bug fixed

src/app/sections/group/components/list.section.component.ts

@@ -1,12 +1,21 @@
+import { Observable } from 'rxjs';
+
 import { Component, OnInit, OnDestroy } from '@angular/core';
 
 import { LogService } from '@ucap/ng-logger';
 import {
   VirtualScrollStrategy,
   FixedSizeVirtualScrollStrategy,
-  VIRTUAL_SCROLL_STRATEGY
+  VIRTUAL_SCROLL_STRATEGY,
+  CdkVirtualScrollViewport
 } from '@angular/cdk/scrolling';
 
+export class GroupVirtualScrollStrategy extends FixedSizeVirtualScrollStrategy {
+  constructor() {
+    super(60, 150, 200); // (itemSize, minBufferPx, maxBufferPx)
+  }
+}
+
 @Component({
   selector: 'app-sections-group-list',
   templateUrl: './list.section.component.html',
@@ -14,7 +23,7 @@ import {
   providers: [
     {
       provide: VIRTUAL_SCROLL_STRATEGY,
-      useValue: new FixedSizeVirtualScrollStrategy(60, 3, 3)
+      useClass: GroupVirtualScrollStrategy
     }
   ]
 })

src/app/sections/group/components/list.section.strategy.ts

@@ -0,0 +1,31 @@
+import { Observable, Subject } from 'rxjs';
+
+import {
+  VirtualScrollStrategy,
+  CdkVirtualScrollViewport
+} from '@angular/cdk/scrolling';
+import { distinctUntilChanged } from 'rxjs/operators';
+
+export class GroupVirtualScrollStrategy implements VirtualScrollStrategy {
+  scrolledIndexChange: Observable<number>;
+
+  private indexSubject = new Subject<number>();
+  private viewport: CdkVirtualScrollViewport | null = null;
+
+  constructor() {
+    this.scrolledIndexChange = this.indexSubject.pipe(distinctUntilChanged());
+  }
+
+  attach(viewport: CdkVirtualScrollViewport): void {
+    this.viewport = viewport;
+  }
+  detach(): void {
+    this.indexSubject.complete();
+    this.viewport = null;
+  }
+  onContentScrolled(): void {}
+  onDataLengthChanged(): void {}
+  onContentRendered(): void {}
+  onRenderedOffsetChanged(): void {}
+  scrollToIndex(index: number, behavior: ScrollBehavior): void {}
+}