Getting the hidden field value in c#.net

Question

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Hi coders,

Here i am giving the small example about my requirement

I am using one java script function like

My aspx page Code:

JavaScript

<script type="text/Jscript"> 
function getvalue() {
    
                document.getElementById("hdnResultValue").value = 123;
            }
</script>

ASP.NET

<asp:HiddenField ID="hdnResultValue" Value="0" runat="server" />
<asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />
    </form>

My aspx page cs Code:

C#

protected void Button1_Click(object sender, EventArgs e)
        {
Page.ClientScript.RegisterStartupScript(this.GetType(),null, "getvalue();", true);
 string codeBehindValue = hdnResultValue.Value;
}

Here when I hit my button first time I am not getting the hdnResultValue value(Here I am getting 0), If I hit second time I am getting the hdnResultValue value(here I am getting 123)

This might be happening due to post back.

my problem is how can I can get the hdnResultValue value when hit my button first time.

Posted 9-Oct-13 0:20am

D-Kishore

Updated 9-Oct-13 0:50am

v2

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Comments

Thanks7872 9-Oct-13 6:30am

Why you called getvalue()? If you want to have 123 then why used 0?

D-Kishore 9-Oct-13 6:35am

Hi, here I have given just example.
In my initial requirement I am doing some calculations and storing that value to hidden filed.

Thanks7872 9-Oct-13 6:37am

Still not clear. Why you used JavaSCript here? Why not to simply do all that stuff inside Button1_Click? Use reply button while making comment.

D-Kishore 9-Oct-13 6:44am

Ok, I will explain.

Here I am converting my gridview to image.

For this I am using
<script type="text/javascript" src="Styles/html2canvas.js"></script>
<script type="text/Jscript">
function getvalue() {
var canvas1 = document.getElementById("myCanvas");
html2canvas(document.getElementById("kk"), {

onrendered: function (canvas1) {
document.body.appendChild(canvas1);

var image = canvas1.toDataURL("image/png");
image = image.replace('data:image/png;base64,', '');
document.getElementById("hdnResultValue").value = image;
}
});
}
</script>

using the hidden field data in my button click event I am exporting as a image.
string codeBehindValue = hdnResultValue.Value;
string fileNameWitPath = path + DateTime.Now.ToString().Replace("/", "-").Replace(" ", "- ").Replace(":", "") + ".png";

using (FileStream fs = new FileStream(fileNameWitPath, FileMode.Create))
{

using (BinaryWriter bw = new BinaryWriter(fs))
{

byte[] data = Convert.FromBase64String(codeBehindValue);

bw.Write(data);

bw.Close();

}

}

D-Kishore 9-Oct-13 6:49am

These java script function I am unable to wrote in button click event at codebehind.
because of this I am wrote the function in aspx page then I am calling the function in button click event using Page.ClientScript.RegisterStartupScript

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Kornfeld Eliyahu Peter · Answer 1 · 2013-10-09T00:28:00

Solution 1

Asp:Button's onclick is binding to server side handler.
If you want to run some js you need a client side handler. Something like this...

ASP.NET

<asp:Button ID="Button1" runat="server" Text="Button" OnClientClick="getvalue();" />

Posted 9-Oct-13 0:28am

Kornfeld Eliyahu Peter

Updated 9-Oct-13 2:57am

v2

Comments

D-Kishore 9-Oct-13 6:37am

But I need to fire this function in button click event only.
Kindly suggest any other possibilities.

Kornfeld Eliyahu Peter 10-Oct-13 7:16am

You ARE firing on button click. The ASP.NET rendering will render client-side onclick event based on your OnClientClick declaration...

You may read here http://msdn.microsoft.com/en-us/library/7ytf5t7k(v=vs.100).ASPX

**VICK** · Answer 2 · 2013-10-09T01:23:00

Do try the Request.Form to get the hidden field's current value.

Request.Form["Hiddenfieldname"].ToString();

For Example if you have a hidden field like

<asp:HiddenField name="hdnResultValue" Value="0" runat="server" />

than you can get the value like

C#

Request.Form["hdnResultValue"].ToString();

Hope it will help.

sankarsan parida · Answer 3 · 2013-10-09T02:32:00

See
You are using both client and server side method
For this You have to call client side in client event and server side in server event
For this I have showing modifited code in following below

XML

<div>
       <asp:HiddenField ID="hdnResultValue" runat="server" />
       <asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" OnClientClick="getvalue();"/>
   </div>

Server button click event should for test purpose is that

C#

protected void Button1_Click(object sender, EventArgs e)
   {
      // Page.ClientScript.RegisterStartupScript(this.GetType(), null, "getvalue();", true);
       string codeBehindValue = hdnResultValue.Value;
       Response.Write(codeBehindValue);
   }

Getting the hidden field value in c#.net

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