Proposal: Extensibility hooks in generated main

[DrusTheAxe]

Proposal: Extensibility hooks in generated main

Summary

Optionally add hooks in the generated main code for developers to provide code to execute before any WPF code. Bonus points for hooks at the end of the generated main and other useful points for developers to add functionality without manually editing or otherwise hacking generated files in fragile ways.

Rationale

• MSIX Dynamic Dependencies requires API calls before using WPF in a Framework package

MSIX Dynamic Dependencies supports non-packaged processes using Framework package goods by calling APIs at runtime, accomplishing what packaged apps do via <PackageDependency> in their appxmanifest.xml. For non-packaged apps to use WPF via a Framework package the app needs to call APIs before accessing WPF.

This is currently impossible with WPF's generated main method. There's no opportunity for the developer to provide code to execute before the generated main uses WPF (not without fragile manual editing of the generated main). Per microsoft/WindowsAppSDK#89 (comment)

Developers shouldn't have to write code in their main method. Maybe this is fine for frameworks where the app author owns the main method. But in WPF and WinUI, the main method is generated by tooling.

The generated main should have extensibility hooks, e.g. the generated main has pre() and post() calls to InsertYourCodeHere? Maybe a new main-extensions.cpp is created with a new WPF project with void WpfMainPre() { /insert code here/ } and WpfMainPost() for devs to inject logic into their app's startup flow?

There may be other reasons (e.g. a crash handler).

See Proposal: Extensibility hooks in generated main #3408 for the equivalent ask of XAML.

Scope

Capability	Priority
Optionally support a 'pre-Main' callout for developers to provide code before the generated main logic w/o editing generated files	Must
Optionally support a 'post-Main' callout for developers to provide code after the generated main logic w/o editing generated files	Should

Open Questions

Are there other desirable extension points in generated files/code?

[miloush]

The tooling generation of the Main method can be turned off by not using ApplicationDefinition build action (typically on App.xaml). You can create your own stable Main method, and simply call new Application().Run() in there.