将属性值从一个对象自动应用到另一个相同类型的对象？

There's ICloneable and object.MemberwiseClone (shallow copy) (these create a whole new object, so might not meet your requirements).

You could use reflection to do it yourself (inherit from a base class so you don't have to re-implement).

Or you could code generate it.

If you want something like ApplyProperties, you could write an extension method on Object which would do what you need. Just realize that such an extension method wouldn't be "pure", or side-effect free. But if you need the capability, its a way to accomplish it.

You can use serialization to deep clone the object:

public static T DeepClone<T>(this T objectToClone) where T: BaseClass
{
BinaryFormatter bFormatter = new BinaryFormatter();
MemoryStream stream = new MemoryStream();
bFormatter.Serialize(stream, objectToClone);
stream.Seek(0, SeekOrigin.Begin);
T clonedObject = (T)bFormatter.Deserialize(stream);
return clonedObject;
}

Classes would just have to be marked Serializable of course.

I have a type in MiscUtil called PropertyCopy which does something similar - although it creates a new instance of the target type and copies the properties into that.

It doesn't require the types to be the same - it just copies all the readable properties from the "source" type to the "target" type. Of course if the types are the same, that's more likely to work :) It's a shallow copy, btw.

In the code block at the bottom of this answer, I've extended the capabilities of the class. To copy from one instance to another, it uses simple PropertyInfo values at execution time - this is slower than using an expression tree, but the alternative would be to write a dynamic method, which I'm not too hot on. If performance is absolutely critical for you, let me know and I'll see what I can do. To use the method, write something like:

MyType instance1 = new MyType();
// Do stuff
MyType instance2 = new MyType();
// Do stuff


PropertyCopy.Copy(instance1, instance2);

(where Copy is a generic method called using type inference).

I'm not really ready to do a full MiscUtil release, but here's the updated code, including comments. I'm not going to rewrap them for the SO editor - just copy the whole chunk.

(I'd also probably redesign the API a bit in terms of naming if I were starting from scratch, but I don't want to break existing users...)

#if DOTNET35
using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Reflection;


namespace MiscUtil.Reflection
{
/// <summary>
/// Non-generic class allowing properties to be copied from one instance
/// to another existing instance of a potentially different type.
/// </summary>
public static class PropertyCopy
{
/// <summary>
/// Copies all public, readable properties from the source object to the
/// target. The target type does not have to have a parameterless constructor,
/// as no new instance needs to be created.
/// </summary>
/// <remarks>Only the properties of the source and target types themselves
/// are taken into account, regardless of the actual types of the arguments.</remarks>
/// <typeparam name="TSource">Type of the source</typeparam>
/// <typeparam name="TTarget">Type of the target</typeparam>
/// <param name="source">Source to copy properties from</param>
/// <param name="target">Target to copy properties to</param>
public static void Copy<TSource, TTarget>(TSource source, TTarget target)
where TSource : class
where TTarget : class
{
PropertyCopier<TSource, TTarget>.Copy(source, target);
}
}


/// <summary>
/// Generic class which copies to its target type from a source
/// type specified in the Copy method. The types are specified
/// separately to take advantage of type inference on generic
/// method arguments.
/// </summary>
public static class PropertyCopy<TTarget> where TTarget : class, new()
{
/// <summary>
/// Copies all readable properties from the source to a new instance
/// of TTarget.
/// </summary>
public static TTarget CopyFrom<TSource>(TSource source) where TSource : class
{
return PropertyCopier<TSource, TTarget>.Copy(source);
}
}


/// <summary>
/// Static class to efficiently store the compiled delegate which can
/// do the copying. We need a bit of work to ensure that exceptions are
/// appropriately propagated, as the exception is generated at type initialization
/// time, but we wish it to be thrown as an ArgumentException.
/// Note that this type we do not have a constructor constraint on TTarget, because
/// we only use the constructor when we use the form which creates a new instance.
/// </summary>
internal static class PropertyCopier<TSource, TTarget>
{
/// <summary>
/// Delegate to create a new instance of the target type given an instance of the
/// source type. This is a single delegate from an expression tree.
/// </summary>
private static readonly Func<TSource, TTarget> creator;


