Angular Material Tree 不显示填充了数组的子元素

Question

我试图在用户展开节点时动态加载子节点。

问题是当我填充孩子数组时，mat-tree 没有显示孩子。如果我使用简单的 *ngFor 显示相同的数据，当子数组添加了元素时，它会显示它们。

我在这里有一个工作示例：stackblitz example 这是代码和html

ts

    import {NestedTreeControl} from '@angular/cdk/tree';
    import {Component} from '@angular/core';
    import {MatTreeNestedDataSource} from '@angular/material/tree';


    export class PropertyLevel {
       constructor(
        public code : string,
        public hasSubLevels: boolean,
        public subproperties : PropertyLevel[]
       ){}
    }

    @Component({
      selector: 'my-app',
      templateUrl: './app.component.html',
      styleUrls: [ './app.component.css' ]
    })
    export class AppComponent  {
      name = 'Angular';
        nestedTreeControl: NestedTreeControl<PropertyLevel>;
      nestedDataSource: MatTreeNestedDataSource<PropertyLevel>;

    constructor() {
        this.nestedTreeControl = new NestedTreeControl<PropertyLevel>(this._getChildren);
        this.nestedDataSource = new MatTreeNestedDataSource();

     this.nestedDataSource.data = [
      new PropertyLevel( '123', false, []),
      new PropertyLevel( '345', true, [
        new PropertyLevel( '345.a', false, null),
        new PropertyLevel( '345.b', true, []),
      ]),
      new PropertyLevel( '567', false,[]),
    ]; 
      } 

      hasNestedChild = (_: number, nodeData: PropertyLevel) => nodeData.subproperties;

      private _getChildren = (node: PropertyLevel) => node.subproperties;

      expandToggle(node: PropertyLevel, isExpanded: boolean): void {
        if (node.subproperties && node.subproperties.length == 0) {
          if(node.code == '123') {
            node.subproperties.push(new PropertyLevel('123.a', false, null))
          } 
          else if(node.code == '567') {
            node.subproperties.push(new PropertyLevel('567.a', false, null));
            node.subproperties.push(new PropertyLevel('567.b', false, null));
            node.subproperties.push(new PropertyLevel('567.c', false, null));
          } 
        }
      }
    }

html

    <mat-tree [dataSource]="nestedDataSource" [treeControl]="nestedTreeControl" class="example-tree">
      <mat-tree-node *matTreeNodeDef="let node" matTreeNodeToggle>
        <li class="mat-tree-node">
          <button mat-icon-button disabled></button>
          {{node.code}}
        </li>
      </mat-tree-node>

      <mat-nested-tree-node *matTreeNodeDef="let node; when: hasNestedChild">
        <li>
          <div class="mat-tree-node">
            <button mat-icon-button matTreeNodeToggle
                  (click)="expandToggle(node, nestedTreeControl.isExpanded(node))"
                    [attr.aria-label]="'toggle ' + node.filename">
              <mat-icon class="mat-icon-rtl-mirror">
                {{nestedTreeControl.isExpanded(node) ? 'expand_more' : 'chevron_right'}}
              </mat-icon>
            </button>
            {{node.code}}
          </div>
          <ul [class.example-tree-invisible]="!nestedTreeControl.isExpanded(node)">
            <ng-container matTreeNodeOutlet></ng-container>
          </ul>
        </li>
      </mat-nested-tree-node>
    </mat-tree>
    <div>
      <ul>
        <li *ngFor="let node of nestedDataSource.data">
          {{node.code}}<br />
          <ul>
            <li *ngFor="let subnode of node.subproperties">
              {{subnode.code}}
            </li>
          </ul>
        </li>
      </ul>
    </div>

Answer 1

这个故事的寓意（如果我错了，请纠正我）是在 Angular vs Angularjs，或者至少是 Material Tree 中，开发人员必须提供更改事件，而不是自动对所有内容进行更改检测，这减少了很多幕后对象的创建，使 Angular 更快更精简。

所以，解决方案是不要为孩子使用数组，而是使用 BehaviorSubject，并在类中添加方法 addChild。

我回到嵌套节点树 (https://material.angular.io/components/tree/examples) 示例 (https://stackblitz.com/angular/ngdvblkxajq)，调整 FileNode 类并添加了 addChild 和 addChildren 方法

export class FileNode {
  kids: FileNode[] = [];
  children:BehaviorSubject<FileNode[]> = new BehaviorSubject<FileNode[]>(this.kids);
  filename: string;
  type: any;
  addChild(node:FileNode):void {
    this.kids.push(node);
    this.children.next(this.kids);
  }
  addchildren(nodes:FileNode[]) {
    this.kids = this.kids.concat(this.kids, nodes);
    this.children.next(this.kids);
  }
}

