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ASP.Net: Validate the accepted file type of a file upload using RegularExpressionValidator

While working with file upload control, it is common requirement that user should upload only flie type that suits requirement. For example there is option of uploading resume in your application, resume is normally word or Pdf document, now suppose there is no validation of required file types and user uploaded image file or excel file instead of document, so here come loophole in your application.

We can validate required file type either using JavaScript or we can use RegularExpression Validator to validate file.

Here I am writing example for RegularExpressionValidator: 
<asp:FileUpload ID="fileUpload" runat="server" />

<asp:RegularExpressionValidator ID="regFileType" runat="server" ControlToValidate=" fileUpload" Text="*Only accepted file formats are pdf, doc and docx" ValidationExpression="^.+(.pdf|.PDF|.doc|.DOC|.docx|.DOCX)$" ValidationGroup="vg" ForeColor="Red">
</asp:RegularExpressionValidator>

So here I have one file upload control and I have used RegularExpressionValidator to validate this file upload control.

Now add the button control to test this validation.
<asp:Button ID="btnSave" runat="server" Text="Save" ValidationGroup="vg" />

Here main thing to notice is “ValidationExpression”.

You can also change the ValidationExpression as per file extension you want to allow for upload. For example if you want to allow images to be uploaded then you can simply change the ValidationExpression as:
ValidationExpression="^.+(.jpg|.JPG|.jpeg|.JPEG|.gif|.GIF|.png|.PNG)$"

Programming say love me or leave me..:P
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