chore(*): Change detect on runtime strategy change.

Author: MKirova

projects/igniteui-angular/src/lib/grids/grid-base.directive.ts

@@ -2510,6 +2510,9 @@ export abstract class IgxGridBaseDirective implements GridType,
     }
     public set  mergeStrategy(value) {
         this._mergeStrategy = value;
+        if (!this._init) {
+            this.cdr.detectChanges();
+        }
     }
 
     /**

src/app/grid-cellMerging/grid-cellMerging.component.html

@@ -111,7 +111,7 @@ <h4 class="sample-title">Hierarchical grid with cell merge</h4>
 </igx-hierarchical-grid>
 
 <h4 class="sample-title">Tree grid with cell merge</h4>
-
+<button (click)="toggleStrategy()">Toggle strategy</button>
 <igx-tree-grid [autoGenerate]="false" [rowSelection]="'single'" [data]="treeData" [cellMergeMode]="'always'" [mergeStrategy]="treeGridMergeStrategy"
 childDataKey="ChildCompanies" primaryKey="ID" [expansionDepth]="1" width="800px" [height]="'550px'">
 <igx-column field="ContactName" width="200px">

src/app/grid-cellMerging/grid-cellMerging.component.ts

@@ -1,6 +1,7 @@
 import { Component, HostBinding, ViewChild } from '@angular/core';
 import { FormsModule } from '@angular/forms';
 import {
+    DefaultTreeGridMergeStrategy,
     IgxActionStripComponent,
     IgxButtonDirective,
     IgxCellTemplateDirective,
@@ -65,6 +66,14 @@ export class GridCellMergingComponent {
     @ViewChild('grid1', { static: true }) public grid: IgxGridComponent;
     public data = INVOICE_DATA;
 
+    public toggleStrategy() {
+        if (this.treeGridMergeStrategy instanceof ByLevelTreeGridMergeStrategy) {
+            this.treeGridMergeStrategy = new DefaultTreeGridMergeStrategy();
+        } else {
+            this.treeGridMergeStrategy = new ByLevelTreeGridMergeStrategy();
+        }
+    }
+
     public searchKeyDown(ev) {
         if (ev.key === 'Enter' || ev.key === 'ArrowDown' || ev.key === 'ArrowRight') {
             ev.preventDefault();