Angular importing FormsModule in app.module vs child.module

问题

I'm using Angular with lazy loading modules. Each component has its own module. If I import a module in the root module (app.module) it must work fine. For example, I imported HttpClientModule in app.module and can use it in child components.

But about FormsModule, this doesn't work fine. I must import it in the child module, otherwise, I get the following errors:

Can't bind to 'ngModel' since it isn't a known property of 'input'. ("

Do you have any idea why this happens?

回答1:

I found the answer here:

• if the module is imported for components, you’ll need to import it in each module needing them,
• if the module is imported for services, you’ll need to import it only once, in the first app module.

回答2:

create the SharedModule

@NgModule({

 imports: [
    CommonModule,
    FormsModule,
  ],
  declarations: [
  ],
  exports: [
    CommonModule,
    FormsModule,
  ]
})
export class SharedModule {
}

and add this to app.module.ts

 imports: [ SharedModule.forRoot(),
// Core Module
CoreModule.forRoot()]

来源：https://stackoverflow.com/questions/54957210/angular-importing-formsmodule-in-app-module-vs-child-module