Hm why are you doing that? Why are you encoding a WideString to Utf8 just to store it again back to WideString. You are obviously using a unicode version of windows API. So there is no need to use Utf8Encoded string. Or am I missing something.
Because Windows API function are either Unicode (2 bytes) or Ansi (1 byte). Utf8 would be wrong choice here because mainly it contains 1 byte per character but for characters above the ASCII base it uses 2 or more bytes.
Otherwise the equivalent for your old code in unicode Delphi would be:
var
UnicodeStr: string;
UTF8Str: string;
begin
UnicodeStr:='some unicode text';
UTF8Str:=UTF8Encode(UnicodeStr);
Windows.SomeFunction(PWideChar(UTF8Str), ...)
end;
WideString and string (UnicodeString) are similar, but the new UnicodeString is faster because it is reference counted and WideString is not.
You code was not correct because the Utf8 string has variable bytes per character. "A" is stored as one byte. Just an ASCII byte code. "ü" on the other hand would be stored as two bytes. And because you are then using PWideChar the function always expects 2 bytes per character.
There is another difference. In older delphi versions (ansi) Utf8String was just and AnsiString, in unicode versions of Delphi Utf8String is a string with a Utf8 code page behind it. So it behaves different.
EDIT:
Forgot to add. The old code would still work correctly:
var
UnicodeStr: WideString;
UTF8Str: WideString;
begin
UnicodeStr:='some unicode text';
UTF8Str:=UTF8Encode(UnicodeStr);
Windows.SomeFunction(PWideChar(UTF8Str), ...)
end;
Would act the same as it did in Delphi 2007. So maybe you have a problem elsewhere.
EDIT2:
Mick you are correct. The compiler does some extra work behind the scenes. So in order to avoid this you can do something like this:
var
UTF8Str: AnsiString;
UnicodeStr: WideString;
TempString: RawByteString;
ResultString: WideString;
begin
UnicodeStr := 'some unicode text';
TempString := UTF8Encode(UnicodeStr);
SetLength(UTF8Str, Length(TempString));
Move(TempString[1], UTF8Str[1], Length(UTF8Str));
ResultString := UTF8Str;
end;
I checked and it works just the same. Because I move bytes directly in memory there is no codepage conversion done in the background. I am sure it can be done with greater eleganece but the point is that I see this as the way for what you want to achieve.