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Add Reactor (Microsoft.UI.Reactor) dotnet new templates - #6620

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Add Reactor (Microsoft.UI.Reactor) dotnet new templates#6620
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@azchohfi azchohfi commented Jul 15, 2026 •
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Summary

Adds four Reactor (Microsoft.UI.Reactor) project templates to the existing Microsoft.WindowsAppSDK.WinUI.CSharp.Templates dotnet new pack, mirroring the WinUI templates from #6407 but for Reactor's declarative, pure-C# (no XAML) model.

Template Short names What it scaffolds
Reactor Blank App reactor, reactor-blank Minimal Hello-World Reactor app
Reactor MVU App reactor-mvu Model-View-Update counter using UseReducer
Reactor NavigationView App reactor-navview NavigationView shell with multiple pages
Reactor TabView App reactor-tabview TabView shell with multiple tabs

What changed

  • dev/Templates/templates.props — four new rows in the DotnetNewOnlyProjectTemplate slot (dotnet-new only, no VSIX). Reactor apps run unpackaged, so there is no Package.appxmanifest (RenameManifestFrom left unset). This reuses the repo's existing single-source-of-truth pack pipeline.
  • dev/Templates/Source/ProjectTemplates/Desktop/CSharp/Reactor* — the app sources: a shared ProjectTemplate.csproj (references Microsoft.UI.Reactor + Microsoft.WindowsAppSDK, WindowsAppSDKSelfContained, Debug-only Reactor devtools), a single-file App.cs per pattern, and Properties/launchSettings.json (default + Devtools F5 profiles).
  • dev/Templates/Dotnet/templates/reactor-* — the .template.config for each (template.json, dotnetcli.host.json, ide.host.json, icon.png). Defaults: Reactor 0.1.0-preview.12, Windows App SDK 2.1.3, net10.0; overridable via --reactor-version / --wasdk-version.
  • dev/Templates/Dotnet/README.md — documents the new Reactor templates.
  • dev/Templates/Dotnet/Test-DotnetNewTemplates.ps1 — adds the four to the scaffold/build validation loop.

Validation

Validated end-to-end against the live Microsoft.UI.Reactor 0.1.0-preview.12: dotnet pack → dotnet new install → all four register → dotnet new → dotnet build (Debug + Release) → dotnet run. All four launch cleanly, including the title-bar app-mark icon (which relies on the IconResolver fix from microsoft/microsoft-ui-reactor#855, shipped in preview.12).

A Microsoft employee must use /azp run to validate using the PR pipelines.

azchohfi and others added 3 commits July 13, 2026 11:53
@azchohfi
Add Reactor (Microsoft.UI.Reactor) dotnet new templates
fc86e0b 
Adds four Reactor project templates to the Microsoft.WindowsAppSDK.WinUI.CSharp.Templates dotnet-new pack, mirroring the WinUI templates but for Microsoft.UI.Reactor (pure C#, no XAML):

- Reactor Blank App        (reactor, reactor-blank)
- Reactor MVU App          (reactor-mvu)
- Reactor NavigationView   (reactor-navview)
- Reactor TabView App      (reactor-tabview)

Wired into dev/Templates/templates.props via the DotnetNewOnlyProjectTemplate
slot (dotnet-new only, no VSIX, no manifest; Reactor apps run unpackaged).
Each shares a common csproj referencing Microsoft.UI.Reactor +
Microsoft.WindowsAppSDK, bundles the WinAppSDK runtime self-contained, and
enables the Debug-only Reactor devtools surface. README and
Test-DotnetNewTemplates.ps1 updated to document and validate the new templates.

Validated end-to-end: pack -> install -> dotnet new -> build (Debug + Release)
for all four templates.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@azchohfi
Fix Reactor template runtime crash: remove TitleBar icon
7079826 
TitleBar(...).Icon(FontIcon(...)) threw System.ArgumentException (E_INVALIDARG)
at runtime when Reactor set TitleBar.IconSource on Windows App SDK 2.1.3, so
the scaffolded Blank, MVU, and TabView apps crashed on launch. The glyph was
only a placeholder, so drop the icon; the title bar still shows the title text
and all four templates now launch cleanly (validated with dotnet run).

