fix(cdk/tree): expandAll not expanding all nodes

src/cdk/tree/tree.spec.ts

@@ -1481,6 +1481,32 @@ describe('CdkTree', () => {
       .withContext(`expect an expanded node`)
       .toBe(1);
   });
+
+  it('should expand/collapse all nested nodes when calling expandAll/collapseAll', () => {
+    configureCdkTreeTestingModule([IsExpandableOrderingTest]);
+    const fixture = TestBed.createComponent(IsExpandableOrderingTest);
+    const component = fixture.componentInstance;
+    const data = fixture.componentInstance.dataSource;
+    treeElement = fixture.nativeElement.querySelector('cdk-tree');
+
+    data[0].children[0].children.push(new MinimalTestData('extra'));
+    data[0].children[0].children[0].children.push(new MinimalTestData('extra'));
+    fixture.detectChanges();
+
+    component.tree.expandAll();
+    fixture.detectChanges();
+    expect(getNodes(treeElement).map(n => n.getAttribute('aria-expanded'))).toEqual([
+      'true',
+      'true',
+      'true',
+      'true',
+    ]);
+
+    component.tree.collapseAll();
+    fixture.detectChanges();
+
+    expect(getNodes(treeElement).map(n => n.getAttribute('aria-expanded'))).toEqual(['false']);
+  });
 });
 
 export class TestData {
@@ -1698,10 +1724,6 @@ class SimpleCdkTreeApp {
 
   @ViewChild(CdkTree) tree: CdkTree<TestData>;
   @ViewChildren(CdkTreeNodePadding) paddingNodes: QueryList<CdkTreeNodePadding<TestData>>;
-
-  expandAll() {
-    this.tree.expandAll();
-  }
 }
 
 @Component({

src/cdk/tree/tree.ts

@@ -716,10 +716,7 @@ export class CdkTree<T, K = T>
     if (this.treeControl) {
       this.treeControl.expandAll();
     } else if (this._expansionModel) {
-      const expansionModel = this._expansionModel;
-      expansionModel.select(
-        ...this._flattenedNodes.value.map(child => this._getExpansionKey(child)),
-      );
+      this._forEachExpansionKey(keys => this._expansionModel?.select(...keys));
     }
   }
 
@@ -728,10 +725,7 @@ export class CdkTree<T, K = T>
     if (this.treeControl) {
       this.treeControl.collapseAll();
     } else if (this._expansionModel) {
-      const expansionModel = this._expansionModel;
-      expansionModel.deselect(
-        ...this._flattenedNodes.value.map(child => this._getExpansionKey(child)),
-      );
+      this._forEachExpansionKey(keys => this._expansionModel?.deselect(...keys));
     }
   }
 
@@ -776,13 +770,7 @@ export class CdkTree<T, K = T>
           if (!expanded) {
             return [];
           }
-          return this._findChildrenByLevel(
-            levelAccessor,
-            flattenedNodes,
-
-            dataNode,
-            1,
-          );
+          return this._findChildrenByLevel(levelAccessor, flattenedNodes, dataNode, 1);
         }),
       );
     }
@@ -1153,6 +1141,28 @@ export class CdkTree<T, K = T>
       this._ariaSets.set(parentKey, group);
     }
   }
+
+  /** Invokes a callback with all node expansion keys. */
+  private _forEachExpansionKey(callback: (keys: K[]) => void) {
+    const toToggle: K[] = [];
+    const observables: Observable<T[]>[] = [];
+
+    this._nodes.value.forEach(node => {
+      toToggle.push(this._getExpansionKey(node.data));
+      observables.push(this._getDescendants(node.data));
+    });
+
+    if (observables.length > 0) {
+      combineLatest(observables)
+        .pipe(take(1), takeUntil(this._onDestroy))
+        .subscribe(results => {
+          results.forEach(inner => inner.forEach(r => toToggle.push(this._getExpansionKey(r))));
+          callback(toToggle);
+        });
+    } else {
+      callback(toToggle);
+    }
+  }
 }
 
 /**