如何以编程方式从CS文件访问ASPX页面上的控件

Question

How can I access a control on an aspx page from the cs file in a programmatic way?

For instance, if I have a set of asp:Panel controls each with an ID named by a city (id="atlanta", id="chicago", id="pittsburgh", etc.) and then in the cs I grab a value from the database to match up to the control names what would I use?

I tried to use FindControl() as shown and it returns null.

aspx page:

<asp:Panel ID="atlanta" runat="server" Visible="false"></asp:Panel>

cs file:

controlName = storeLocation.City.ToLower();
Panel cityPanel = (Panel)FindControl(controlName);
cityPanel.Visible = true;

I suppose FindControl() is really for use in cases like Repeaters or Grids where you pass in the ItemTemaplate. In my case its just a simple content page with a content tag with a bunch of panels in it.

Thanks in advanced! :)

Answer 1

FindControl() isn't recursive, which may be your problem. However, there are many implementations of a recursive version, such as this one .

If you are creating the panels dynamically and you want access to them later in the page lifecycle, you can add them all to a Dictionary<string, Panel> where the ID is the key.

Answer 2

You can use this extension method to find controls recursively:

public static class ControlExtension
{

    public static IEnumerable<Control> GetAllControls(this Control parent)
    {
        foreach (Control control in parent.Controls)
        {
            yield return control;
            foreach (Control child in control.GetAllControls())
            {
                yield return child;
            }
        }
    }
}

And then in your code behind page you could do something like this if you prefix your labels:

IEnumerable<Control> city_controls = this.GetAllControls().Where(x => x.Id.Contains("city_"))

or a single control:

var city = this.GetAllControls().Single(x => x.Id = "atlanta");

Where the this is your ASPX code behind page.

It also works on controls such as panels, so if you want to find all controls inside a panel etc.

Answer 3

If you know the containing control you may be able to use the FindControl() function of that control to find it. This method will be much faster and safer than using a recursive method.

Microsoft did not include a recursive FindControl() function for a reason, it will slow your page down over time as more controls get added to the page. If that doesn't work use a recursive function like other responses suggested.

Answer 4

This should work for you since the panels are nested in the asp:Content control.

    Panel cityPanel =
(Panel)Master.FindControl("ContentPlaceHolderId").FindControl(controlName);

Where off course, ContentPlaceHolderId is the Id of the corresponding ContentPlaceHolder in the Master page you are implementing.