Sunday 6 September 2020

Delphi and the WinRT API


The WinRT (Windows Runtime) API was introduced with Windows 8, although it’s fair to say that most of us have tried our level best to forget that particular Windows release and pretend it never happened. Anyway, Microsoft has been trying to convince us that new Windows APIs will be introduced in the WinRT API and what we normally refer to as the Windows API might well remain as it is. We’ll see how true that becomes. The WinRT API reference can be found documented here.

The nice thing about WinRT is that it is not another step on the .NET journey; indeed it is nothing to do with .NET whatsoever. WinRT is implemented as native code and it is made available to whatever language wishes to consume it by language projections. Microsoft offers a C# language projection to consume it in .NET but it also offers a native C++ language projection (C++/WinRT).

Each WinRT class implements various interfaces to offer up methods and properties to call. There may also be static methods (i.e. class methods) and factory methods through which you can create an instance of the class. The Microsoft language projections make all the methods implemented through all the supported interfaces directly available once you create an instance of a WinRT class.

WinRT metadata

Anyone else can make their own language projections by analysing the API metadata (which are available in .winmd files in the C:\Windows\System32\WinMetadata folder). Metadata files are rather like COM type libraries in that they describe all the WinRT classes and methods etc., but they are actually files that share the same format as Win32 executables and .NET assemblies: PE files. You can find detailed information on these files from Microsoft here. Microsoft’s C++ .winmd file parser is open-sourced and available on github.

WinRT and Delphi

Embarcadero folks started looking at how to consume the WinRT API back in 2011 and Thom Gerdes wrote a few posts on how got on. He talks about these metadata files in this old post available on the Wayback Machine.

So, do we have a Delphi language projection? Well, kinda... We have import units that pull in a good chunk of the WinRT API, but things aren’t quite as transparent and trivial to use as they are in C++and C#. However, depending on how persistent we are we can get results. Indeed there are some uses of the WinRT API in the Delphi / C++Builder RTL; it is used for Windows desktop notifications and for share contracts.

This post looks into how we might use the WinRT API directly to perform a simple task, namely to trigger a Windows notification message. This might seem an odd thing to do, given the RTL already covers this quite nicely in the TNotificationCenter class but it serves as a simple, visual example.