Copying the contents of a base class from a derived class

Question

I currently have a derived class and a base class. How can I make the base class of the derived class equal to a base class that I have? Will a shallow copy work?

Answer 1

Based on mnyarar code, it would be necessary update the way to obtain the properties:

public static T Map<T, TU>(this T target, TU source)
{


    // list of writable properties of the destination
    List<PropertyInfo> tprops = typeof(T).GetTypeInfo().DeclaredProperties
                                        .Where(x => x.CanWrite == true).ToList();

    tprops.ForEach(prop =>
            {
                // check whether source object has the the property
                var sp = source.GetType().GetProperty(prop.Name);
                if (sp != null)
                {
                    // if yes, copy the value to the matching property
                    var value = sp.GetValue(source, null);
                    target.GetType().GetProperty(prop.Name).SetValue(target, value, null);
                }
            });
}

Answer 2

Just change this.

Derived d = (Derived)b;

Also, your name data type should be string, not int

Answer 3

You can always use Object.MemberwiseClone to copy it.

http://msdn.microsoft.com/en-us/library/system.object.memberwiseclone.aspx

Or implement the IClonable interface: http://msdn.microsoft.com/en-us/library/system.icloneable.aspx

Answer 4

I found EMIT may help you for this.

For we will spend too long in reflection but we can be fast in Emit.

  private static void CloneObjectWithIL<T>(T source, T los)
    {
        var dynamicMethod = new DynamicMethod("Clone", null, new[] { typeof(T), typeof(T) });
        ILGenerator generator = dynamicMethod.GetILGenerator();

        foreach (var temp in typeof(T).GetProperties().Where(temp=>temp.CanRead&&temp.CanWrite))
        {
            generator.Emit(OpCodes.Ldarg_1);// los
            generator.Emit(OpCodes.Ldarg_0);// s
            generator.Emit(OpCodes.Callvirt,temp.GetMethod);
            generator.Emit(OpCodes.Callvirt, temp.SetMethod);
        }
        generator.Emit(OpCodes.Ret);
        var clone = (Action<T, T>) dynamicMethod.CreateDelegate(typeof(Action<T, T>));
        clone(source, los);
    }

It can be use as this code:

public class Base
{
    public string BaseField;
}

public class Derived : Base
{
    public string DerivedField;
}

Base base = new Base();
//some alother code
Derived derived = new Derived();
CloneObjectWithIL(base, derived);

The more fast code is to cache it.

    // ReSharper disable once InconsistentNaming
    public static void CloneObjectWithIL<T>(T source, T los)
    {
        //See http://lindexi.oschina.io/lindexi/post/C-%E4%BD%BF%E7%94%A8Emit%E6%B7%B1%E5%85%8B%E9%9A%86/
        if (CachedIl.ContainsKey(typeof(T)))
        {
            ((Action<T, T>) CachedIl[typeof(T)])(source, los);
            return;
        }
        var dynamicMethod = new DynamicMethod("Clone", null, new[] { typeof(T), typeof(T) });
        ILGenerator generator = dynamicMethod.GetILGenerator();

        foreach (var temp in typeof(T).GetProperties().Where(temp => temp.CanRead && temp.CanWrite))
        {
            if (temp.GetAccessors(true)[0].IsStatic)
            {
                continue;
            }

            generator.Emit(OpCodes.Ldarg_1);// los
            generator.Emit(OpCodes.Ldarg_0);// s
            generator.Emit(OpCodes.Callvirt, temp.GetMethod);
            generator.Emit(OpCodes.Callvirt, temp.SetMethod);
        }
        generator.Emit(OpCodes.Ret);
        var clone = (Action<T, T>) dynamicMethod.CreateDelegate(typeof(Action<T, T>));
        CachedIl[typeof(T)] = clone;
        clone(source, los);
    }

    private static Dictionary<Type, Delegate> CachedIl { set; get; } = new Dictionary<Type, Delegate>();

Answer 5

I came up with a pretty good pattern for dealing with this situation.

public class Base
{
    public int BaseField;

    /// <summary>
    /// Apply the state of the passed object to this object.       
    /// </summary>
    public virtual void ApplyState(Base obj)
    {
        BaseField = obj.BaseField;
    }
}

public class Derived : Base
{
    public int DerivedField;

    public override void ApplyState(Base obj)
    {
        var src = srcObj as Derived;

        if (src != null)
        {
            DerivedField = src.DerivedField;
        }

        base.ApplyState(srcObj);        
    }
}

Given any two objects that share type 'Base', you can apply A to B or B to A.

Answer 6

Another approach would be to map the base class to derived class:

/// <summary>
/// Maps the source object to target object.
/// </summary>
/// <typeparam name="T">Type of target object.</typeparam>
/// <typeparam name="TU">Type of source object.</typeparam>
/// <param name="target">Target object.</param>
/// <param name="source">Source object.</param>
/// <returns>Updated target object.</returns>
public static T Map<T, TU>(this T target, TU source)
{
    // get property list of the target object.
    // this is a reflection extension which simply gets properties (CanWrite = true).
    var tprops = target.GetProperties();

    tprops.Where(x=>x.CanWrite == true).ToList().ForEach(prop =>
    {
        // check whether source object has the the property
        var sp = source.GetType().GetProperty(prop);
        if (sp != null)
        {
            // if yes, copy the value to the matching property
            var value = sp.GetValue(source, null);
            target.GetType().GetProperty(prop).SetValue(target, value, null);
        }
    });

    return target;
}

Example:

var derivedClass = new DerivedClass();
derivedClass.Map(baseClass);