DispatcherQueueDemo

Instruction file imported from JDKoll1982/MTM_Waitlist (.github/instructions/demos/Platform/DispatcherQueueDemo.instructions.md). Copyright stays with the author.

DispatcherQueue

What it teaches

The UI thread's work queue. Every XAML touch from a background thread has to be marshalled through it.

How the demo is built

The page is a UserControl at Platform/DispatcherQueueDemo.xaml, paired with DispatcherQueueDemo.xaml.cs. The shell hosts it inside Shell/DemoPage.xaml, which also shows both files verbatim — the snippet viewer reads the same source the app compiles, so what is displayed is always what runs.

Layout. Root UserControl with 17 element(s).

Named elements the code-behind touches: RunButton, Progress, ThreadText, PriorityText, LastActionText.

Wired in XAML: OnRunClicked(), OnCompareClicked().

Code-behind. Handlers OnRunClicked(), OnCompareClicked(). 130 line(s), including the comments that record what the control does that the docs do not say.

Anything the demo cannot show is explained on the page rather than faked: the same rules the rest of the repo follows are in .github/instructions/winui3-api-rules.instructions.md.

MTM use case

MTM_Waitlist › Settings persistence and start-up

Effective settings are resolved from several scopes and cached at start-up, and every change is versioned in a history table. Persistence, the UI thread and theme resolution are the plumbing that has to keep working when nothing is being demoed.

Schema this mirrors: config_settings_values, config_settings_history, usr_settings. Sample data for the page comes from src/WinUI3LearningLab.Core/LabData.cs — part numbers, bins, dunnage types and work orders, never Item 1 or John Doe.

Gotchas

• GetForCurrentThread returns null on a thread that has no queue — capture the UI queue once at start-up.
• TryEnqueue fails (returns false) when the queue is shutting down, so check the result instead of assuming.
• DispatcherQueue has no SynchronizationContext by itself in early WinUI 3 versions; awaiting a Task on a background thread does not return to the UI thread.
• EnqueuePriority.Low is right for non-urgent refreshes and keeps input responsive.

Try this

• Run WinUI3LearningLab.App.exe --demo dispatcher-queue. The page shows DispatcherQueueDemo.xaml and DispatcherQueueDemo.xaml.cs beside the live demo, so the next edit can be made against something already running.
• Change one value in the XAML and rebuild; the snippet viewer re-reads the file, so what is shown stays the code that compiled.

Documentation

• Microsoft.UI.Dispatching.DispatcherQueue
• WinUI 3 API rules for this repo
• Design system

Generated from DemoCatalog by --export-instructions. Do not edit by hand: change the descriptor in src/WinUI3LearningLab.Core/Catalog/Platform.cs or the demo source, then regenerate.