feat(tree): support array of data as children in nested tree

src/cdk/tree/control/base-tree-control.ts

@@ -34,7 +34,7 @@ export abstract class BaseTreeControl<T> implements TreeControl<T> {
   isExpandable: (dataNode: T) => boolean;
 
   /** Gets a stream that emits whenever the given data node's children change. */
-  getChildren: (dataNode: T) => Observable<T[]>;
+  getChildren: (dataNode: T) => (Observable<T[]> | T[]);
 
   /** Toggles one single data node's expanded/collapsed state. */
   toggle(dataNode: T): void {

src/cdk/tree/control/nested-tree-control.spec.ts

@@ -91,6 +91,95 @@ describe('CdkNestedTreeControl', () => {
       expect(treeControl.expansionModel.selected.length)
         .toBe(totalNumber, `Expect ${totalNumber} expanded nodes`);
     });
+
+    describe('with children array', () => {
+      let getStaticChildren = (node: TestData) => node.children;
+
+      beforeEach(() => {
+        treeControl = new NestedTreeControl<TestData>(getStaticChildren);
+      });
+
+      it('should be able to expand and collapse dataNodes', () => {
+        const nodes = generateData(10, 4);
+        const node = nodes[1];
+        const sixthNode = nodes[5];
+        treeControl.dataNodes = nodes;
+
+        treeControl.expand(node);
+
+
+        expect(treeControl.isExpanded(node)).toBeTruthy('Expect second node to be expanded');
+        expect(treeControl.expansionModel.selected)
+          .toContain(node, 'Expect second node in expansionModel');
+        expect(treeControl.expansionModel.selected.length)
+          .toBe(1, 'Expect only second node in expansionModel');
+
+        treeControl.toggle(sixthNode);
+
+        expect(treeControl.isExpanded(node)).toBeTruthy('Expect second node to stay expanded');
+        expect(treeControl.expansionModel.selected)
+          .toContain(sixthNode, 'Expect sixth node in expansionModel');
+        expect(treeControl.expansionModel.selected)
+          .toContain(node, 'Expect second node in expansionModel');
+        expect(treeControl.expansionModel.selected.length)
+          .toBe(2, 'Expect two dataNodes in expansionModel');
+
+        treeControl.collapse(node);
+
+        expect(treeControl.isExpanded(node)).toBeFalsy('Expect second node to be collapsed');
+        expect(treeControl.expansionModel.selected.length)
+          .toBe(1, 'Expect one node in expansionModel');
+        expect(treeControl.isExpanded(sixthNode)).toBeTruthy('Expect sixth node to stay expanded');
+        expect(treeControl.expansionModel.selected)
+          .toContain(sixthNode, 'Expect sixth node in expansionModel');
+      });
+
+      it('should toggle descendants correctly', () => {
+        const numNodes = 10;
+        const numChildren = 4;
+        const numGrandChildren = 2;
+        const nodes = generateData(numNodes, numChildren, numGrandChildren);
+        treeControl.dataNodes = nodes;
+
+        treeControl.expandDescendants(nodes[1]);
+
+        const expandedNodesNum = 1 + numChildren + numChildren * numGrandChildren;
+        expect(treeControl.expansionModel.selected.length)
+          .toBe(expandedNodesNum, `Expect expanded ${expandedNodesNum} nodes`);
+
+        expect(treeControl.isExpanded(nodes[1])).toBeTruthy('Expect second node to be expanded');
+        for (let i = 0; i < numChildren; i++) {
+
+          expect(treeControl.isExpanded(nodes[1].children[i]))
+            .toBeTruthy(`Expect second node's children to be expanded`);
+          for (let j = 0; j < numGrandChildren; j++) {
+            expect(treeControl.isExpanded(nodes[1].children[i].children[j]))
+              .toBeTruthy(`Expect second node grand children to be expanded`);
+          }
+        }
+      });
+
+      it('should be able to expand/collapse all the dataNodes', () => {
+        const numNodes = 10;
+        const numChildren = 4;
+        const numGrandChildren = 2;
+        const nodes = generateData(numNodes, numChildren, numGrandChildren);
+        treeControl.dataNodes = nodes;
+
+        treeControl.expandDescendants(nodes[1]);
+
+        treeControl.collapseAll();
+
+        expect(treeControl.expansionModel.selected.length).toBe(0, `Expect no expanded nodes`);
+
+        treeControl.expandAll();
+
+        const totalNumber = numNodes + (numNodes * numChildren)
+          + (numNodes * numChildren * numGrandChildren);
+        expect(treeControl.expansionModel.selected.length)
+          .toBe(totalNumber, `Expect ${totalNumber} expanded nodes`);
+      });
+    });
   });
 });
 

src/cdk/tree/control/nested-tree-control.ts

@@ -13,7 +13,7 @@ import {BaseTreeControl} from './base-tree-control';
 export class NestedTreeControl<T> extends BaseTreeControl<T> {
 
