How can I pass a list of properties to a method using lambda expressions

Question

Let's say I have a method, which prints the names and values of some properties of an object:

public void PrintProperties(object o, params string[] propertyNames)
{
    foreach (var propertyName in propertyNames)
    {
        // get the property info,
        // then get the property's value,
        // print property-name and -value
    }
}
// method can be used like this
PrintProperties(user, "FirstName", "LastName", "Email");

Now instead of having to pass a list of strings to the method, I'd like to change that method so that the properties can be specified using lambda expressions (not sure if that's the correct term).

E.g. I'd like to be able to call my method (somehow) like this:

PrintProperties(user, u->u.FirstName, u->u.LastName, u->u.Email);

The goal is, to give the user of the method intellisense support, to prevent typing errors. (Similar to the ASP.NET MVC helper methods, like TextBoxFor(u=>u.Name)).

How do I have to define my method, and how can I then get the PropertyInfos inside the method?

score 8 · Answer 1 · edited May 23 '17 at 12:16

Use a declaration like this:

void PrintProperties<T>(T obj,
                        params Expression<Func<T, object>>[] propertySelectors)
{
   ...
}

Callable like:

PrintProperties(user, u => u.FirstName, u => u.LastName, u => u.Email);

As for getting property-names out from each lambda, see Retrieving Property name from lambda expression. Do note that you have may have to go a little bit deeper than what is provided in that answer in case the property is a value-type like int (in this case, the compiler will generate a unary Convert expression over the member-access that you want, in order to box the struct).

How do I then get the values of the object using the property selectors? — ozz, Oct 13 '16 at 15:04

score 1 · Answer 2 · answered May 02 '13 at 15:36

1

Reflection allows you to access fields, properties, events, etc.

public void PrintProperties(object o, params string[] propertyNames)
{
    foreach (var propertyName in propertyNames)
    {
        // Dont have VS now, but it's something like that
        Console.WriteLine(o.GetType().GetProperty(propertyName).GetValue(o, null));
    }
}

I don't have VS now, so it might not even compile, but along these names you can get along with auto-completion...

answered May 02 '13 at 15:36

SimpleVar

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That's what I have now. Please read the second part of the question :-) – M4N May 02 '13 at 15:37
If you pass the the properties themselves, though... you can't know which property you just got from a lambda expression, so you won't be able to print it's name. I assumed you wanted something like `"A: 3, B: 5, Name: Hi"` – SimpleVar May 02 '13 at 15:38
That's correct: I need to get the properties' names and values – M4N May 02 '13 at 15:42
So that's the way to do it. Why no reflection? – SimpleVar May 02 '13 at 16:29

How can I pass a list of properties to a method using lambda expressions

2 Answers2