Child control not found.

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Hello Friends,

I have a child control nested within a parent control.

For example:

1>I used a details view control.
2>I wanted to customize the pager, so i did something like below:

XML

<asp:DetailsView ID="dv" runat="server">
     <PagerTemplate>
        <asp:CheckBoxList ID="cbl"  ToolTip="hi" runat="server" />
     </PagerTemplate>
    </asp:DetailsView>

Now i wanted to access the CheckBoxList in a button click's event handler. So in the event handler of the button, i did:

CheckBoxList cbl = (CheckBoxList)(dv.FindControl("cbl"));

here i applied a break point, i observed that "cbl" turned out to be "null".

I tried one more thing:

C#

foreach (Control c in dv.Controls)
      {
          if (c is CheckBoxList)
          {
              Response.Write("true");
          }
      }

again i applied a break point on

Response.Write("true");

this is within the "if", it does not execute.

then i tried:

CheckBoxList cbl = (CheckBoxList)dv.BottomPagerRow.Cells[0].FindControl("cbl");

again "cbl" is null.

finally, i tried:

CheckBoxList cbl = (CheckBoxList)Page.FindControl("cbl");

"cbl" is null again.

I cant understand, why is that control "null"?

any suggestions?

Thanks and regards,
Rahul

Posted 23-Apr-14 8:33am

Rahul VB

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Sergey Alexandrovich Kryukov · Accepted Answer · 2014-04-23T09:54:00

Solution 1

It's the matter of the scope of the search. Please see: http://msdn.microsoft.com/en-us/library/31hxzsdw%28v=vs.110%29.aspx[^].

MSDN says:
The method searches only the page's immediate, or top-level, container; it does not recursively search for controls in naming containers contained on the page. To access controls in a subordinate naming container, call the FindControl method of that container.

Thes same is told about Control.FindControl. Here is what you can do: if your have only the top context of the search, some Page: get all its controls: http://msdn.microsoft.com/en-us/library/system.web.ui.control.controls%28v=vs.110%29.aspx[^].

Then, for each control, use its you can use the same Control property referenced above, as the page is also Control. Do it recursively:

C#

class SomeType {

     static Control FindControl(Control control, string id) {
        if (control.ID == id) return control;
        if (control.FindControl(id) != null) return control;
        foreach(Control child in control.Controls) {
            Control foundControl = child.FindControl(id);
            if (foundControl != nill)
                return foundControl;
        }
        return null;
    }

    //...

    void SomeMethod() {
        Control requiredControl = FindControl(Page, "cbl");
    }

} //class SomeType

Good luck,

—SA

Posted 23-Apr-14 9:54am

Sergey Alexandrovich Kryukov

Updated 23-Apr-14 19:34pm

v3

Comments

Rahul VB 23-Apr-14 23:37pm

Respected Sir,
I do understand what you are saying. If the control is nested within a parent control, we cant use Page.Findcontrol(). Because it finds only the top level or immediate controls. To dig deeper i need to use the parent control, traverse through it and then find the child. Am i correct?

Sergey Alexandrovich Kryukov 24-Apr-14 1:34am

Well, you can, but not just it. Yes, that's right. You can test my code to see.
Will you accept the answer formally now?
—SA

Rahul VB 24-Apr-14 2:29am

Hello Sir,
I used your code. But still it shows null value. I will have to work on it. However i will accept your answer. But there are few things to be done.

Firstly my doubt is, that in the event handler, i will have to type cast the child control using the properties of the parent control. But this is not working.

Or else i will have to use the specific command event args of the child control to get the proper cast, which i am unable to do.

Let me just have a look at it. Thanks for the help Sir.

Sergey Alexandrovich Kryukov 24-Apr-14 2:43am

You are welcome.
I don't understand about the case. It won't be the problem once you implement finding control by id and get non-null.
Create some simplified cases to test the technique, make sure they work, and then get back to the goal...
—SA

Rahul VB 24-Apr-14 14:11pm

Hello sir, got it, i understood my fault. I will show you the below code:

<asp:DetailsView ID="dv" runat="server">////i have not set allow paging to true
<PagerTemplate>
<asp:CheckBoxList ID="cbl" ToolTip="hi" runat="server">
</PagerTemplate>

On the button click i say something like this:
public void click(object sender, EventArgs e)
{

CheckBoxList cbl = (CheckBoxList)dv.BottomPagerRow.Cells[0].FindControl("cbl");

}
As i have not set allow paging to true, i am unable to find the control in the pager, and so it is always null.

if i set allow paging to true: the code works fine, i am also able to find the child control in the pager.

Thanks a ton,
Rahul

Sergey Alexandrovich Kryukov 24-Apr-14 14:18pm

Great.
You are very welcome.
Good luck, call again.
—SA

Rahul VB 24-Apr-14 14:24pm

Sir,
I request you to add even this part in your solution. I mean the "allow paging=true" part. Because then the answer will be full proof. I hope you dint mind. I am saying this because, this problem is faced by many developers. It should be included.

Thanks again,
Rahul

Sergey Alexandrovich Kryukov 24-Apr-14 15:54pm

I'm afraid I'm not well familiar with the paging problem. Anyway, it is not directly related to the problem you posed in your question.
—SA

Espen Harlinn 24-Apr-14 11:58am

Found it :-)

Sergey Alexandrovich Kryukov 24-Apr-14 12:03pm

Thank you, Espen.
—SA