   /** Construct with nested tree function getChildren. */
-  constructor(public getChildren: (dataNode: T) => Observable<T[]>) {
+  constructor(public getChildren: (dataNode: T) => (Observable<T[]> | T[])) {
     super();
   }
 
@@ -41,10 +41,13 @@ export class NestedTreeControl<T> extends BaseTreeControl<T> {
   /** A helper function to get descendants recursively. */
   protected _getDescendants(descendants: T[], dataNode: T): void {
     descendants.push(dataNode);
-    this.getChildren(dataNode).pipe(take(1)).subscribe(children => {
-      if (children && children.length > 0) {
+    const childrenNodes = this.getChildren(dataNode);
+    if (Array.isArray(childrenNodes)) {
+      childrenNodes.forEach((child: T) => this._getDescendants(descendants, child));
+    } else if (childrenNodes instanceof Observable) {
+      childrenNodes.pipe(take(1)).subscribe(children => {
         children.forEach((child: T) => this._getDescendants(descendants, child));
-      }
-    });
+      });
+    }
   }
 }

src/cdk/tree/control/tree-control.ts

@@ -60,5 +60,5 @@ export interface TreeControl<T> {
   readonly isExpandable: (dataNode: T) => boolean;
 
   /** Gets a stream that emits whenever the given data node's children change. */
-  readonly getChildren: (dataNode: T) => Observable<T[]>;
+  readonly getChildren: (dataNode: T) => Observable<T[]> | T[];
 }

src/cdk/tree/nested-node.ts

@@ -15,6 +15,7 @@ import {
   OnDestroy,
   QueryList,
 } from '@angular/core';
+import {Observable} from 'rxjs';
 import {takeUntil} from 'rxjs/operators';
 
 import {CdkTree, CdkTreeNode} from './tree';
@@ -73,11 +74,13 @@ export class CdkNestedTreeNode<T> extends CdkTreeNode<T> implements AfterContent
     if (!this._tree.treeControl.getChildren) {
       throw getTreeControlFunctionsMissingError();
     }
-    this._tree.treeControl.getChildren(this.data).pipe(takeUntil(this._destroyed))
-        .subscribe(result => {
-          this._children = result;
-          this.updateChildrenNodes();
-        });
+    const childrenNodes = this._tree.treeControl.getChildren(this.data);
+    if (Array.isArray(childrenNodes)) {
+      this.updateChildrenNodes(childrenNodes as T[]);
+    } else if (childrenNodes instanceof Observable) {
+      childrenNodes.pipe(takeUntil(this._destroyed))
+        .subscribe(result => this.updateChildrenNodes(result));
+    }
     this.nodeOutlet.changes.pipe(takeUntil(this._destroyed))
         .subscribe(() => this.updateChildrenNodes());
   }
@@ -88,7 +91,10 @@ export class CdkNestedTreeNode<T> extends CdkTreeNode<T> implements AfterContent
   }
 
   /** Add children dataNodes to the NodeOutlet */
-  protected updateChildrenNodes(): void {
+  protected updateChildrenNodes(children?: T[]): void {
+    if (children) {
+      this._children = children;
+    }
     if (this.nodeOutlet.length && this._children) {
       const viewContainer = this.nodeOutlet.first.viewContainer;
       this._tree.renderNodeChanges(this._children, this._dataDiffer, viewContainer, this._data);

src/cdk/tree/tree.spec.ts

@@ -478,6 +478,33 @@ describe('CdkTree', () => {
       });
     });
 
