传递类的属性作为参数？

Question

I need to pass in a property of a class which is used twice in an extension method, to check for duplicate values in this property.

public static class MatchedProductsExtensionMethods
{
    public static bool IdenticalValues(this List<Product> matchedProducts)
    {
        var itemToMatch = matchedProducts.First();
        if (matchedProducts.All(p => p.PROPERTYTHATCANCHANGE == itemToMatch.PROPERTYTHATCANCHANGE))
            return true;
        else
            return false;
    }
}

So I need to be able to pass in the name of a property of the Product class and then that replaces PROPERTYTHATCANCHANGE . For example, the properties in the Product class could be ProdName or ProdUsers and then I would need to check to see if there are items in the matchedProducts list which have the same values for these properties.

Thanks in advance!

Answer 1

To pass in a string property name you're going to have to use reflection, which is not compile-time safe and is relatively slow. A more type-safe way would be to pass in a delegate instead of a property name:

public static bool IdenticalValues<T>(this List<Product> matchedProducts, Func<Product, T> matchExpression)
{
    var itemToMatch = matchedProducts.First();
    if (matchedProducts.All(p => EqualityComparer<T>.Default.Equals(matchExpression(p), matchExpression(itemToMatch))))
        return true;
    else
        return false;
}

And call it like this:

bool allMatch = collection.IdenticalValues(i => i.PROPERTYTHATCANCHANGE );

You could even make it completely generic:

public static bool IdenticalValues<TEntity, TProperty>(this IEnumerable<TEntity> matchedEntities, Func<TEntity, TProperty> matchExpression)
{
    var itemToMatch = matchedEntities.First();
    if (matchedEntities.All(p => EqualityComparer<TProperty>.Default.Equals(matchExpression(p), matchExpression(itemToMatch))))
        return true;
    else
        return false;
}

Answer 2

I suggest doing this in a type-safe way:

public static bool IdenticalValues<T>(this List<Product> matchedProducts, Func<Product, T> selector)
{
    var itemToMatch = matchedProducts.First();
    if (matchedProducts.All(p => selector(p) == selector(p)))
        return true;
    else
        return false;
}

and then calling it like

matchesProducts.IdenticalValues(p => p.SomeProperty)