Flutter调试工具devTools是如何工作的

Package devtools is currently active at version 0.1.14.
Resolving dependencies...
+ args 1.5.2
+ async 2.4.0
+ browser_launcher 0.1.5
+ charcode 1.1.3
+ collection 1.14.12
+ convert 2.1.1
+ crypto 2.1.4
+ devtools 0.1.15
+ devtools_server 0.1.14
+ devtools_shared 0.2.0
+ http 0.12.0+4
+ http_multi_server 2.2.0
+ http_parser 3.1.3
+ intl 0.16.1
+ logging 0.11.4
+ meta 1.1.8
+ mime 0.9.6+3
+ path 1.6.4
+ pedantic 1.9.0
+ shelf 0.7.5
+ shelf_static 0.2.8
+ source_span 1.6.0
+ sse 3.1.2
+ stack_trace 1.9.3
+ stream_channel 2.0.0
+ string_scanner 1.0.5
+ term_glyph 1.1.0
+ typed_data 1.1.6
+ usage 3.4.1
+ uuid 2.0.4
+ vm_service 2.3.1
+ webkit_inspection_protocol 0.5.0
Downloading devtools 0.1.15...

// Now run the app.
  runApp(
    DevToolsApp(),
  );

 /// The routes that the app exposes.
  final Map<String, UrlParametersBuilder> _routes = {
    '/': (_, params) => Initializer(
          url: params['uri'],
          builder: (_) => DevToolsScaffold(
            tabs: const [
              InspectorScreen(),
              TimelineScreen(),
              MemoryScreen(),
              PerformanceScreen(),
              // TODO(https://github.com/flutter/flutter/issues/43783): Put back
              // the debugger screen.
              if (showNetworkPage)
                NetworkScreen(),
              LoggingScreen(),
              InfoScreen(),
            ],

setState(() {
      inspectorController?.dispose();
      summaryTreeController = InspectorTreeControllerFlutter();
      detailsTreeController = InspectorTreeControllerFlutter();
      inspectorController = InspectorController(
        inspectorTree: summaryTreeController,
        detailsTree: detailsTreeController,
        inspectorService: inspectorService,
        treeType: FlutterTreeType.widget,
        onExpandCollapseSupported: _onExpandCollapseSupported,
        onLayoutExplorerSupported: _onLayoutExplorerSupported,
      );

class InspectorController extends DisposableController
    with AutoDisposeControllerMixin
    implements InspectorServiceClient

  static Future<InspectorService> create(VmService vmService) async {
    assert(_inspectorDependenciesLoaded);
    assert(serviceManager.hasConnection);
    assert(serviceManager.service != null);
    final inspectorLibrary = EvalOnDartLibrary(
      inspectorLibraryUriCandidates,
      vmService,
    );

    final libraryRef = await inspectorLibrary.libraryRef.catchError(
      (_) => throw FlutterInspectorLibraryNotFound(),
      test: (e) => e is LibraryNotFound,
    );
    final libraryFuture = inspectorLibrary.getLibrary(libraryRef, null);
    final library = await libraryFuture;
    Future<Set<String>> lookupFunctionNames() async {
      for (ClassRef classRef in library.classes) {
        if ('WidgetInspectorService' == classRef.name) {
          final classObj = await inspectorLibrary.getClass(classRef, null);
          final functionNames = <String>{};
          for (FuncRef funcRef in classObj.functions) {
            functionNames.add(funcRef.name);
          }
          return functionNames;
        }
      }
      // WidgetInspectorService is not available. Either this is not a Flutter
      // application or it is running in profile mode.
      return null;
    }

    final supportedServiceMethods = await lookupFunctionNames();
    if (supportedServiceMethods == null) return null;
    return InspectorService(
      vmService,
      inspectorLibrary,
      supportedServiceMethods,
    );
  }

 Future<void> _attemptUrlConnection() async {
    final uri = normalizeVmServiceUri(widget.url);
    final connected = await FrameworkCore.initVmService(
      '',
      explicitUri: uri,
      errorReporter: (message, error) =>
          Notifications.of(context).push('$message, $error'),
    );
    if (!connected) {
      _navigateToConnectPage();
    }
  }

Future<void> maybeLoadUI() async {
    if (!visibleToUser || !isActive) {
      return;
    }

    if (flutterAppFrameReady) {
      // We need to start by querying the inspector service to find out the
      // current state of the UI.
      await inspectorService.inferPubRootDirectoryIfNeeded();
      await updateSelectionFromService(firstFrame: true);
    } else {
      final ready = await inspectorService.isWidgetTreeReady();
      flutterAppFrameReady = ready;
      if (isActive && ready) {
        await maybeLoadUI();
      }
    }
  }

// TODO(jacobr): remove flutter_web entry once flutter_web and flutter are
// unified.
const inspectorLibraryUriCandidates = [
  'package:flutter/src/widgets/widget_inspector.dart',
  'package:flutter_web/src/widgets/widget_inspector.dart',
];

 /// If the widget tree is not ready, the application should wait for the next
  /// Flutter.Frame event before attempting to display the widget tree. If the
  /// application is ready, the next Flutter.Frame event may never come as no
  /// new frames will be triggered to draw unless something changes in the UI.
  Future<bool> isWidgetTreeReady() {
    return invokeBoolServiceMethodNoArgs('isWidgetTreeReady');
  }

@protected
  bool isWidgetTreeReady([ String groupName ]) {
    return WidgetsBinding.instance != null &&
           WidgetsBinding.instance.debugDidSendFirstFrameEvent;
  }

Future<String> inferPubRootDirectoryIfNeeded() async {
    final group = createObjectGroup('temp');
    final root = await group.getRoot(FlutterTreeType.widget);

    if (root == null) {
      // No need to do anything as there isn't a valid tree (yet?).
      await group.dispose();
      return null;
    }
    final children = await root.children;
    if (children?.isNotEmpty == true) {
      // There are already widgets identified as being from the summary tree so
      // no need to guess the pub root directory.
      return null;
    }

    final List<RemoteDiagnosticsNode> allChildren =
        await group.getChildren(root.dartDiagnosticRef, false, null);
    final path = allChildren.first.creationLocation?.path;
    if (path == null) {
      await group.dispose();
      return null;
    }

    // this directory rather than guessing based on url structure.
    final parts = path.split('/');
    String pubRootDirectory;
    for (int i = parts.length - 1; i >= 0; i--) {
      String part;
      if (part == 'lib' || part == 'web') {
        pubRootDirectory = parts.sublist(0, i).join('/');
        break;
      }

      if (part == 'packages') {
        pubRootDirectory = parts.sublist(0, i + 1).join('/');
        break;
      }
    }
    pubRootDirectory ??= (parts..removeLast()).join('/');

    await setPubRootDirectories([pubRootDirectory]);
    await group.dispose();
    return pubRootDirectory;
  }

 /// Returns a JSON representation of the subtree rooted at the
  /// [DiagnosticsNode] object that `diagnosticsNodeId` references providing
  /// information needed for the details subtree view.
  ///
  /// The number of levels of the subtree that should be returned is specified
  /// by the [subtreeDepth] parameter. This value defaults to 2 for backwards
  /// compatibility.
  ///
  /// See also:
  ///
  ///  * [getChildrenDetailsSubtree], a method to get children of a node
  ///    in the details subtree.
  String getDetailsSubtree(
    String id,
    String groupName, {
    int subtreeDepth = 2,
  }) {
    return _safeJsonEncode(_getDetailsSubtree( id, groupName, subtreeDepth));
  }