+    describe('with static children', () => {
+      let fixture: ComponentFixture<StaticNestedCdkTreeApp>;
+      let component: StaticNestedCdkTreeApp;
+
+      beforeEach(() => {
+      configureCdkTreeTestingModule([StaticNestedCdkTreeApp]);
+      fixture = TestBed.createComponent(StaticNestedCdkTreeApp);
+
+      component = fixture.componentInstance;
+      dataSource = component.dataSource as FakeDataSource;
+      tree = component.tree;
+      treeElement = fixture.nativeElement.querySelector('cdk-tree');
+
+      fixture.detectChanges();
+    });
+
+    it('with the right data', () => {
+      expectNestedTreeToMatch(treeElement,
+        [`topping_1 - cheese_1 + base_1`],
+        [`topping_2 - cheese_2 + base_2`],
+        [_, `topping_4 - cheese_4 + base_4`],
+        [_, _, `topping_5 - cheese_5 + base_5`],
+        [_, _, `topping_6 - cheese_6 + base_6`],
+        [`topping_3 - cheese_3 + base_3`]);
+    });
+  });
+
     describe('with when node', () => {
       let fixture: ComponentFixture<WhenNodeNestedCdkTreeApp>;
       let component: WhenNodeNestedCdkTreeApp;
@@ -1073,6 +1100,36 @@ class NestedCdkTreeApp {
   @ViewChild(CdkTree) tree: CdkTree<TestData>;
 }
 
+@Component({
+  template: `
+    <cdk-tree [dataSource]="dataSource" [treeControl]="treeControl">
+      <cdk-nested-tree-node *cdkTreeNodeDef="let node" class="customNodeClass">
+                     {{node.pizzaTopping}} - {{node.pizzaCheese}} + {{node.pizzaBase}}
+         <ng-template cdkTreeNodeOutlet></ng-template>
+      </cdk-nested-tree-node>
+    </cdk-tree>
+  `
+})
+class StaticNestedCdkTreeApp {
+  getChildren = (node: TestData) => node.children;
+
+  treeControl: TreeControl<TestData> = new NestedTreeControl(this.getChildren);
+
+  dataSource: FakeDataSource;
+
+  @ViewChild(CdkTree) tree: CdkTree<TestData>;
+
+  constructor() {
+    const dataSource = new FakeDataSource(this.treeControl);
+    const data = dataSource.data;
+    const child = dataSource.addChild(data[1], false);
+    dataSource.addChild(child, false);
+    dataSource.addChild(child, false);
+
+    this.dataSource = dataSource;
+  }
+}
+
 @Component({
   template: `
     <cdk-tree [dataSource]="dataSource" [treeControl]="treeControl">

src/cdk/tree/tree.ts

@@ -40,7 +40,6 @@ import {
   getTreeNoValidDataSourceError
 } from './tree-errors';
 
-
 /**
  * CDK tree component that connects with a data source to retrieve data of type `T` and renders
  * dataNodes with hierarchy. Updates the dataNodes when new data is provided by the data source.
@@ -338,17 +337,24 @@ export class CdkTreeNode<T>  implements FocusableOption, OnDestroy {
     this._elementRef.nativeElement.focus();
   }
 
-  private _setRoleFromData(): void {
+  protected _setRoleFromData(): void {
     if (this._tree.treeControl.isExpandable) {
       this.role = this._tree.treeControl.isExpandable(this._data) ? 'group' : 'treeitem';
     } else {
       if (!this._tree.treeControl.getChildren) {
         throw getTreeControlFunctionsMissingError();
       }
-      this._tree.treeControl.getChildren(this._data).pipe(takeUntil(this._destroyed))
-        .subscribe(children => {
-          this.role = children && children.length ? 'group' : 'treeitem';
-        });
+      const childrenNodes = this._tree.treeControl.getChildren(this._data);
+      if (Array.isArray(childrenNodes)) {
+        this._setRoleFromChildren(childrenNodes as T[]);
+      } else if (childrenNodes instanceof Observable) {
+        childrenNodes.pipe(takeUntil(this._destroyed))
+            .subscribe(children => this._setRoleFromChildren(children));
+      }
     }
   }
+
+  protected _setRoleFromChildren(children: T[]) {
+    this.role = children && children.length ? 'group' : 'treeitem';
+  }
 }

src/demo-app/tree/tree-demo.ts

@@ -13,7 +13,6 @@ import {
   MatTreeFlattener,
   MatTreeNestedDataSource
 } from '@angular/material/tree';
-import {Observable, of as ofObservable} from 'rxjs';
 import {FileDatabase, FileFlatNode, FileNode} from './file-database';
 
 
@@ -69,7 +68,7 @@ export class TreeDemo {
 
   isExpandable = (node: FileFlatNode) => { return node.expandable; };
 
