Is there a delegate available for properties in C#?

Question

Given the following class:

class TestClass {
  public void SetValue(int value) { Value = value; }
  public int Value { get; set; }
}

I can do

TestClass tc = new TestClass();
Action<int> setAction = tc.SetValue;
setAction.Invoke(12);

which is all good. Is it possible to do the same thing using the property instead of the method? Preferably with something built in to .net.

Answer 1

Properties are really wrappers around methods in .Net, so using reflection you should be able to get the delegate (set_PROPERTY and get_PROPERTY) and then execute them...

See System.Reflection.PropertyInfo

If has two methods which you can use to get/ set the value - GetGetMethod and GetSetMethod.

So you could write:

var propertyInfo = typeof (TestClass).GetProperty ("Value");

var setMethod = property.GetSetMethod (); // This will return a MethodInfo class.

Answer 2

There are three ways of doing this; the first is to use GetGetMethod()/GetSetMethod() and create a delegate with Delegate.CreateDelegate. The second is a lambda (not much use for reflection!) [i.e. x=>x.Foo]. The third is via Expression (.NET 3.5).

The lambda is the easiest ;-p

    class TestClass
    {
        public int Value { get; set; }
    }
    static void Main()
    {
        Func<TestClass, int> lambdaGet = x => x.Value;
        Action<TestClass, int> lambdaSet = (x, val) => x.Value = val;

        var prop = typeof(TestClass).GetProperty("Value");
        Func<TestClass, int> reflGet = (Func<TestClass, int>) Delegate.CreateDelegate(
            typeof(Func<TestClass, int>), prop.GetGetMethod());
        Action<TestClass, int> reflSet = (Action<TestClass, int>)Delegate.CreateDelegate(
            typeof(Action<TestClass, int>), prop.GetSetMethod());
    }

To show usage:

        TestClass foo = new TestClass();
        foo.Value = 1;
        Console.WriteLine("Via property: " + foo.Value);

        lambdaSet(foo, 2);
        Console.WriteLine("Via lambda: " + lambdaGet(foo));

        reflSet(foo, 3);
        Console.WriteLine("Via CreateDelegate: " + reflGet(foo));

Note that if you want the delegate pointing to the specific instance, you can use closures for the lambda, or the overload of CreateDelegate that accepts and instance.

Answer 3

You could create the delegate using reflection :

Action<int> valueSetter = (Action<int>)Delegate.CreateDelegate(typeof(Action<int>), tc, tc.GetType().GetProperty("Value").GetSetMethod());

or create a delegate to an anonymous method which sets the property;

Action<int> valueSetter = v => tc.Value = v;

Edit: used wrong overload for CreateDelegate(), need to use the one that takes and object as target. Fixed.