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ASP.NET Textbox - Avoid Copy Paste of few characters

Answer 1

+3 A:

First of all, you really shouldn't be accessing the user's clipboard, even if some versions of IE allow it. For reasons of integrity, that's simply nothing a browser should be dealing with. Either way, you could check the textbox value after paste, rather than inspecting the clipboard content during paste.

However, better still would probably be to perform this validation on submit. Try the built in regular expression validators. Because really, you worry about users submitting dangerous characters, right, not about the fact that they actually pasted them?

EDIT (example)

<asp:TextBox ID="txtName" runat="server"/>
<asp:RegularExpressionValidator ID="regexpName" runat="server"     
    ErrorMessage="This expression does not validate." 
    ControlToValidate="txtName" Display="Dynamic"
    ValidationExpression="^[^<>]$" />

David Hedlund 2009-07-09 13:59:57

Thanks d.We tried this and this works fine in most of the case. There is only on problem here. Just wanted opinion on whether we can handle this more gracefully than what I am thinking.When users pastes dangerous characters, and clicks on other controls which cause post back e.g. Checkbox, the submit request identifies the characters and halts the post back. But the Check Box values gets changed. Same happens with Drop down. Am thinking of storing these values and reset them incase submit is halted. Is there any cleaner way?Thanks,Atul

Atul 2009-07-09 14:18:10

+1 also, if that field is required be sure to use the RequiredFieldValidator on it as well since the RegularExpressionValidator alone does not make the field mandatory, it only checks it if there's content (whitespace or a blank entry is allowed and not validated).

Ahmad Mageed 2009-07-09 14:18:19

@Atul: if I understood you correctly I think you can add EnableClientScript="false" in the validator tag. This will prevent client side validation, so there won't be immediate feedback but it will validate on submit. See if that helps.

Ahmad Mageed 2009-07-09 14:21:35

@Ahmad: That would require actually submitting the dangerous characters, though, which will throw an exception if EventValidation isn't disabled

David Hedlund 2009-07-09 14:32:20

Answer 2

A:

Are you trying to modify what is in the users clipboard before the paste? Why not attach a onchange event that does any validation that you require? You could replace out any characters that you don't want in there.

Alex 2009-07-09 14:03:16

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ASP.NET Textbox - Avoid Copy Paste of few characters

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