Develop Reference

Deep Copy of OrderedDictionary

What is the simplest way to create a deep copy of an OrderedDictionary? I tried making a new variable like this:
var copy = dict[x] as OrderedDictionary;
But if I update the values/keys in copy, the dictionary in dict[x] gets updated as well.
Edit: dict is another OrderedDictionary.

You should be able to use a generic deep cloning method. An example of deep cloning from msdn magazine:
Object DeepClone(Object original)
{
// Construct a temporary memory stream
MemoryStream stream = new MemoryStream();
// Construct a serialization formatter that does all the hard work
BinaryFormatter formatter = new BinaryFormatter();
// This line is explained in the "Streaming Contexts" section
formatter.Context = new StreamingContext(StreamingContextStates.Clone);
// Serialize the object graph into the memory stream
formatter.Serialize(stream, original);
// Seek back to the start of the memory stream before deserializing
stream.Position = 0;
// Deserialize the graph into a new set of objects
// and return the root of the graph (deep copy) to the caller
return (formatter.Deserialize(stream));
}

What type of objects are you storing in your dictionary ?
You'll need to iterate over the content of the Dictionary and clone/duplicate the contents in some way.
If your object implements ICloneable you could do something like,
Dictionary<int, MyObject> original = new Dictionary<int, MyObject>();
... code to populate original ...
Dictionary<int, MyObject> deepCopy = new Dictionary<int, MyObject>();
foreach(var v in a)
{
MyObject clone = v.Value.Clone();
b.Add(v.Key, clone);
}

I can't tell from your question if dict is a dictionary of dictionaries? The simplest way to make a deep copy of a collection is to iterate through its members and clone each one.
If your value implements ICloneable:
OrderedDictionary newDict = new OrderedDictionary();
foreach(DictionaryEntry entry in OriginalDictionary)
{
newDict[entry.Key] = entry.Value.Clone();
}
If your values can't be Clone()d, you'll have to copy them another way.
OrderedDictionary newDict = new OrderedDictionary();
foreach(DictionaryEntry entry in OriginalDictionary)
{
MyClass x = new MyClass();
x.myProp1 = entry.Value.myProp1 as primitive value;
x.myProp2 = entry.Value.myProp2 as primitive value;
newDict[entry.Key] = x;
}

How to assign List<T> without it being a reference to the original List<T>?

For example
List<string> name_list1 = new List<string>();
List<string> name_list2 = new List<string>();
later in the code:
name_list1.Add("McDonald");
name_list1.Add("Harveys");
name_list1.Add("Wendys");
name_list2 = name_list1; // I make a copy of namelist1 to namelist2
So, from this point I would like to keep adding element or making changes in name_list2 without affecting name_list1. How do I do that?

name_list2 = new List<string>(name_list1);
This will clone the list.
Edit: This solution only works for primitive types. For objects, see other responses below.

Another Options is : Deep Cloning
public static T DeepCopy<T>(T item)
{
BinaryFormatter formatter = new BinaryFormatter();
MemoryStream stream = new MemoryStream();
formatter.Serialize(stream, item);
stream.Seek(0, SeekOrigin.Begin);
T result = (T)formatter.Deserialize(stream);
stream.Close();
return result;
}
so,
you can use :
name_list2 = DeepCopy<List<string>>(name_list1);
OR:
name_list2 = DeepCopy(name_list1);
will also work.

For Primitive Types you can do this:
List<string> CopyList = new List<string>(OriginalList);
For non-primitve/user-difined types you can do this:
List<Person> CopyList = new List<Person>();
foreach(var item in OriginalList)
{
CopyList.Add(new Person {
Name = item.Name,
Address = item.Address
});
}

name_list2 = new List<string>(name_list1); // Clone list into a different object
At this point, the two lists are different objects. You can add items to list2 without affecting list1

The problem is the assignment. Until the assignment name_list2 = name_list1;, you have two different List objects on the heap pointed to by the variables name_list1 and name_list2. You fill up name_list1, which is fine. But the assignment says, "make name_list2 point to the same object on the heap as name_list1." The List that name_list2 used to point to is no longer accessible and will be garbage collected. What you really want is to copy the contents of name_list1 into name_list2. You can do this with List.AddRange. Note that this will result in a "shallow" copy, which is fine for the example you cite, where the list contents are strings, but may not be what you want when the list members are more complex objects. It all depends on your needs.

