fix(tree): fix nested node cannot expand/collapse multiple times (#10671)

Author: tinayuangao

src/cdk/tree/nested-node.ts

@@ -93,13 +93,17 @@ export class CdkNestedTreeNode<T> extends CdkTreeNode<T> implements AfterContent
     if (this.nodeOutlet.length && this._children) {
       const viewContainer = this.nodeOutlet.first.viewContainer;
       this._tree.renderNodeChanges(this._children, this._dataDiffer, viewContainer);
+    } else {
+      // Reset the data differ if there's no children nodes displayed
+      this._dataDiffer.diff([]);
     }
   }
 
   /** Clear the children dataNodes. */
   protected _clear(): void {
     if (this.nodeOutlet && this.nodeOutlet.first) {
       this.nodeOutlet.first.viewContainer.clear();
+      this._dataDiffer.diff([]);
     }
   }
 }

src/cdk/tree/tree.spec.ts

@@ -442,7 +442,7 @@ describe('CdkTree', () => {
         fixture.detectChanges();
       });
 
-      it('should expand/collapse the node', () => {
+      it('should expand/collapse the node multiple times', () => {
         component.toggleRecursively = false;
         let data = dataSource.data;
         const child = dataSource.addChild(data[1], false);
@@ -477,6 +477,17 @@ describe('CdkTree', () => {
           [`topping_3 - cheese_3 + base_3`]);
         expect(component.treeControl.expansionModel.selected.length)
           .toBe(0, `Expect node collapsed`);
+
+        (getNodes(treeElement)[1] as HTMLElement).click();
+        fixture.detectChanges();
+
+        expect(component.treeControl.expansionModel.selected.length)
+          .toBe(1, `Expect node expanded`);
+        expectNestedTreeToMatch(treeElement,
+          [`topping_1 - cheese_1 + base_1`],
+          [`topping_2 - cheese_2 + base_2`],
+          [_, `topping_4 - cheese_4 + base_4`],
+          [`topping_3 - cheese_3 + base_3`]);
       });
 
       it('should expand/collapse the node recursively', () => {