fix(datetime): switching months in wheel picker now selected nearest neighbor

core/src/components/picker-column-internal/picker-column-internal.tsx

@@ -36,6 +36,70 @@ export class PickerColumnInternal implements ComponentInterface {
    * A list of options to be displayed in the picker
    */
   @Prop() items: PickerColumnItem[] = [];
+  @Watch('items')
+  itemsChange(currentItems: PickerColumnItem[], previousItems: PickerColumnItem[]) {
+    const { value } = this;
+
+    /**
+     * When the items change, it is possible for the item
+     * that was selected to no longer exist. In that case, we need
+     * to automatically select the nearest item. If we do not,
+     * then the scroll position will be reset to zero and it will
+     * look like the first item was automatically selected.
+     *
+     * If we cannot find a closest item then we do nothing, and
+     * the browser will reset the scroll position to 0.
+     */
+    const findCurrentItem = currentItems.find((item) => item.value === value);
+    if (!findCurrentItem) {
+      /**
+       * The default behavior is to assume
+       * that the new set of data is similar to the old
+       * set of data, just with some items filtered out.
+       * We walk backwards through the data to find the
+       * closest enabled picker item and select it.
+       *
+       * Developers can also swap the items out for an entirely
+       * new set of data. In that case, the value we select
+       * here likely will not make much sense. For this use case,
+       * developers should update the `value` prop themselves
+       * when swapping out the data.
+       */
+      const findPreviousItemIndex = previousItems.findIndex((item) => item.value === value);
+      if (findPreviousItemIndex === -1) {
+        return;
+      }
+
+      /**
+       * Step through the current items backwards
+       * until we find a neighbor we can select.
+       * We start at the last known location of the
+       * current selected item in order to
+       * account for data that has been added. This
+       * search prioritizes stability in that it
+       * tries to keep the scroll position as close
+       * to where it was before the update.
+       * Before Items: ['a', 'b', 'c'], Selected Value: 'b'
+       * After Items:  ['a', 'dog', 'c']
+       * Even though 'dog' is a different item than 'b',
+       * it is the closest item we can select while
+       * preserving the scroll position.
+       */
+      let nearestItem;
+      for (let i = findPreviousItemIndex; i >= 0; i--) {
+        const item = currentItems[i];
+        if (item !== undefined && item.disabled !== true) {
+          nearestItem = item;
+          break;
+        }
+      }
+
+      if (nearestItem) {
+        this.setValue(nearestItem.value);
+        return;
+      }
+    }
+  }
 
   /**
    * The selected option in the picker.

core/src/components/picker-column-internal/test/update-items/picker-column-internal.e2e.ts

