Create List accessible for other classes

Question

I currently am making a list like this in a winform:

var NationEligable = 
(from p in playerPeople
orderby p.NationClubContracted
where p.NationClubContracted!= -1 
group p by new { p.NationalityName,p.NationClubContracted } 
into mygroup
select new
{
mygroup.First().NationalityName
,NationCallUp =  mygroup.First().NationClubContracted
}).ToList();

i know this is a "anonymous type" but need to be able to access the list across classes/other forms in my projects.

I don't mind if it needs to get re-written from linq/lambda or whatever..

Basically need the list accessible across other classes/form in my project to populate comboboxes.

Any help would be appreciated.

Vulpes · Answer

OK I've made a few changes (highlighted) to hopefully get that to compile: using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace Foo { public class Nation { public string NationalityName { get; set; } public int NationCallup { get; set; } } } In the code behind my Form1 I have: namespace Foo { public class Form1 : System.Windows.Forms.Form { // // public System.Collections.Generic.List Nations; //this errors - Foo.Form1.Nation' is a 'field' but is used like a 'type' // // // Public Form1() { // // //playerPeople is created here // List NationEligable = (from p in playerPeople orderby p.NationClubContracted where p.NationClubContracted!= -1 group p by new { p.NationalityNamep.NationClubContracted } into mygroup select new Nation() { NationalityName = mygroup.First().NationalityName NationCallUp = mygroup.First().NationClubContracted }).ToList(); Nations = NationEligable ; // // } The code for Form2 will now be along these lines: class Form2 : Form { // ... private void SomeMethod() { // get list of Nations from Form1 Form1 f1 = (Form1)Application.OpenForms[Form1]; List nations = f1.Nations; // show them in a combobox foreach(Nation n in nations) { comboBox1.Items.Add(String.Format({0} - {1} n.NationalityName n.NationCallup)); } } // other members }

Vulpes · Answer

I wasn't sure how you wanted to present the Nations in the combobox so I just created strings consisting of both properties. However if you want to use databinding with DisplayMember and ValueMember properties you can do this: private void SomeMethod() { // get list of Nations from Form1 Form1 f1 = (Form1)Application.OpenForms[Form1]; List nations = f1.Nations; // show them in a combobox comboBox1.DataSource = nations; comboBox1.DisplayMember = NationalityName; comboBox1.ValueMember = NationCallUp; comboBox1.SelectedIndex = 0; } The following is a summary of what we've done: 1. Replaced the anonymous type with a named class Nation so that we can expose the List of Nations to all classes in the application. 2. The List is exposed as a public field Nations of Form1 which is populated in the constructor. As a constructor never returns a value we simply set the field to the result of the query. 3. Form2 can now access this field by first getting a reference to the current instance of Form1 (using Application.OpenForms) f1 and then using f1.Nations. 4. The combobox can now be filled either by databinding to the List or generating strings from the Nation properties and adding them to the Items collection.

Vulpes · Answer

Without seeing all the code it's difficult for me to guess how this List is going to slot into the application. But here's a typical scenario (code off top of my head): class Nation // this is top level not nested in another class { public string NationalityName {get; set;} public int NationCallup {get; set;} } class Form1 : Form { public List GetNations(/* maybe some parameters in here */) { //.... List NationEligable = (from p in playerPeople orderby p.NationClubContracted where p.NationClubContracted!= -1 group p by new { p.NationalityNamep.NationClubContracted } into mygroup select new Nation() { NationalityName = mygroup.First().NationalityName NationCallUp = mygroup.First().NationClubContracted }).ToList(); return NationEligable; } // other members } class Form2 : Form { // ... private void SomeMethod() { // get list of Nations from Form1 Form1 f1 = (Form1)Application.OpenForms[Form1]; List nations = f1.GetNations(/* any parameters */); // show them in a combobox foreach(Nation n in nations) { comboBox1.Items.Add(String.Format({0} - {1} n.NationalityName n.NationCallup)); } } // other members }

