NativeScript TextField [(ngModel)] does not work

Make sure you import NativeScriptFormsModule on the module that declare AddProductComponent Component not only in AppModule.

Example:

componentName.module.ts

import { NativeScriptCommonModule, NativeScriptFormsModule } from "nativescript-angular";
import { ComponentName } from "./componentName.component";

@NgModule({
  imports: [
    NativeScriptFormsModule
  ],
  declarations: [
    ComponentName
  ],
  schemas: [
    NO_ERRORS_SCHEMA
  ]
})
export class ComponentModule { }