fix(elements): Do not destroy elements inside tmpl wrapper on detach.

projects/igniteui-angular-elements/src/app/custom-strategy.spec.ts

@@ -1,4 +1,5 @@
 import { IgxColumnComponent, IgxGridComponent, IgxHierarchicalGridComponent } from 'igniteui-angular';
+import { html } from 'lit-html';
 import { firstValueFrom, fromEvent, skip, timer } from 'rxjs';
 import { ComponentRefKey, IgcNgElement } from './custom-strategy';
 import hgridData from '../assets/data/projects-hgrid.js';
@@ -52,6 +53,43 @@ describe('Elements: ', () => {
             const columnComponent = (await columnEl.ngElementStrategy[ComponentRefKey]).instance as IgxColumnComponent;
             expect(gridComponent.columnList.toArray()).toContain(columnComponent);
         });
+
+        it(`should keep IgcNgElement instance in template of another IgcNgElement #15678`, async () => {
+            const gridEl = document.createElement("igc-grid");
+            testContainer.appendChild(gridEl);
+            const columnEl = document.createElement("igc-column") as IgcNgElement;
+            gridEl.appendChild(columnEl);
+            gridEl.primaryKey = 'id';
+            gridEl.data = [{ id: '1' }];
+            (gridEl as any).detailTemplate = (ctx) => {
+                return html`<div>
+                    <igc-grid id="child${ctx.implicit.id}"></igc-grid>
+                </div>`;
+            }
+
+            // TODO: Better way to wait - potentially expose the queue or observable for update on the strategy
+            await firstValueFrom(timer(10 /* SCHEDULE_DELAY */ * 2));
+
+            // sigh (。﹏。*)
+            (gridEl as any).toggleRow('1');
+            await firstValueFrom(timer(10 /* SCHEDULE_DELAY */ * 2));
+
+            let detailGrid = document.querySelector<IgcNgElement>('#child1');
+            expect(detailGrid).toBeDefined();
+            let detailGridComponent = (await detailGrid?.ngElementStrategy[ComponentRefKey])?.instance as IgxGridComponent;
+            expect(detailGridComponent).toBeDefined();
+
+            // close and re-expand row detail:
+            (gridEl as any).toggleRow('1');
+            await firstValueFrom(timer(10 /* SCHEDULE_DELAY */ * 2));
+            (gridEl as any).toggleRow('1');
+            await firstValueFrom(timer(10 /* SCHEDULE_DELAY */ * 2));
+
+            detailGrid = document.querySelector<IgcNgElement>('#child1');
+            expect(detailGrid).toBeDefined();
+            detailGridComponent = (await detailGrid?.ngElementStrategy[ComponentRefKey])?.instance as IgxGridComponent;
+            expect(detailGridComponent).toBeDefined("Detail child grid was destroyed on re-expand");
+        });
     });
 
     describe('Grid integration scenarios.', () => {

projects/igniteui-angular-elements/src/app/custom-strategy.ts

@@ -1,4 +1,5 @@
-import { ApplicationRef, ChangeDetectorRef, ComponentFactory, ComponentRef, Injector, OnChanges, QueryList, Type, ViewContainerRef, reflectComponentType } from '@angular/core';
+import { ApplicationRef, ChangeDetectorRef, ComponentFactory, ComponentRef, DestroyRef, Injector, OnChanges, QueryList, Type, ViewContainerRef, reflectComponentType } from '@angular/core';
+import { takeUntilDestroyed } from '@angular/core/rxjs-interop';
 import { NgElement } from '@angular/elements';
 import { fromEvent } from 'rxjs';
 import { takeUntil } from 'rxjs/operators';
@@ -48,6 +49,14 @@ class IgxCustomNgElementStrategy extends ComponentNgElementStrategy {
         return this._templateWrapper;
     }
 
+    private _configSelectors: string;
+    public get configSelectors(): string {
+        if (!this._configSelectors) {
+            this._configSelectors = this.config.map(x => x.selector).join(',');
+        }
+        return this._configSelectors;
+    }
+
     constructor(private _componentFactory: ComponentFactory<any>, private _injector: Injector, private config: ComponentConfig[]) {
         super(_componentFactory, _injector);
     }
@@ -233,6 +242,14 @@ class IgxCustomNgElementStrategy extends ComponentNgElementStrategy {
             }
             value = this.templateWrapper.addTemplate(value);
             // TODO: discard oldValue
+
+            // check template for any angular-element components
+            this.templateWrapper.templateRendered.pipe(takeUntilDestroyed(componentRef.injector.get(DestroyRef))).subscribe((element) => {
+                element.querySelectorAll<IgcNgElement>(this.configSelectors)?.forEach((c) => {
+                    // tie to angularParent lifecycle for cached scenarios like detailTemplate:
+                    c.ngElementStrategy.angularParent = componentRef;
+                });
+            });
         }
         if (componentRef && componentConfig?.boolProps?.includes(property)) {
             // bool coerce:

projects/igniteui-angular-elements/src/app/wrapper/wrapper.component.ts

@@ -1,4 +1,5 @@
 import { ChangeDetectorRef, Component, QueryList, TemplateRef, ViewChildren } from '@angular/core';
+import { Subject } from 'rxjs';
 import { TemplateRefWrapper } from './template-ref-wrapper';
 
 import { render, TemplateResult } from 'lit-html';
@@ -14,6 +15,7 @@ type TemplateFunction = (arg: any) => TemplateResult;
 export class TemplateWrapperComponent {
 
     public templateFunctions: TemplateFunction[] = [];
+    public templateRendered = new Subject<HTMLElement>();
 
     /**
      * All template refs
@@ -27,6 +29,7 @@ export class TemplateWrapperComponent {
 
     public litRender(container: HTMLElement, templateFunc: (arg: any) => TemplateResult, arg: any) {
         render(templateFunc(arg), container);
+        this.templateRendered.next(container);
     }
 
     public addTemplate(templateFunc: TemplateFunction): TemplateRef<any> {

projects/igniteui-angular-elements/src/index.html

@@ -195,7 +195,11 @@ <h3 class="ig-typography__h6">Flat Grid (MRL column layout)</h3>
             <igc-combo ${ref(focusCallback)} style="width:100%; height:100%" .data=${northwindProducts} value-key="ProductName" @igcChange=${(e) => ctx.cell.editValue = e.detail.newValue} single-select>
             </igc-combo>
         `;
-        grid1.detailTemplate = (ctx) => html`<div><span class="categoryStyle">Stock: ${ctx.implicit.InStock}</span></div>`;
+        grid1.detailTemplate = (ctx) => {
+            return html`<div>
+            <igc-grid auto-generate="true"></igc-grid>
+        </div>`;
+        }
 
         grid2.querySelector('igc-column[field="ProductName"]').inlineEditorTemplate = (ctx) =>
             html`