expand to collapse all other nodes in angular 12

Guri Bee

2 min read

·

21-10-2024

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Expanding and Collapsing All Nodes in Angular 12: A Comprehensive Guide

Managing nested data structures in Angular applications can be complex, particularly when you need to provide users with interactive tree-like views. Expanding and collapsing individual nodes within a tree is a common requirement, but sometimes you need to toggle the state of all nodes at once. This article will explore how to achieve this functionality in Angular 12, drawing upon insights from GitHub discussions and providing practical solutions.

Understanding the Challenge:

The core issue lies in finding an efficient way to trigger a cascade of state updates throughout your tree structure. Directly manipulating individual node states can be tedious and error-prone. This is where Angular's reactivity and data binding come into play.

Solution Approaches:

Several approaches can be used to implement "expand all" and "collapse all" functionality. We'll discuss two popular methods:

1. Using a Custom Service:

This method provides a centralized and maintainable way to manage tree state updates.

Example (from GitHub):

import { Injectable } from '@angular/core';
import { BehaviorSubject } from 'rxjs';

interface TreeNode {
  name: string;
  expanded: boolean;
  children?: TreeNode[];
}

@Injectable({
  providedIn: 'root'
})
export class TreeService {
  private _treeData = new BehaviorSubject<TreeNode[]>([]);
  treeData$ = this._treeData.asObservable();

  expandAll(nodes: TreeNode[]) {
    this._treeData.next(nodes.map(node => ({ ...node, expanded: true })));
    nodes.forEach(node => {
      if (node.children) {
        this.expandAll(node.children);
      }
    });
  }

  collapseAll(nodes: TreeNode[]) {
    this._treeData.next(nodes.map(node => ({ ...node, expanded: false })));
    nodes.forEach(node => {
      if (node.children) {
        this.collapseAll(node.children);
      }
    });
  }
}

Explanation:

• The TreeService holds the tree data using a BehaviorSubject.
• The expandAll and collapseAll methods recursively traverse the tree, setting the expanded property for all nodes.
• The _treeData.next method triggers updates, ensuring the UI reflects the changes.

2. Implementing Expansion Logic Within the Tree Component:

This approach allows for more granular control and can be simpler for smaller tree structures.

Example (from GitHub):

import { Component, Input } from '@angular/core';

@Component({
  selector: 'app-tree',
  template: `
    <ul>
      <li *ngFor="let node of data; trackBy: trackByFn">
        <span>{{ node.name }}</span>
        <button (click)="toggleNode(node)">Toggle</button>
        <ul *ngIf="node.expanded">
          <app-tree [data]="node.children"></app-tree>
        </ul>
      </li>
    </ul>
  `
})
export class TreeComponent {
  @Input() data: TreeNode[];

  trackByFn(index: number, node: TreeNode): any {
    return node.name;
  }

  toggleNode(node: TreeNode) {
    node.expanded = !node.expanded;
  }

  expandAll() {
    this.data.forEach(node => {
      this.toggleNode(node);
      if (node.children) {
        this.expandAll(node.children);
      }
    });
  }

  collapseAll() {
    this.data.forEach(node => {
      this.toggleNode(node);
      if (node.children) {
        this.collapseAll(node.children);
      }
    });
  }
}

Explanation:

• The expandAll and collapseAll methods are directly in the TreeComponent.
• toggleNode handles individual node expansion/collapse, which is used within the recursive methods.

Considerations and Best Practices:

• Performance: For large trees, using a custom service can be more efficient. However, if your tree is relatively small, the component-based approach might suffice.
• Maintainability: A service provides a clear separation of concerns, making it easier to modify and test your tree logic.
• State Management: When dealing with large and complex trees, consider using a state management library like NgRx or NgXS to manage state changes effectively.

Conclusion:

Expanding and collapsing all nodes in a tree in Angular 12 is achievable through various methods. Choosing the right approach depends on your specific needs and the complexity of your application. Remember to prioritize maintainability, performance, and a clean separation of concerns. By utilizing the power of Angular's reactivity and data binding, you can create user-friendly and dynamic tree views.