Jay S · Answer

So..I have created a new FirstNames class (similar to what we did before) using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Data; namespace FMSaveEditor { public class FirstNames { public string Fname { get; set; } public int FirstNameID { get; set; } } } In form1 I've done: List FirstNames = (from fn in list2 join nm in list.Select((FName z) => new { FName z }) on fn.FirstNameID equals nm.z group new { fn nm } by new { fn.FirstNameID nm.z } into mygroup select new FirstNames() { FirstNameID = mygroup.First().fn.FirstNameID Fname = mygroup.First().nm.FName }).Distinct().ToList(); Which all seems to work..nothing errors and the list populates. In form2 I do: Form1 f1 = (Form1)Application.OpenForms[Form1]; List Names = f1.FirstNames; Names.Sort((FirstNames x FirstNames y) => x.Fname.CompareTo(y.Fname)); It fails as the object comes back as null? EDIT: Sorted it out...forgot: this.FirstNames = FirstNames; Idiot!

Jay S · Answer

I've worked it out... var foo = (from sn in list2 join nm in list.Select((SName z) => new { SName z }) on (sn.SecondNameID + num5) equals nm.z select new { realSnID = sn.SecondNameID + num5 nm.SName }).Distinct(); var fooList = foo.ToList(); Now :/ Just need to do what you did last time and make the list avaliable to all classes :s

Jay S · Answer

As always your solution is perfect :) I have another list issue (sorry if i should start a new thread...) Currently creating a list like this: int i = 0; string text2 = string.Empty; System.Collections.Generic.List list = new System.Collections.Generic.List (); while (i { byte b = binaryReader.ReadByte(); if (b != 0) { text2 += (char)b; } else { list.Add(text2); text2 = string.Empty; } i++; } its perfect and operates as i need. I'm creating a second list (this can be changed if you thinks best...just mocked it up) var FirstNameIds = (from fn in list2 orderby fn.FirstNameID group fn by new { fn.FirstNameID } into grouping from fn in grouping.DefaultIfEmpty() select fn.FirstNameID).Distinct().ToList(); int FirstNameIdsCount = FirstNameIds.Count(); What it does is fine..though you may think theres a better way.. What I need to do now is join them.. I need to join FirstNameID in the FirstNameIds list to the index number? in the list list list is just a 1 column list but the item number in list matches the FirstNameID So when I try to do a join in my linq I have nothing to join on.. Any suggestions?

Vulpes · Answer

As you say once the combobox is data-bound you can't change the Items collection. However what you can do is to change your List before you bind to it. So if you want to add a blank entry: List nations = f1.Nations; Nation blank = new Nation() { NationalityName =  NationCallUp = 0 // say }; nations.Insert(0 blank); // insert at first position in List comboBox1.DataSource = nations;

Jay S · Answer

Is there anyway to add a blank selection at for my combobox? ..Once its bound i can't use the Items.Add.. Would reflection be needed?!

Jay S · Answer

I worked it out in the end.. Instead of using this: foreach (NationEligable n in form.NationEligable) { this.cboIntNation.Items.Add(String.Format(n.NationalityName n.NationCallup)); } (changed some of the names) I did as you suggested a couple of posts above: Form1 f1 = (Form1)Application.OpenForms[Form1]; List nations = f1.NationEligable; cboIntNation.DataSource = nations; cboIntNation.DisplayMember = NationalityName; cboIntNation.ValueMember = NationCallUp; And then just did this rather than looking back on the list: this.Person.NationClubContracted = Convert.ToInt16(cboIntNation.SelectedValue); this.Person.NationName = Convert.ToString(cboIntNation.Text);

Vulpes · Answer

If you set the DataSource property you're using the data-binding infrastructure. You can bind to any collection which implements the IList interface such as arrays ArrayLists generic Lists and DataSets. When you do this the Items property contains objects of the relevant type rather than strings. So if you bind to a List  the Items property (and hence the SelectedItem property) contains Nation objects. The DisplayMember property will then represent a property of the underlying Nation object which actually is displayed in the combobox. The ValueMember property will represent another property of the Nation object which is not actually displayed but can be thought of as the 'value' of the object and which is therefore useful from a programmatic viewpoint. In contrast when in my earlier example I was generating strings from the Nation objects and adding them to the Items collection then the Items will actually be those strings. Incidentally they need not necessarily be strings (Items is an object collection) but if they're something else the ToString() method will be applied to them to display them in the combobox. If you're not sure what your Items actually are then you can easily discover their type with this line: MessageBox.Show(comboBox1.SelectedItem.GetType().ToString());

Jay S · Answer

How do I know if I'm binding it? My knowledge of terminology is poor... Wouldn't all my combo box be strings regardless?!

