Remember most recently expanded panel size in local storage

packages/react-resizable-panels-website/src/routes/examples/ImperativePanelApi.tsx

@@ -221,6 +221,7 @@ function Content({
       </div>
       <div className={sharedStyles.PanelGroupWrapper}>
         <PanelGroup
+          autoSaveId="ImperativePanelApi"
           className={sharedStyles.PanelGroup}
           direction="horizontal"
           id="imperative-Panel-api"

packages/react-resizable-panels-website/tests/Storage.spec.ts

@@ -3,32 +3,26 @@ import { createElement } from "react";
 import { Panel, PanelGroup, PanelResizeHandle } from "react-resizable-panels";
 
 import { verifyAriaValues } from "./utils/aria";
+import { imperativeCollapsePanel, imperativeExpandPanel } from "./utils/panels";
 import { goToUrl } from "./utils/url";
 
 const panelGroupABC = createElement(
   PanelGroup,
   { autoSaveId: "test-group", direction: "horizontal" },
-  createElement(Panel, { minSize: 10, order: 1 }),
+  createElement(Panel, {
+    minSize: 10,
+    order: 1,
+  }),
   createElement(PanelResizeHandle),
-  createElement(Panel, { minSize: 10, order: 2 }),
+  createElement(Panel, {
+    minSize: 10,
+    order: 2,
+  }),
   createElement(PanelResizeHandle),
-  createElement(Panel, { minSize: 10, order: 3 })
-);
-
-const panelGroupBC = createElement(
-  PanelGroup,
-  { autoSaveId: "test-group", direction: "horizontal" },
-  createElement(Panel, { minSize: 10, order: 2 }),
-  createElement(PanelResizeHandle),
-  createElement(Panel, { minSize: 10, order: 3 })
-);
-
-const panelGroupAB = createElement(
-  PanelGroup,
-  { autoSaveId: "test-group", direction: "horizontal" },
-  createElement(Panel, { minSize: 10, order: 1 }),
-  createElement(PanelResizeHandle),
-  createElement(Panel, { minSize: 10, order: 2 })
+  createElement(Panel, {
+    minSize: 10,
+    order: 3,
+  })
 );
 
 test.describe("Storage", () => {
@@ -64,8 +58,7 @@ test.describe("Storage", () => {
         now: 80,
       });
 
-      // Wait for localStorage write debounce
-      await new Promise((resolve) => setTimeout(resolve, 250));
+      await waitForLocalStorageWrite();
 
       // Values should be remembered after a page reload
       await page.reload();
@@ -80,6 +73,22 @@ test.describe("Storage", () => {
     test("should store layouts separately per panel combination", async ({
       page,
     }) => {
+      const panelGroupBC = createElement(
+        PanelGroup,
+        { autoSaveId: "test-group", direction: "horizontal" },
+        createElement(Panel, { minSize: 10, order: 2 }),
+        createElement(PanelResizeHandle),
+        createElement(Panel, { minSize: 10, order: 3 })
+      );
+
+      const panelGroupAB = createElement(
+        PanelGroup,
+        { autoSaveId: "test-group", direction: "horizontal" },
+        createElement(Panel, { minSize: 10, order: 1 }),
+        createElement(PanelResizeHandle),
+        createElement(Panel, { minSize: 10, order: 2 })
+      );
+
       await goToUrl(page, panelGroupABC);
 
       const resizeHandles = page.locator("[data-panel-resize-handle-id]");
@@ -93,8 +102,7 @@ test.describe("Storage", () => {
         now: 33,
       });
 
-      // Wait for localStorage write debounce
-      await new Promise((resolve) => setTimeout(resolve, 250));
+      await waitForLocalStorageWrite();
 
       // Hide the first panel and then resize things
       await goToUrl(page, panelGroupBC);
@@ -104,8 +112,7 @@ test.describe("Storage", () => {
         now: 10,
       });
 
-      // Wait for localStorage write debounce
-      await new Promise((resolve) => setTimeout(resolve, 250));
+      await waitForLocalStorageWrite();
 
