DevFlow: IApplication binding for Comet/custom hosts + Comet view resolution + IView scroll

[davidortinau]

Final batch of DevFlow extractions from feature/comet so the Comet branch contains zero DevFlow changes. Stacked on top of #174 in spirit (adjacent scope) — both target main independently.

Commits

1. 40be3367 — fix: DevFlow _app binding for Comet/IApplication hosts (cherry-pick of 02bf58fa)

   • Adds _iApp field + BoundApplication property (prefers Application, falls back to IApplication)
   • StartServerOnly() now calls TryResolveIApplicationFromDI() via IPlatformApplication.Current.Services so Comet apps that register IApplication (but never set Application.Current) work out of the box
   • New BindIApp(IApplication) for late-binding non-Application hosts
   • Migrates _app → BoundApplication in all endpoint handlers (status, tree, element, query, hittest, gestures, properties, network)
   • Adds IApplication overloads for VisualTreeWalker.WalkTree/GetElementById/HitTestByBounds/Query/QueryCss
   • HitTestByBounds safely casts IWindow → Window for Page/Navigation access
   • AgentServiceExtensions: no net change — main's EnsureAgentStarted/StartWhenApplicationAvailableAsync already provide the same app-less-start fallback that 02bf58f added inline
   • Conflict resolutions kept main's _disposed checks, PublishUiEvent, and the rich nested status payload

2. 0d3593f4 — feat: DevFlow improve Comet view resolution and IView scroll support (cherry-pick of 4179da8e)

   • CometViewResolver extended for richer IView scroll handling
   • DFAS handles IView scroll commands

3. 02b650d4 — fix: align IAppDriver.GetTreeAsync with includeLayout + suppress TFM warnings

   • Interface caught up with AppDriverBase (the Yoga-layout commit added includeLayout to the impl but missed the interface)
   • Driver.csproj adds SuppressTfmSupportBuildWarnings

Result

After this PR + #174 merge, feature/comet should contain zero DevFlow additions vs main. Remaining diffs are all feature/comet deletions of features that landed on main after the Comet branch was cut (BLE Monitoring, Skills system), which is a feature/comet-merge concern, not a DevFlow extraction concern.

Verification

• Build: relies on CI (sandbox can't fetch Arcade SDK)
• Conflict resolution required: 4 hunks in DFAS (StartServerOnly, BindApp/BindIApp, status payload, tree handler), 1 hunk in VTW (WalkTree overloads), 2 hunks in AgentServiceExtensions (resolved to keep main entirely)
• Bulk migration of remaining _app → BoundApplication callsites done via scripted regex; verified all leftover _app references are intentional (field, assignments, IsAppBound)

[Copilot]

Pull request overview

This PR continues the DevFlow extractions needed to keep the feature/comet branch free of DevFlow-specific changes by improving agent binding for Comet/custom hosts and enhancing Comet view introspection (including Yoga layout snapshots and improved IView handling). It also aligns the public Driver interface with the agent’s tree capabilities and updates CLI/MCP surfaces to request layout when desired.

Changes:

• Add support for binding DevFlow agent endpoints to IApplication (fallback when Application.Current is not set) and update tree/query/element flows to use a unified bound-application abstraction.
• Improve Comet view resolution in the visual tree (native bounds/visibility/native properties/text extraction) and add optional Yoga layout snapshots (?layout=1, --layout, MCP layout).
• Update Driver API (IAppDriver.GetTreeAsync) and client calls to support includeLayout, and suppress TFM support warnings in the Driver project.

