Handle currentWidget in KernelWidgetTracker

packages/labextension/src/index.ts

@@ -169,8 +169,8 @@ const kernelUsagePlugin: JupyterFrontEndPlugin<void> = {
         });
 
         panel = new KernelUsagePanel({
-          currentChanged: tracker.currentChanged,
-          trans: trans,
+          tracker,
+          trans,
         });
         shell.add(panel, 'right', { rank: 200 });
       }

packages/labextension/src/panel.ts

@@ -1,10 +1,8 @@
 import { Message } from '@lumino/messaging';
-import { ISignal } from '@lumino/signaling';
 import { TranslationBundle } from '@jupyterlab/translation';
 import { StackedPanel } from '@lumino/widgets';
 import { LabIcon } from '@jupyterlab/ui-components';
 import { KernelUsageWidget } from './widget';
-import { IWidgetWithSession } from './types';
 import { KernelWidgetTracker } from './tracker';
 
 import tachometer from '../style/tachometer.svg';
@@ -13,7 +11,7 @@ const PANEL_CLASS = 'jp-KernelUsage-view';
 
 export class KernelUsagePanel extends StackedPanel {
   constructor(props: {
-    currentChanged: ISignal<KernelWidgetTracker, IWidgetWithSession | null>;
+    tracker: KernelWidgetTracker;
     trans: TranslationBundle;
   }) {
     super();
@@ -27,7 +25,7 @@ export class KernelUsagePanel extends StackedPanel {
     this.title.closable = true;
 
     const widget = new KernelUsageWidget({
-      currentChanged: props.currentChanged,
+      tracker: props.tracker,
       panel: this,
       trans: props.trans,
     });

packages/labextension/src/tracker.ts

@@ -16,20 +16,33 @@ export class KernelWidgetTracker {
         const widget = update.newValue;
         if (widget && hasKernelSession(widget)) {
           this._currentChanged.emit(widget);
+          this._currentWidget = widget;
         } else {
           this._currentChanged.emit(null);
+          this._currentWidget = null;
         }
       });
     } else {
       notebookTracker.currentChanged.connect((_, widget) => {
         this._currentChanged.emit(widget);
+        this._currentWidget = widget;
       });
       if (consoleTracker) {
         consoleTracker.currentChanged.connect((_, widget) => {
           this._currentChanged.emit(widget);
+          this._currentWidget = widget;
         });
       }
     }
+    // handle an existing current widget in case the KernelWidgetTracker
+    // is created a bit later, or if there is already a Notebook widget available
+    // on page load like in Notebook 7.
+    if (labShell?.currentWidget && hasKernelSession(labShell?.currentWidget)) {
+      this._currentWidget = labShell.currentWidget;
+    } else {
+      this._currentWidget =
+        notebookTracker.currentWidget ?? consoleTracker?.currentWidget ?? null;
+    }
   }
 
   /**
@@ -44,10 +57,16 @@ export class KernelWidgetTracker {
     return this._currentChanged;
   }
 
+  get currentWidget(): IWidgetWithSession | null {
+    return this._currentWidget;
+  }
+
   private _currentChanged: Signal<
     KernelWidgetTracker,
     IWidgetWithSession | null
   >;
+
+  private _currentWidget: IWidgetWithSession | null = null;
 }
 
 /**

packages/labextension/src/widget.tsx

@@ -1,5 +1,4 @@
 import React, { useRef, useState, useEffect } from 'react';
-import { ISignal } from '@lumino/signaling';
 import { ReactWidget, ISessionContext } from '@jupyterlab/apputils';
 import { IChangedArgs } from '@jupyterlab/coreutils';
 import { Kernel } from '@jupyterlab/services';
@@ -123,7 +122,7 @@ const BlankReason = (props: {
 };
 
 const KernelUsage = (props: {
-  currentChanged: ISignal<KernelWidgetTracker, IWidgetWithSession | null>;
+  tracker: KernelWidgetTracker;
   panel: KernelUsagePanel;
   trans: TranslationBundle;
 }) => {
@@ -234,9 +233,12 @@ const KernelUsage = (props: {
         }
       }
     };
-    props.currentChanged.connect(notebookChangeCallback);
+    props.tracker.currentChanged.connect(notebookChangeCallback);
+    if (props.tracker.currentWidget) {
+      notebookChangeCallback(props.tracker, props.tracker.currentWidget);
+    }
     return () => {
-      props.currentChanged.disconnect(notebookChangeCallback);
+      props.tracker.currentChanged.disconnect(notebookChangeCallback);
       // In the ideal world we would disconnect kernelChangeCallback from
       // last panel here, but this can lead to a race condition. Instead,
       // we make sure there is ever only one callback active by holding
@@ -368,19 +370,16 @@ const KernelUsage = (props: {
 };
 
 export class KernelUsageWidget extends ReactWidget {
-  private _currentChanged: ISignal<
-    KernelWidgetTracker,
-    IWidgetWithSession | null
-  >;
+  private _tracker: KernelWidgetTracker;
   private _panel: KernelUsagePanel;
   private _trans: TranslationBundle;
   constructor(props: {
-    currentChanged: ISignal<KernelWidgetTracker, IWidgetWithSession | null>;
+    tracker: KernelWidgetTracker;
     panel: KernelUsagePanel;
     trans: TranslationBundle;
   }) {
     super();
-    this._currentChanged = props.currentChanged;
+    this._tracker = props.tracker;
     this._panel = props.panel;
     this._trans = props.trans;
     this.addClass(KERNEL_USAGE_CLASS);
@@ -389,7 +388,7 @@ export class KernelUsageWidget extends ReactWidget {
   protected render(): React.ReactElement<any> {
     return (
       <KernelUsage
-        currentChanged={this._currentChanged}
+        tracker={this._tracker}
         panel={this._panel}
         trans={this._trans}
       />