115046: Fixed performance issues in virtual metadata popup

src/app/item-page/edit-item-page/virtual-metadata/virtual-metadata.component.html

@@ -5,9 +5,9 @@
         </button>
     </div>
     <div class="modal-body">
-        <ng-container *ngFor="let item of items; trackBy: trackItem">
-            <div *ngVar="(isSelectedVirtualMetadataItem(item) | async) as selected"
-                 (click)="setSelectedVirtualMetadataItem(item, !selected)"
+        <ng-container *ngFor="let itemDTO of itemDTOs$ | async; trackBy: trackItemDTO">
+            <div *ngVar="(itemDTO.isSelectedVirtualMetadataItem$ | async) as selected"
+                 (click)="setSelectedVirtualMetadataItem(itemDTO.item, !selected)"
                  class="item d-flex flex-row">
                 <div class="m-2">
                     <label>
@@ -15,9 +15,9 @@
                     </label>
                 </div>
                 <div class="flex-column">
-                    <ds-listable-object-component-loader [object]="item">
+                    <ds-listable-object-component-loader [object]="itemDTO.item">
                     </ds-listable-object-component-loader>
-                    <div *ngFor="let metadata of virtualMetadata.get(item.uuid)">
+                    <div *ngFor="let metadata of virtualMetadata.get(itemDTO.item.uuid)">
                         <div class="font-weight-bold">
                             {{metadata.metadataField}}
                         </div>
@@ -31,7 +31,7 @@
         <div class="d-flex flex-row-reverse m-2">
             <button class="btn btn-primary save"
                     (click)="save.emit()">
-                <i class="fas fa-save"></i> {{"item.edit.metadata.save-button" | translate}}
+                <i aria-hidden="true" class="fas fa-save"></i> {{ 'item.edit.metadata.save-button' | translate }}
             </button>
         </div>
     </div>

src/app/item-page/edit-item-page/virtual-metadata/virtual-metadata.component.spec.ts

@@ -77,6 +77,7 @@ describe('VirtualMetadataComponent', () => {
     comp.url = url;
     comp.leftItem = item;
     comp.rightItem = relatedItem;
+    comp.ngOnChanges();
     comp.relationshipId = relationshipId;
 
     fixture.detectChanges();

src/app/item-page/edit-item-page/virtual-metadata/virtual-metadata.component.ts

@@ -8,11 +8,17 @@ import {
   EventEmitter,
   Inject,
   Input,
+  OnChanges,
+  OnDestroy,
   OnInit,
   Output,
 } from '@angular/core';
 import { TranslateModule } from '@ngx-translate/core';
-import { Observable } from 'rxjs';
+import {
+  BehaviorSubject,
+  Observable,
+  Subscription,
+} from 'rxjs';
 
 import {
   APP_CONFIG,
@@ -21,9 +27,18 @@ import {
 import { ObjectUpdatesService } from '../../../core/data/object-updates/object-updates.service';
 import { Item } from '../../../core/shared/item.model';
 import { MetadataValue } from '../../../core/shared/metadata.models';
+import { hasValue } from '../../../shared/empty.util';
 import { ListableObjectComponentLoaderComponent } from '../../../shared/object-collection/shared/listable-object/listable-object-component-loader.component';
 import { VarDirective } from '../../../shared/utils/var.directive';
 
+interface ItemDTO {
+
+  item: Item;
+
+  isSelectedVirtualMetadataItem$: Observable<boolean>;
+
+}
+
 @Component({
   selector: 'ds-virtual-metadata',
   templateUrl: './virtual-metadata.component.html',
@@ -42,7 +57,7 @@ import { VarDirective } from '../../../shared/utils/var.directive';
  * The component is shown when a relationship is marked to be deleted.
  * Each item has a checkbox to indicate whether its virtual metadata should be saved as real metadata.
  */
-export class VirtualMetadataComponent implements OnInit {
+export class VirtualMetadataComponent implements OnInit, OnChanges, OnDestroy {
 
   /**
    * The current url of this page
@@ -83,9 +98,9 @@ export class VirtualMetadataComponent implements OnInit {
   /**
    * Get an array of the left and the right item of the relationship to be deleted.
    */
-  get items() {
-    return [this.leftItem, this.rightItem];
-  }
+  itemDTOs$: BehaviorSubject<ItemDTO[]> = new BehaviorSubject([]);
+
+  subs: Subscription[] = [];
 
   public virtualMetadata: Map<string, VirtualMetadata[]> = new Map<string, VirtualMetadata[]>();
 
@@ -137,14 +152,33 @@ export class VirtualMetadataComponent implements OnInit {
   /**
    * Prevent unnecessary rerendering so fields don't lose focus
    */
-  trackItem(index, item: Item) {
-    return item && item.uuid;
+  trackItemDTO(index, itemDTO: ItemDTO): string {
+    return itemDTO?.item?.uuid;
   }
 
   ngOnInit(): void {
-    this.items.forEach((item) => {
-      this.virtualMetadata.set(item.uuid, this.getVirtualMetadata(item));
-    });
+    this.subs.push(this.itemDTOs$.subscribe((itemDTOs: ItemDTO[]) => {
+      itemDTOs.forEach((itemDTO: ItemDTO) => this.virtualMetadata.set(itemDTO.item.uuid, this.getVirtualMetadata(itemDTO.item)));
+    }));
+  }
+
+  ngOnChanges(): void {
+    if (hasValue(this.leftItem) && hasValue(this.rightItem)) {
+      this.itemDTOs$.next([
+        {
+          item: this.leftItem,
+          isSelectedVirtualMetadataItem$: this.isSelectedVirtualMetadataItem(this.leftItem),
+        },
+        {
+          item: this.rightItem,
+          isSelectedVirtualMetadataItem$: this.isSelectedVirtualMetadataItem(this.rightItem),
+        },
+      ]);
+    }
+  }
+
+  ngOnDestroy(): void {
+    this.subs.forEach((sub: Subscription) => sub.unsubscribe());
   }
 }