docs(tree): add tree examples (#9585)

Author: tinayuangao

src/demo-app/demo-app/demo-module.ts

@@ -58,7 +58,6 @@ import {
 import {ToolbarDemo} from '../toolbar/toolbar-demo';
 import {TooltipDemo} from '../tooltip/tooltip-demo';
 import {TreeDemo} from '../tree/tree-demo';
-import {JsonDatabase} from '../tree/json-database';
 import {TypographyDemo} from '../typography/typography-demo';
 import {DemoApp, Home} from './demo-app';
 import {DEMO_APP_ROUTES} from './routes';
@@ -134,7 +133,6 @@ import {BadgeDemo} from '../badge/badge-demo';
   ],
   providers: [
     {provide: OverlayContainer, useClass: FullscreenOverlayContainer},
-    JsonDatabase
   ],
   entryComponents: [
     ContentElementDialog,

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

@@ -0,0 +1,119 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+import {Injectable} from '@angular/core';
+import {BehaviorSubject} from 'rxjs/BehaviorSubject';
+
+/**
+ * File node data with nested structure.
+ * Each node has a filename, and a type or a list of children.
+ */
+export class FileNode {
+  children: FileNode[];
+  filename: string;
+  type: any;
+}
+
+/** Flat node with expandable and level information */
+export class FileFlatNode {
+  filename: string;
+  type: any;
+  level: number;
+  expandable: boolean;
+}
+
+/**
+ * The file structure tree data in string. The data could be parsed into a Json object
+ */
+const TREE_DATA = `{"Tina":
+  {
+    "Documents": {
+      "angular": {
+        "src": {
+          "core": "ts",
+          "compiler": "ts"
+        }
+      },
+      "material2": {
+        "src": {
+          "button": "ts",
+          "checkbox": "ts",
+          "input": "ts"
+        }
+      }
+    },
+    "Downloads": {
+        "Tutorial": "html",
+        "November": "pdf",
+        "October": "pdf"
+    },
+    "Pictures": {
+        "Sun": "png",
+        "Woods": "jpg",
+        "Photo Booth Library": {
+          "Contents": "dir",
+          "Pictures": "dir"
+        }
+    },
+    "Applications": {
+        "Chrome": "app",
+        "Calendar": "app",
+        "Webstorm": "app"
+    }
+}}`;
+
+/**
+ * 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: BehaviorSubject<FileNode[]> = 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(value: any, level: number) {
+    let data: any[] = [];
+    for (let k in value) {
+      let v = value[k];
+      let node = new FileNode();
+      node.filename = `${k}`;
+      if (v === null || v === undefined) {
+        // no action
+      } else if (typeof v === 'object') {
+        node.children = this.buildFileTree(v, level + 1);
+      } else {
+        node.type = v;
+      }
+      data.push(node);
+    }
+    return data;
+  }
+}