Show a summary per file

File	Description
src/DevFlow/Microsoft.Maui.DevFlow.Driver/Microsoft.Maui.DevFlow.Driver.csproj	Suppress TFM support warnings for the Driver build.
src/DevFlow/Microsoft.Maui.DevFlow.Driver/IAppDriver.cs	Add includeLayout parameter to Driver tree API.
src/DevFlow/Microsoft.Maui.DevFlow.Driver/ElementInfo.cs	Add layout DTO support for tree responses.
src/DevFlow/Microsoft.Maui.DevFlow.Driver/AppDriverBase.cs	Plumb includeLayout through to AgentClient.
src/DevFlow/Microsoft.Maui.DevFlow.Driver/AgentClient.cs	Add layout=1 query support via includeLayout.
src/DevFlow/Microsoft.Maui.DevFlow.Agent/VisualTreeWalker.cs	Platform-specific native bounds/visibility/native-info support for non-VisualElement IView.
src/DevFlow/Microsoft.Maui.DevFlow.Agent.Core/VisualTreeWalker.cs	Add IApplication overloads + optional Yoga layout snapshot population.
src/DevFlow/Microsoft.Maui.DevFlow.Agent.Core/LayoutInspectorAdapter.cs	New reflection adapter to project Comet Yoga snapshots into wire DTOs.
src/DevFlow/Microsoft.Maui.DevFlow.Agent.Core/ElementInfo.cs	Add layout DTO support on the agent side.
src/DevFlow/Microsoft.Maui.DevFlow.Agent.Core/DevFlowAgentService.cs	Bind via IApplication (DI + explicit late-binding), and plumb layout query param into tree handler.
src/DevFlow/Microsoft.Maui.DevFlow.Agent.Core/CometViewResolver.cs	Improve handler PlatformView reflection safety + add Comet text extraction fallback.
src/Cli/Microsoft.Maui.Cli/DevFlow/Mcp/Tools/TreeTool.cs	Add MCP layout parameter and request layout-enabled tree.
src/Cli/Microsoft.Maui.Cli/DevFlow/DevFlowCommands.cs	Add --layout flag and print layout snapshots in CLI tree output.

Copilot's findings

Comments suppressed due to low confidence (1)

src/DevFlow/Microsoft.Maui.DevFlow.Agent/VisualTreeWalker.cs:301

• ResolveIViewPlatformVisibility: the Android size check uses Width <= 0 && Height <= 0. A view with either dimension 0 should be considered not visible; use || to avoid reporting zero-width/zero-height native views as visible.

            if (platformView is global::Android.Views.View androidView)
            {
                if (androidView.Visibility != global::Android.Views.ViewStates.Visible) return false;
                if (androidView.Alpha <= 0) return false;
                if (androidView.Width <= 0 && androidView.Height <= 0) return false;
                return true;

• Files reviewed: 13/13 changed files
• Comments generated: 7

[Copilot]

_includeLayout is stored as mutable instance state. Methods like WalkElement(...) and Query(...) also call CreateElementInfo(...) but do not set/reset _includeLayout, so a prior WalkTree(..., includeLayout: true) call can cause subsequent element/query results to unexpectedly include layout (and concurrent requests could race). Consider threading includeLayout as a parameter (or scoping it with a local/using pattern) rather than keeping it on the instance.

See below for a potential fix:

        var previousIncludeLayout = _includeLayout;
        _includeLayout = includeLayout;

        try
        {
            var results = new List<ElementInfo>();
            if (app is not IVisualTreeElement appElement)
                return results;

            if (windowIndex != null)
            {
                if (windowIndex.Value < 0 || windowIndex.Value >= app.Windows.Count)
                    return results;
                var window = app.Windows[windowIndex.Value];
                if (window is IVisualTreeElement windowElement)
                {
                    var info = WalkElement(windowElement, null, 1, maxDepth);
                    if (info != null)
                        results.Add(info);
                }
                return results;
            }

            foreach (var child in appElement.GetVisualChildren())
            {
                var info = WalkElement(child, null, 1, maxDepth);
                if (info != null)
                    results.Add(info);
            }

            return results;
        }
        finally
        {
            _includeLayout = previousIncludeLayout;
        }

[Copilot]

InspectorInterface() will rescan loaded assemblies on every call when Comet isn’t present because the early-return only triggers when _inspectorInterface != null. Given this runs per element when ?layout=1 is enabled, it can become very expensive for non-Comet apps. Consider caching the "not found" result (or throttling rescans, e.g. with an attempt counter/time window) so repeated calls return quickly when Comet isn’t loaded.

