Compact Framework - how do I dynamically create type with no default constructor?

Question

I'm using the .NET CF 3.5. The type I want to create does not have a default constructor so I want to pass a string to an overloaded constructor. How do I do this?

Code:

Assembly a = Assembly.LoadFrom("my.dll");
Type t = a.GetType("type info here");
// All ok so far, assembly loads and I can get my type

string s = "Pass me to the constructor of Type t";
MyObj o = Activator.CreateInstance(t); // throws MissMethodException

Answer 1

See if this works for you (untested):

Type t = a.GetType("type info here");
var ctors = t.GetConstructors();
string s = "Pass me to the ctor of t";
MyObj o = ctors[0].Invoke(new[] { s }) as MyObj;

If the type has more than one constructor then you may have to do some fancy footwork to find the one that accepts your string parameter.

Edit: Just tested the code, and it works.

Edit2: Chris' answer shows the fancy footwork I was talking about! ;-)

Answer 2

Activator.CreateInstance does not have a params array overload on the Compact Framework? Why not?

Answer 3

@Jonathan Because the Compact Framework has to be as slim as possible. If there's another way to do something (like the code I posted) then they generally don't duplicate the functionality.

Rory Blyth once described the Compact Framework as "a wrapper around System.NotImplementedExcetion". :)

Answer 4

MyObj o = null;
Assembly a = Assembly.LoadFrom("my.dll");
Type t = a.GetType("type info here");

ConstructorInfo ctor = t.GetConstructor(new Type[] { typeof(string) });
if(ctor != null)
   o = ctor.Invoke(new object[] { s });

Answer 5

Ok, here's a funky helper method to give you a flexible way to activate a type given an array of parameters:

static object GetInstanceFromParameters(Assembly a, string typeName, params object[] pars) 
{
    var t = a.GetType(typeName);

    var c = t.GetConstructor(pars.Select(p => p.GetType()).ToArray());
    if (c == null) return null;

    return c.Invoke(pars);
}

And you call it like this:

Foo f = GetInstanceFromParameters(a, "SmartDeviceProject1.Foo", "hello", 17) as Foo;

So you pass the assembly and the name of the type as the first two parameters, and then all the constructor's parameters in order.