C# Language Get a Strongly-Typed Delegate to a Method or Property via Reflection


Example

When performance is a concern, invoking a method via reflection (i.e. via the MethodInfo.Invoke method) is not ideal. However, it is relatively straightforward to obtain a more performant strongly-typed delegate using the Delegate.CreateDelegate function. The performance penalty for using reflection is incurred only during the delegate-creation process. Once the delegate is created, there is little-to-no performance penalty for invoking it:

// Get a MethodInfo for the Math.Max(int, int) method...
var maxMethod = typeof(Math).GetMethod("Max", new Type[] { typeof(int), typeof(int) });
// Now get a strongly-typed delegate for Math.Max(int, int)...
var stronglyTypedDelegate = (Func<int, int, int>)Delegate.CreateDelegate(typeof(Func<int, int, int>), null, maxMethod);
// Invoke the Math.Max(int, int) method using the strongly-typed delegate...
Console.WriteLine("Max of 3 and 5 is: {0}", stronglyTypedDelegate(3, 5));

This technique can be extended to properties as well. If we have a class named MyClass with an int property named MyIntProperty, the code to get a strongly-typed getter would be (the following example assumes 'target' is a valid instance of MyClass):

// Get a MethodInfo for the MyClass.MyIntProperty getter...
var theProperty = typeof(MyClass).GetProperty("MyIntProperty");
var theGetter = theProperty.GetGetMethod();
// Now get a strongly-typed delegate for MyIntProperty that can be executed against any MyClass instance...
var stronglyTypedGetter = (Func<MyClass, int>)Delegate.CreateDelegate(typeof(Func<MyClass, int>), theGetter);
// Invoke the MyIntProperty getter against MyClass instance 'target'...
Console.WriteLine("target.MyIntProperty is: {0}", stronglyTypedGetter(target));

...and the same can be done for the setter:

// Get a MethodInfo for the MyClass.MyIntProperty setter...
var theProperty = typeof(MyClass).GetProperty("MyIntProperty");
var theSetter = theProperty.GetSetMethod();
// Now get a strongly-typed delegate for MyIntProperty that can be executed against any MyClass instance...
var stronglyTypedSetter = (Action<MyClass, int>)Delegate.CreateDelegate(typeof(Action<MyClass, int>), theSetter);
// Set MyIntProperty to 5...
stronglyTypedSetter(target, 5);