如何使用反射来更改缺少setter的属性？

Question

I have two classes with property getters only

public class A 
{
    public A(string name) 
    {
        Name = name;
    }
    public string Name { get; }
    public string Value { get; set;}
    public string Data { get; set;}
}

public class B
{
    public B(string name) 
    {
        Name = name;
    }
    public string Name { get; }
    public string Value { get; set;}
}

They are different in shape but share some of the same property names and types. How can I copy values when they only have getters?

This is a typical scenario when I send an object as a constructor parameter to extract values from in the new object. Then I need to copy values one by one. This can produce lots of code and is hard to maintain.

Can this be made simpler? Is there a way to use reflection to copy objects when the target only has getter properties?

Answer 1

It is possible to create a helper function that copies two objects where the target object only has property getters.

Try this;

public static void CopyItem<U, T>(U source, T target)
{
    // Need a way to rename the backing-field name to the property Name ("<A>k__BackingField" => "A")
    Func<string, string> renameBackingField = key => new string(key.Skip(1).Take(key.IndexOf('>') - 1).ToArray());

    // Get public source properties (change BindingFlags if you need to copy private memebers as well)
    var sourceProperties = source.GetType().GetProperties().ToDictionary(item => item.Name);
    // Get "missing" property setter's backing field
    var targetFields = typeof(T).GetFields(BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.SetField).ToDictionary(item => renameBackingField(item.Name));

    // Copy properties where target name matches the source property name
    foreach(var sourceProperty in sourceProperties)
    {
        if (targetFields.ContainsKey(sourceProperty.Key) == false)
            continue; // No match. skip

        var sourceValue = sourceProperty.Value.GetValue(source);
        targetFields[sourceProperty.Key].SetValue(target, sourceValue);
    }
}

This is a generic description. You will probably want to check the property and field data types as well before you copy the value to prevent exceptions. Both name and data type should match.

Use CopyItem to copy matching source properties in a constructor;

public class SomeClass
{
    public SomeClass(SomeSourceClass source)
    {
        Helper.CopyItem(source, this);
    }
}