@@ -0,0 +1,175 @@
+import { expect } from '@playwright/test';
+import { test } from '@utils/test/playwright';
+
+test.describe('picker-column-internal: updating items', () => {
+  test('should select nearest neighbor when updating items', async ({ page }) => {
+    await page.setContent(`
+      <ion-picker-internal>
+        <ion-picker-column-internal></ion-picker-column-internal>
+      </ion-picker-internal>
+
+      <script>
+        const column = document.querySelector('ion-picker-column-internal');
+        column.items = [
+          { text: '1', value: 1 },
+          { text: '2', value: 2 },
+          { text: '3', value: 3 },
+          { text: '4', value: 4 },
+          { text: '5', value: 5 },
+        ];
+        column.value = 5;
+      </script>
+    `);
+
+    const pickerColumn = page.locator('ion-picker-column-internal');
+    await expect(pickerColumn).toHaveJSProperty('value', 5);
+
+    await pickerColumn.evaluate((el: HTMLIonPickerColumnInternalElement) => {
+      el.items = [
+        { text: '1', value: 1 },
+        { text: '2', value: 2 },
+      ];
+    });
+
+    await page.waitForChanges();
+    await expect(pickerColumn).toHaveJSProperty('value', 2);
+  });
+  test('should select same position item even if item value is different', async ({ page }) => {
+    await page.setContent(`
+      <ion-picker-internal>
+        <ion-picker-column-internal></ion-picker-column-internal>
+      </ion-picker-internal>
+
+      <script>
+        const column = document.querySelector('ion-picker-column-internal');
+        column.items = [
+          { text: '1', value: 1 },
+          { text: '2', value: 2 },
+          { text: '3', value: 3 },
+          { text: '4', value: 4 },
+          { text: '5', value: 5 },
+        ];
+        column.value = 5;
+      </script>
+    `);
+
+    const pickerColumn = page.locator('ion-picker-column-internal');
+    await expect(pickerColumn).toHaveJSProperty('value', 5);
+
+    await pickerColumn.evaluate((el: HTMLIonPickerColumnInternalElement) => {
+      el.items = [
+        { text: '1', value: 1 },
+        { text: '2', value: 2 },
+        { text: '3', value: 3 },
+        { text: '4', value: 4 },
+        { text: '1000', value: 1000 },
+      ];
+    });
+
+    await page.waitForChanges();
+    await expect(pickerColumn).toHaveJSProperty('value', 1000);
+  });
+  test('should not select a disabled item', async ({ page }) => {
+    await page.setContent(`
+      <ion-picker-internal>
+        <ion-picker-column-internal></ion-picker-column-internal>
+      </ion-picker-internal>
+
+      <script>
+        const column = document.querySelector('ion-picker-column-internal');
+        column.items = [
+          { text: '1', value: 1 },
+          { text: '2', value: 2 },
+          { text: '3', value: 3 },
+          { text: '4', value: 4 },
+          { text: '5', value: 5 },
+        ];
+        column.value = 5;
+      </script>
+    `);
+
+    const pickerColumn = page.locator('ion-picker-column-internal');
+    await expect(pickerColumn).toHaveJSProperty('value', 5);
+
+    await pickerColumn.evaluate((el: HTMLIonPickerColumnInternalElement) => {
+      el.items = [
+        { text: '1', value: 1 },
+        { text: '2', value: 2 },
+        { text: '3', value: 3, disabled: true },
+      ];
+    });
+
+    await page.waitForChanges();
+    await expect(pickerColumn).toHaveJSProperty('value', 2);
+  });
+  test('should reset to the first item if no good item was found', async ({ page }) => {
+    await page.setContent(`
+      <ion-picker-internal>
+        <ion-picker-column-internal></ion-picker-column-internal>
+      </ion-picker-internal>
+
+      <script>
+        const column = document.querySelector('ion-picker-column-internal');
+        column.items = [
+          { text: '1', value: 1 },
+          { text: '2', value: 2 },
+          { text: '3', value: 3 },
+          { text: '4', value: 4 },
+          { text: '5', value: 5 },
+        ];
+        column.value = 5;
+      </script>
+    `);
+
+    const pickerColumn = page.locator('ion-picker-column-internal');
+    await expect(pickerColumn).toHaveJSProperty('value', 5);
+
+    await pickerColumn.evaluate((el: HTMLIonPickerColumnInternalElement) => {
+      el.items = [
+        { text: '1', value: 1 },
+        { text: '2', value: 2, disabled: true },
+        { text: '3', value: 3, disabled: true },
+      ];
+    });
+
+    await page.waitForChanges();
+    await expect(pickerColumn).toHaveJSProperty('value', 1);
+  });
+  test('should still select correct value if data was added', async ({ page }) => {
+    await page.setContent(`
+      <ion-picker-internal>
+        <ion-picker-column-internal></ion-picker-column-internal>
+      </ion-picker-internal>
+
+      <script>
+        const column = document.querySelector('ion-picker-column-internal');
+        column.items = [
+          { text: '1', value: 1 },
+          { text: '2', value: 2 },
+          { text: '3', value: 3 },
+          { text: '4', value: 4 },
+          { text: '5', value: 5 },
+        ];
+        column.value = 5;
+      </script>
+    `);
+
+    const pickerColumn = page.locator('ion-picker-column-internal');
+    await expect(pickerColumn).toHaveJSProperty('value', 5);
+
+    await pickerColumn.evaluate((el: HTMLIonPickerColumnInternalElement) => {
+      el.items = [
+        { text: '1', value: 1 },
+        { text: '2', value: 2 },
+        { text: '3', value: 3 },
+        { text: '4', value: 4 },
+        { text: '6', value: 6 },
+        { text: '7', value: 7 },
+        { text: '5', value: 5 },
+      ];
+    });
+
+    await page.waitForChanges();
+    await expect(pickerColumn).toHaveJSProperty('value', 5);
+  });
+});