/**
 * Activate the widget extension.
 */
function activateWidgetExtension(app: JupyterFrontEnd, tracker: INotebookTracker, rendermime: IRenderMimeRegistry, settingRegistry: ISettingRegistry, menu: IMainMenu | null): base.IJupyterWidgetRegistry {

  const {commands} = app;


  settingRegistry.load(plugin.id).then((settings: ISettingRegistry.ISettings) => {
    settings.changed.connect(updateSettings);
    updateSettings(settings);
  }).catch((reason: Error) => {
    console.error(reason.message);
  });

  // Add a placeholder widget renderer.
  rendermime.addFactory(
    {
      safe: false,
      mimeTypes: [WIDGET_VIEW_MIMETYPE],
      createRenderer: options => new WidgetRenderer(options)
    },
    0
  );

  tracker.forEach(panel => {
    registerWidgetManager(
      panel.context,
      panel.content.rendermime,
      chain(
        widgetRenderers(panel.content),
        outputViews(app, panel.context.path)
      )
    );
  });
  tracker.widgetAdded.connect((sender, panel) => {
    registerWidgetManager(
      panel.context,
      panel.content.rendermime,
      chain(
        widgetRenderers(panel.content),
        outputViews(app, panel.context.path)
      )
    );
  });

  // Add a command for creating a new Markdown file.
  commands.addCommand('@jupyter-widgets/jupyterlab-manager:saveWidgetState', {
    label: 'Save Widget State Automatically',
    execute: args => {
      return settingRegistry
        .set(plugin.id, 'saveState', !SETTINGS.saveState)
        .catch((reason: Error) => {
          console.error(`Failed to set ${plugin.id}: ${reason.message}`);
        });
    },
    isToggled: () => SETTINGS.saveState
  });

  if (menu) {
    menu.settingsMenu.addGroup([
      {command: '@jupyter-widgets/jupyterlab-manager:saveWidgetState'}
    ]);
  }

  WIDGET_REGISTRY.push({
    name: '@jupyter-widgets/base',
    version: base.JUPYTER_WIDGETS_VERSION,
    exports: {
      WidgetModel: base.WidgetModel,
      WidgetView: base.WidgetView,
      DOMWidgetView: base.DOMWidgetView,
      DOMWidgetModel: base.DOMWidgetModel,
      LayoutModel: base.LayoutModel,
      LayoutView: base.LayoutView,
      StyleModel: base.StyleModel,
      StyleView: base.StyleView
    }
  });

  WIDGET_REGISTRY.push({
    name: '@jupyter-widgets/controls',
    version: JUPYTER_CONTROLS_VERSION,
    exports: () => {
      return new Promise((resolve, reject) => {
        (require as any).ensure(['@jupyter-widgets/controls'], (require: NodeRequire) => {
          resolve(require('@jupyter-widgets/controls'));
        },
        (err: any) => {
          reject(err);
        },
        '@jupyter-widgets/controls'
        );
      });
    }
  });

  WIDGET_REGISTRY.push({
    name: '@jupyter-widgets/output',
    version: OUTPUT_WIDGET_VERSION,
//.........这里部分代码省略.........

 isActive: () => {
   const current = app.shell.currentWidget;
   return (
     current &&
     (notebookTracker.has(current) || consoleTracker.has(current))
   );
 }

 app.shell.currentChanged.connect((sender, args) => {
   let widget = args.newValue;
   if (!widget || !notebooks.has(widget)) {
     return;
   }
   let source = handlers[widget.id];
   if (source) {
     manager.source = source;
   }
 });

    app.shell.currentChanged.connect((shell, change) => {
      const { oldValue, newValue } = change;

      // Check if we need to disconnect the console listener
      // or the notebook active cell listener
      if (oldValue && consoleTracker.has(oldValue)) {
        (oldValue as ConsolePanel).console.promptCellCreated.disconnect(
          onPromptCreated
        );
      } else if (oldValue && notebookTracker.has(oldValue)) {
        (oldValue as NotebookPanel).content.activeCellChanged.disconnect(
          onActiveCellChanged
        );
      }

      // Wire up the new editor to the model if it exists
      if (newValue && consoleTracker.has(newValue)) {
        (newValue as ConsolePanel).console.promptCellCreated.connect(
          onPromptCreated
        );
        const prompt = (newValue as ConsolePanel).console.promptCell;
        item.model!.editor = prompt && prompt.editor;
      } else if (newValue && notebookTracker.has(newValue)) {
        (newValue as NotebookPanel).content.activeCellChanged.connect(
          onActiveCellChanged
        );
        const cell = (newValue as NotebookPanel).content.activeCell;
        item.model!.editor = cell && cell.editor;
      } else if (newValue && editorTracker.has(newValue)) {
        item.model!.editor = (newValue as IDocumentWidget<
          FileEditor
        >).content.editor;
      } else {
        item.model!.editor = null;
      }
    });