How to prevent postback when button is clicked

Question

I have a code that save file in database. I have this function in my code behind:

protected void AttachFile(object sender, EventArgs e)
    {
        if (txtFile.HasFile)
        {
            string filename = Path.GetFileName(txtFile.PostedFile.FileName);
            string contentType = txtFile.PostedFile.ContentType;

            using (Stream fs = txtFile.PostedFile.InputStream)
            {
                using (BinaryReader br = new BinaryReader(fs))
                {
                    Random ran = new Random();

                    byte[] bytes = br.ReadBytes((Int32)fs.Length);
                    NewRequestService newrequest = new NewRequestService();

                    string temp_id = "";
                    temp_id = ran.Next(100000, 999999).ToString();

                    saveAttachFile(filename, contentType, bytes, temp_id);
                    hdnAttachID.Value = temp_id;
                    lblAttach.InnerHtml = msg;
                }
            }

        }
        else { lblAttach.InnerHtml = "\"Please browse the file to attach.\""; }

    }

And here's my HTML:

<asp:Button ID="btnAttached" runat="server" Text="Attach File" OnClick="AttachFile" />
<asp:FileUpload ID="txtFile" size="46" runat="server" />

By simply clicking "Attach File" button, it will call the code behind function and save the file browse by the user. It work just fine but when I refresh the page it goes to the function again and repeat the saving process ending with duplicate of records. How can I avoid this to happend?

Some I tried are:

1. Adding if (!IsPostBack) {} condition.
2. Adding onClientClick="return false" attribute in my button.

But it did not solve the problem. Thank you in advance.

Answer 1

Use this technique to prevent the double trigger on your control events after refreshing:

1. Add this code to your code behind page PreRender event

   protected void Page_PreRender(object sender, EventArgs e)
   {
       ViewState["CheckRefresh"] = Session["CheckRefresh"];
   }
   

2. Add this line on your Page_Load event.

   protected void Page_Load(object sender, EventArgs e)
   {
     if (!IsPostBack)
     {
       Session["CheckRefresh"] = Server.UrlDecode(System.DateTime.Now.ToString());
       // rest of your code here ...
     }
   }
   

3. On your controls event, like your button click or any other control that you want to prevent this on page refresh check these condition first.

   protected void AttachFile(object sender, EventArgs e)
   {
       if (Session["CheckRefresh"].ToString() == ViewState["CheckRefresh"].ToString())
       {
          // your code starts here ..
   
          if (txtFile.HasFile)
          {
             //...
          }
   
          // your code ends here ..
   
          Session["CheckRefresh"] = Server.UrlDecode(System.DateTime.Now.ToString());
       }
   }
   

Cheers

Answer 2

You can use Post/Redirect/Get (PRG) pattern to overcome this. You can see a similar question answered here. how to prevent data from sending if user press F5 or refresh in asp.net?