feat: new findFirstVisibleItemIndex method

Author: farfromrefug

src/collectionview/index-common.ts

@@ -179,6 +179,7 @@ export abstract class CollectionViewBase extends View implements CollectionViewD
     public abstract eachChildAsync(callback);
     public abstract refreshVisibleItems();
     public abstract isItemAtIndexVisible(index: number);
+    public abstract findFirstVisibleItemIndex(): number;
     public abstract scrollToIndex(index: number, animated: boolean);
     public abstract scrollToOffset(value: number, animated?: boolean): any;
 

src/collectionview/index.android.ts

@@ -968,6 +968,17 @@ export class CollectionView extends CollectionViewBase {
         }
         return false;
     }
+    public findFirstVisibleItemIndex() {
+        const view = this.nativeViewProtected;
+        if (!view) {
+            return -1;
+        }
+        const layoutManager = this.layoutManager as androidx.recyclerview.widget.LinearLayoutManager;
+        if (layoutManager['findFirstVisibleItemPosition']) {
+            return layoutManager.findFirstVisibleItemPosition();
+        }
+        return -1;
+    }
 
     _layedOut = false;
     @profile

src/collectionview/index.ios.ts

@@ -666,7 +666,13 @@ export class CollectionView extends CollectionViewBase {
 
         return indexes.some((visIndex) => visIndex.row === itemIndex);
     }
-
+    public findFirstVisibleItemIndex() {
+        const view = this.nativeViewProtected;
+        if (!view) {
+            return -1;
+        }
+        return view.indexPathsForVisibleItems?.objectAtIndex(0)?.row ?? -1;
+    }
     @profile
     public refresh() {
         if (!this.isLoaded || !this.nativeView) {