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@azchohfi
Bump Reactor templates to preview.12 and restore title-bar icon
572c23a 
microsoft/microsoft-ui-reactor#855 fixes the IconResolver FontSize=NaN crash
(FontIcon in an IconSource slot without an explicit size threw
ArgumentException from TitleBar.set_IconSource). That fix ships in
Microsoft.UI.Reactor 0.1.0-preview.12, so restore the placeholder title-bar
app-mark icon in the Blank, MVU, and TabView templates and bump the default
reactorVersion 0.1.0-preview.11 -> 0.1.0-preview.12 across all four templates.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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@azchohfi
azchohfi marked this pull request as ready for review July 15, 2026 05:01
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@beth-panx
beth-panx requested review from DinahK-2SO and Scottj1s July 23, 2026 20:46
@azchohfi

azchohfi commented Jul 23, 2026

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/azp run

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@azchohfi
Provision .NET 10 SDK in dotnet-new templates test stage
a6bc434 
The template smoke-test stage installed only .NET SDK 8.0.x, so scaffolding
and building the Reactor templates failed with NETSDK1045 (Reactor targets
net10.0 and declares a [10.0,) sdk-version constraint). The WinUI templates
auto-detect their TFM from the active SDK, so they built net8.0 and passed,
masking the gap.

Add a second UseDotNet@2 step (param reactorDotnetSdkVersion, default 10.0.x)
to the shared Test-Stage template so the agent has the .NET 10 SDK. Verified
locally that the WinUI templates still build cleanly on the .NET 10 SDK, so
existing coverage is unaffected. Both the official and PR pipelines consume
this shared stage.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@azchohfi

azchohfi commented Jul 23, 2026

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DinahK-2SO
DinahK-2SO requested changes Jul 24, 2026
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Comment thread ...s/Source/ProjectTemplates/Desktop/CSharp/ReactorNavigationApp/Properties/launchSettings.json Outdated
Comment thread dev/Templates/Source/ProjectTemplates/Desktop/CSharp/ReactorBlankApp/ProjectTemplate.csproj Outdated
<Platforms>x64;ARM64;x86</Platforms>
<UseWinUI>true</UseWinUI>
<!-- Reactor apps run unpackaged. -->
<WindowsPackageType>None</WindowsPackageType>

@DinahK-2SO DinahK-2SO Jul 24, 2026 •
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Why not make them packaged apps? Dotnet run supports packaged apps now.

@azchohfi You can reference the existing winui templates, when you launch them, there will be an app id.

For instance,
Image

@azchohfi azchohfi Jul 28, 2026 •
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Good call - done in 94e206a. All four are single-project MSIX now, matching the WinUI templates: EnableMsixTooling, a Package.appxmanifest, and a reference to Microsoft.Windows.SDK.BuildTools.WinApp so plain dotnet run registers the loose layout and launches with package identity.

DinahK-2SO
DinahK-2SO reviewed Jul 24, 2026
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Comment thread dev/Templates/Source/ProjectTemplates/Desktop/CSharp/ReactorTabViewApp/App.cs
{
public override Element Render()
{
var (selectedIndex, setSelectedIndex) = UseState(0);

@DinahK-2SO DinahK-2SO Jul 24, 2026 •
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Hi @azchohfi, can we integrate the tabs into the title bar? That would be cleaner and save some vertical space.

You can reference the winui-tabview template about the config.
image

in contrast, the current reactor-tabview is stacking tabs below title bar:
image

@azchohfi azchohfi Jul 28, 2026 •
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Done in c15e219 - the tabs are in the title bar now, following the winui-tabview config: ExtendsContentIntoTitleBar, the tab strip footer registered via SetTitleBar, an app icon in TabStripHeader, and the footer MinWidth tracking TitleBar.RightInset converted to DIPs so the caption buttons don't overlap tabs on high-DPI displays.

