Deep copy of List<T>_问答_开发者_运维开发者技术经验分享

I'm trying to make a deep copy of a generic list, and am wondering if there is any other way then creating the copying method and actually copying over each member one at a time. I have a class that looks somewhat like this:

public class Data
{            
    private string comment;
    public string Comment
    {
        get { return comment; }
        set { comment = value; }
    }

    private List<double> traceData;
    public List<double> TraceData
    {
        get { return traceData; }
        set { traceData = value; }
    }
}

And I have a list of the above data, i.e List<Data>. What I'm trying to do is plot a trace data of the subset of List onto a graph, possibly with some scaling or sweeping on the data. I obviously don't need to plot ev开发者_高级运维erything in the list because they don't fit into the screen.

I initially tried getting the subset of the list using the List.GetRange() method, but it seems that the underneath List<double> is being shallow copied instead of deep copied. When I get the subset again using List.GetRange(), I get previously modified data, not the raw data retrieved elsewhere.

Can anyone give me a direction on how to approach this? Thanks a lot.

The idiomatic way to approach this in C# is to implement ICloneable on your Data, and write a Clone method that does the deep copy (and then presumably a Enumerable.CloneRange method that can clone part of your list at once.) There isn't any built-in trick or framework method to make it easier than that.

Unless memory and performance are a real concern, I suggest that you try hard to redesign it to operate on immutable Data objects, though, instead. It'll wind up much simpler.

You can try this

    public static object DeepCopy(object obj)
    {
        if (obj == null)
            return null;
        Type type = obj.GetType();

        if (type.IsValueType || type == typeof(string))
        {
            return obj;
        }
        else if (type.IsArray)
        {
            Type elementType = Type.GetType(
                 type.FullName.Replace("[]", string.Empty));
            var array = obj as Array;
            Array copied = Array.CreateInstance(elementType, array.Length);
            for (int i = 0; i < array.Length; i++)
            {
                copied.SetValue(DeepCopy(array.GetValue(i)), i);
            }
            return Convert.ChangeType(copied, obj.GetType());
        }
        else if (type.IsClass)
        {

            object toret = Activator.CreateInstance(obj.GetType());
            FieldInfo[] fields = type.GetFields(BindingFlags.Public |
                        BindingFlags.NonPublic | BindingFlags.Instance);
            foreach (FieldInfo field in fields)
            {
                object fieldValue = field.GetValue(obj);
                if (fieldValue == null)
                    continue;
                field.SetValue(toret, DeepCopy(fieldValue));
            }
            return toret;
        }
        else
            throw new ArgumentException("Unknown type");
    }

Thanks to DetoX83 article on code project.

If IClonable way is too tricky for you. I suggest converting to something and back. It can be done with BinaryFormatter or a Json Converter like Servicestack.Text since it is the fastest one in .Net.

Code should be something like this:

MyClass mc = new MyClass();
string json = mc.ToJson();
MyClass mcCloned = json.FromJson<MyClass>();

mcCloned will not reference mc.

The most easiest (but dirty) way is to implement ICloneable by your class and use next extension method:

public static IEnumerable<T> Clone<T>(this IEnumerable<T> collection) where T : ICloneable
{
    return collection.Select(item => (T)item.Clone());
}

Usage:

var list = new List<Data> { new Data { Comment = "comment", TraceData = new List { 1, 2, 3 } };
var newList = list.Clone();

another thing you can do is mark your class as serializable and use binary serialization. Here is a working example

   public class Program
    {
        [Serializable]
        public class Test
        {
            public int Id { get; set; }
            public Test()
            {

            }
        }

        public static void Main()
        {   
            //create a list of 10 Test objects with Id's 0-10
            List<Test> firstList = Enumerable.Range(0,10).Select( x => new Test { Id = x } ).ToList();
            using (var stream = new System.IO.MemoryStream())

            {
                 var binaryFormatter = new System.Runtime.Serialization.Formatters.Binary.BinaryFormatter();
                 binaryFormatter.Serialize(stream, firstList); //serialize to stream
                 stream.Position = 0;
                 //deserialize from stream.
                 List<Test> secondList = binaryFormatter.Deserialize(stream) as List<Test>; 
            }


            Console.ReadKey();
        }
    }

If you make your objects immutable you don't need to worry about passing around copies of them, then you could do something like:

var toPlot = list.Where(d => d.ShouldBePlotted());

Since your collection is mutable, you need to implement the deep copy programmatically:

public class Data
{
    public string Comment { get; set; }
    public List<double> TraceData { get; set; }

    public Data DeepCopy()
    {
        return new Data
        {
            Comment = this.Comment, 
            TraceData = this.TraceData != null
                ? new List<double>(this.TraceData)
                : null;
        }
    }
}

The Comment field can be shallow copied because its already an immutable class. You need to create a new list for TraceData, but the elements themselves are immutable and require no special handling to copy them.

When I get the subset again using List.GetRange(), I get previously modified data, not the raw data retrieved elsewhere.

Use your new DeepCopy method as such:

var pointsInRange = dataPoints
    .Select(x => x.DeepCopy())
    .GetRange(start, length);

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

namespace DeepListCopy_testingSome
{
    class Program
    {
        static void Main(string[] args)
        {
            List<int> list1 = new List<int>();
            List<int> list2 = new List<int>();

            //populate list1
            for (int i = 0; i < 20; i++)
            {
                list1.Add(1);
            }

            ///////
            Console.WriteLine("\n int in each list1 element is:\n");
            ///////

            foreach (int i in list1)
            {
                Console.WriteLine(" list1 elements: {0}", i);
                list2.Add(1);
            }

            ///////
            Console.WriteLine("\n int in each list2 element is:\n");
            ///////

            foreach (int i in list2)
            {
                Console.WriteLine(" list2 elements: {0}", i);
            }

            ///////enter code here

            for (int i = 0; i < list2.Count; i++)
            {
                list2[i] = 2;
            }



            ///////
            Console.WriteLine("\n Printing list1 and list2 respectively to show\n"
                            + " there is two independent lists,i e, two differens"
                            + "\n memory locations after modifying list2\n\n");
            foreach (int i in list1)
            {
                Console.WriteLine(" Printing list1 elements: {0}", i);
            }

            ///////
            Console.WriteLine("\n\n");
            ///////

            foreach (int i in list2)
            {
                Console.WriteLine(" Printing list2 elements: {0}", i);
            }

            Console.ReadKey();
        }//end of Static void Main
    }//end of class
}

One quick and generic way to deeply serialize an object is to use JSON.net. The following extension method allows serializing of a list of any arbitrary objects, but is able to skip Entity Framework navigation properties, since these may lead to circular dependencies and unwanted data fetches.

Method

public static List<T> DeepClone<T>(this IList<T> list, bool ignoreVirtualProps = false)
{
    JsonSerializerSettings settings = new JsonSerializerSettings();
    if (ignoreVirtualProps)
    {
        settings.ContractResolver = new IgnoreNavigationPropsResolver();
        settings.PreserveReferencesHandling = PreserveReferencesHandling.None;
        settings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
        settings.Formatting = Formatting.Indented;
    }

    var serialized = JsonConvert.SerializeObject(list, settings);
    return JsonConvert.DeserializeObject<List<T>>(serialized);
}

Usage