Populating a ListView with objects from a List<>

I am currently converting what was a Console Application into a Windows Form application. Fortunatly i initially designed the application to work with a GUI in the future so there was not much code to change.

I have a UserCollection class which itself holds a List<> of type User/Member (Member is derives from User).

What i would like to do is to add each item in the UserCollection List<> to the ListView, so i can see each entry and have the multiple entries list vertically.

I have tried to implement this myself firstly by using:

        private void UpdatePeopleListings()
    {
        foreach (User person in newCollection)
        {
            listViewPeople.Items.Add(person.ToString());
        }
    }

Where newCollection is the new object created from the UserCollection class in the main windows form.

I recieve the error:

foreach statement cannot operate on variables of type 'Collection.UserCollection' because 'Collection.UserCollection' does not contain a public definition for 'GetEnumerator'

I then tried to make a small workaround, so in my UserCollection i created the following method:

        public User ReturnUser()
    {
        foreach (User person in _userCollection)
        {
            return person;
        }
        return null;
    }

(_userCollection is the List<> of Users/Members in UserCollection.cs)

And then use it like this:

private void UpdatePeopleListings()
    {
        listViewPeople.Items.Add(newCollection.ReturnUser().ToString());
    }

Although this does populate the ListView with an entry, it only populates the first entry. If i was to add more than one User/Member to the newCollection then it simply repeats the first entry.

How would i go about populating the ListView with ALL objects in the collection properly and how would i prevent it from repeating only one object.

UserCollecton.cs

///////////////////////////////////////////////////////////
//  UserCollection.cs
//  Implementation of the Class UserCollection
//  Generated by Enterprise Architect
//  Created on:      22-Oct-2009 22:40:30
///////////////////////////////////////////////////////////

#region Using Statements

using System;

using System.Collections.Generic;

using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;

using System.IO;

#endregion

namespace Collection
{
    //Allows the class to be saved
    [Serializable()]

    public class UserCollection
    {
        #region Fields

        //Declares a list of type User (Which also holds derived Member objects)
        private List<User> _userCollection = new List<User>();


        //Holds number of members
        int nMember = 0;
        //Holds number of users
        int nUser = 0;

        #endregion

        #region Add Operations

        /// <summary>
        /// Adds a new user
        /// </summary>
        /// <param name="user"></param>
        public void AddUser(User user)
        {
            //Adds the user given in the operation parameters to the collection
            _userCollection.Add(user);
            nUser++;

            //Sorts the collection using the CompareTo() specified in the User class.
            _userCollection.Sort();

            //Console.WriteLine used for testing purposes
            //Console.WriteLine("added");
        }


        ///<summary>
        ///Adds a new Member
        ///</summary>
        /// <param name="member"></param>
        public void AddMember(Member member)
        {
            //Adds the member given in the operation parameters to the collection
            _userCollection.Add(member);
            nMember++;

            //Sorts the collection using the CompareTo() specified in the User class.
            _userCollection.Sort();

            //Console.WriteLine used for testing purposes
            //Console.WriteLine("added");
        }

        #endregion

        #region Removal Operations

        ///<summary>
        ///Removes a user based on FirstName,LastName and PostCode
        ///</summary> 
        /// <param name="person"></param>
        public void RemoveUser(User person)
        {
            //Only search collection for users if there is data in it
            if (_userCollection.Count > 0)
            {
                //Create a temp list for any matched found
                List<User> tempList = new List<User>();

                foreach (User u in _userCollection)
                {
                    //If the details stored in the collection match the details given in the search
                    if (u.FName == person.FName && u.LName == person.LName && u.PostCode == person.PostCode)
                    {
                        //Add any matches to the temp list
                        tempList.Add(u);
                    }
                    else
                    {
                        throw new ArgumentException("User not found");
                    }
                }

                //Delete any matches 
                foreach (User u in tempList)
                {
                    _userCollection.Remove(u);
                    //Decrement user count
                    nUser--;
                }
            }
            else
            {
                throw new AccessViolationException("No data in collection");
            }
        }

        /// <summary>
        /// Removes a user using Membership number
        /// </summary>
        /// <param name="number"></param>
        public void RemoveMember(int number)
        {
                //Create a temp list of type Member
                Member temp = new Member();

                //Use the temp list to compare types and store all objects of type member
                //found in the collection to it.
                List<User> Mems = _userCollection.FindAll(delegate(User u)
                { return u.GetType() == temp.GetType(); });

                //Delete any matches
                foreach (Member m in Mems)
                {
                    if (m.mNum == number)
                    {
                        _userCollection.Remove(m);
                        //Decrement member count
                        nMember--;
                    }
                    else
                    {
                        throw new ArgumentException("Member not found");
                    }
                }
        }

        #endregion

        #region Search Operations

        ///<summary>
        ///Returns member by Membership number
        /// </summary>
        /// 
        /// <param name="_mNumber"></param>
        public Member FindByMNo(int number)
        {
            //Create a temp list of type Member
         开发者_如何学C   Member temp = new Member();

            //Use the temp list to compare types and store all objects of type member
            //found in the collection to it.
            List<User> Mems = _userCollection.FindAll(delegate(User u)
            { return u.GetType() == temp.GetType(); });

