C# to traverse through a ChechBoxList using LINQ

Helios · September 19th, 2008, 01:04 PM

Hello,

This is probably one of the simplest of questions that anyone can ask. Most of you can probably answer this in your sleep :)

I am absolutely new to ASP.NET and I am trying to get my feet wet by parcticing simple excercises using version 3.5 (both VB and C#). I thank Imar for coming up with such a simple yet effective way of teaching in his book "Beginning ASP.NET 3.5 In C# and VB". I am thoroughly enjoying it and learning at a good pace.

I am trying to accomplish a simple logic to do the following. I have created a CheckBoxList with 4 items

Apple
Orange
Banana
Peach

The code from my test.aspx looks as follows...

<asp:CheckBoxList ID="cblFruits" runat="server">
<asp:ListItem Value="1">Apple</asp:ListItem>
        <asp:ListItem Value="2">Orange</asp:ListItem>
        <asp:ListItem Value="3">Banana</asp:ListItem>
        <asp:ListItem Value="4">Peach</asp:ListItem>
</asp:CheckBoxList>

I also have a Submit button as well as a label to display the result as follows...

<asp:Button ID="btnSubmit" runat="server" Text="Submit" onclick="btnSubmit_Click" />
<br />

<asp:Label ID="lblResult" runat="server" Height="80px" Width="500px"></asp:Label>
<br />

If the user checks Apple and Banana and clicks on the submit button, I want to display something like below...

In the Check Box List you selected Apple with value 1
In the Check Box List you selected Banana with value 3

I used the following c# code in btnSubmit_Click to accomplish it and it works fine.

//Loop through the Check Box list and for each selected item, display its name with appropriate message

foreach (ListItem item in cblFruits.Items)
{
if (item.Selected == true)
lblResult.Text += "In the Check Box List you selected " + item.Text + " with value " + item.Value + "<br />";
}

Now I want to accomplish the same using LINQ. I was able to do it in VB with the following code...

        Dim selectionResults = From member In cblFruits.Items _
                      Where member.Selected = True _
                      Select member

        For Each item As ListItem In selectionResults
            lblResult.Text &= "In Check Box List you selected " & item.Text & _
                              " with value " & item.Value & "<br />"
        Next

How can I translate the above snippet of code (that uses LINQ to traverse through the CheckBoxList items) in C#? Your help is grately appreciated.

Thanks in advance
Helios

Imar · September 20th, 2008, 04:35 AM

Hi Helios,

Good question, and an interesting idea to use LINQ to solve this problem. The following code would work:

Code:

var selectionResults = from ListItem item in cblFruits.Items
                       where item.Selected == true
                       select item;

foreach (ListItem item in selectionResults)
{
  lblResult.Text += "In Check Box List you selected " + item.Text +
           " with value " + item.Value + "<br />";
}

The trick here is that you need to specify the type of the item (ListItem) in the LINQ query.

Instead of selecting ListItem instances, you can also select the entire string with LINQ:

Code:

var selectionResults = from ListItem item in cblFruits.Items
                       where item.Selected == true
                       select "In Check Box List you selected " + item.Text + 
                           " with value " + item.Value + "<br />";

foreach (string item in selectionResults)
{
  lblResult.Text += item;
}

This isn't necessarily better (data is mixed with presentational / formatting code) but it's fun to see how easy these things can be accomplished with LINQ.

Hope this helps, and it's good to hear you're enjoying the book so much.

Cheers,

Imar

---------------------------------------
Imar Spaanjaars
http://Imar.Spaanjaars.Com
Everyone is unique, except for me.
Author of Beginning ASP.NET 3.5 : in C# and VB, ASP.NET 2.0 Instant Results and Dreamweaver MX 2004
Want to be my colleague? Then check out this post.

Helios · September 20th, 2008, 11:40 AM

Imar,

Thanks for your response. It is very much appreciated.

Quote:

quote:Originally posted by Imar
This isn't necessarily better (data is mixed with presentational / formatting code) but it's fun to see how easy these things can be accomplished with LINQ.

Exactly, Imar. My idea was to explore LINQ a little bit and get a feel of how it works.I would absolutely agree that in real world this is not a good candidate for LINQing. :)

Regards,
Helios

Imar · September 20th, 2008, 12:06 PM

Not sure which example you are referring to, but I was referring to my second. That is, the one that returns the already formatted example isn't a very good practice. However, your initial example makes perfect sense, and is a typical scenario for what LINQ is built for....

Imar

---------------------------------------
Imar Spaanjaars
http://Imar.Spaanjaars.Com
Everyone is unique, except for me.
Author of Beginning ASP.NET 3.5 : in C# and VB, ASP.NET 2.0 Instant Results and Dreamweaver MX 2004
Want to be my colleague? Then check out this post.

Helios · September 26th, 2008, 04:37 PM

Imar,

Thanks for the clarification. It was my misinterpretation of LINQ. Now that I read more on the topic, I started to understand it better.

Regards,
Helios