Text input validation for textbox in .NET 4.0

Question

I want to validate (in some simple way) if the input text for a textbox is a number, I would use this code: LINK

But here's a problem: I use .NET 4.0 not 4.5, so I don't havePreviewTextInput event.

I could use TextChanged, but now it doesn't have e.Handled validator.

Is there any simple solution for this (I want to avoid tons of code)?

can you use the `char.IsNumeric` function much easier in my opinion — MethodMan, Jul 29 '13 at 14:58
Use `TryParse` and deal with the exception. Or, if you wish to be adventurous, try RegEx! For just validation that it is a number, RegEx is actually pretty simple. — Daniel Underwood, Jul 29 '13 at 14:59
@DJKRAZE Wouldn't `char.IsNumeric` only work with single digit numbers? — Daniel Underwood, Jul 29 '13 at 15:01
@danielu13: If it works for single numbers making it work for an entire string is trivial. — Guvante, Jul 29 '13 at 15:03
it will work on a string if the `OP` wants to check the whole string char by char in a for loop or foreach loop — MethodMan, Jul 29 '13 at 15:03
@danielu13 - A simple way to address your concern would be to convert the `String` into a `char` array and check each element of the array if its a number. You could strip certain characters away from the string to prevent it say failing when `999-999-9999` was entered. — Security Hound, Jul 29 '13 at 15:04
I wanted to cancel the event if it's not numeric. Im not retarded:D I know how to check if the string is a number. But I wanted to know if I should remember the old value of the textbox, then validate the new, if not a number, write the old. `PreviewTextInput` supports event cancellation, but it's not available in 4.0 framework — Nickon, Jul 30 '13 at 07:16

score 2 · Accepted Answer · answered Jul 29 '13 at 15:24

2

If you have access to the property that will hold the value, you can use a DataAnnotation on the property.

[RegularExpression(Pattern="[0-9]+")]
public string MyProperty { get; set; }

This MSDN article goes abit more in depth about the subject.

answered Jul 29 '13 at 15:24

ywm

score 0 · Answer 2 · answered Jul 29 '13 at 15:16

0

It is difficult to determine what a number is and isn't. I would use TryParse. If it fails it's not a number.

string s = "12345";

int number;
bool result = int.TryParse(s, out number);

if(!result)
{
    // not a number.
}

answered Jul 29 '13 at 15:16

Sam Leach

Ye, but I said I don't have `e.Handled` validator. So I can't escape the event I thought there's some simple way to do this. Like `PreviewTextInput` in 4.5 – Nickon Jul 30 '13 at 07:12

2 Answers2