Based on #Mrunal answer I created an extension method:
public static T Clone<T>(this T source)
{
// Don't serialize a null object, simply return the default for that object
if (source == null)
{
return default;
}
// initialize inner objects individually
// for example in default constructor some list property initialized with some values,
// but in 'source' these items are cleaned -
// without ObjectCreationHandling.Replace default constructor values will be added to result
var deserializeSettings = new JsonSerializerSettings { ObjectCreationHandling = ObjectCreationHandling.Replace };
return JsonConvert.DeserializeObject<T>(JsonConvert.SerializeObject(source), deserializeSettings);
}
And you can call it like this:
L2 = L1.Select(x => x.Clone()).ToList();

I like linq for this...
If list elements are primitives or structures then...
L2 = L1.ToList()
If list elements are classes then...
L2 = L1.Select(x => x.Copy()).ToList();
Where Copy could simply be a shallow copy exposure of MemberWiseClone, or it could be some implementation of a deep copy.

I prefer Json converter method to serialize and deserialize, this way you don't have to mark the classes for serialization, especially you have numerous child classes.
https://www.newtonsoft.com/json/help/html/SerializingJSON.htm

Here is an alternative solution:
List<string> name_list1 = new List<string>();
List<string> name_list2 = new List<string>();
name_list1.Add("McDonald");
name_list1.Add("Harveys");
name_list1.Add("Wendys");
name_list2.AddRange(name_list1.ToArray());
The ToArray() method copies 'name_list1' to a new array, which we then add to name_list2 via the AddRange() method.

For primitive types:
List ClonedList = new list(OriginalList);
For non-primitive/User Defined types:
We need to perform a deep copy:
Deep Copy is used to make a complete deep copy of the internal reference types, for this we need to configure the object returned by MemberwiseClone().
Step1- In your class inherit from ICloneable:
public class MyClass:ICloneable
Step2- Implement method
public MyClass Clone()
{
MyClass MyClassObj =new MyClass();
MyClassObj.Property1 = this.Property1;
.
.
MyClassObj.Property_N = this.Property_N;
return MyClass;
}
Step3- now clone your List
List<MyClass> MyClassClone = new List<MyClass>();
for(i=0; i<Count; i++)
{
MyClassClone.Add(OriginalClaaObj[i].Clone());
}
This will make deep copy of each item of the object.

None of the above solutions worked for me when using lists of class objects.
This can be used for copying any object to another object with shared property names.
public static void ObjectToObject(object source, object destination)
{
// Purpose : Use reflection to set property values of objects that share the same property names.
Type s = source.GetType();
Type d = destination.GetType();
const BindingFlags flags = BindingFlags.Public | BindingFlags.Instance;
var objSourceProperties = s.GetProperties(flags);
var objDestinationProperties = d.GetProperties(flags);
var propertyNames = objSourceProperties
.Select(c => c.Name)
.ToList();
foreach (var properties in objDestinationProperties.Where(properties => propertyNames.Contains(properties.Name)))
{
try
{
PropertyInfo piSource = source.GetType().GetProperty(properties.Name);
properties.SetValue(destination, piSource.GetValue(source, null), null);
}
catch (Exception ex)
{
throw;
}
}
}
public static List<T> CopyList<T>(this List<T> lst)
{
List<T> lstCopy = new List<T>();
foreach (var item in lst)
{
var instanceOfT = Activator.CreateInstance<T>();
ObjectToObject(item, instanceOfT);
lstCopy.Add(instanceOfT);
}
return lstCopy;
}
For lists use this:
list2 = list1.CopyList();

If both the lists are of the same complex type then you can do something like below:-
SomeClass List2 = new List();
List1.ForEach(u => List2.Add(u));
What I am doing is to loop through each element of List1 and keep adding it to List2.
I believe this is the shortest way to do it.

While it could be potential performance-threat solution, but it would copy the values property-by-property eloquently.
using Newstonsoft.Json;
ClassA classA = new ClassA();
ClassA classACopyWithoutReference = JsonConvert.DeserializeObject<ClassA>(JsonConvert.SerializeObject(classA));

this solution works For complex objects (Replace T with name of your Type):
list2 = list1.Concat(new List<T> { object }).ToList();
or:
list2 = list1.ToArray().Append(object).ToList()

You can clone the complex object by serialize and deserialize it, it will remove you object reference and create new object without reference
using Newstonsoft.Json;
List<string> name_list1 = new List<string>();
name_list1.Add("McDonald");
name_list1.Add("Harveys");
name_list1.Add("Wendys");
name_list2 = name_list1;
List<string> name_list2 = JsonConvert.DeserializeObject<List<string>>
(JsonConvert.SerializeObject(name_list1)); // Ii make a copy of namelist1 to namelist2

this is working for me using LINQ...
lst1= lst2.ToList();

Read HttpRuntime.Cache item as read-only

I am using a HttpRuntime.Cache to store a list of objects that will be accessing frequently across sessions.
I use the following line of code to get the item from the cache:
List<chartData_Type> _chartData =
(List<chartData_Type>)HttpRuntime.Cache.Get("rollingMonth");
But, unfortunately when I update the _chartData, it updates the cached item too.
How can I simply get a copy of the cached item?