       // Hide the last panel and then resize things
       await goToUrl(page, panelGroupAB);
@@ -115,8 +122,7 @@ test.describe("Storage", () => {
         now: 90,
       });
 
-      // Wait for localStorage write debounce
-      await new Promise((resolve) => setTimeout(resolve, 250));
+      await waitForLocalStorageWrite();
 
       // Reload and verify all of the different layouts are remembered individually
       await goToUrl(page, panelGroupABC);
@@ -137,5 +143,105 @@ test.describe("Storage", () => {
         now: 90,
       });
     });
+
+    test("should remember the most recent expanded size for collapsed panels", async ({
+      page,
+    }) => {
+      const panelGroup = createElement(
+        PanelGroup,
+        { autoSaveId: "test-group", direction: "horizontal" },
+        createElement(Panel, {
+          collapsible: true,
+          id: "left",
+          minSize: 10,
+          order: 1,
+        }),
+        createElement(PanelResizeHandle),
+        createElement(Panel, {
+          collapsible: true,
+          id: "middle",
+          minSize: 10,
+          order: 2,
+        }),
+        createElement(PanelResizeHandle),
+        createElement(Panel, {
+          collapsible: true,
+          id: "right",
+          minSize: 10,
+          order: 3,
+        })
+      );
+
+      await goToUrl(page, panelGroup);
+
+      const resizeHandles = page.locator("[data-panel-resize-handle-id]");
+      const first = resizeHandles.first();
+      const last = resizeHandles.last();
+
+      await verifyAriaValues(first, {
+        now: 33,
+      });
+      await verifyAriaValues(last, {
+        now: 33,
+      });
+
+      // Change panel sizes
+      await first.focus();
+      await page.keyboard.press("ArrowLeft");
+      await last.focus();
+      await page.keyboard.press("ArrowRight");
+
+      // Verify sizes
+      await verifyAriaValues(first, {
+        now: 23,
+      });
+      await verifyAriaValues(last, {
+        now: 53,
+      });
+
+      await waitForLocalStorageWrite();
+
+      // Collapse panels
+      await imperativeCollapsePanel(page, "left");
+      await imperativeCollapsePanel(page, "right");
+
+      // Verify sizes
+      await verifyAriaValues(first, {
+        now: 0,
+      });
+      await verifyAriaValues(last, {
+        now: 100,
+      });
+
+      await waitForLocalStorageWrite();
+
+      // Reload page
+      await page.reload();
+
+      // Verify collapsed sizes resized
+      await verifyAriaValues(first, {
+        now: 0,
+      });
+      await verifyAriaValues(last, {
+        now: 100,
+      });
+
+      // Expand panels
+      await imperativeExpandPanel(page, "left");
+      await imperativeExpandPanel(page, "right");
+
+      // Verify sizes
+      await verifyAriaValues(first, {
+        now: 23,
+      });
+      await verifyAriaValues(last, {
+        now: 53,
+      });
+    });
   });
 });
+
+// Wait for localStorage write debounce
+async function waitForLocalStorageWrite() {
+  await new Promise((resolve) => setTimeout(resolve, 250));
+}

packages/react-resizable-panels-website/tests/utils/panels.ts

@@ -149,6 +149,22 @@ export async function dragResizeTo(
   await page.mouse.up();
 }
 
+export async function imperativeCollapsePanel(page: Page, panelId: string) {
+  const panelIdSelect = page.locator("#panelIdSelect");
+  await panelIdSelect.selectOption(panelId);
+
+  const button = page.locator("#collapseButton");
+  await button.click();
+}
+
+export async function imperativeExpandPanel(page: Page, panelId: string) {
+  const panelIdSelect = page.locator("#panelIdSelect");
+  await panelIdSelect.selectOption(panelId);
+
+  const button = page.locator("#expandButton");
+  await button.click();
+}
+
 export async function imperativeResizePanel(
   page: Page,
   panelId: string,
@@ -161,8 +177,8 @@ export async function imperativeResizePanel(
   await sizeInput.focus();
   await sizeInput.fill(`${size}%`);
 
