C＃返回ConcurrentBag的副本

Question

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Collections.Concurrent;

namespace Crystal_Message
{
    class Message
    {
        private int messageID;
        private string message;
        private ConcurrentBag <Employee> messageFor;
        private Person messageFrom;
        private string calltype;

        public Message(int iden,string message, Person messageFrom, string calltype, string telephone)
        {
            this.messageID = iden;
            this.messageFor = new ConcurrentBag<Employee>();
            this.Note = message;
            this.MessageFrom = messageFrom;
            this.CallType = calltype;
        }

        public ConcurrentBag<Employee> ReturnMessageFor
        {
            get
            {

                return messageFor;
            }

        }

        public int MessageIdentification
        {
            get { return this.messageID; }

            private set
            {
                if(value == 0)
                {
                    throw new ArgumentNullException("Must have Message ID");
                }

                this.messageID = value;
            }

        }

        public string Note
        {
            get { return message; }

            private set
            {
                if (string.IsNullOrWhiteSpace(value))
                {
                    throw new ArgumentException("Must Have a Message");

                }
                this.message = value;


            }

        }

        public Person MessageFrom
        {
            get { return messageFrom; }

            private set
            {
                this.messageFrom = value;
            }

        }

        public string CallType
        {
            get { return this.calltype; }

            private set
            {
                if (string.IsNullOrWhiteSpace(value))
                {
                    throw new ArgumentNullException("Please specify call type");
                }

                this.calltype = value;

            }

        }

        public void addEmployee(Employee add)
        {
            messageFor.Add(add);
        }


        public override string ToString()
        {
            return "Message: " + this.message + " From: " + this.messageFrom + " Call Type: " + this.calltype + " For: " + this.returnMessagefor();
        }

        private string returnMessagefor() 
        {
            string generate="";

            foreach(Employee view in messageFor)
            {
                generate += view.ToString() + " ";
            }

            return generate;
        }

        public override bool Equals(object obj)
        {
            if (obj == null)
            {
                return false;
            }

            Message testEquals = obj as Message;

            if((System.Object)testEquals == null)
            {
                return false;
            }

            return (this.messageID == testEquals.messageID) && (this.message == testEquals.message) && (this.messageFor == testEquals.messageFor) && (this.messageFrom == testEquals.messageFrom) && (this.calltype == testEquals.calltype);

        }

        public bool Equals(Message p)
        {
            if ((Object)p == null)
            {
                return false;
            }

            return (this.messageID == p.messageID) && (this.message == p.message) && (this.messageFor == p.messageFor) && (this.messageFrom == p.messageFrom) && (this.calltype == p.calltype);

        }

        public override int GetHashCode()
        {


            unchecked
            {
                return this.messageID.GetHashCode() * 33 ^ this.message.GetHashCode() * 33 ^ this.messageFor.GetHashCode() * 33 ^ this.messageFrom.GetHashCode() * 33 ^ this.calltype.GetHashCode();
            }


        }

    }
}

I have a Message class where a user could leave a message for more than one person. I have a getter for it, however, is returning a ConcurrentBag<> the way I've done proper practice? If not, how do i return the ConcurrentBag<> so I can loop through it and display it?

Answer 1

ConcurrentBag<T> is an IEnumerable<T> . You can loop through it as usual. However, as this is a thread safe collection, there are performance concerns to using it.

If you want to get rid of the performance impact while looping, call ToArray on it and return the new array instead.

    public IEnumerable<Employee> ReturnMessageFor
    {
        get
        {

            return messageFor.ToArray();
        }

    }

Answer 2

It's not clear to me what you are trying to accomplish.

Are you trying to externalize the Bag for all operations? Because that's what you did...

If you want to externalize something you can iterate over you should either return the Bag as IEnumerable or return an array or a list copied from the Bag.

Either way it's safe to iterate over. Might not be the best in terms of performance, but that's another question.

    // Option 1
    public IEnumerable<Employee> ReturnMessageFor
    {
        get
        {
            return messageFor;
        }
    }

    // Option 2
    public Employee[] ReturnMessageFor
    {
        get
        {
            return messageFor.ToArray();
        }
    }

Notes:

• You might want to make messageFor readonly (in the code you posted it is readonly).
• Remember that a ConcurrentBag allows you to safely iterate over a snapshot of the collection in a thread safe manner, but it does not lock the items in the collection.