One thing worth flagging in this file: the page surface sets MinHeight from the window height. That's a workaround - Reactor tab content currently sizes to its text instead of filling the tab body, so without it the background is two-tone where the winui-tabview equivalent is uniform. Filed upstream as microsoft/microsoft-ui-reactor#914; once that's fixed the MinHeight can come out and the page helper goes back to just a background + padding.

DinahK-2SO
DinahK-2SO reviewed Jul 24, 2026
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Comment thread dev/Templates/Dotnet/templates/reactor-blank-app/.template.config/template.json Outdated
azchohfi and others added 5 commits July 24, 2026 10:48
@azchohfi
Address PR review: trim launchSettings comments, use per-template icons
5d76a37 
Review feedback from @DinahK-2SO on #6620:
- Remove the explanatory comment block from the Reactor launchSettings.json
  files (the content overlapped the package README).
- Give the MVU, NavigationView, and TabView templates their own icon.png
  (reusing the existing WinUI mvvm/navigation/tabview template icons) instead
  of all reusing the blank-app icon.

The packaging/taskbar-icon, tabs-in-title-bar, and winui-* short-name comments
are still open pending a check with the Reactor team.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@azchohfi
Add winui-reactor* short-name aliases to Reactor templates
47bcf4f 
Review feedback from @DinahK-2SO on #6620: give each Reactor template a
winui-reactor* alias (winui-reactor, winui-reactor-mvu, winui-reactor-navview,
winui-reactor-tabview) so they also surface under 'dotnet new list winui'
alongside the other WinUI templates. README updated to note the aliases.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@azchohfi
reactor-tabview: integrate tabs into the title bar
c15e219 
Review feedback from @DinahK-2SO on #6620: instead of stacking a separate
TitleBar row above the TabView, put the tabs up in the title bar (Edge/Terminal
style) to look cleaner and save vertical space.

Uses supported Reactor APIs: UseWindow().NativeWindow with
ExtendsContentIntoTitleBar + SetTitleBar, the TabView TabStripHeader (app name
at the leading edge) and TabStripFooter (draggable region), and UseDpi +
UseWindowSize to reserve the caption-button inset (RightInset) across DPI and
resize. Verified by scaffolding the template, building, running, and
screenshotting the window: the tabs render inline in the title bar with the
caption buttons clear.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@azchohfi
Make Reactor templates packaged (MSIX) and match the WinUI templates
94e206a 
Per review direction, the four Reactor templates now:

1. Are single-project MSIX packaged (like the WinUI templates) instead of
   unpackaged. Each gains app.manifest, Package.appxmanifest (EntryPoint
   Windows.FullTrustApplication since Reactor has no XAML App class), the shared
   Assets, and PublishProfiles. The csproj switches to EnableMsixTooling +
   Microsoft.Windows.SDK.BuildTools + Microsoft.Windows.SDK.BuildTools.WinApp so
   'dotnet run' registers a loose package and launches with MSIX identity.
   templates.props sets RenameManifestFrom and the template.json files gain the
   publisher / guid / build-tools-version symbols and the \\$
   modifier.

2. Visually match their WinUI counterparts:
   - reactor      -> title bar (app icon) + empty content (blank canvas).
   - reactor-mvu  -> centered 'Hello, WinUI!' + [+]/[-] icon counter (keeps the
     UseReducer MVU pattern under the same UI).
   - reactor-navview -> title bar + NavigationView Home/About + built-in Settings;
     pages render 'Title' + 'This is the X page'.
   - reactor-tabview -> MicaAlt, app-icon TabStripHeader, closable Home/About tabs
     with a '+' add button, tabs in the title bar.

Validated end-to-end for all four: pack -> install -> scaffold -> build ->
dotnet run (launches packaged with identity) -> screenshot matches the WinUI
counterpart. README updated (templates are now packaged).

