feat: eachChildAsync method

Author: farfromrefug

src/collectionview/index.android.ts

@@ -635,6 +635,19 @@ export class CollectionView extends CollectionViewBase {
         }
         return result;
     }
+    private async enumerateViewHoldersAsync<T = any>(cb: (v: CollectionViewCellHolder) => Promise<T>) {
+        let result: T, v: CollectionViewCellHolder;
+        for (let it = this._viewHolders.values(), cellItemView: CollectionViewCellHolder = null; (cellItemView = it.next().value); ) {
+            if (cellItemView['position'] === undefined  ) {
+                continue;
+            }
+            result = await cb(cellItemView);
+            if (result) {
+                return result;
+            }
+        }
+        return result;
+    }
     public startDragging(index: number) {
         if (this.reorderEnabled && this._itemTouchHelper) {
             // let viewHolder: CollectionViewCellHolder;
@@ -906,6 +919,22 @@ export class CollectionView extends CollectionViewBase {
             }
         });
     }
+
+    async eachChildAsync(callback) {
+        return this.enumerateViewHoldersAsync(async (v) => {
+            const view = v.view;
+            if (view) {
+                if (view.parent instanceof CollectionView) {
+                    await callback(view);
+                } else {
+                    // in some cases (like item is unloaded from another place (like angular) view.parent becomes undefined)
+                    if (view.parent) {
+                        await callback(view.parent);
+                    }
+                }
+            }
+        });
+    }
     refreshVisibleItems() {
         const view = this.nativeViewProtected;
         if (!view) {

src/collectionview/index.d.ts

@@ -21,6 +21,7 @@ export class CollectionView extends CollectionViewBase {
     // if you use a drag "handle" just pass the touch event main pointer
     // to delta the dragging to be good
     startDragging(index: number, pointer?: Pointer);
+    async eachChildAsync(callback);
 }
 
 export interface CollectionViewItemEventData extends EventData {

src/collectionview/index.ios.ts

@@ -179,6 +179,23 @@ export class CollectionView extends CollectionViewBase {
             }
         });
     }
+
+    async eachChildAsync(callback) {
+        // used for css updates (like theme change)
+        const children = Object.values(this._map);
+        for (let index = 0; index < children.length; index++) {
+            const view = children[index];
+            if (view.parent instanceof CollectionView) {
+                await callback(view);
+            }
+            else {
+                // in some cases (like item is unloaded from another place (like angular) view.parent becomes undefined)
+                if (view.parent) {
+                    await callback(view.parent);
+                }
+            }
+        }
+    }
     public getViewForItemAtIndex(index: number): View {
         let result: View;
         if (this.nativeViewProtected) {