In C #, only numbers can be entered in the implementation text box.

Code

 Keypress event of the text box:
Write the following code in the keypress event of the text box (such as txtnum) You want to enter:
Private void txtnum_keypress (Object sender, keypresseventargs E)
{
If (! Char. isnumber (E. keychar) & E. keychar! = (Char) keys. Back)
{
E. Handled = true;
}
}

Implementation with method: ^ [0-9] {1,} $ Regular Expression in the textchanged event
RegEx r = new RegEx ("^ [0-9] {1, }$ ");
If (! R. ismatch (textbox1.text ))
{
MessageBox. Show ("enter a number ");
}

Text Box onkeydown event:
Txt1.attributes. Add ("onkeydown", "If (! (Event. keycode> = 48 & event. keycode <= 57) | (event. keycode> = 96 & event. keycode <= 105) & (event. keycode! = 8 )&&

(Event. keycode! = 9) & (event. keycode! = 13) & (event. keycode! = 46) {alert ('Enter the number'); Return false ;}");

Text Box keypress event:
Private void txtnumber_keypress (Object sender, system. Windows. Forms. keypresseventargs E)
{
If (E. keychar> = '0' & E. keychar <= '9 ')
{
E. Handled = false;
Return;
}
E. Handled = true;
}

Restrictions on using regular expressions:
Use regular expressions to restrict text box input in a webpage form:
You can only enter Chinese characters using regular expressions: onkeyup = "value = value. replace (/[^ \ u4e00-\ u9fa5]/g, '')" onbeforepaste = "clipboardData. setdata ('text', clipboardData. getdata ('text '). replace (/

[^ \ U4e00-\ u9fa5]/g ,''))"
1. you can only enter the full-width characters: onkeyup = "value = value. replace (/[^ \ uff00-\ Uffff]/g, '')" onbeforepaste = "clipboardData. setdata ('text', clipboardData. getdata

('Text'). Replace (/[^ \ uff00-\ Uffff]/g ,''))"
2. use a regular expression to limit that only numbers can be entered: onkeyup = "value = value. replace (/[^ \ D]/g, '')" onbeforepaste = "clipboardData. setdata ('text', clipboardData. getdata ('text '). replace (/[^ \ D]/g ,''))"


3. you can only enter numbers and English letters using regular expressions: onkeyup = "value = value. replace (/[\ W]/g, '')" onbeforepaste = "clipboardData. setdata ('text', clipboardData. getdata ('text '). replace (/

[^ \ D]/g ,''))"



Text Box amount input: <asp: regularexpressionvalidator id = "regularexpressionvalidator1" runat = "server" controltovalidate = "txtamount"
Display = "NONE" errormessage = "the payment amount can only be a number, up to four decimal places" validationexpression = "^ [0-9] + (\. [0-9] {0, 4 })? $ "> </ASP: regularexpressionvalidator>