gradually move towards cellAt index asset.

src/vs/workbench/api/browser/mainThreadNotebookEditors.ts

@@ -150,11 +150,13 @@ export class MainThreadNotebookEditors implements MainThreadNotebookEditorsShape
 		if (!notebookEditor.hasModel()) {
 			return;
 		}
-		const cell = notebookEditor.cellAt(range.start);
-		if (!cell) {
+
+		if (range.start >= notebookEditor.getLength()) {
 			return;
 		}
 
+		const cell = notebookEditor.cellAt(range.start);
+
 		switch (revealType) {
 			case NotebookEditorRevealType.Default:
 				return notebookEditor.revealCellRangeInView(range);

src/vs/workbench/contrib/notebook/browser/contrib/clipboard/notebookClipboard.ts

@@ -202,7 +202,7 @@ export function runCutCells(accessor: ServicesAccessor, editor: INotebookEditor,
 
 	if (!containingSelection) {
 		// focus is out of any selection, we should only cut this cell
-		const targetCell = editor.cellAt(focus.start)!;
+		const targetCell = editor.cellAt(focus.start);
 		clipboardService.writeText(targetCell.getText());
 		const newFocus = focus.end === editor.getLength() ? { start: focus.start - 1, end: focus.end - 1 } : focus;
 		const newSelections = selections.map(selection => (selection.end <= focus.start ? selection : { start: selection.start - 1, end: selection.end - 1 }));

src/vs/workbench/contrib/notebook/browser/contrib/find/findModel.ts

@@ -160,9 +160,7 @@ export class FindModel extends Disposable {
 
 		if (oldCurrMatchCellIndex < 0) {
 			// the cell containing the active match is deleted
-			const focusedCell = this._notebookEditor.cellAt(this._notebookEditor.getFocus().start);
-
-			if (!focusedCell) {
+			if (this._notebookEditor.getLength() === 0) {
 				this.set(findMatches, false);
 				return;
 			}

src/vs/workbench/contrib/notebook/browser/contrib/fold/folding.ts

@@ -211,6 +211,10 @@ registerAction2(class extends Action2 {
 			return;
 		}
 
+		if (!editor.hasModel()) {
+			return;
+		}
+
 		const levels = args && args.levels || 1;
 		const direction = args && args.direction === 'up' ? 'up' : 'down';
 		let index: number | undefined = undefined;
@@ -227,7 +231,7 @@ registerAction2(class extends Action2 {
 
 		const controller = editor.getContribution<FoldingController>(FoldingController.id);
 		if (index !== undefined) {
-			const targetCell = editor.cellAt(index);
+			const targetCell = (index < 0 || index >= editor.getLength()) ? undefined : editor.cellAt(index);
 			if (targetCell?.cellKind === CellKind.Code && direction === 'down') {
 				return;
 			}
@@ -238,8 +242,8 @@ registerAction2(class extends Action2 {
 				controller.setFoldingStateDown(index, CellFoldingState.Collapsed, levels);
 			}
 
-			const viewIndex = editor._getViewModel()!.getNearestVisibleCellIndexUpwards(index);
-			editor.focusElement(editor.cellAt(viewIndex)!);
+			const viewIndex = editor._getViewModel().getNearestVisibleCellIndexUpwards(index);
+			editor.focusElement(editor.cellAt(viewIndex));
 		}
 	}
 });

src/vs/workbench/contrib/notebook/browser/contrib/navigation/arrow.ts

@@ -63,12 +63,12 @@ registerAction2(class extends NotebookCellAction {
 			return;
 		}
 
-		const newCell = editor.cellAt(idx + 1);
-
-		if (!newCell) {
+		if (idx >= editor.getLength()) {
+			// last one
 			return;
 		}
 
+		const newCell = editor.cellAt(idx + 1);
 		const newFocusMode = newCell.cellKind === CellKind.Markup && newCell.getEditState() === CellEditState.Preview ? 'container' : 'editor';
 		editor.focusNotebookCell(newCell, newFocusMode);
 		editor.cursorNavigationMode = true;
@@ -105,17 +105,12 @@ registerAction2(class extends NotebookCellAction {
 			return;
 		}
 
-		if (idx < 1) {
+		if (idx < 1 || editor.getLength() === 0) {
 			// we don't do loop
 			return;
 		}
 
 		const newCell = editor.cellAt(idx - 1);
-
-		if (!newCell) {
-			return;
-		}
-
 		const newFocusMode = newCell.cellKind === CellKind.Markup && newCell.getEditState() === CellEditState.Preview ? 'container' : 'editor';
 		editor.focusNotebookCell(newCell, newFocusMode);
 		editor.cursorNavigationMode = true;
@@ -139,14 +134,12 @@ registerAction2(class extends NotebookAction {
 
 	async runWithContext(accessor: ServicesAccessor, context: INotebookActionContext): Promise<void> {
 		const editor = context.notebookEditor;
-		if (!editor.getLength()) {
+		if (editor.getLength() === 0) {
 			return;
 		}
 
 		const firstCell = editor.cellAt(0);
-		if (firstCell) {
-			editor.focusNotebookCell(firstCell, 'container');
-		}
+		editor.focusNotebookCell(firstCell, 'container');
 	}
 });
 
