In C# How to dynamically specify a member of a object, like obj["abc"] in PHP

Question

Say I have a class

public class Employee { public string name = ""; public int age = 20; }

now I want a function that can dynamically get the value of a specified member of Employee

public class Util<T> { public static string GetValue(T obj, string member) { // how to write } }

so that I can use it like

Employee p1 = new Employee(); string a = Util<Employee>.GetValue(p1, "age"); // a should be "20"

How to do it? like access member use obj["???"] in PHP

I never knew you could use $obj['property'] in PHP. Did you mean JavaScript? — BoltClock
– BoltClock, Commented Apr 19, 2011 at 13:03
That sounds like associative arrays. I thought PHP syntax for dynamic member access was $obj->$var. Are you trying to get values from an anonymous type? If so, it might be easier to try the "Cast by Example" trick. — Mauricio
– Mauricio, Commented Apr 19, 2011 at 13:14
something like $_REQUEST["type"] in PHP (well its not a object of a class...), or like actionscript3 — demaxSH
– demaxSH, Commented Apr 19, 2011 at 13:17
While this is possible in C# using reflection (see the answers below), it's unidiomatic and very verbose. I suggest that you solve your problem in a different way. If you need a loosely-typed collection of properties indexed by string, for example, try a Dictionary<string, object>. — JSBձոգչ
– JSBձոգչ, Commented Apr 19, 2011 at 13:18
Here is my problem: I have several collections ObserverableCollection<Employee> <Student> <Patient>, and I need a function to calculate the average age of these kind of collections. since all the class of Employ/Student/Patient has the member of "age", the function will looks like: int ave = GetAverage(students, "age") — demaxSH
– demaxSH, Commented Apr 19, 2011 at 13:51

Community · Accepted Answer · 2017-05-23 12:26:28Z

Reflection. Take a look here:

Reflection: Property Value by Name

Oh, and also here in our very own SO!

Update

Sigh... It's all about "teh codez"... Here you go:

p1.GetType().GetProperty("age").GetValue(p1,null);

But do check the links, there's stuff to learn!

Community · Accepted Answer · 2017-05-23 10:27:24Z

0

yes, it's called Reflection. See Get property value from string using reflection in C#

edited May 23, 2017 at 10:27

CommunityBot

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answered Apr 19, 2011 at 13:10

Adam Straughan

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Comments

Andrei Andrushkevich · Accepted Answer · 2011-04-19 13:14:42Z

try following code:

// get value of private field: private double _number int value = (int)typeof(p1).InvokeMember("age", BindingFlags.GetField | BindingFlags.Instance | BindingFlags.NonPublic, null, p1, null);

or

 // Get the FieldInfo of MyClass. FieldInfo[] myFields = typeof(p1).GetFields(BindingFlags.Public | BindingFlags.Instance); var age = myFields[i].GetValue(p1);

check link for more details

Ben Voigt · Accepted Answer · 2011-04-19 13:20:34Z

0

Where does the parameter "age" come from? You should think about other designs where the choice of property isn't stored in a string.

For example, if you want to display a drop-down allowing the user to choose a column to sort by, you would want to pass a Comparer<Employee> from the view to the model, this will be much MUCH faster, and also use the correct numeric sort instead of lexicographic.

answered Apr 19, 2011 at 13:20

Ben Voigt

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2 Comments

demaxSH Over a year ago

Here is my problem: I have several collections ObserverableCollection<Employee> <Student> <Patient>, and I need a function to calculate the average age of these kind of collections. since all the class of Employ/Student/Patient has the member of "age", the function will looks like: int ave = GetAverage(students, "age")

Ben Voigt Over a year ago

@demaxSH: It would be much better to pass a lambda, like GetAverage(students, s => s.age). You can probably even find a function in the LINQ library that will already do the averaging for you.

Mathijs Segers · Accepted Answer · 2017-06-14 05:57:49Z

While I see a lot of usage of reflection here, maybe in your usecase you can do

object p1 = new Employee(); var employee = p1 as Employee; // optionally you could do a nullcheck string a = employee.age; // a should be "20"

Reflection works, but in your case I would just not go that far. but maybe you need generics then yes, go with reflection instead.

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