/// <summary>
/// List of properties to grab values from. The corresponding targetProperties
/// list contains the same properties in the target type. Unfortunately we can't
/// use expression trees to do this, because we basically need a sequence of statements.
/// We could build a DynamicMethod, but that's significantly more work :) Please mail
/// me if you really need this...
/// </summary>
private static readonly List<PropertyInfo> sourceProperties = new List<PropertyInfo>();
private static readonly List<PropertyInfo> targetProperties = new List<PropertyInfo>();
private static readonly Exception initializationException;


internal static TTarget Copy(TSource source)
{
if (initializationException != null)
{
throw initializationException;
}
if (source == null)
{
throw new ArgumentNullException("source");
}
return creator(source);
}


internal static void Copy(TSource source, TTarget target)
{
if (initializationException != null)
{
throw initializationException;
}
if (source == null)
{
throw new ArgumentNullException("source");
}
for (int i = 0; i < sourceProperties.Count; i++)
{
targetProperties[i].SetValue(target, sourceProperties[i].GetValue(source, null), null);
}


}


static PropertyCopier()
{
try
{
creator = BuildCreator();
initializationException = null;
}
catch (Exception e)
{
creator = null;
initializationException = e;
}
}


private static Func<TSource, TTarget> BuildCreator()
{
ParameterExpression sourceParameter = Expression.Parameter(typeof(TSource), "source");
var bindings = new List<MemberBinding>();
foreach (PropertyInfo sourceProperty in typeof(TSource).GetProperties(BindingFlags.Public | BindingFlags.Instance))
{
if (!sourceProperty.CanRead)
{
continue;
}
PropertyInfo targetProperty = typeof(TTarget).GetProperty(sourceProperty.Name);
if (targetProperty == null)
{
throw new ArgumentException("Property " + sourceProperty.Name + " is not present and accessible in " + typeof(TTarget).FullName);
}
if (!targetProperty.CanWrite)
{
throw new ArgumentException("Property " + sourceProperty.Name + " is not writable in " + typeof(TTarget).FullName);
}
if ((targetProperty.GetSetMethod().Attributes & MethodAttributes.Static) != 0)
{
throw new ArgumentException("Property " + sourceProperty.Name + " is static in " + typeof(TTarget).FullName);
}
if (!targetProperty.PropertyType.IsAssignableFrom(sourceProperty.PropertyType))
{
throw new ArgumentException("Property " + sourceProperty.Name + " has an incompatible type in " + typeof(TTarget).FullName);
}
bindings.Add(Expression.Bind(targetProperty, Expression.Property(sourceParameter, sourceProperty)));
sourceProperties.Add(sourceProperty);
targetProperties.Add(targetProperty);
}
Expression initializer = Expression.MemberInit(Expression.New(typeof(TTarget)), bindings);
return Expression.Lambda<Func<TSource, TTarget>>(initializer, sourceParameter).Compile();
}
}
}
#endif

You might try something like this....

MyType destination = new MyType();
MyType source = new MyType();


// Iterate the Properties of the destination instance and
// populate them from their source counterparts


PropertyInfo[] destinationProperties = destination.GetType().GetProperties();
foreach (PropertyInfo destinationPI in destinationProperties)
{
PropertyInfo sourcePI = source.GetType().GetProperty(destinationPI.Name);


destinationPI.SetValue(destination,
sourcePI.GetValue(source, null),
null);
}

Building off of Steve's method, I went with the extension method approach. This uses my base class as type but should be useable even using object as the param types. Works great for my uses.

using System.Reflection;
//*Namespace Here*
public static class Ext
{
public static void CopyProperties(this EntityBase source, EntityBase destination)
{
// Iterate the Properties of the destination instance and
// populate them from their source counterparts
PropertyInfo[] destinationProperties = destination.GetType().GetProperties();
foreach (PropertyInfo destinationPi in destinationProperties)
{
PropertyInfo sourcePi = source.GetType().GetProperty(destinationPi.Name);
destinationPi.SetValue(destination, sourcePi.GetValue(source, null), null);
}
}
}

Usage looks like this:

item1.CopyProperties(item2);

Now Item2 has the same property data as item1.

