I've got a generic dictionary Dictionary<string, T> that I would like to essentially make a Clone() of ..any suggestions.
Okay, the .NET 2.0 answers:
If you don't need to clone the values, you can use the constructor overload to Dictionary which takes an existing IDictionary. (You can specify the comparer as the existing dictionary's comparer, too.)
If you do need to clone the values, you can use something like this:
public static Dictionary<TKey, TValue> CloneDictionaryCloningValues<TKey, TValue>
(Dictionary<TKey, TValue> original) where TValue : ICloneable
{
Dictionary<TKey, TValue> ret = new Dictionary<TKey, TValue>(original.Count,
original.Comparer);
foreach (KeyValuePair<TKey, TValue> entry in original)
{
ret.Add(entry.Key, (TValue) entry.Value.Clone());
}
return ret;
}
That relies on TValue.Clone() being a suitably deep clone as well, of course.
(Note: although the cloning version is potentially useful, for a simple shallow copy the constructor I mention in the other post is a better option.)
How deep do you want the copy to be, and what version of .NET are you using? I suspect that a LINQ call to ToDictionary, specifying both the key and element selector, will be the easiest way to go if you're using .NET 3.5.
For instance, if you don't mind the value being a shallow clone:
var newDictionary = oldDictionary.ToDictionary(entry => entry.Key,
entry => entry.Value);
If you've already constrained T to implement ICloneable:
var newDictionary = oldDictionary.ToDictionary(entry => entry.Key,
entry => (T) entry.Value.Clone());
(Those are untested, but should work.)
Dictionary<string, int> dictionary = new Dictionary<string, int>();
Dictionary<string, int> copy = new Dictionary<string, int>(dictionary);
For .NET 2.0 you could implement a class which inherits from Dictionary and implements ICloneable.
public class CloneableDictionary<TKey, TValue> : Dictionary<TKey, TValue> where TValue : ICloneable
{
public IDictionary<TKey, TValue> Clone()
{
CloneableDictionary<TKey, TValue> clone = new CloneableDictionary<TKey, TValue>();
foreach (KeyValuePair<TKey, TValue> pair in this)
{
clone.Add(pair.Key, (TValue)pair.Value.Clone());
}
return clone;
}
}
You can then clone the dictionary simply by calling the Clone method. Of course this implementation requires that the value type of the dictionary implements ICloneable, but otherwise a generic implementation isn't practical at all.
You could always use serialization. You could serialize the object then deserialize it. That will give you a deep copy of the Dictionary and all the items inside of it. Now you can create a deep copy of any object that is marked as [Serializable] without writing any special code.
Here are two methods that will use Binary Serialization. If you use these methods you simply call
object deepcopy = FromBinary(ToBinary(yourDictionary));
public Byte[] ToBinary()
{
MemoryStream ms = null;
Byte[] byteArray = null;
try
{
BinaryFormatter serializer = new BinaryFormatter();
ms = new MemoryStream();
serializer.Serialize(ms, this);
byteArray = ms.ToArray();
}
catch (Exception unexpected)
{
Trace.Fail(unexpected.Message);
throw;
}
finally
{
if (ms != null)
ms.Close();
}
return byteArray;
}
public object FromBinary(Byte[] buffer)
{
MemoryStream ms = null;
object deserializedObject = null;
try
{
BinaryFormatter serializer = new BinaryFormatter();
ms = new MemoryStream();
ms.Write(buffer, 0, buffer.Length);
ms.Position = 0;
deserializedObject = serializer.Deserialize(ms);
}
finally
{
if (ms != null)
ms.Close();
}
return deserializedObject;
}
Binary Serialization method works fine but in my tests it showed to be 10x slower than a non-serialization implementation of clone. Tested it on Dictionary<string , List<double>>
The best way for me is this:
Dictionary<int, int> copy= new Dictionary<int, int>(yourListOrDictionary);
This works fine for me
// assuming this fills the List
List<Dictionary<string, string>> obj = this.getData();
List<Dictionary<string, string>> objCopy = new List<Dictionary<string, string>>(obj);
As Tomer Wolberg describes in the comments, this does not work if the value type is a mutable class.
Try this if key/values are ICloneable:
public static Dictionary<K,V> CloneDictionary<K,V>(Dictionary<K,V> dict) where K : ICloneable where V : ICloneable
{
Dictionary<K, V> newDict = null;
if (dict != null)
{
// If the key and value are value types, just use copy constructor.
if (((typeof(K).IsValueType || typeof(K) == typeof(string)) &&
(typeof(V).IsValueType) || typeof(V) == typeof(string)))
{
newDict = new Dictionary<K, V>(dict);
}
else // prepare to clone key or value or both
{
newDict = new Dictionary<K, V>();
foreach (KeyValuePair<K, V> kvp in dict)
{
K key;
if (typeof(K).IsValueType || typeof(K) == typeof(string))
{
key = kvp.Key;
}
else
{
key = (K)kvp.Key.Clone();
}
V value;
if (typeof(V).IsValueType || typeof(V) == typeof(string))
{
value = kvp.Value;
}
else
{
value = (V)kvp.Value.Clone();
}
newDict[key] = value;
}
}
}
return newDict;
}
Replying on old post however I found it useful to wrap it as follows:
using System;
using System.Collections.Generic;
public class DeepCopy
{
public static Dictionary<T1, T2> CloneKeys<T1, T2>(Dictionary<T1, T2> dict)
where T1 : ICloneable
{
if (dict == null)
return null;
Dictionary<T1, T2> ret = new Dictionary<T1, T2>();
foreach (var e in dict)
ret[(T1)e.Key.Clone()] = e.Value;
return ret;
}
public static Dictionary<T1, T2> CloneValues<T1, T2>(Dictionary<T1, T2> dict)
where T2 : ICloneable
{
if (dict == null)
return null;
Dictionary<T1, T2> ret = new Dictionary<T1, T2>();
foreach (var e in dict)
ret[e.Key] = (T2)(e.Value.Clone());
return ret;
}
public static Dictionary<T1, T2> Clone<T1, T2>(Dictionary<T1, T2> dict)
where T1 : ICloneable
where T2 : ICloneable
{
if (dict == null)
return null;
Dictionary<T1, T2> ret = new Dictionary<T1, T2>();
foreach (var e in dict)
ret[(T1)e.Key.Clone()] = (T2)(e.Value.Clone());
return ret;
}
}
来源：https://stackoverflow.com/questions/139592/what-is-the-best-way-to-clone-deep-copy-a-net-generic-dictionarystring-t