Communication: Fix conversations not keeping scroll position when opened

src/main/webapp/app/communication/course-conversations-components/layout/conversation-messages/conversation-messages.component.spec.ts

@@ -64,6 +64,14 @@ examples.forEach((activeConversation) => {
         let examplePost: Post;
         const course = { id: 1 } as Course;
 
+        beforeAll(() => {
+            (window as any).ResizeObserver = class {
+                observe() {}
+                unobserve() {}
+                disconnect() {}
+            };
+        });
+
         beforeEach(waitForAsync(() => {
             TestBed.configureTestingModule({
                 imports: [FormsModule, ReactiveFormsModule, FaIconComponent],

src/main/webapp/app/communication/course-conversations-components/layout/conversation-messages/conversation-messages.component.ts

@@ -245,6 +245,18 @@ export class ConversationMessagesComponent implements OnInit, AfterViewInit, OnD
             childList: true,
             subtree: true,
         });
+
+        const resizeObserver = new ResizeObserver((event, observer) => {
+            const entry = event.first();
+            if (entry && entry.contentRect.height) {
+                // Stop observing as soon as height is non-zero
+                observer.unobserve(el);
+            }
+            if (!this.createdNewMessage && this.posts.length > 0) {
+                this.scrollToStoredId();
+            }
+        });
+        resizeObserver.observe(el);
     }
 
     ngOnDestroy(): void {
@@ -264,6 +276,8 @@ export class ConversationMessagesComponent implements OnInit, AfterViewInit, OnD
         }
         if (savedScrollId) {
             requestAnimationFrame(() => this.goToLastSelectedElement(savedScrollId, this.isOpenThreadOnFocus));
+        } else {
+            this.scrollToBottomOfMessages();
         }
     }