-  getChildren = (node: FileNode): Observable<FileNode[]> => { return ofObservable(node.children); };
+  getChildren = (node: FileNode): FileNode[] => { return node.children; };
 
   hasChild = (_: number, _nodeData: FileFlatNode) => { return _nodeData.expandable; };
 

src/lib/tree/data-source/flat-data-source.ts

@@ -50,25 +50,35 @@ export class MatTreeFlattener<T, F> {
   constructor(public transformFunction: (node: T, level: number) => F,
               public getLevel: (node: F) => number,
               public isExpandable: (node: F) => boolean,
-              public getChildren: (node: T) => Observable<T[]>) {}
+              public getChildren: (node: T) => Observable<T[]> | T[]) {}
 
   _flattenNode(node: T, level: number,
                resultNodes: F[], parentMap: boolean[]): F[] {
     const flatNode = this.transformFunction(node, level);
     resultNodes.push(flatNode);
 
     if (this.isExpandable(flatNode)) {
-      this.getChildren(node).pipe(take(1)).subscribe(children => {
-        children.forEach((child, index) => {
-          let childParentMap: boolean[] = parentMap.slice();
-          childParentMap.push(index != children.length - 1);
-          this._flattenNode(child, level + 1, resultNodes, childParentMap);
+      const childrenNodes = this.getChildren(node);
+      if (Array.isArray(childrenNodes)) {
+        this._flattenChildren(childrenNodes, level, resultNodes, parentMap);
+      } else {
+        childrenNodes.pipe(take(1)).subscribe(children => {
+          this._flattenChildren(children, level, resultNodes, parentMap);
         });
-      });
+      }
     }
     return resultNodes;
   }
 
+  _flattenChildren(children: T[], level: number,
+                   resultNodes: F[], parentMap: boolean[]): void {
+    children.forEach((child, index) => {
+      let childParentMap: boolean[] = parentMap.slice();
+      childParentMap.push(index != children.length - 1);
+      this._flattenNode(child, level + 1, resultNodes, childParentMap);
+    });
+  }
+
   /**
    * Flatten a list of node type T to flattened version of node F.
    * Please note that type T may be nested, and the length of `structuredData` may be different

src/lib/tree/tree.md

@@ -63,8 +63,10 @@ rendered data (such as expand/collapse) should be propagated through the table's
 
 The `TreeControl` controls the expand/collapse state of tree nodes. Users can expand/collapse a tree
 node recursively through tree control. For nested tree node, `getChildren` function need to pass to
-the `NestedTreeControl` to make it work recursively. For flattened tree node, `getLevel` and
-`isExpandable` functions need to pass to the `FlatTreeControl` to make it work recursively.
+the `NestedTreeControl` to make it work recursively. The `getChildren` function may return an 
+observable of children for a given node, or an array of children. 
+For flattened tree node, `getLevel` and `isExpandable` functions need to pass to the 
+`FlatTreeControl` to make it work recursively.
 
 ### Toggle
 

src/material-examples/tree-checklist/tree-checklist-example.ts

@@ -2,7 +2,7 @@ import {SelectionModel} from '@angular/cdk/collections';
 import {FlatTreeControl} from '@angular/cdk/tree';
 import {Component, Injectable} from '@angular/core';
 import {MatTreeFlatDataSource, MatTreeFlattener} from '@angular/material/tree';
-import {BehaviorSubject, Observable, of as observableOf} from 'rxjs';
+import {BehaviorSubject} from 'rxjs';
 
 /**
  * Node for to-do item
@@ -146,7 +146,7 @@ export class TreeChecklistExample {
 
   isExpandable = (node: TodoItemFlatNode) => node.expandable;
 
-  getChildren = (node: TodoItemNode): Observable<TodoItemNode[]> => observableOf(node.children);
+  getChildren = (node: TodoItemNode): TodoItemNode[] => node.children;
 
   hasChild = (_: number, _nodeData: TodoItemFlatNode) => _nodeData.expandable;
 

src/material-examples/tree-nested-overview/tree-nested-overview-example.ts

@@ -1,7 +1,7 @@
 import {NestedTreeControl} from '@angular/cdk/tree';
 import {Component, Injectable} from '@angular/core';
 import {MatTreeNestedDataSource} from '@angular/material/tree';
-import {BehaviorSubject, of as observableOf} from 'rxjs';
+import {BehaviorSubject} from 'rxjs';
 
 /**
  * Json node data with nested structure. Each node has a filename and a value or a list of children
@@ -125,5 +125,5 @@ export class TreeNestedOverviewExample {
 
   hasNestedChild = (_: number, nodeData: FileNode) => !nodeData.type;
 
-  private _getChildren = (node: FileNode) => observableOf(node.children);
+  private _getChildren = (node: FileNode) => node.children;
 }