Access a content control in C# when using Master Pages

asp.netfindcontrolmaster-pages

Good day everyone,

I am building a page in ASP.NET, and using Master Pages in the process.

I have a Content Place Holder name "cphBody" in my Master Page, which will contain the body of each Page for which that Master Page is the Master Page.

In the ASP.NET Web page, I have a Content tag (referencing "cphBody") which also contains some controls (buttons, Infragistics controls, etc.), and I want to access these controls in the CodeBehind file. However, I can't do that directly (this.myControl …), since they are nested in the Content tag.

I found a workaround with the FindControl method.

ContentPlaceHolder contentPlaceHolder = (ContentPlaceHolder) Master.FindControl("cphBody");
ControlType myControl = (ControlType) contentPlaceHolder.FindControl("ControlName");

That works just fine. However, I am suspecting that it's not a very good design. Do you guys know a more elegant way to do so?

Thank you!

Guillaume Gervais.

Best Answer

I try and avoid FindControl unless there is no alternative, and there's usually a neater way.

How about including the path to your master page at the top of your child page

<%@ MasterType VirtualPath="~/MasterPages/PublicUI.Master" %>

Which will allow you to directly call code from your master page code behind.

Then from your master page code behind you could make a property return your control, or make a method on the master page get your control etc.

public Label SomethingLabel
{
    get { return lblSomething; }
}
//or
public string SomethingText
{
    get { return lblSomething.Text; }
    set { lblSomething.Text = value; }
}

Refers to a label on the master page

<asp:Label ID="lblSomething" runat="server" />

Usage:

Master.SomethingLabel.Text = "some text";
//or
Master.SomethingText = "some text";

Why does a ASP.NET page need a form element?

ASP.NET pages try to emulate the WinForms environment, by provided state persistance through the PostBack model. This provides an element of state to a stateless environment. In order to do this, the runtime needs to be able to have the ability to maintain this state within each "form". It does this by posting back data to itself. It's important to note that:

There is nothing really fancy about a PostBack.
It uses a HTTP form and POST, the same as any other form, from any other stack.
Just because it looks like it might be doing something special, its not, all that happens is it POST's back with some info about what caused it, so you can do things like handle client-side events, in server-side code.

So why only one?

This to me was the million pound question (I am British). I understand that ASP.NET needs this, especially if you are using ASP.NET server controls, but why the hell can't I make my own additional forms?

So, I thought screw it, just make your own form!

And I did. I added a bog-standard, simple form with a submit action of "#". This then performs a POST to the current page, with the Form data for the given form in the request.

Guess what? It all worked fine. So I ended up with:

A master page, with a HTML form in
This form posts back to the current page (basically the page using the master).
In the Page_Load code-behind for the master, I then added code to check the request to see what data was passed in the request. If it contains data (say a hidden field) then I know the post was sourced from the Form on the master page, if not, then it is most liekly a PostBack from content, and can be ignored.
I then surrounded the Content tags with <form runat="server" id="aspNetForm"...> </form> tags. This meant that all content pages automatically had a form to work with.

This provided me with a relatively simple, clean solution to my problem. My login form works fine in tandem with all the content forms created, some of which are complex forms, others use lots of server controls and many PostBacks, and so on.

I hope this helps others.

C# – Finding controls inside nested master pages

Finding controls is a pain, and I've been using this method which I got from the CodingHorror blog quite a while ago, with a single modification that returns null if an empty id is passed in.

/// <summary>
/// Recursive FindControl method, to search a control and all child
/// controls for a control with the specified ID.
/// </summary>
/// <returns>Control if found or null</returns>
public static Control FindControlRecursive(Control root, string id)
{
    if (id == string.Empty)
        return null;

    if (root.ID == id)
        return root;

    foreach (Control c in root.Controls)
    {
        Control t = FindControlRecursive(c, id);
        if (t != null)
        {
            return t;
        }
    }
    return null;
}

In your case, I think you'd need the following:

Label lblName = (Label) FindControlRecursive(Page, "lblName");

Using this method is generally much more convenient, as you don't need to know exactly where the control resides to find it (assuming you know the ID, of course), though if you have nested controls with the same name, you'll probably get some strange behavior, so that might be something to watch out for.

Best Answer

Related Solutions

Form Elements in ASP.NET Master Pages and Content Pages

Why does a ASP.NET page need a form element?

So why only one?

C# – Finding controls inside nested master pages

Related Topic