That is the way which .NET works because Cache just reference to the pointer of List. Don't know whether you chartData_Type is value type or reference type.
If value type, it is easy to use:
List<chartData_Type> list = new List<chartData_Type>(_chartData);
But if reference type, it comes to complicated, you need to implement DeepCopy method for your class, then do DeepCopy for each object in list.
DeepClone method:
public static class CloneHelper
{
public static T DeepClone<T>(T obj)
{
using (var ms = new MemoryStream())
{
var formatter = new BinaryFormatter();
formatter.Serialize(ms, obj);
ms.Position = 0;
return (T) formatter.Deserialize(ms);
}
}
}
In order to use this method, class chartData_Type must be marked [Serializable]:
[Serializable]
class chartData_Type
{}
So, you can do deep clone manually:
var cloneChartData = _chartData.Select(d =>
CloneHelper.DeepClone<chartData_Type>(d))
.ToList();

Use:
List<chartData_Type> list = new List<chartData_Type>(_chartData);
It will copy all items from _chartData to list.

List is a reference type and _chartData holds the address of the original object stored in the cache. That is why when you update _chartData, it updates the cached object too. If you want a separate object then clone the cached object. See below reference
http://www.codeproject.com/Articles/33364/ASP-NET-Runtime-Cache-Clone-Objects-to-Preserve-Ca
http://www.codeproject.com/Articles/45168/ASP-NET-Runtime-Cache-Clone-Objects-to-Preserve-Ca

Use a parameter System.Type T in List<T>

Suppose I have a function:
public static IList GetAllItems(System.Type T)
{
XmlSerializer deSerializer = new XmlSerializer(T);
TextReader tr = new StreamReader(GetPathBasedOnType(T));
IList items = (IList) deSerializer.Deserialize(tr);
tr.Close();
return items;
}
In order to retrieve a list of Articles, I would like to call GetAllItems(typeof(Article)) instead of GetAllItems(typeof(List<Article>)) but still return a list.
Question: how can I, without changing the function declaration/prototype, avoid requiring unnecessary List<> portion when calling this function?
That is, I am looking for something like this:
public static IList GetAllItems(System.Type T)
{
/* DOES NOT WORK: Note new List<T> that I want to have */
XmlSerializer deSerializer = new XmlSerializer(List<T>);
TextReader tr = new StreamReader(GetPathBasedOnType(T));
IList items = (IList) deSerializer.Deserialize(tr);
tr.Close();
return items;
}

If I understand you correctly, you have a serialized List in the stream, yes? If so, then just change this, in your second example:
XmlSerializer deSerializer = new XmlSerializer(List<T>);
To something like this:
if (!T.IsGenericType || T.GetGenericTypeDefinition() != typeof(List<>))
T = typeof(List<>).MakeGenericType(new Type[] { T });
XmlSerializer deSerializer = new XmlSerializer(T);
This will examine the type passed in; if it is a List<T> then it will be used unmodified. Otherwise, the appropriate List<T> type will be used instead.
In other words, if you pass in typeof(Foo) then T will become List<Foo>. But if you pass in typeof(List<Foo>) then T will stay List<Foo>.

You're calling GetAllItems(typeof(Article)), so I assume you know the type statically. If that is indeed the case, how about:
public static IList<T> GetAllItems<T>() //Note T is now a type agrument
{
//the using statement is better practice than manual Close()
using (var tr = new StreamReader(GetPathBasedOnType(typeof(T))))
return (List<T>)new XmlSerializer(typeof(List<T>)).Deserialize(tr);
}
You'd now call GetAllItems<Article>().
Also, consider using DataContractSerializer rather than XmlSerializer.

c# List<myObject> myList.copyTo() keeps a reference?

I've got a List and I used .copyTo() method. So it copies my List into one dimensional array.
So I loop this array and add each myObject to another List, then I'm changing things in this new List.
After this I'm showing the difference between the new values in my second List and the old values that are in my first List. But there is always no difference. So I'm thinking that the copyTo() method keeps a reference.
Are there other methods that doesn't keep a reference?

Yes. .CopyTo() performs a shallow copy, which means it copies the references. What you need is a deep copy, by cloning each object.
The best way is to make you myObject class implement IClonable
public class YourClass
{
public object Clone()
{
using (var ms = new MemoryStream())
{
var bf = new BinaryFormatter();
bf.Serialize(ms, this);
ms.Position = 0;
object obj = bf.Deserialize(ms);
ms.Close();
return obj;
}
}
}
Then you can cole .Clone() on each object and add that to a new List.
List<YourClass> originalItems = new List<YourClass>() { new YourClass() };
List<YourClass> newItemList = originalItems.Select(x => x.Clone() as YourClass).ToList();

If you've got a List of reference types, and you use the the CopyTo method to copy to an array, the contents of the List which are references will be copied across, so when you modify the objects in your array, they'll still refer to the same objects on the heap which are referenced from your list.