one. } else if (e.Key == Windows.System.VirtualKey.Back) // allow backspace isGoodData = true; else isGoodData = false; // everything else is bad if (!isGoodData) // mark bad data as handled e.Handled = true; } 
Use a MaskedTextBox control. For numerals only, just use the Mask property to specify the characters and the length, if any. e.g. if you want only five numbers to be entered, you set the mask property to "00000". Simple as that. Windows handles the restriction for you.
