Passing the value from a listbox to a object

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Hi All,
I am having a little difficulty sending the value from a listbox to an object.The lboxStudentIDs contains 4 values.
1111
2222
3333
4444

When I run the debugger I see that the "SelectedValue" is correct BUT aStudent remains null. The values in the listbox are integers. Any help is appreciated.
Thanks!

SchoolIDS aStudent  = lboxStudentIDs.SelectedValue as SchoolIDS;

Posted 11-May-11 14:05pm

WhiskeyBusiness

Updated 11-May-11 14:56pm

v2

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Wonde Tadesse 11-May-11 20:27pm

Can you elaborate how you populate the list box ?.

WhiskeyBusiness 11-May-11 20:33pm

Hi Wonde,
The listbox is databound. So lbboxStudentIDs.DataSource = something;

Wonde Tadesse 11-May-11 21:02pm

Quick qn.Fill in the blank.
1. Are you talking about Asp.Net ? If so

ListBox1.DataSource = "blank";
ListBox1.DataTextField = "blank";
ListBox1.DataValueField = "blank";

2 Window Application ? If so,

listBox1.DataSource = "blank";
listBox1.DisplayMember="blank";
listBox1.ValueMember="blank";

WhiskeyBusiness 11-May-11 21:18pm

Hi Wonde,

It is a Window Application

So
listBox1.DataSource = something;
something is a list.
listBox1.DisplayMember="StudentName";
listBox1.ValueMember="StudentID";

Wonde Tadesse 11-May-11 22:33pm

What is "something" in your case. Is it SchoolIDS or what ?. If I don't know that it's difficult to answer.

WhiskeyBusiness 11-May-11 22:37pm

Hi Wonde,
Something is a Binding List that contains the Name string of the student and their StudentIDs integer. Thanks for your help.

Wonde Tadesse 11-May-11 22:40pm

Ok What is StudentIDs ?

WhiskeyBusiness 11-May-11 22:42pm

That is the number an integer
1111
2222
etc

Wonde Tadesse 11-May-11 22:44pm

So why you declare like this

SchoolIDS aStudent = lboxStudentIDs.SelectedValue as SchoolIDS;
This means you have a Class or Structure named SchoolIDs and you want to cast it from ListBox value.

WhiskeyBusiness 11-May-11 22:47pm

If I dont declare it like this I will not be able to access the methods in the SchoolIDS class. What do you suggest ?

Wonde Tadesse 11-May-11 22:57pm

Sorry. I think there are a lot of information you need to elaborate. Generally if you need an object to be returned from ListBox then bind the list box as follows.

listBox1.Items.Add(new Student(){Name="Mike",ID=1});
listBox1.Items.Add(new Student(){Name="John",ID=2});
listBox1.Items.Add(new Student(){Name="Hanna",ID=3});

if you want to cast

Student aStudent = listbox1.SelectedItem as Student();

Good luck.

Chris Maunder 11-May-11 20:34pm

What type is "lboxStudentIDs.SelectedValue" and what type is "SchoolIDS"? You can't just cast between different types and expect it to work

WhiskeyBusiness 11-May-11 20:44pm

Hi Chris,
SchoolIDs in an integer. Is there a way I can cast it so the object aStudent will accept it ? I am not sure on how to cast exactly. Any help is appreciated. Thank you.

Sergey Alexandrovich Kryukov 11-May-11 23:11pm

Tag it! Forms, WPF, ASP.NET, what?
--SA

Wonde Tadesse 11-May-11 23:14pm

It's window application. Just look in the comments.

Sergey Alexandrovich Kryukov 11-May-11 23:24pm

Wonder, I don't understand your comment. Window application can be WPF, Forms...
We should stop answering questions which are not tagged properly. What a waste of time, in particular, for exchange of comments like the one we're doing right now...
--SA

Wonde Tadesse 11-May-11 23:31pm

I accept your comment.It is totally valid.Just trying to help the guy.That's all

Sergey Alexandrovich Kryukov 12-May-11 0:51am

Sure, I understand. I just say this guy and every other inquirers would help themselves even more if they tag questions properly. This guesswork irritates.
--SA

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AspDotNetDev · Answer 1 · 2011-05-11T14:41:00

Solution 1

Assuming ASP.NET...

SelectedValue is of type string. Strings do not store instances of type StudentIDS. I'm guessing you are storing strings of the ID's (e.g., "1111"). Convert that SelectedValue to an integer, then use that integer to look up your student wherever you are storing students (I'm guessing in a database).

FYI, if the type of instance you are attempting to cast using the "as" keyword does not match the type you are trying to cast to, null will be returned. That's why you are seeing null (because strings aren't of type StudentIDS).

Posted 11-May-11 14:41pm

AspDotNetDev

Comments

WhiskeyBusiness 11-May-11 20:46pm

Hi AspDotNetDev,
The value of the ID's is an integer. So would I not cast as SchoolIDs to convert to the appropriate type ?

AspDotNetDev 11-May-11 21:16pm

No, it is a serialized int, you need to parse it. Use int.Parse().

AspDotNetDev 11-May-11 21:22pm

I see you added comments above that indicate your data source is a list. Once you have parsed your ID, loop through your list to find the student that has that ID.