fix(cdk/tree): assorted bug fixes

src/cdk/tree/tree.ts

@@ -23,6 +23,7 @@ import {
 import {
   AfterContentChecked,
   AfterContentInit,
+  AfterViewInit,
   ChangeDetectionStrategy,
   ChangeDetectorRef,
   Component,
@@ -111,7 +112,13 @@ type RenderingData<T> =
   imports: [CdkTreeNodeOutlet],
 })
 export class CdkTree<T, K = T>
-  implements AfterContentChecked, AfterContentInit, CollectionViewer, OnDestroy, OnInit
+  implements
+    AfterContentChecked,
+    AfterContentInit,
+    AfterViewInit,
+    CollectionViewer,
+    OnDestroy,
+    OnInit
 {
   /** Subject that emits when the component has been destroyed. */
   private readonly _onDestroy = new Subject<void>();
@@ -248,6 +255,7 @@ export class CdkTree<T, K = T>
 
   /** The key manager for this tree. Handles focus and activation based on user keyboard input. */
   _keyManager: TreeKeyManagerStrategy<CdkTreeNode<T, K>>;
+  private _viewInit = false;
 
   constructor(
     private _differs: IterableDiffers,
@@ -288,6 +296,10 @@ export class CdkTree<T, K = T>
     this._initializeDataDiffer();
   }
 
+  ngAfterViewInit() {
+    this._viewInit = true;
+  }
+
   private _updateDefaultNodeDefinition() {
     const defaultNodeDefs = this._nodeDefs.filter(def => !def.when);
     if (defaultNodeDefs.length > 1 && (typeof ngDevMode === 'undefined' || ngDevMode)) {
@@ -449,7 +461,9 @@ export class CdkTree<T, K = T>
   }
 
   private _initializeDataDiffer() {
-    this._dataDiffer = this._differs.find([]).create(this.trackBy);
+    // Provide a default trackBy based on `_getExpansionKey` if one isn't provided.
+    const trackBy = this.trackBy ?? ((_index: number, item: T) => this._getExpansionKey(item));
+    this._dataDiffer = this._differs.find([]).create(trackBy);
   }
 
   private _checkTreeControlUsage() {
@@ -484,11 +498,19 @@ export class CdkTree<T, K = T>
     parentData?: T,
   ) {
     const changes = dataDiffer.diff(data);
-    if (!changes) {
+
+    // Some tree consumers expect change detection to propagate to nodes
+    // even when the array itself hasn't changed; we explicitly detect changes
+    // anyways in order for nodes to update their data.
+    //
+    // However, if change detection is called while the component's view is
+    // still initing, then the order of child views initing will be incorrect;
+    // to prevent this, we only exit early if the view hasn't initialized yet.
+    if (!changes && !this._viewInit) {
       return;
     }
 
-    changes.forEachOperation(
+    changes?.forEachOperation(
       (
         item: IterableChangeRecord<T>,
         adjustedPreviousIndex: number | null,
@@ -682,12 +704,12 @@ export class CdkTree<T, K = T>
 
   /** Level accessor, used for compatibility between the old Tree and new Tree */
   _getLevelAccessor() {
-    return this.treeControl?.getLevel ?? this.levelAccessor;
+    return this.treeControl?.getLevel?.bind(this.treeControl) ?? this.levelAccessor;
   }
 
   /** Children accessor, used for compatibility between the old Tree and new Tree */
   _getChildrenAccessor() {
-    return this.treeControl?.getChildren ?? this.childrenAccessor;
+    return this.treeControl?.getChildren?.bind(this.treeControl) ?? this.childrenAccessor;
   }
 
   /**

src/material/tree/testing/node-harness.ts

@@ -35,6 +35,11 @@ export class MatTreeNodeHarness extends ContentContainerComponentHarness<string>
     return coerceBooleanProperty(await (await this.host()).getAttribute('aria-expanded'));
   }
 
+  /** Whether the tree node is expandable. */
+  async isExpandable(): Promise<boolean> {
+    return (await (await this.host()).getAttribute('aria-expanded')) !== null;
+  }
+
   /** Whether the tree node is disabled. */
   async isDisabled(): Promise<boolean> {
     return coerceBooleanProperty(await (await this.host()).getProperty('aria-disabled'));

src/material/tree/tree.spec.ts

@@ -604,11 +604,12 @@ describe('MatTree', () => {
       });
 
       it('ignores clicks on disabled items', () => {
-        underlyingDataSource.data[0].isDisabled = true;
+        underlyingDataSource.data[1].isDisabled = true;
         fixture.detectChanges();
 
         // attempt to click on the first child
         nodes[1].click();
+        fixture.detectChanges();
 
         expect(nodes.map(x => x.getAttribute('tabindex')).join(', ')).toEqual(
           '0, -1, -1, -1, -1, -1',

tools/public_api_guard/cdk/tree.md

@@ -6,6 +6,7 @@
 
 import { AfterContentChecked } from '@angular/core';
 import { AfterContentInit } from '@angular/core';
+import { AfterViewInit } from '@angular/core';
 import { BehaviorSubject } from 'rxjs';
 import { ChangeDetectorRef } from '@angular/core';
 import { CollectionViewer } from '@angular/cdk/collections';
@@ -76,7 +77,7 @@ export class CdkNestedTreeNode<T, K = T> extends CdkTreeNode<T, K> implements Af
 }
 
 // @public
-export class CdkTree<T, K = T> implements AfterContentChecked, AfterContentInit, CollectionViewer, OnDestroy, OnInit {
+export class CdkTree<T, K = T> implements AfterContentChecked, AfterContentInit, AfterViewInit, CollectionViewer, OnDestroy, OnInit {
     constructor(_differs: IterableDiffers, _changeDetectorRef: ChangeDetectorRef, _dir: Directionality);
     childrenAccessor?: (dataNode: T) => T[] | Observable<T[]>;
     collapse(dataNode: T): void;
@@ -106,6 +107,8 @@ export class CdkTree<T, K = T> implements AfterContentChecked, AfterContentInit,
     // (undocumented)
     ngAfterContentInit(): void;
     // (undocumented)
+    ngAfterViewInit(): void;
+    // (undocumented)
     ngOnDestroy(): void;
     // (undocumented)
     ngOnInit(): void;

tools/public_api_guard/material/tree-testing.md

@@ -27,6 +27,7 @@ export class MatTreeNodeHarness extends ContentContainerComponentHarness<string>
     getText(): Promise<string>;
     static hostSelector: string;
     isDisabled(): Promise<boolean>;
+    isExpandable(): Promise<boolean>;
     isExpanded(): Promise<boolean>;
     toggle(): Promise<void>;
     // (undocumented)