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@azchohfi
reactor-mvu: greet 'Hello, Reactor!'; use WinUI type-ramp styles for …
74f8df0 
…font parity

- MVU greeting is now 'Hello, Reactor!' (was 'Hello, WinUI!').
- Switch the Reactor text from Heading()/.SemiBold() (raw 28px Bold-700) to the
  type-ramp factories Title()/BodyStrong()/Body(), which apply the actual WinUI
  styles (TitleTextBlockStyle 28px Semibold-600, BodyStrongTextBlockStyle,
  BodyTextBlockStyle). This makes the Reactor headings/body render with the same
  weight and Segoe UI Variable optical size as the WinUI templates instead of a
  heavier bold. Applied to the mvu, navview, and tabview page text.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
azchohfi and others added 9 commits July 24, 2026 12:25
@azchohfi
reactor-tabview: give tab pages a solid background to match WinUI
768ac67 
The WinUI TabView template's pages set Background=SolidBackgroundFillColorTertiaryBrush,
which covers the window's Mica in the tab content area. The Reactor version left
the pages transparent, so MicaAlt showed through the content. Wrap the tab page
content in a Border painted with that same tertiary brush so the content is a
solid surface and only the tab strip / title bar show Mica, matching X_Tab.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@azchohfi
reactor-tabview: stretch the tab page surface to fill the content area
cbeb825 
The solid tertiary page background only covered the text at the top because
Reactor sizes the tab content to the element's desired size. Force the page
Border to HorizontalAlignment/VerticalAlignment Stretch so the solid surface
fills the whole tab content region, matching the WinUI TabView template
(verified: the content is a uniform solid fill down to the window bottom).

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@azchohfi
Fill reactor-tabview page surface to window height
bb5bc93 
Match the WinUI TabView template's uniform tertiary content background by
sizing the shared page surface to the window height, so it fills the whole
tab content area instead of shrinking to its text (two-tone with Mica below).

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 16d7d2fc-3d7c-41e8-9999-0c2084ba9ea1
@azchohfi
Use Reactor's navigation system in reactor-navview
cdee0c2 
Match the WinUI NavigationView template's shell: the title bar owns the back
and pane toggle buttons, and NavigationView's own copies are hidden.

Switch from hand-rolled tag state to Reactor's navigation handle
(UseNavigation + NavigationHost), so the title bar back button is wired by
.WithNavigation(nav) and tracks the back stack instead of never appearing.
Also request the tall title bar layout the WinUI template uses.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 16d7d2fc-3d7c-41e8-9999-0c2084ba9ea1
@azchohfi
Toggle the nav pane on the control instead of mirrored state
6b4aebf 
NavigationView opens and closes its pane on its own (light dismiss, display
mode changes), so a separate IsPaneOpen state copy drifted out of sync and
the title bar toggle needed two clicks to take effect.

Flip IsPaneOpen on the control directly, the same way the WinUI template's
code-behind does.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 16d7d2fc-3d7c-41e8-9999-0c2084ba9ea1
@azchohfi
Match the WinUI page transition in reactor-navview
2898bec 
Reactor's NavigationHost slides pages in from the side, while WinUI's Frame
defaults to an entrance transition that rises the new page up into place.
Slide from the bottom so switching pages animates the same way.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 16d7d2fc-3d7c-41e8-9999-0c2084ba9ea1
@azchohfi
Trim the Reactor templates to match the XAML templates' style
9dc32b9 
The Reactor templates carried long comments explaining Reactor concepts and
how they differ from XAML, which made them read like documentation rather
than a starting point. Keep only the brief, functional comments the XAML
templates use, and a single pointer to the Reactor project info.

Also drop the explicit navigation transition from reactor-navview: matching
the XAML Frame's entrance animation added verbosity and called out a
difference between the two, so use Reactor's default instead.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 16d7d2fc-3d7c-41e8-9999-0c2084ba9ea1
@azchohfi
Mark the Reactor templates as experimental
d0b3e47 
Microsoft.UI.Reactor is prerelease and its API may still change, so label the
templates accordingly: add `(Experimental)` to each template name, an
`Experimental` classification so it shows in the dotnet new tags column, and
a note in each description and in the README.

