Mobile application development is a very new field for me. Being a university professor has got me through some VB courses that were not so deep, but I might not call myself a professional developer. Anyway, few weeks ago I had an increasing interest in mobile application development and I decided to start with WP7 development because I had some experience in the VB environment.
I installed the Visual Studio 2010 Express for Windows Phone. I started having some trouble when I needed to get a TextBox (which is a simple text entry space) to receive only numbers from the user and not allow the user to enter anything but numbers.
A simple solution would be the use of an event called KeyDown that is triggered whenever a key is pressed. Afterwards, I need to filter the pressed key such that if it is a number, it would pass, and any other key would be ignored. The easiest way to do this is through the key codes from 48 to 57 which are the correspondent codes to the keys “0”, “1”, “2”,….”9″. So I wrote a simple line of code to do the required:
[crayon lang=”vb”]Private Sub YOURTEXTBOX_KeyDown(sender As Object, e As System.Windows.Input.KeyEventArgs) Handles YOURTEXTBOX.KeyDown
if e.PlatformKeyCode < 48 or e.PlatformKeyCode > 57 then e.Handled=true
End Sub[/crayon]
This line basically ends the handling of the key that is pressed if it is not a digit.
What came as a shock to me was that when testing the app on the emulator on the computer, I found out that other characters (some symbols) where also showing up in the textbox along with the numbers. Symbols like ( ) $ % where also “pressable” in the text box. After digging for a while, I found out that these symbols had the same key codes as the digits ..!!!
To get a solid ground of this finding, I created a simplified app that simply shows the key code of the key that you are pressing on the virtual keyboard. Yes. Numbers and few symbols have the same key codes. After testing, the numbers and the symbols having the same key codes such as were frustrating; number 2 and @, number 3 and #, and all the others. The capital and small letters also have the same codes.
Apparently, I was not the only one who had this few other developers also had that issue. Since I have not yet received my Windows phone, I was not able to confirm that this is an Emulator glitch or an OS glitch.
If you have an unlocked Windows phone and Visual Studio, and you would like to confirm, or deny, that issue, download the .xap file of the app I did to view the codes of pressed keys and comment back in here. Here is the app download link to the KeyCodeDisplay.xap.
Moving on to the app development, if you are wondering how to go around this in the WP7 app that you are developing, here is one of the solutions. Use an event called KeyUp instead of the KeyDown used earlier, and put this code in it
[crayon lang=”vb”]Private Sub YOURTEXTBOX_KeyUp(sender As Object, e As System.Windows.Input.KeyEventArgs) Handles YOURTEXTBOX.KeyUp
Dim T As String, a As Char, b as Integer
T = “”
b=YOUTEXTBOX.SelectionStart
For i = 1 To YOURTEXTBOX.Text.Length
a = YOURTEXTBOX.Text.Chars(i – 1)
If a = “0” Or a = “1” Or a = “2” Or a = “3” Or a = “4” Or a = “5” Or a = “6” Or a = “7” Or a = “8” Or a = “9” Then
T = T + YOURTEXTBOX.Text.Chars(i – 1)
End If
Next i
YOURTEXTBOX.Text = T
If T <> “” Then YOURTEXTBOX.SelectionStart = b
End Sub
[/crayon]
I know that changing the InputScope can handle the situation with a PhoneNumberInputScope, but still the special characters such as “.” can cause you a problem. Another case is when you need a limited number of characters to be acceptable instead of the whole keyboard. I needed to use a similar method in my app PassworderPro when I had to create a textbox that accepts only capital letters.
