PreviousPage Doesn't Work???

[Jonathan Wood]

In Microsoft Press' Introducing Microsoft ASP.NET 2.0, and also on sites
like http://msdn2.microsoft.com/en-us/library/ms178139.aspx, I've found a
number of examples that look something like this:

if (Page.PreviousPage != null)
{
TextBox SourceTextBox = (TextBox)PreviousPage.FindControl("TextBox1");
if (SourceTextBox != null)
{
Label1.Text = SourceTextBox.Text;
}
}

Yet, PreviousPage.FindControl always returns null for me. Using
PreviousPage.Title, I could verify that the previous page was the expected
page. But FindControl() isn't working.

I searched the Web but all I could really find is examples like the one
above, and posts where other people complained that this code does not work
for them either.

Any help?

Jonathan

 

[bruce barker]

PreviousPage.FindControl will only find controls at the page root. if
the control is a child of another then it will not find it.

you need to do a recursive search.

-- bruce (sqlwork.com)

 

[Teemu Keiski]

Hi,

is TextBox perhaps contained in a another control (which would be a naming
container)?

 

[David Wier]

Are you, by any chance, using a Master Page?

David Wier
http://aspnet101.com
http://iWritePro.com - One click PDF, convert .doc/.rtf/.txt to HTML with no
bloated markup

 

[Jonathan Wood]

I do have a few layers of <div> tags, if that's what you mean.

However, when I traverse the PreviousPage.Controls collection, the only one
that shows up is "ASP.default_master." None of the <div> tags seem to show
up, unless they would be "inside" the master--that doesn't make any sense.

Thanks.

 

[Jonathan Wood]

Yup. Does that affect this?

Thanks.

 

[Jonathan Wood]

That's the issue. The following code works:

protected String GetField(String field)
{
ContentPlaceHolder ph =
(ContentPlaceHolder)PreviousPage.Master.FindControl("ContentPlaceHolder1");
if (ph != null)
{
TextBox tb = (TextBox)ph.FindControl(field);
if (tb != null)
return tb.Text;
}
return String.Empty;
}

Thanks.

 

[bruce barker]

if you have a master page, then all the controls in the content are
children of the master (which is a control on the page).

the controls on a page are in a tree, the page has a control list, and
every control in that list has a list of controls. so, to find a
control, you need to find its parent, for which you need find its parent
until you get to the page.

if your control id is unique, you can just do a recursive search.

(note: air code)

Control myControl = DeepFind(Page,"myID");

Control DeepFind(Control parent, string id)
{
if (parent.ID == id)
return parent;
foreach (Control child in parent.Controls)
{
Control c = DeepFind(child,id);
if (c != null)
return c;

}
return null;
}

-- bruce (sqlwork.com)

 

[Jonathan Wood]

Thanks. That is a more comprehensive approach to finding any control. Please
see my reply to David for the solution I ended up with.