@@ -166,7 +159,7 @@ registerAction2(class extends NotebookAction {
 
 	async runWithContext(accessor: ServicesAccessor, context: INotebookActionContext): Promise<void> {
 		const editor = context.notebookEditor;
-		if (!editor.hasModel() || !editor.getLength()) {
+		if (!editor.hasModel() || editor.getLength() === 0) {
 			return;
 		}
 

src/vs/workbench/contrib/notebook/browser/contrib/outline/notebookOutline.ts

@@ -8,7 +8,7 @@ import { Codicon } from 'vs/base/common/codicons';
 import { Emitter, Event } from 'vs/base/common/event';
 import { combinedDisposable, IDisposable, Disposable, DisposableStore, MutableDisposable, toDisposable } from 'vs/base/common/lifecycle';
 import { IThemeService, ThemeIcon } from 'vs/platform/theme/common/themeService';
-import { ICellViewModel } from 'vs/workbench/contrib/notebook/browser/notebookBrowser';
+import { IActiveNotebookEditor, ICellViewModel } from 'vs/workbench/contrib/notebook/browser/notebookBrowser';
 import { NotebookEditor } from 'vs/workbench/contrib/notebook/browser/notebookEditor';
 import { CellKind } from 'vs/workbench/contrib/notebook/common/notebookCommon';
 import { IOutline, IOutlineComparator, IOutlineCreator, IOutlineListConfig, IOutlineService, IQuickPickDataSource, IQuickPickOutlineElement, OutlineChangeEvent, OutlineConfigKeys, OutlineTarget } from 'vs/workbench/services/outline/browser/outline';
@@ -371,13 +371,19 @@ export class NotebookCellOutline extends Disposable implements IOutline<OutlineE
 		this._activeEntry = undefined;
 		this._entries.length = 0;
 
-		const notebookEditorWidget = this._editor.getControl();
+		const notebookEditorControl = this._editor.getControl();
+
+		if (!notebookEditorControl) {
+			return;
+		}
 
-		if (!notebookEditorWidget) {
+		if (!notebookEditorControl.hasModel()) {
 			return;
 		}
 
-		if (!notebookEditorWidget.hasModel()) {
+		const notebookEditorWidget: IActiveNotebookEditor = notebookEditorControl;
+
+		if (notebookEditorWidget.getLength() === 0) {
 			return;
 		}
 
@@ -394,10 +400,6 @@ export class NotebookCellOutline extends Disposable implements IOutline<OutlineE
 
 		for (let i = 0; i < notebookEditorWidget.getLength(); i++) {
 			const cell = notebookEditorWidget.cellAt(i);
-			if (!cell) {
-				continue;
-			}
-
 			const isMarkdown = cell.cellKind === CellKind.Markup;
 			if (!isMarkdown && !includeCodeCells) {
 				continue;
@@ -515,12 +517,14 @@ export class NotebookCellOutline extends Disposable implements IOutline<OutlineE
 		const notebookEditorWidget = this._editor.getControl();
 
 		if (notebookEditorWidget) {
-			const cell = notebookEditorWidget.cellAt(notebookEditorWidget.getFocus().start);
-			if (cell) {
-				for (let entry of this._entries) {
-					newActive = entry.find(cell, []);
-					if (newActive) {
-						break;
+			if (notebookEditorWidget.hasModel() && notebookEditorWidget.getLength() > 0) {
+				const cell = notebookEditorWidget.cellAt(notebookEditorWidget.getFocus().start);
+				if (cell) {
+					for (let entry of this._entries) {
+						newActive = entry.find(cell, []);
+						if (newActive) {
+							break;
+						}
 					}
 				}
 			}

src/vs/workbench/contrib/notebook/browser/controller/cellOperations.ts

@@ -67,11 +67,6 @@ export async function changeCellToKind(kind: CellKind, context: INotebookActionC
 			};
 		}, undefined, true);
 		const newCell = notebookEditor.cellAt(idx);
-
-		if (!newCell) {
-			return;
-		}
-
 		notebookEditor.focusNotebookCell(newCell, cell.getEditState() === CellEditState.Editing ? 'editor' : 'container');
 	} else if (context.selectedCells) {
 		const selectedCells = context.selectedCells;
@@ -131,7 +126,7 @@ export function runDeleteAction(editor: IActiveNotebookEditor, cell: ICellViewMo
 			editType: CellEditType.Replace, index: selection.start, count: selection.end - selection.start, cells: []
 		}));
 
-		const nextCellAfterContainingSelection = editor.cellAt(containingSelection.end);
+		const nextCellAfterContainingSelection = containingSelection.end >= editor.getLength() ? undefined : editor.cellAt(containingSelection.end);
 
 		textModel.applyEdits(edits, true, { kind: SelectionStateType.Index, focus: editor.getFocus(), selections: editor.getSelections() }, () => {
 			if (nextCellAfterContainingSelection) {

src/vs/workbench/contrib/notebook/browser/viewModel/notebookViewModel.ts

@@ -194,7 +194,7 @@ export class NotebookViewModel extends Disposable implements EditorFoldingStateD
 	private get selectionHandles() {
 		const handlesSet = new Set<number>();
 		const handles: number[] = [];
-		cellRangesToIndexes(this._selectionCollection.selections).map(index => this.cellAt(index)).forEach(cell => {
+		cellRangesToIndexes(this._selectionCollection.selections).map(index => index < this.length ? this.cellAt(index) : undefined).forEach(cell => {
 			if (cell && !handlesSet.has(cell.handle)) {
 				handles.push(cell.handle);
 			}