Because I believe Jon's version is a tad too complicated and and Steve's version is too simple, and I like Daniel's idea of an extension class.

Plus a Generic version is pretty but unnecessary as all items are objects.

I would like to volunteer my lean and mean version. Credits to all the above. :D

Code:

using System;
using System.Reflection;
/// <summary>
/// A static class for reflection type functions
/// </summary>
public static class Reflection
{
/// <summary>
/// Extension for 'Object' that copies the properties to a destination object.
/// </summary>
/// <param name="source">The source.</param>
/// <param name="destination">The destination.</param>
public static void CopyProperties(this object source, object destination)
{
// If any this null throw an exception
if (source == null || destination == null)
throw new Exception("Source or/and Destination Objects are null");
// Getting the Types of the objects
Type typeDest = destination.GetType();
Type typeSrc = source.GetType();


// Iterate the Properties of the source instance and
// populate them from their desination counterparts
PropertyInfo[] srcProps = typeSrc.GetProperties();
foreach (PropertyInfo srcProp in srcProps)
{
if (!srcProp.CanRead)
{
continue;
}
PropertyInfo targetProperty = typeDest.GetProperty(srcProp.Name);
if (targetProperty == null)
{
continue;
}
if (!targetProperty.CanWrite)
{
continue;
}
if (targetProperty.GetSetMethod(true) != null && targetProperty.GetSetMethod(true).IsPrivate)
{
continue;
}
if ((targetProperty.GetSetMethod().Attributes & MethodAttributes.Static) != 0)
{
continue;
}
if (!targetProperty.PropertyType.IsAssignableFrom(srcProp.PropertyType))
{
continue;
}
// Passed all tests, lets set the value
targetProperty.SetValue(destination, srcProp.GetValue(source, null), null);
}
}
}

Usage:

/// <summary>
/// ExampleCopyObject
/// </summary>
/// <returns></returns>
public object ExampleCopyObject()
{
object destObject = new object();
this.CopyProperties(destObject); // inside a class you want to copy from


Reflection.CopyProperties(this, destObject); // Same as above but directly calling the function


TestClass srcClass = new TestClass();
TestStruct destStruct = new TestStruct();
srcClass.CopyProperties(destStruct); // using the extension directly on a object


Reflection.CopyProperties(srcClass, destObject); // Same as above but directly calling the function


//so on and so forth.... your imagination is the limits :D
return srcClass;
}


public class TestClass
{
public string Blah { get; set; }
}
public struct TestStruct
{
public string Blah { get; set; }
}

As I was bored and a linq version was suggested by a comment

using System;
using System.Linq;
using System.Reflection;
/// <summary>
/// A static class for reflection type functions
/// </summary>
public static class Reflection
{
/// <summary>
/// Extension for 'Object' that copies the properties to a destination object.
/// </summary>
/// <param name="source">The source.</param>
/// <param name="destination">The destination.</param>
public static void CopyProperties(this object source, object destination)
{
// If any this null throw an exception
if (source == null || destination == null)
throw new Exception("Source or/and Destination Objects are null");
// Getting the Types of the objects
Type typeDest = destination.GetType();
Type typeSrc = source.GetType();
// Collect all the valid properties to map
var results = from srcProp in typeSrc.GetProperties()
let targetProperty = typeDest.GetProperty(srcProp.Name)
where srcProp.CanRead
&& targetProperty != null
&& (targetProperty.GetSetMethod(true) != null && !targetProperty.GetSetMethod(true).IsPrivate)
&& (targetProperty.GetSetMethod().Attributes & MethodAttributes.Static) == 0
&& targetProperty.PropertyType.IsAssignableFrom(srcProp.PropertyType)
select new { sourceProperty = srcProp, targetProperty = targetProperty };
//map the properties
foreach (var props in results)
{
props.targetProperty.SetValue(destination, props.sourceProperty.GetValue(source, null), null);
}
}
}

Here's a short and sweet version, since you said both of your objects are of the same type:

foreach (PropertyInfo property in typeof(YourType).GetProperties().Where(p => p.CanWrite))
{
property.SetValue(targetObject, property.GetValue(sourceObject, null), null);
}

Modification of Daniel version to avoid exceptions.

