How do I create a C# array using Reflection and only type info?

Question

I can't figure out how to make this work:

object x = new Int32[7];
Type t = x.GetType();

// now forget about x, and just use t from here.

// attempt1 
object y1 = Activator.CreateInstance(t); // fails with exception

// attempt2
object y2 = Array.CreateInstance(t, 7);  // creates an array of type Int32[][] ! wrong

What's the secret sauce? I can make the second one work if I can get the type of the elements of the array, but I haven't figured that one out either.

Answer 1

You need Type.GetElementType() to get the non-array type:

object x = new Int32[7];
Type t = x.GetType();
object y = Array.CreateInstance(t.GetElementType(), 7);

Alternatively, if you can get the type of the element directly, use that:

Type t = typeof(int);
object y = Array.CreateInstance(t, 7);

Basically, Array.CreateInstance needs the element type of the array to create, not the final array type.

Answer 2

Just to add to Jon's answer. The reason attempt 1 fails is because there's no default constructor for Int32[]. You need to supply a length. If you use the overload, which takes an array of arguments it will work:

// attempt1 
object y1 = Activator.CreateInstance(t, new object[] { 1 }); // Length 1