Angular 服务依赖注入：告别基类构造器空值与拥抱现代实践

// 基类
export abstract class MyBaseClass {
  constructor(protected toastService?: ToastService) {}

  showToast(message: string): void {
    if (this.toastService) {
      this.toastService.info(message);
    } else {
      console.warn('ToastService is not available.');
    }
  }
}

// 子类
export class MyChildService extends MyBaseClass {
  constructor() {
    // 如果不在这里传递 toastService，父类中的 toastService 将为 null
    super();
  }

  doSomethingAndNotify(): void {
    // 此时 this.toastService 在 MyBaseClass 中为 null
    this.showToast('Operation completed!');
  }
}

import { inject, Injectable } from '@angular/core';

// 假设 ToastService 是一个可注入的服务
@Injectable({ providedIn: 'root' })
export class ToastService {
  info(message: string): void {
    console.log(`Toast (Info): ${message}`);
  }
}

// 使用 inject 函数的基类
export abstract class MyBaseClassWithInject {
  protected toastService = inject(ToastService); // 直接注入，无需构造函数传递

  showToast(message: string): void {
    this.toastService.info(message); // toastService 保证不为 null
  }
}

// 继承该基类的子类
@Injectable({ providedIn: 'root' })
export class MyChildServiceWithInject extends MyBaseClassWithInject {
  constructor() {
    super(); // 即使子类构造函数简单调用 super()，toastService 也已在父类中注入
  }

  doSomethingAndNotify(): void {
    this.showToast('Operation completed with modern injection!');
  }
}

import { inject, Injectable } from '@angular/core';

// 封装通用逻辑的服务
@Injectable({ providedIn: 'root' })
export class CommonLogicService {
  private toastService = inject(ToastService);

  performCommonOperation(data: any): void {
    console.log('Performing common operation with:', data);
    this.toastService.info('Common operation completed!');
  }
}

// 需要通用逻辑的类，通过组合使用 CommonLogicService
@Injectable({ providedIn: 'root' })
export class MyFeatureService {
  private commonLogic = inject(CommonLogicService);

  processFeatureData(featureData: string): void {
    console.log(`Processing feature data: ${featureData}`);
    this.commonLogic.performCommonOperation({ featureData });
    // 其他特定于 MyFeatureService 的逻辑
  }
}

// 另一个需要通用逻辑的类
@Injectable({ providedIn: 'root' })
export class AnotherFeatureService {
  private commonLogic = inject(CommonLogicService);

  handleUserAction(action: string): void {
    console.log(`Handling user action: ${action}`);
    this.commonLogic.performCommonOperation({ action });
  }
}