            //Return any matches found
            foreach (Member i in Mems)
            {
                if (i.mNum == number)
                {
                    return i;
                }
            }
            throw new ArgumentException("Member not found");
        }

        ///<summary>
        ///Returns a list of Users matching details given
        ///</summary>
        /// 
        /// <param name="_fName"></param>
        /// <param name="_lName"></param>
        public List<User> FindByName(User person)
        {
            //Create a temp list to store any matches
            List<User> temp = new List<User>();

            //Add matches found to the temp list
            foreach (User u in _userCollection)
            {
                if (u.LName == person.LName)
                {
                    temp.Add(u);
                }
            }

            if (temp.Count > 0)
            {
                //Return the list that holds any matches
                return temp;
            }

            throw new ArgumentException("User not found");
        }

        public User ReturnUser()
        {
            foreach (User person in _userCollection)
            {
                return person;
            }
            return null;
        }

        #endregion

        #region Edit Operations

        ///<summary>
        ///Edits a members membership expiry
        ///</summary>
        /// 
        /// <param name="member"></param>
        public void EditMemStatus(int member, DateTime newDate)
        {
                //Create a temp list of type Member
                Member temp = new Member();

                //Use the temp list to compare types and store all objects of type member
                //found in the collection to it.
                List<User> Mems = _userCollection.FindAll(delegate(User u)
                { return u.GetType() == temp.GetType(); });

                //Search for the member that matches the number given in the parameter
                foreach (Member m in Mems)
                {
                    if (m.mNum == member)
                    {
                        //Replace the match with the new expiry
                        m.mExp = newDate;
                    }
                    else
                    {
                        throw new ArgumentException("Date cannot be changed");
                    }
                }
        }

        #endregion

        #region I/O Operations

        public bool SaveData()
        {
            try
            {
                //Open the stream using the Data.txt file
                using (Stream stream = File.Open("Data.txt", FileMode.Create))
                {
                    //Create a new formatter
                    BinaryFormatter bin = new BinaryFormatter();
                    //Copy data in collection to the file specified earlier
                    bin.Serialize(stream, _userCollection);
                    bin.Serialize(stream, nMember);
                    bin.Serialize(stream, nUser);
                    //Close stream to release any resources used
                    stream.Close();
                }
                return true;
            }
            catch (IOException ex)
            {
                throw new ArgumentException(ex.ToString());
            }
        }

        public bool LoadData()
        {
            //Check if file exsists, otherwise skip
            if (File.Exists("Data.txt"))
            {
                try
                {
                    using (Stream stream = File.Open("Data.txt", FileMode.Open))
                    {
                        BinaryFormatter bin = new BinaryFormatter();

                        //Copy data back into collection fields
                        _userCollection = (List<User>)bin.Deserialize(stream);
                        nMember = (int)bin.Deserialize(stream);
                        nUser = (int)bin.Deserialize(stream);
                        stream.Close();

                        //Sort data to ensure it is ordered correctly after being loaded
                        _userCollection.Sort();
                        return true;

                    }
                }
                catch (IOException ex)
                {
                    throw new ArgumentException(ex.ToString());
                }
            }
            else
            {
                //Console.WriteLine present for testing purposes
                Console.WriteLine("\nLoad failed, Data.txt not found");
                return false;
            }
        }

        #endregion

        #region Properties

        //Gets amount of Members in collection
        public int GetNMember
        {
            get
            {
                return nMember;
            }
        }

        //Gets amount of Users in collectioj
        public int GetNUser
        {
            get
            {
                return nUser;
            }
        }

        #endregion

    }//end UserCollection
}

Ignore any random Console stuff, i've not finished the cleanup yet.

---

The foreach doesn't work because your UserCollection class doesn't implement the IEnumerable interface.

The ListItems is not what you expected, because you do not understand how the ListView / ListViewItems work. A ListView consists of ListViewItems, and a ListViewItem can consists of SubItems (which are only displayed when the ListView's viewstyle is set to 'report').

When you add a ListViewItem using the method that you're using, only the 'caption' of the ListViewItem is defined. This means, that you'll have to use another overload of the Add method; the method which takes a ListViewItem object as an argument. Then, you can do this:

ListViewItem item = new ListViewItem();
item.Text = "bar";
item.SubItems.Add ("foo");
item.SubItems.Add ("foo2");
myListView.Items.Add (item);

On the question that only one item is added to your list: - you are only adding one item ... More specifically, you're adding the collection itself, rather then creating a ListViewItem for each object that is in your collection.

So what you have to do is:

• iterate over your list (using foreach (means you have to implement IEnumerable on the collection class), or using a for loop (but you'll have to make sure that you can access the contents of the collection using an indexer for instance))
• create a ListViewItem for each object that exists in the list.

I wonder why you've created your custom UserCollection in the first place though. I see that you've implemented some specific functionality, but .... I think there are better solutions. Nonetheless, you should implement the IEnumerable interface, the IList interface, etc... for that class. By doing so, your class will be a 'real collection', and then you can work with it like any other collection class. (Iterate using foreach, or using a for loop, etc..)

---

In conjunction with Frederik Gheysel's answer, it would be wise to implement IEnumerator also. Remember to override Equals, GetHashCode and ToString when doing so.