Are there files missing from Windows SDK 10.0.26100.0 and how can I update them?

That page, which is what I am using, says...

For complete examples that demonstrate using the XAML hosting API to host a WinRT XAML control, see the following code files:

• C++ desktop (Win32): See the XamlBridge.cpp file in the XAML Islands code samples repo.

The first example there - DesktopWin32App uses this header.

#include "resource.h"
#include <winrt/Windows.Foundation.Collections.h>
#include <winrt/Windows.system.h>
#include <winrt/windows.ui.xaml.hosting.h>
#include <windows.ui.xaml.hosting.desktopwindowxamlsource.h>
#include <winrt/windows.ui.xaml.controls.h>
#include <winrt/Windows.ui.xaml.media.h>
#include <winrt/Windows.UI.Core.h>
#include <winrt/UwpApplication.h>

I'm in the learning stage.

Does the XamlBridge.cpp only apply?

If it's the DesktopApp I should be looking at, I'm getting the same error when I try to include the header

#include <winrt/windows.ui.xaml.hosting.desktopwindowxamlsource.h>

So, I do need the headers, in any case.

There wouldn't be a winrt/Windows.UI.Xaml.Hosting.DesktopWindowXamlSource.h. The windows.ui.xaml.hosting.desktopwindowxamlsource.h header is an interop header, it is not part of the projection, this means that C++/WinRT will not touch it.

Anything that is part of the projection would be documented on the documentation page. It shows that IClosable is implemented, but nothing else. You would have to create the DesktopWindowXamlSource object, then once that is done, use .as<IDesktopWindowXamlSourceNative>() or .as<IDesktopWindowXamlSourceNative2>(). This is by design.

For any other headers potentially missing in the winrt namespace. Remember that C++/WinRT is a tool. Visual Studio runs cppwinrt.exe that is either part of the NuGet package referenced by the project, or as a fallback, the version that is part of the Windows SDK. It generates headers from the .winmd files referenced by the project.

The minimum headers for XAML Islands are in the page at :

#include <windows.h>
#include <stdlib.h>
#include <string.h>

#include <winrt/Windows.Foundation.Collections.h>
#include <winrt/Windows.system.h>
#include <winrt/windows.ui.xaml.hosting.h>
#include <windows.ui.xaml.hosting.desktopwindowxamlsource.h>
#include <winrt/windows.ui.xaml.controls.h>
#include <winrt/Windows.ui.xaml.media.h>

I usually copy this part, then I add other .h depending on what I need.

For example,

for Button click, I add

#include <winrt/windows.ui.xaml.controls.primitives.h>

for MessageDialog

#include <winrt/Windows.UI.Popups.h>

and so on...