Create recomputeViewableItems method

CHANGELOG.md

@@ -7,6 +7,9 @@ and adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+- Add recomputeViewableItems method
+  - https://github.com/Shopify/flash-list/pull/1296
+
 ## [1.7.0] - 2024-07-03
 
 - Update internal dependency and fixture app to `react-native@0.72`.

documentation/docs/fundamentals/usage.md

@@ -549,6 +549,14 @@ recordInteraction();
 
 Tells the list an interaction has occurred, which should trigger viewability calculations, e.g. if `waitForInteractions` is true and the user has not scrolled. You should typically call `recordInteraction()` when user for example taps on an item or invokes a navigation action.
 
+### `recomputeViewableItems()`
+
+```tsx
+recomputeViewableItems();
+```
+
+Retriggers viewability calculations. Useful to imperatively trigger viewability calculations.
+
 ### `scrollToEnd()`
 
 ```tsx

src/FlashList.tsx

@@ -870,6 +870,13 @@ class FlashList<T> extends React.PureComponent<
   public recordInteraction = () => {
     this.viewabilityManager.recordInteraction();
   };
+
+  /**
+   * Retriggers viewability calculations. Useful to imperatively trigger viewability calculations.
+   */
+  public recomputeViewableItems = () => {
+    this.viewabilityManager.recomputeViewableItems();
+  };
 }
 
 export default FlashList;

src/viewability/ViewabilityHelper.ts

@@ -118,6 +118,10 @@ class ViewabilityHelper {
     }
   }
 
+  public clearLastReportedViewableIndices() {
+    this.lastReportedViewableIndices = [];
+  }
+
   private isItemViewable(
     index: number,
     horizontal: boolean,

src/viewability/ViewabilityManager.ts

@@ -88,6 +88,14 @@ export default class ViewabilityManager<T> {
     });
   };
 
+  public recomputeViewableItems = () => {
+    this.viewabilityHelpers.forEach((viewabilityHelper) =>
+      viewabilityHelper.clearLastReportedViewableIndices()
+    );
+
+    this.updateViewableItems();
+  };
+
   /**
    * Creates a new `ViewabilityHelper` instance with `onViewableItemsChanged` callback and `ViewabilityConfig`
    * @returns `ViewabilityHelper` instance