NullInjectorError：No provider for MyNewService

错误消息：

ERROR NullInjectorError: R3InjectorError(AppModule)[MyService -> MyNewService -> MyNewService -> MyNewService]: NullInjectorError: No provider for MyNewService! at NullInjector.get (http://localhost:4200/vendor.js:62758:27) at R3Injector.get (http://localhost:4200/vendor.js:76765:33) at R3Injector.get (http://localhost:4200/vendor.js:76765:33) at R3Injector.get (http://localhost:4200/vendor.js:76765:33) at injectInjectorOnly (http://localhost:4200/vendor.js:62613:33) at ɵɵinject (http://localhost:4200/vendor.js:62623:57) at Object.factory (http://localhost:4200/vendor.js:77142:19) at R3Injector.hydrate (http://localhost:4200/vendor.js:77003:63) at R3Injector.get (http://localhost:4200/vendor.js:76753:33) at NgModuleRef$1.get (http://localhost:4200/vendor.js:94067:33)

查看我的依赖注入相关的代码：

发现上图的MyNewService在app.module.ts里缺少了providers定义。

将这个缺失的定义加入之后，问题消失：