update master page variable value from the content page by javascript.

[sweetneel]

hi all, thanks in advance. I need a help , its urgent.

I am developing a webapplication with maser page. there i have a lebel, control. i need to update its value from the content page, and only by the javadscript.

i am doing:

var btnpjt = document.getEle mentById( '<%=((Label)thi s.Master.FindCo ntrol("lblBtnPr ojectValue")).C lientID %>');
btnpjt.value='V P';
in my content page content page. But it is not working.
Depending on the Value stored by the Javascript in the master page label, i have to redirect my content page to the another page.

The second question is, how could i initialize(to NULL) my master page value from the content page .

Please reply , i have urgency.

[Frinavale]

You don't need to use JavaScript to accomplish this task.
You can reference a control on the MasterPage using the MasterPage's FindControl method.

For example, if you want to set the text value of a Label that is located in the MasterPage from a content page then you would have something like this:

(VB.NET)

 CType(Master.FindControl("myLabel"), Label).Text = "the text to display"

(C#)

 (Label) Master.FindControl("myLabel").Text = "the text to display";

If you must updated it using JavaScript (this doesn't make sense) then I would recommend that you make a Protected/Public Property in the content page that exposes the ClientID of the Label in the MasterPage to your ASP code.

For example:
In your VB.NET code you would have a Public Property:

Public ReadOnly Property LabelClientID As String
  Get
   return Ctype(Master.FindControl("lblBtnProject"),String).ClientID
  End Get
End Property

C#

    public string LabelClientID 
    {
        get { 
         return  (Label) Master.FindControl("lblBtnProject").ClientID;
        }
    }

Then in your JavaScript (in your ASPX page):

var btnpjt = document.getElementById( '<%=LabelClientID %>');

Actually when I was copy/pasting your code I think I fo und the problem.
You aren't locating the control properly because you aren't using the ID for the lblBtnProject control (you have "lblBtnProj ect Value" but it should just be "lblBtnProject" )

The Null/Nothing problem can easily be solved:
var btnpjt = document.getEle mentById( '<%

If( (Label) Master.FindControl("lblBtnProject") != null)
{ (Label)this.Master.FindControl("lblBtnProject")).ClientID}
else{""}
%>');

Or even simplify it to:

var btnpjt = document.getElementById( '<%=(String)Master.FindControl("lblBtnProject")!= null ? Master.FindControl("lblBtnProject").ClientID: "") %>');
...

In your JavaScript code you should always check to make sure that the element you're working with exists before you use it. For example:

var btnpjt = document.getElementById( '<%=(String)Master.FindControl("lblBtnProject")!= null ? Master.FindControl("lblBtnProject").ClientID: "") %>');

//checks to make sure that btnpjt is not null/nothing
if(btnpjt)
{
}

-Frinny

[sweetneel]

hi Frinny, thank u for ur reply. But when i am using the property as described u in my aspx.cs page i am getting error as
"Error

"Cannot convert type 'string' to 'System.Web.UI. WebControls.Lab el'

[Frinavale]

Try creating the Public Property that returns the string.