强制转换通用类型然后使用Ref

Question

I need some clarity for my problem.

I have a method which does this:

public static void SetEntityValue<TEntity>(ref TEntity entityToTransform, PropertyHelper entityProperty)
{
   // create type from entity
   Type t = entityToTransform.GetType();
   // get the property to set
   var prop = t.GetProperty(entityProperty.Name);
   // set the property value to the one parsed
   prop.SetValue(entityToTransform, entityProperty.Value, null);
}

The PropertyHelper just contains two properties, Name and Value.

So, I have a method that takes an Generic Type and then needs to initialise a new one and fill its properties with values, will this method do that:

TEntity ReadIntoEntity<TEntity>(TEntity entity, XElement node)
{
    if (!node.HasElements)
        throw new IllFormedDocumentException("Entity found but contains no properties");

    var xmlProps = node.Elements();

    Type t1 = entity.GetType();

    // the line which initialises a new TEntity same as string myString = new string();
    TEntity newEntity = Activator.CreateInstance<TEntity>();

    var props = t1.GetProperties();
    var readableProps = props.Select(x => new PropertyHelper(GenericHelper.GetEntityProperty(x), GenericHelper.GetEntityValueAsObject<TEntity>(entity, x)));

    List<string> foundAProp = new List<string>();

    foreach (var el in xmlProps)
    {
        // iterate through all xml elements

        foreach (var prop in readableProps)
        {
            // check the prop exists in the xml set

            // We found a prop that exists!
            if (el.Name.ToString() == prop.Name.ToString())
            {
                foundAProp.Add(prop.Name.ToString());

                GenericHelper.SetEntityValue<TEntity>(ref newEntity, prop);
            }
        }
    }

}

Will this work like Non Generics would do:

MyEntity ReadIntoEntity(XElement node)
{
    if (!node.HasElements)
        throw new IllFormedDocumentException("Entity found but contains no properties");

    var xmlProps = node.Elements();

    MyEntity newEntity = new MyEntity();

    var props = typeof(MyEntity).GetProperties();
    var readableProps = props.Select(x => new PropertyHelper(GenericHelper.GetEntityProperty(x), GenericHelper.GetEntityValueAsObject<TEntity>(entity, x)));

    List<string> foundAProp = new List<string>();

    foreach (var el in xmlProps)
    {
        // iterate through all xml elements

        foreach (var prop in readableProps)
        {
            // check the prop exists in the xml set

            // We found a prop that exists!
            if (el.Name.ToString() == prop.Name.ToString())
            {
                foundAProp.Add(prop.Name.ToString());

                GenericHelper.SetEntityValue<MyEntity>(ref newEntity, prop);
            }
        }
    }

}

So Effectively is:

TEntity newEntity = Activator.CreateInstance<TEntity>();

Equivalent to this:

MyEntity newEntity = new MyEntity();

Thanks

Answer 1

Will that method do the thing? Try it and see.

However:

TEntity newEntity = Activator.CreateInstance<TEntity>();

should be replaced with

TEntity newEntity = new TEntity();

after adding the new() generic constraint for the parameter. This will add compile time checks to ensure that the entity has a valid parameterless constructor. Ie:

TEntity ReadIntoEntity<TEntity>(TEntity entity, XElement node)
    where TEntity : class, new()
{
    // ...

And you don't need ref in your first method, assuming all your entities are class types.