How do you get the ID of a control in ASP.NET

Question

I am attempting to loop through an array of numbers, match them to the checkbox they they are associated with, and checkmark that box.

My checkbox is set up like:

<input type="checkbox" runat="server" id="someID" name="somename" value="1234" />

My code when the page loads currently looks like:

foreach (string interest in interests_Var){
   foreach (var c in Page.Controls)
   {
   }
}

interests_Var is my array containing different numbers. We'll assume one of them is 1234 . While looping through the page controls, I want to compare the value of the control to my number. If it equals my number, I want to then apply the attribute checked="checked" . I'm assuming I have to find the ID of the control I am using, then use that ID to add a new attribute. Or is there a way I can add the attribute using the c variable?

I'm not dead set on this setup, so if you know a better way, I'm all ears. Thanks for any help and suggestions.

Thanks

Lots of good suggestions. I will try these in a bit. Got side-tracked on another project.

Solved

Ok, so here's my end code. Thanks for the help James.

foreach (string interest in interests_Var)
{
       foreach (var chkCtrl in Panel1.Controls.OfType<CheckBox>())
       {
           if (chkCtrl.Attributes["value"].ToString() == interest.ToString())
          {
               chkCtrl.Checked = true;
          }
     }
}

Answer 1

I assume you are using multiple checkboxes and have multiple values stored. It is best to use the Asp:Checkbox, rather thatn simply assigning the runat="server" attribute to your input-control.

Let's assume you have a datasource like this:

public class MyClass
{
   public String Name {get;set;}
   public int Number {get;set;}
}

Use this server-control:

<asp:CheckBoxList ID="cblMyList" runat="server" DataTextField="Name" DataValueField="Number">

The Name property will be used as a displaystring, where as the Number is the value that actually is part of the HTTP Post.

In the OnInit-Eventhandler you would probably bind like this:

List<MyClass> values = //...
cblMyList.DataSource = values;
cblMyList.DataBind();
foreach (ListItem item in this.cblMyList.Items)
{
   if(interests.Contains(item.Value))
   {
    item.Selected = true;
   }
}

Getting all selected values would be done with this piece of code:

List<int> selectedValues = cblMyList.Items.Cast<ListItem>().Where(x => x.Selected).Select(x => int.Parse(x.Value)).ToList();

I chose int as the datatype for the DataValueField. Of course you can use other types, just replace the int with the datatype of your choice.

Answer 2

If you assign your check boxes an ID like "interest" + value , then you can use FindControl to look up your check box by interest:

foreach (string interest in interests_Var)
{
    HtmlInputCheckBox checkBox = (HtmlInputCheckBox)this.FindControl("interest" + interest);
    if (checkBox == null)
        throw new InvalidOperationException("Missing check box for " + interest);
    checkBox.Checked = true;
}

Answer 3

You would be best served putting the CheckBox controls into a Panel or a PlaceHolder , because then you won't have to worry about recursive logic to traverse the control hierarchy.

<asp:Panel ID="Panel1" runat="server">
    <asp:CheckBox ID="CheckBox1" runat="server" Text="Testing" value="1234" />
    ...
</asp:Panel>

By putting the controls into a container, you can just loop through the child controls of that element:

foreach (string interest in interests_Var)
{
    foreach (var chkCtrl in Panel1.Controls.OfType<CheckBox>())
    {
        chkCtrl.Checked = chkCtrl.Attributes["value"].Contains(interest.ToString());
    }
}

Assuming interests_Var is a List , here's a shorter way to do it using LINQ:

interests_Var.ForEach(str => plcInvoiceDetail.Controls.OfType<CheckBox>()
    .Select(chk => chk.Checked = chk.Attributes["value"] == str));

Answer 4

If this is a Web Forms app, and you aren't dead set on doing it how you described, you can change your markup to this instead:

<asp:CheckBox id="someID" runat="server" />

Then it will be defined in the.designer.cs file. That way, you can simply reference it in your code like this:

if ( someID.Checked )
{
    // do whatever
}

Note that if it is a control that is dynamically added, you'll still have to use the FindControl() method mentioned by others, because Visual Studio won't have added it to the.designer.cs file for you.

Answer 5

You may use the Array of Controls as described at the following articles:-
http://msdn.microsoft.com/en-us/library/aa289500%28v=VS.71%29.aspx
http://www.codeproject.com/Articles/21159/How-to-Create-a-Control-Array-in-C
For traversing values from the controls you may use the following for reference:-
Add array of controls to an aspx page

And I would recommend you to use ASP.NET Checkbox instead of HTML < input type="checkbox">.