foreach (PropertyInfo property in typeof(YourType).GetProperties())
{
if (property.CanWrite)
{
property.SetValue(marketData, property.GetValue(market, null), null);
}
}

This short and simple Extension method will allow you to copy matching properties from one object to another with the check of Null value and is writable.

public static void CopyPropertiesTo(this object fromObject, object toObject)
{
PropertyInfo[] toObjectProperties = toObject.GetType().GetProperties();
foreach (PropertyInfo propTo in toObjectProperties)
{
PropertyInfo propFrom = fromObject.GetType().GetProperty(propTo.Name);
if (propFrom!=null && propFrom.CanWrite)
propTo.SetValue(toObject, propFrom.GetValue(fromObject, null), null);
}
}

For several years I'm using a popular library for that named ValueInjecter

nuget: https://www.nuget.org/packages/ValueInjecter/

github: https://github.com/omuleanu/ValueInjecter

target.InjectFrom(source);
target.InjectFrom<Injection>(source);
target.InjectFrom(new Injection(parameters), source);
target.InjectFrom<Injection>(); // without source

Note that even that the basic solutions are pretty simple (see other answers), there are plenty of edge cases (e.g. deep copy, generics, null values) and optimizations (e.g cache the reflected properties) so better to use maintained library for that.

Basically in 2019 we should probably use more up-to-date language features, like expression trees and compiled lambda-expressions, instead of Reflection

As I was unable to find a "shallow cloner" that meets my requirements (speed most of all), I decided to create one myself. It enumerates all gettable/settable properties and then creates a Block expression that's then compiled and cached. Which makes it almost 13 times faster than the popular AutoMapper. Usage is very simple:

DestType destObject = PropMapper<SourceType, DestType>.From(srcObj);

You can view the full source here: https://github.com/jitbit/PropMapper

Maybe this post is a little bit old, answers are good but when you need to map a lot of objects into a target Type - looping through properties could be costly (Imaging 100 props and more).

I use this AutoMapFactory method (only require LinQ), it will iterates only once in the properties and the mapping of each object will be fast (100000 props/seconds)

private Func<S,T> AutoMapFactory<S,T>() where T: class, new() where S : class
{
List<Action<T, S>> mapActions = typeof(T).GetProperties().Where(tp => tp.CanWrite)
.SelectMany(tp => typeof(S).GetProperties().Where(sp => sp.CanRead)
.Where(sp => sp.Name == tp.Name && tp.PropertyType.IsAssignableFrom(sp.PropertyType))
.Select(sp => (Action<T,S>)((targetObj, sourceObj) =>
tp.SetValue(targetObj, sp.GetValue(sourceObj)))))
.ToList();


return sourceObj => {
if (sourceObj == null) return null;


T targetObj = new T();
mapActions.ForEach(action => action(targetObj, sourceObj));
return targetObj;
};
}

How to use this:

...
var autoMapper = AutoMapFactory<SourceType, TargetType>(); //Get Only 1 instance of the mapping function
...
someCollection.Select(item => autoMapper(item)); //Almost instantaneous
...

public TestClass {
public TestName {get;set;}
}
public void submain()
{
var originalTestClass = new TestClass()
{
TestName  ="Test Name";
};


var newTestClass = new TestClass();
newTestClass.CopyPropertiesFrom(originalTestClass);
}

Expanding on @Azerothians answer, i needed some additional requirements:

1. needed a way to ignore null properties on the source object
2. needed a way to ignore explicit properties
3. wanted a way to coerce the datatype where possible to match e.g. int? to decimal? or long to int (due to unfortunate early schema decisions from a predecessor)

4. wanted to know if properties had been copied or not (to determine if db update would be required)