Suggested change

	// retry (lazy via the ScanAttempt counter) so apps that load Comet after the
	// agent starts still work.
	private static Type? _inspectorInterface;
	private static bool _scanned;
	private static readonly object _gate = new();
	private static Type? InspectorInterface()
	{
	if (_scanned && _inspectorInterface != null)
	return _inspectorInterface;
	lock (_gate)
	{
	if (_inspectorInterface != null)
	return _inspectorInterface;
	// retry so apps that load Comet after the agent starts still work, without
	// rescanning loaded assemblies on every call.
	private static Type? _inspectorInterface;
	private static bool _scanned;
	private static long _lastScanTickCount;
	private static readonly object _gate = new();
	private const int RetryIntervalMilliseconds = 5000;
	private static Type? InspectorInterface()
	{
	if (_inspectorInterface != null)
	return _inspectorInterface;
	var now = Environment.TickCount64;
	if (_scanned && (now - Volatile.Read(ref _lastScanTickCount)) < RetryIntervalMilliseconds)
	return null;
	lock (_gate)
	{
	if (_inspectorInterface != null)
	return _inspectorInterface;
	now = Environment.TickCount64;
	if (_scanned && (now - _lastScanTickCount) < RetryIntervalMilliseconds)
	return null;
	_lastScanTickCount = now;

[Copilot]

XML doc comments: there are two consecutive <summary> blocks here, which will produce malformed/duplicated documentation. Combine into a single <summary> (and use <remarks> if you want additional context).

[Copilot]

object tabView = null; assigns null to a non-nullable object, which will generate nullable warnings (and may be treated as errors depending on settings). Use object? tabView = null; (or similar) for correctness.

[Copilot]

BindIApp(...) doesn’t mirror BindApp(...) behavior: it doesn’t publish the lifecycle "started" UI event, so UI-event subscribers may never observe a start transition for Comet/custom hosts (including the DI-resolved path in StartServerOnly). Consider reusing the same lifecycle publish logic used in BindApp when an app becomes available via IApplication.

[Copilot]

There are existing lifecycle tests covering StartServerOnly + BindApp, but the new Comet/custom-host binding paths (BindIApp and DI resolution in StartServerOnly) aren’t covered. Adding a test that binds a non-Controls IApplication (or simulates DI resolution) and asserts status/tree endpoints succeed would help prevent regressions.

[Copilot]

ResolveIViewPlatformVisibility: the bounds check uses Width <= 0 && Height <= 0. If either dimension is 0 (but not both), this returns visible even though the native view has no renderable area. Consider using || so zero width or zero height is treated as not visible.

This issue also appears on line 296 of the same file.

[github-actions]

Review Summary

Reviewed the Comet/IApplication integration changes. The _app → BoundApplication migration and IApplication fallback are well-structured. Three issues found:

#	Severity	Issue
1	🟡 MODERATE	TrySwitchCometTabDiag uses ReferenceEquals(child, view) instead of ReferenceEquals(child, current) — tab switching silently fails for nested descendants
2	🟡 MODERATE	IsAppBound still checks only _app != null, ignoring _iApp — semantic inconsistency, latent regression for future callers
3	🟡 MODERATE	LayoutInspectorAdapter.InspectorInterface() rescans all assemblies on every call when Comet isn't loaded — performance issue during --layout tree walks

The tab-switch bug (#1) is the most impactful — it causes silent failure of a user-facing feature. The performance bug (#3) can cause noticeable latency on tree requests with layout=1 in non-Comet apps.

Generated by Expert Code Review (auto) for issue #177 · ● 24.2M