fix(ios): listview scrollToIndex crash with async data (#6182)

manoldonev · vakrilov · commit ca6cccb211a4 · 2018-09-11T14:27:14.000+03:00
diff --git a/tests/app/ui/list-view/list-view-tests.ts b/tests/app/ui/list-view/list-view-tests.ts
@@ -759,6 +759,33 @@ export class ListViewTest extends UITest<ListView> {
         TKUnit.assertEqual(lastNativeElementVisible, false, "Last element is not visible");
     }
 
+    public test_scrollToIndex_should_coerce_negative_index_to_zero_index() {
+        var listView = this.testView;
+
+        listView.items = MANY_ITEMS;
+        listView.scrollToIndex(-1);
+        TKUnit.wait(0.1);
+
+        var firstNativeElementVisible = this.checkItemVisibleAtIndex(listView, 0);
+        TKUnit.assertEqual(firstNativeElementVisible, true, "first element is visible");        
+    }
+
+    public test_scrollToIndex_should_coerce_larger_index_to_last_item_index() {
+        var listView = this.testView;
+
+        listView.items = MANY_ITEMS;
+        listView.scrollToIndex(10000);
+        TKUnit.wait(0.1);
+
+        var lastNativeElementVisible = this.checkItemVisibleAtIndex(listView, MANY_ITEMS.length - 1);
+        TKUnit.assertEqual(lastNativeElementVisible, true, "last element is visible");        
+    }
+
+    public test_scrollToIndex_should_not_throw_if_items_not_set() {
+        var listView = this.testView;
+        listView.scrollToIndex(10000);
+    }
+
     private checkItemVisibleAtIndex(listView: ListView, index: number): boolean {
         return listView.isItemAtIndexVisible(index);
     }
diff --git a/tns-core-modules/ui/list-view/list-view.ios.ts b/tns-core-modules/ui/list-view/list-view.ios.ts
@@ -1,11 +1,12 @@
-﻿import { ItemEventData } from ".";
+import { ItemEventData } from ".";
 import {
     ListViewBase, View, KeyedTemplate, Length, Observable, Color,
     separatorColorProperty, itemTemplatesProperty, iosEstimatedRowHeightProperty, layout, EventData
 } from "./list-view-common";
 import { StackLayout } from "../layouts/stack-layout";
 import { ProxyViewContainer } from "../proxy-view-container";
 import { profile } from "../../profiling";
+import * as trace from "../../trace";
 
 export * from "./list-view-common";
 
@@ -261,16 +262,31 @@ export class ListView extends ListViewBase {
     }
 
     public scrollToIndex(index: number) {
-        if (this._ios) {
-            this._ios.scrollToRowAtIndexPathAtScrollPositionAnimated(NSIndexPath.indexPathForItemInSection(index, 0),
-                UITableViewScrollPosition.Top, false);
-        }
+        this._scrollToIndex(index, false);
     }
 
     public scrollToIndexAnimated(index: number) {
-        if (this._ios) {
+        this._scrollToIndex(index);
+    }
+
+    private _scrollToIndex(index: number, animated: boolean = true) {
+        if (!this._ios) {
+            return;
+        }
+
+        const itemsLength = this.items ? this.items.length : 0;
+        // mimic Android behavior that silently coerces index values within [0, itemsLength - 1] range
+        if (itemsLength > 0) {
+            if (index < 0) {
+                index = 0
+            } else if (index >= itemsLength) {
+                index = itemsLength - 1;
+            }
+
             this._ios.scrollToRowAtIndexPathAtScrollPositionAnimated(NSIndexPath.indexPathForItemInSection(index, 0),
-                UITableViewScrollPosition.Top, true);
+                UITableViewScrollPosition.Top, animated);
+        } else if (trace.isEnabled()) {
+            trace.write(`Cannot scroll listview to index ${index} when listview items not set`, trace.categories.Binding);
         }
     }
 