   /// <summary>
   /// Extension for 'Object' that copies the properties to a destination object.
   /// </summary>
   /// <param name="source">The source.</param>
   /// <param name="destination">The destination.</param>
   /// <param name="PropertiesToIgnore">an optional list of property names which will NOT be copied</param>
   /// <param name="IgnoreNullProperties">when true will not update properties where the source is null</param>
   /// <param name="CoerceDataType">when true, will attempt to coerce the source property to the destination property (e.g. int to decimal) </param>
   /// <param name="ThrowOnTypeMismatch">when true, will throw a InvalidCastException if the data cannot be coerced</param>
   /// <exception cref="InvalidCastException">if there is a data type mismatch between source/destination and ThrowOnTypeMismatch is enabled and unable to coerce the data type.</exception>
   /// <returns>true if any properties were changed</returns>
   public static bool CopyProperties(this object source, object destination, IEnumerable<string> PropertiesToIgnore = null, bool IgnoreNullProperties = false, bool ThrowOnTypeMismatch = true, bool CoerceDataType = true)
   {
   if (source is null)
   throw new ArgumentNullException(nameof(source));
   
   
   if (destination is null)
   throw new ArgumentNullException(nameof(destination));
   
   
   // Getting the Types of the objects
   Type typeDest = destination.GetType();
   Type typeSrc = source.GetType();
   
   
   // Collect all the valid properties to map
   var results = (from srcProp in typeSrc.GetProperties()
   let targetProperty = typeDest.GetProperty(srcProp.Name)
   where srcProp.CanRead
   && targetProperty != null
   && (targetProperty.GetSetMethod(true) != null && !targetProperty.GetSetMethod(true).IsPrivate)
   && (targetProperty.GetSetMethod().Attributes & MethodAttributes.Static) == 0
   && !(
   from i in PropertiesToIgnore ?? Enumerable.Empty<string>()
   select i
   ).Contains(srcProp.Name)
   && (!IgnoreNullProperties || srcProp.GetValue(source, null) != null)
   select new { sourceProperty = srcProp, targetProperty = targetProperty }).ToList();
   
   
   bool PropertyChanged = false;
   //map the properties
   foreach (var props in results)
   {
   var srcValue = props.sourceProperty.GetValue(source, null);
   var dstValue = props.targetProperty.GetValue(destination, null);
   if (props.targetProperty.PropertyType.IsAssignableFrom(props.sourceProperty.PropertyType))
   props.targetProperty.SetValue(destination, srcValue, null);
   else
   {
   try
   {
   if (!CoerceDataType)
   throw new InvalidCastException($"Types do not match, source: {props.sourceProperty.PropertyType.FullName}, target: {props.targetProperty.PropertyType.FullName}.");
   
   
   if (srcValue != null)
   {
   // determine if nullable type
   Type tgtType = Nullable.GetUnderlyingType(props.targetProperty.PropertyType);
   // if it is, use the underlying type
   // without this we cannot convert int? -> decimal? when value is not null
   if (tgtType != null)
   props.targetProperty.SetValue(destination, Convert.ChangeType(srcValue, tgtType, CultureInfo.InvariantCulture), null);
   else // otherwise use the original type
   props.targetProperty.SetValue(destination, Convert.ChangeType(srcValue, props.targetProperty.PropertyType, CultureInfo.InvariantCulture), null);
   }
   else // if null we can just set it as null
   props.targetProperty.SetValue(destination, null, null);
   }
   catch (Exception ex)
   {
   if (ThrowOnTypeMismatch)
   throw new InvalidCastException($"Unable to copy property {props.sourceProperty.Name} with value {srcValue} from object of type ({typeSrc.FullName}) to type ({typeDest.FullName}), Error: {ex.Message}");
   // else ignore update
   }
   var newdstValue = props.targetProperty.GetValue(destination, null);
   if (newdstValue == null && dstValue != null || !newdstValue.Equals(dstValue))
   PropertyChanged = true;
   }
   }
   
   
   return PropertyChanged;
   }
   

I have taken all what has been written above by @Shimmy Weitzhandler and sligtly modified. Since I use this method when I have to define several object with the same properties I made a function accepting a variable number of elements:

public static void CopyProperties<T>(T source, params T[] dests)
{
if(source == null)
return;


foreach (var dest in dests)
{
foreach (System.Reflection.PropertyInfo property in typeof(Button).GetProperties().Where(p => p.CanWrite))
property.SetValue(dest, property.GetValue(source, null), null);
}
}

With that you can define one or several elements. E.g.:

Helper.CopyProperties(btn_Src, bt_Dest1);

or

Helper.CopyProperties(btn_Src, bt_Dest1, btn_Dest2, btn_Dest3);

I made it static for I have it in my Helper library