refactor(android-tabview): tab adapter data changed event is called too many times (#5364)

tns-core-modules/ui/tab-view/tab-view.android.ts

@@ -414,11 +414,6 @@ export class TabView extends TabViewBase {
         this._viewPager = viewPager;
         this._pagerAdapter = (<any>viewPager).adapter;
         (<any>this._pagerAdapter).owner = this;
-
-        const items = this.items;
-        if (items) {
-            this.setAdapterItems(items)
-        }
     }
 
     public onLoaded(): void {
@@ -434,9 +429,7 @@ export class TabView extends TabViewBase {
     }
 
     public disposeNativeView() {
-        (<any>this._pagerAdapter).items = null;
         this._tabLayout.setItems(null, null);
-        this._pagerAdapter.notifyDataSetChanged();
         (<any>this._pagerAdapter).owner = null;
         this._pagerAdapter = null;
 
@@ -454,7 +447,41 @@ export class TabView extends TabViewBase {
         return false;
     }
 
+    private shouldUpdateAdapter(items: Array<TabViewItemDefinition>) {
+        const currentPagerAdapterItems = (<any>this._pagerAdapter).items;
+
+        // if both values are null, should not update
+        if (!items && !currentPagerAdapterItems) {
+            return false;
+        }
+
+        // if one value is null, should update
+        if (!items || !currentPagerAdapterItems) {
+            return true;
+        }
+
+        // if both are Arrays but length doesn't match, should update
+        if (items.length !== currentPagerAdapterItems.length) {
+            return true;
+        }
+
+        const matchingItems = currentPagerAdapterItems.filter((currentItem) => {
+            return !!items.filter((item) => { 
+                return item._domId === currentItem._domId
+            })[0];
+        });
+
+        // if both are Arrays and length matches, but not all items are the same, should update
+        if (matchingItems.length !== items.length) {
+            return true;
+        }
+
+        // if both are Arrays and length matches and all items are the same, should not update
+        return false;
+    }
+
     private setAdapterItems(items: Array<TabViewItemDefinition>) {
+        if (this.shouldUpdateAdapter(items)) {
             (<any>this._pagerAdapter).items = items;
 
             const length = items ? items.length : 0;
@@ -481,6 +508,7 @@ export class TabView extends TabViewBase {
 
             this._pagerAdapter.notifyDataSetChanged();
         }
+    }
 
     public updateAndroidItemAt(index: number, spec: org.nativescript.widgets.TabItemSpec) {
         this._tabLayout.updateItemAt(index, spec);