Validating file extension with regularexpressionvalidator

Notice in the following screen capture, we can see the Required Field Validator error message display on the form. The user does not wait on a server round trip to discover errors.This is the exact position the error message will appear if validation fails. This also improves response time on the server because the ASP.

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When validation fails the normal flow of execution continues.

You need to check the Is Valid property to know if a validation check failed.

The "i" flag needs to be set which currently cannot be done with the Regular Expression attribute.

If this is necessary in your scenario then I can suggest to implement a custom attribute that sets flag.

For this first example we do not need to place much code into the code-behind file. NET runtime does not waste time processing a request with invalid information.

We can double click on both of the Button controls on the form to add event handlers for the click events. If you want to disable just client side validation for a specific validation control, you can set the control’s Enable Client Script property to false. NET will always execute validation checks on the server when a button click event arrives requiring validation.

Malicious users might circumvent client side validations in an effort to break-in or damage your servers.

Simply put, never trust the data in an incoming request, and always validate on the server.

Validation occurs when a user clicks any Button control by default, but you can change this behavior by setting the Causes Validation property to false. Whenever the user presses a button on the form, the script executes the validation checks for each validation control on the form.

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