Validate and upload image in code behind in asp.net

Introduction: 

 It is always better to validate the file extension before uploading it i.e. if you want the user can upload only .jpg, .jpeg, .png, .gif , .bmp files then you have to check the extension of the file the user is going to upload before uploading.

Suppose, somewhere in your application if you want to upload profile pic, in that case you have to check the extension of the picture before uploading. So that nobody can upload file with different file extension.

Here is the example with code:

• Place a FileUpload control and a button control on design page(.aspx)

<asp:FileUpload ID="FileUpload1" runat="server" />

        <asp:Button ID="btnUploadImage" runat="server" Text="upload Image"

            onclick="btnUploadImage_Click"  />

C#.Net Code to Validate and upload image files

• In the code behind (.aspx.cs) file write the code: In this example we create a function to validate file extension. If extension of the files is same as we required then this function will return "true". Then we call this function at "btnUploadImage_Click" event of button. If function will return true value then file will be uploaded to the server, otherwise it will give a message "Please upload .jpeg,.png,.gif,.jpg,.bmp image only".

    private bool IsValidExtension(string filePath)

    {

        bool isValid = false;

        string[] fileExtensions = {".bmp",".jpg",".png",".gif",".jpeg",".BMP",".JPG",".PNG",".GIF",".JPEG"};

        for (int i = 0; i <= fileExtensions.Length - 1; i++)

        {

            if (filePath.Contains(fileExtensions[i]))

            {

                isValid = true;

            }

        }

        return isValid;

    }

    protected void btnUploadImage_Click(object sender, EventArgs e)

    {

        if (IsValidExtension(FileUpload1.PostedFile.FileName))

        {

            //write code to upload file

            string filePath = (Server.MapPath("Uploads/") + Guid.NewGuid() + FileUpload1.PostedFile.FileName);

            FileUpload1.SaveAs(filePath);

        }

        else

        {

            Response.Write("Please upload .jpeg,.png,.gif,.jpg,.bmp image only");

        }

    }

VB.Net Code to Validate and upload image files

• In the code behind (.aspx.vb) file write the code:

Private Function IsValidExtension(ByVal filePath As String) As Boolean

        Dim isValid As Boolean = False

        Dim fileExtensions As String() = {".bmp", ".jpg", ".png", ".gif", ".jpeg", ".BMP", _

         ".JPG", ".PNG", ".GIF", ".JPEG"}

        For i As Integer = 0 To fileExtensions.Length - 1

            If filePath.Contains(fileExtensions(i)) Then

                isValid = True

            End If

        Next

        Return isValid

    End Function

    Protected Sub btnUploadImage_Click(ByVal sender As Object, ByVal e As EventArgs)

        If IsValidExtension(FileUpload1.PostedFile.FileName) Then

            'write code to upload file

            Dim filePath As String = (Server.MapPath("Uploads/") + Guid.NewGuid() + FileUpload1.PostedFile.FileName)

            FileUpload1.SaveAs(filePath)

        Else

            Response.Write("Please upload .jpeg, .png, .gif, .jpg, .bmp image only")

        End If

    End Sub

 

Note: In the above application I have uploaded the images to a folder i.e. “Uploads”.