-  const resizeButton = page.locator("#resizeButton");
-  await resizeButton.click();
+  const button = page.locator("#resizeButton");
+  await button.click();
 }
 
 export async function imperativeResizePanelGroup(

packages/react-resizable-panels/CHANGELOG.md

@@ -1,8 +1,12 @@
 # Changelog
 
+## Unreleased
+
+- Remember most recently expanded panel size in local storage (#234)
+
 ## 1.0.2
 
-- Change local storage key for persisted sizes to avoid restoring pixel-based sizes (see #233)
+- Change local storage key for persisted sizes to avoid restoring pixel-based sizes (#233)
 
 ## 1.0.1
 

packages/react-resizable-panels/src/PanelGroup.ts

@@ -20,7 +20,10 @@ import { getResizeHandleElement } from "./utils/dom/getResizeHandleElement";
 import { isKeyDown, isMouseEvent, isTouchEvent } from "./utils/events";
 import { getResizeEventCursorPosition } from "./utils/getResizeEventCursorPosition";
 import { initializeDefaultStorage } from "./utils/initializeDefaultStorage";
-import { loadPanelLayout, savePanelGroupLayout } from "./utils/serialization";
+import {
+  loadPanelGroupState,
+  savePanelGroupState,
+} from "./utils/serialization";
 import { validatePanelConstraints } from "./utils/validatePanelConstraints";
 import { validatePanelGroupLayout } from "./utils/validatePanelGroupLayout";
 import {
@@ -79,7 +82,7 @@ export type PanelGroupProps = Omit<HTMLAttributes<ElementType>, "id"> &
   }>;
 
 const debounceMap: {
-  [key: string]: typeof savePanelGroupLayout;
+  [key: string]: typeof savePanelGroupState;
 } = {};
 
 function PanelGroupWithForwardedRef({
@@ -102,7 +105,6 @@ function PanelGroupWithForwardedRef({
 
   const [dragState, setDragState] = useState<DragState | null>(null);
   const [layout, setLayout] = useState<number[]>([]);
-  const [panelDataArray, setPanelDataArray] = useState<PanelData[]>([]);
 
   const panelIdToLastNotifiedSizeMapRef = useRef<Record<string, number>>({});
   const panelSizeBeforeCollapseRef = useRef<Map<string, number>>(new Map());
@@ -218,16 +220,26 @@ function PanelGroupWithForwardedRef({
       // Limit the frequency of localStorage updates.
       if (debouncedSave == null) {
         debouncedSave = debounce(
-          savePanelGroupLayout,
+          savePanelGroupState,
           LOCAL_STORAGE_DEBOUNCE_INTERVAL
         );
 
         debounceMap[autoSaveId] = debouncedSave;
       }
 
-      // Clone panel data array before saving since this array is mutated.
-      // If we don't clone, we run the risk of saving the wrong panel and layout pair.
-      debouncedSave(autoSaveId, [...panelDataArray], layout, storage);
+      // Clone mutable data before passing to the debounced function,
+      // else we run the risk of saving an incorrect combination of mutable and immutable values to state.
+      const clonedPanelDataArray = [...panelDataArray];
+      const clonedPanelSizesBeforeCollapse = new Map(
+        panelSizeBeforeCollapseRef.current
+      );
+      debouncedSave(
+        autoSaveId,
+        clonedPanelDataArray,
+        clonedPanelSizesBeforeCollapse,
+        layout,
+        storage
+      );
     }
   }, [autoSaveId, layout, storage]);
 
@@ -500,7 +512,13 @@ function PanelGroupWithForwardedRef({
       // default size should be restored from local storage if possible.
       let unsafeLayout: number[] | null = null;
       if (autoSaveId) {
-        unsafeLayout = loadPanelLayout(autoSaveId, panelDataArray, storage);
+        const state = loadPanelGroupState(autoSaveId, panelDataArray, storage);
+        if (state) {
+          panelSizeBeforeCollapseRef.current = new Map(
+            Object.entries(state.expandToSizes)
+          );
+          unsafeLayout = state.layout;
+        }
       }
 
       if (unsafeLayout == null) {