Ionic 中出现 NullInjectorError: No provider for HttpClient 的解决办法

1. 在 app.module.ts 中引入模块

import { HttpClientModule } from '@angular/common/http';

2. 在 @NgModule.imports 中引入它

@NgModule({
    ......
    imports: [
        ......
        HttpClientModule,
        ......
    ],
    ......
})