Vulpes · Answer

I'd expect that code to work as long as you're binding to the List . However if (as the error message suggests) you're populating the Items collection with strings then it won't work and it will be more difficult to get back to the original Nation object.

Jay S · Answer

Thank you for taking your time to explain it to me..I kinda get it..think I will need to study how its done a bit more.. I've been able to bind it to the combobox with no problems.. What I'm not trying to do is to use the combobox selecteditem to search back on this list: Nation EligableNationItem = (Nation)this.cboIntNation.SelectedItem; this.Person.NationClubContracted = (Int16)EligableNationItem.NationCallup; It fails on the first line with: Unable to cast object of type 'System.String' to type 'Foo.Nation' Any ideas?

Jay S · Answer

I've just noticed that by doing: cboIntNation.Items.Add(String.Format({0} - {1} n.NationalityName n.NationCallup): I get a string in the combobox rather than a value and ID?

Jay S · Answer

Perfect..did all that you said in form1 apart from: Nations = NationEligable ; -> this. Nations = NationEligable ; In form2 I did: foreach (Nation n in form.Nations) { cboIntNation.Items.Add(String.Format({0} - {1} n.NationalityName n.NationCallup)); } Got there in the end!! Can you example (as best as you can and if you have time) what you/we did for this just so I can try and understand it

Jay S · Answer

Ok.. Created my top level class: using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace Foo { class Nation { public string NationalityName { get; set; } public int NationCallup { get; set; } } } In the code behind my Form1 I have: namespace Foo { public class Form1 : System.Windows.Forms.Form { // // public System.Collections.Generic.List Nation; //this errors - Foo.Form1.Nation' is a 'field' but is used like a 'type' // // // Public Form1() { // // //playerPeople is created here // List NationEligable = (from p in playerPeople orderby p.NationClubContracted where p.NationClubContracted!= -1 group p by new { p.NationalityNamep.NationClubContracted } into mygroup select new Nation() { NationalityName = mygroup.First().NationalityName NationCallUp = mygroup.First().NationClubContracted }).ToList(); return NationEligable; // // } This errors...The Nation is same above along with the return NationEligable saying : Since 'Foo.Form1.Form1()' returns void a return keyword must not be followed by an object expression

Jay S · Answer

And the errors I'm getting?! My concern is : p in playerPeople Is a list in my Form1 code. No idea how to do a top level class and still have no idea how for example Form2 can call the Nation class to populate a combobox where the Nation class relies on a list in Form1 I'm completely lost at what to do.

Vulpes · Answer

So that the Nation class is easily accessible to all forms and classes in the application I'd make it a 'top level' class rather than nest it within Form1 as you appear to be doing just now. All that the other classes need to know is that they're getting a List of Nations. How this List was generated is not relevant to them.

Jay S · Answer

On and Nation() Error 1 'Form1.Nation' is a 'field' but is used like a 'type' I'm also concerned as in the linq it says: from p in playerPeople playerPeople is a list itself..so if I call this new class from another class it will not know what from p in playerPeople is?!

Vulpes · Answer

As you probably know you can't use an anonymous type as the type of a field (i.e. class level variable) or as a method return value. So I'd create a named class instead: class Nation // or whatever is suitable { public string NationalityName {get; set;} public int NationCallup {get; set;} } and then change your query as follows: List NationEligable = (from p in playerPeople orderby p.NationClubContracted where p.NationClubContracted!= -1 group p by new { p.NationalityNamep.NationClubContracted } into mygroup select new Nation() { NationalityName = mygroup.First().NationalityName NationCallUp = mygroup.First().NationClubContracted }).ToList(); You can now expose NationEligable as a public or internal field of the containing class or return it from a method.