Also correct the templates.props comment, which still described the Reactor
apps as unpackaged with RenameManifestFrom unset; they are packaged
(single-project MSIX) and do set it.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 16d7d2fc-3d7c-41e8-9999-0c2084ba9ea1
@azchohfi
Fix Reactor analyzer warnings in the MVU and TabView templates
37fe726 
The templates tripped four of Reactor's analyzers, so a freshly scaffolded
project did not build clean:

- REACTOR_A11Y_001 (x2): the MVU counter's icon-only buttons had no
  accessible name. Add .AutomationName().
- REACTOR_A11Y_002: the TabView tab strip icon is decorative. Mark it
  .AccessibilityHidden().
- REACTOR_HOOKS_013: the initial tab array was reallocated on every render
  though only read on the first. Wrap it in UseMemo.
- REACTOR_POOL_001: the page surface set MinHeight via .Set(...), which is
  reset when the element returns to the pool, so the tab content fill could
  be lost on re-render. Use the .MinHeight() modifier instead.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 16d7d2fc-3d7c-41e8-9999-0c2084ba9ea1
@azchohfi

azchohfi commented Jul 28, 2026

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Thanks for the review @DinahK-2SO - all seven comments are addressed and replied to inline. Summary:

  • Tabs integrated into the title bar (c15e219)
  • launchSettings.json comments removed (5d76a37)
  • Per-template icons - navigation and tabview now use the same icons as their WinUI counterparts
  • Templates are packaged single-project MSIX with Microsoft.Windows.SDK.BuildTools.WinApp, so dotnet run launches with package identity (94e206a)
  • winui-reactor* short name aliases added (47bcf4f)

Two things changed since you last looked that are worth a glance:

The templates are now marked (Experimental) (d0b3e47) - in the template name, an Experimental classification tag, the description, and a callout in the README. Microsoft.UI.Reactor is prerelease and its API can still change, so this seemed worth being explicit about:

Reactor Blank App (Experimental)           reactor,reactor-blank,winui-reactor    Windows/WinUI/Desktop/Reactor/Experimental
Reactor MVU App (Experimental)             reactor-mvu,winui-reactor-mvu          Windows/WinUI/Desktop/Reactor/Experimental
Reactor NavigationView App (Experimental)  reactor-navview,winui-reactor-navview  Windows/WinUI/Desktop/Reactor/Experimental
Reactor TabView App (Experimental)         reactor-tabview,winui-reactor-tabview  Windows/WinUI/Desktop/Reactor/Experimental

The UI now matches the XAML templates much more closely - same type ramp, backdrops, title bar layout and page surfaces, so the two sets are comparable side by side. All four also build warning-free under Reactor's analyzers, which caught a couple of real issues along the way (including missing accessible names on the MVU counter buttons).

Where the templates still had to work around gaps in Reactor itself, I filed those upstream so they can be cleaned up later rather than lingering here: microsoft/microsoft-ui-reactor#914, #915, #916, #917.

@azchohfi
Use $targetentrypoint$ in the Reactor manifests, like the XAML templates
6ee1260 
The Reactor manifests hardcoded EntryPoint=Windows.FullTrustApplication while
every XAML template uses the $targetentrypoint$ token. The token already
resolves to Windows.FullTrustApplication for these projects, so the generated
AppxManifest.xml is unchanged - this just removes an unexplained difference
between the two sets of templates.

The four Reactor manifests are now byte-identical to their XAML counterparts.

Verified: all four scaffold, build warning-free, generate the same
EntryPoint=Windows.FullTrustApplication, and launch with package identity.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 16d7d2fc-3d7c-41e8-9999-0c2084ba9ea1
@azchohfi

azchohfi commented Jul 28, 2026

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