使用 List<> 中的对象填充 ListView

Question

我目前正在将控制台应用程序转换为 Windows 窗体应用程序。 幸运的是，我最初将应用程序设计为在未来使用 GUI，因此没有太多代码需要更改。

我有一个 UserCollection 类，它本身包含一个用户/成员类型的列表（成员是从用户派生的）。

我想做的是将UserCollection List中的每个项目添加到ListView，这样我就可以看到每个条目并垂直拥有多个条目列表。

我首先尝试自己实现这一点：

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

newCollection 是从主窗口窗体中的 UserCollection 类创建的新对象。

我收到错误：

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

然后我尝试做一个小的解决方法，所以在我的 UserCollection 中我创建了以下方法：

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

（_userCollection 是 UserCollection.cs 中用户/成员的列表）

然后像这样使用它：

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

虽然这确实会使用条目填充 ListView，但它只会填充第一个条目。 如果我要向 newCollection 添加多个用户/成员，那么它只会重复第一个条目。

我将如何正确地使用集合中的所有对象填充 ListView，以及如何防止它仅重复一个对象。

UserColleton.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
            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
}

忽略任何随机的控制台内容，我还没有完成清理。

Answer 1

foreach 不起作用，因为您的 UserCollection 类没有实现 IEnumerable 接口。

ListItems 不是您所期望的，因为您不了解 ListView / ListViewItems 是如何工作的。 ListView 由 ListViewItems 组成，ListViewItem 可以由 SubItems 组成（仅当 ListView 的 viewstyle 设置为 'report' 时才会显示）。

当您使用您正在使用的方法添加 ListViewItem 时，仅定义 ListViewItem 的“标题”。 这意味着，您将不得不使用 Add 方法的另一个重载；将 ListViewItem 对象作为参数的方法。 然后，您可以这样做：

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

关于仅将一项添加到您的列表的问题： - 您只添加一个项目......更具体地说，您正在添加集合本身，而不是为集合中的每个对象创建一个 ListViewItem。

所以你要做的是：

• 遍历您的列表（使用 foreach（意味着您必须在集合类上实现 IEnumerable），或使用 for 循环（但您必须确保您可以使用索引器访问集合的内容实例））
• 为列表中存在的每个对象创建一个 ListViewItem。

我想知道为什么您首先创建了自定义 UserCollection。我看到您已经实现了一些特定的功能，但是....我认为有更好的解决方案。 尽管如此，您应该为该类实现 IEnumerable 接口、IList 接口等。通过这样做，您的类将成为一个“真正的集合”，然后您可以像使用任何其他集合类一样使用它。 （使用 foreach 进行迭代，或者使用 for 循环等。）

Answer 2

结合 Frederik Gheysel 的回答，实施 IEnumerator 也是明智之举。这样做时记得覆盖 Equals、GetHashCode 和 ToString。