How to cast String to TValue? - c++builder

Question

This code throws Invalid typecast at the last line prop->SetValue(control, value).
I assume I am casting "MyString" incorrectly. What's the right way to it?
for (int i = 0; i < MyForm->ControlCount; i++) {
TControl *control = MyForm->Controls[i];
if (control->Name == "MyTEdit") {
TRttiContext ctx;
TRttiType *type = ctx.GetType(control->ClassInfo());
TRttiProperty *prop = type->GetProperty(L"Text");
TValue value = TValue::From("MyString");
prop->SetValue(control, value);
}
}
It's supposed to loop through all the controls in MyForm until it finds the TEdit with the Name of MyTEdit, and change the text in the box to MyString.
My code is based on this answer. Unfortunately it did not provide an example of casting a String literal so a TValue so I am at a loss.
Update
After reading the answer to this question, I changed TValue value = TValue::From("MyString"); to this:
String myString = "MyString";
TValue value = TValue::From<UnicodeString>(myString);
Now I get the following error:
[ilink32 Error] Error: Unresolved external 'System::Rtti::TValue __fastcall System::Rtti::TValue::From<System::UnicodeString>(System::UnicodeString)' referenced from UNIT1.OBJ
I have included this at the top of Unit1.cpp:
#pragma explicit_rtti
#include <System.Rtti.hpp>
So I don't understand why it would say that.
Update 2
The problem disappeared when I switched to 64 bit from 32 bit.

Answer 1

TValue::From<T>() is a Delphi Generic method, and there are documented linker issues using Generics in C++:
How to Handle Delphi Generics in C++.
Try using the assignment operator= instead, as TValue has an assignment operator for UnicodeString:
String myString = "MyString";
TValue value;
value = myString;
TValue value;
value = String("MyString");