Additional migration guidance

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This topic contains additional migration guidance not categorized into a feature area in the feature area guides.

Conditional compilation

The info in this section might be useful if you plan to use the same source code file in both a UWP and a Windows App SDK project.

In C# source code in a Windows App SDK project, you can use preprocessor directives with the WINDOWS_UWP symbol to perform conditional compilation.

#if !WINDOWS_UWP
    // Win32/Desktop code, including Windows App SDK code
#else
    // UWP code
#endif

In C++/WinRT source code in a Windows App SDK project, you can use preprocessor directives with WINAPI_FAMILY_PC_APP to do the same thing. Or you could use WINAPI_FAMILY_DESKTOP_APP instead. A comment in the winapifamily.h header file indicates that WINAPI_FAMILY_APP should be considered deprecated.

#if (WINAPI_FAMILY == WINAPI_FAMILY_DESKTOP_APP)
    // Win32/Desktop code, including Windows App SDK code
#else
    // UWP code
#endif

You can also use conditional compilation in XAML markup.

<Application
    ...
    xmlns:nouwp="condition:!WINDOWS_UWP"
    mc:Ignorable="nouwp">
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <!--Not Needed for UWP-->
                <nouwp:XamlControlsResources xmlns="using:Microsoft.UI.Xaml.Controls" />
                 <!--Other merged dictionaries here--> 
            </ResourceDictionary.MergedDictionaries>
             <!--Other app resources here--> 
        </ResourceDictionary>
    </Application.Resources>
</Application>

Also see Conditional compilation.

Debugging

During the migration process, you might find your app in a state where your XAML markup has references to XAML resource keys, but you haven't yet defined those keys. Such a condition results in a run-time crash that might not be straightforward to debug. But in a debug build, messages about missing resource keys appear in Visual Studio via debug output in the Output pane. So run your app under the debugger, and watch out for such messages.

Unregistering an event handler (C++/WinRT)

In a C++/WinRT project, you can manually revoke (unregister) an event handler such as SizeChanged (for more details, and code examples, see Revoke a registered delegate). But an alternative to manually revoking—and one that you could consider if you're having problems with manually revoking—is to use a C++/WinRT auto event revoker. Again, more details and code examples in Revoke a registered delegate.

See Also