然后我更改了 buildFileTree 中设置子项的行，改为调用 addChildren。 node.children = this.buildFileTree(value, level + 1) 变成了node.addchildren(this.buildFileTree(value, level + 1))

我还添加了一个方法，我可以通过单击按钮调用将子节点添加到图片节点以进行测试。

    addPictureFile():void {
    var picNode = this.data.find((node) => node.filename == 'Pictures');
    var newNode = new FileNode();
    newNode.filename = 'foo';
    newNode.type = 'gif';
    picNode.addChild(newNode);
  }

现在，Material Tree 确实检测到了我对孩子的更改并进行了自我更新。 工作示例https://stackblitz.com/edit/angular-addchildtonestedtree

完整、更新的 ts 文件：

import {NestedTreeControl} from '@angular/cdk/tree';
import {Component, Injectable} from '@angular/core';
import {MatTreeNestedDataSource} from '@angular/material/tree';
import {BehaviorSubject} from 'rxjs';

/**
 * Json node data with nested structure. Each node has a filename and a value or a list of children
 */
export class FileNode {
  kids: FileNode[] = [];
  children:BehaviorSubject<FileNode[]> = new BehaviorSubject<FileNode[]>(this.kids);
  filename: string;
  type: any;
  addChild(node:FileNode):void {
    this.kids.push(node);
    this.children.next(this.kids);
  }
  addchildren(nodes:FileNode[]) {
    this.kids = this.kids.concat(this.kids, nodes);
    this.children.next(this.kids);
  }
}

/**
 * The Json tree data in string. The data could be parsed into Json object
 */
const TREE_DATA = JSON.stringify({
  Applications: {
    Calendar: 'app',
    Chrome: 'app',
    Webstorm: 'app'
  },
  Documents: {
    angular: {
      src: {
        compiler: 'ts',
        core: 'ts'
      }
    },
    material2: {
      src: {
        button: 'ts',
        checkbox: 'ts',
        input: 'ts'
      }
    }
  },
  Downloads: {
    October: 'pdf',
    November: 'pdf',
    Tutorial: 'html'
  },
  Pictures: {
    'Photo Booth Library': {
      Contents: 'dir',
      Pictures: 'dir'
    },
    Sun: 'png',
    Woods: 'jpg'
  }
});

/**
 * File database, it can build a tree structured Json object from string.
 * Each node in Json object represents a file or a directory. For a file, it has filename and type.
 * For a directory, it has filename and children (a list of files or directories).
 * The input will be a json object string, and the output is a list of `FileNode` with nested
 * structure.
 */
@Injectable()
export class FileDatabase {
  dataChange = new BehaviorSubject<FileNode[]>([]);

  get data(): FileNode[] { return this.dataChange.value; }

  constructor() {
    this.initialize();
  }

  initialize() {
    // Parse the string to json object.
    const dataObject = JSON.parse(TREE_DATA);

    // Build the tree nodes from Json object. The result is a list of `FileNode` with nested
    //     file node as children.
    const data = this.buildFileTree(dataObject, 0);

    // Notify the change.
    this.dataChange.next(data);
  }

  /**
   * Build the file structure tree. The `value` is the Json object, or a sub-tree of a Json object.
   * The return value is the list of `FileNode`.
   */
  buildFileTree(obj: {[key: string]: any}, level: number): FileNode[] {
    return Object.keys(obj).reduce<FileNode[]>((accumulator, key) => {
      const value = obj[key];
      const node = new FileNode();
      node.filename = key;

      if (value != null) {
        if (typeof value === 'object') {
          node.addchildren(this.buildFileTree(value, level + 1));
        } else {
          node.type = value;
        }
      }

      return accumulator.concat(node);
    }, []);
  }
    addPictureFile():void {
    var picNode = this.data.find((node) => node.filename == 'Pictures');
    var newNode = new FileNode();
    newNode.filename = 'foo';
    newNode.type = 'gif';
    picNode.addChild(newNode);
  }
}

/**
 * @title Tree with nested nodes
 */
@Component({
  selector: 'tree-nested-overview-example',
  templateUrl: 'tree-nested-overview-example.html',
  styleUrls: ['tree-nested-overview-example.css'],
  providers: [FileDatabase]
})
export class TreeNestedOverviewExample {
  nestedTreeControl: NestedTreeControl<FileNode>;
  nestedDataSource: MatTreeNestedDataSource<FileNode>;

  constructor(private database: FileDatabase) {
    this.nestedTreeControl = new NestedTreeControl<FileNode>(this._getChildren);
    this.nestedDataSource = new MatTreeNestedDataSource();

    database.dataChange.subscribe(data => {
    this.nestedDataSource.data = data;
    }
    );
  }

  hasNestedChild = (_: number, nodeData: FileNode) => !nodeData.type;

  private _getChildren = (node: FileNode) => node.children;
}