Angular 4 Can't bind to <property> since it isn't a known property of <component>

Question

I'm trying to create my own directive in Angular 4. But, I got this error when bind the property of class into component template.

Console error:

Unhandled Promise rejection: Template parse errors: Can't bind to
'data' since it isn't a known property of 'tree'. ("<tree [ERROR
->][data]="data"></tree>"):

My tree-view-component.ts:

@Component({
    selector: 'app-tree-view',
    template: '<tree [data]="data"></tree>'
})
export class TreeViewComponent implements OnInit {

    @Input() data: any[];

    constructor() {
        this.data = [
        {
            label: 'a1',
            subs: [
                {
                    label: 'a11',
                    subs: [
                        {
                            label: 'a111',
                            subs: [
                                {
                                    label: 'a1111'
                                },
                                {
                                    label: 'a1112'
                                }
                            ]
                        },
                        {
                            label: 'a112'
                        }
                    ]
                },
                {
                    label: 'a12',
                }
            ]
         }
     ];
  }

  ngOnInit() { }

}

Here is my complete script file: https://pastebin.com/hDyX2Kjj

Is there anyone know about this? TiA

Azral

You don't need to mark inputs twice, either ` inputs: ['data'],` or @Input() if you have both, one is redundant. Did you add Node to declarations of @NgModule()`? – Arcuation

plnkr.co/edit/tpl:AvJOMERrnz94ekVua0u5 provides a ready to use Angular2 template - just press the "new" button and "Angular". – Arcuation

It was solved with added TreeNodeComponent, TreeComponent, adn TreeViewComponent to declarations array in @NgModule(). Is there another way to include TreeViewComponent only in @NgModule() without TreeNodeComponent and TreeComponent? Because I already included its in TreeViewComponent. – Azral

Sorry, I don't know what you mean with "Because I already included its in TreeViewComponent." Do you mean TreeViewModule? – Arcuation

I did import { TreeNodeComponent } from './tree-view.node.component'; in TreeComponent and import { TreeComponent } from './tree.component'; in TreeViewComponent. Why should I include them again in app.module? Doesn't it enough with just including TreeViewComponent in declarations? – Azral

TypeScript imports and declarations are two entirely different and unrelated concepts. Every component, directive, pipe, needs to be registered in @NgModule({ declaration: []}). Either in AppModule or a module added to imports: [] of AppModule (direct or transitive). – Arcuation

Can it be the same if I create a TreeModule, which means it will be separated with AppModule, and add TreeNodeComponent, TreeComponent, and TreeViewComponent into TreeModule declarations, and then import TreeModule to AppModule, So, I don't need add them into AppModule declarations again? – Azral

Exactly. This is called a feature module and will work fine. This makes it easier to reuse the tree in other modules. You need to import the module that contains directives you use into every module where you use them and directives (and components and pipes) can only be in declarations: [] of exactly one module. – Arcuation

Oh, I see now. Thank you for your great explanation :) – Azral

Answer 1

Every component, directive, and pipe needs to be registered in @NgModule()

@NgModule({
  declarations: [TreeViewComponent]
})
export class AppModule {}

For more details see

• https://angular.io/api/core/NgModule
• https://angular.io/guide/ngmodules
• https://angular.io/guide/ngmodule-api

Aspirator

How about this tree.module.ts: ' ... @NgModule({ declarations: [ TreeNodeComponent, TreeComponent, TreeViewComponent ] ... ... ' and in app.module.ts: ` imports: [ ... TreeModule ... ] ` Can it? – Azral

Yup, as mentioned below your question, that's usually the right way, but usually more difficult to understand for people not yet familiar with @NgModule(). But it seems you got it already ;-) – Arcuation

@GünterZöchbauer: Can you please update the link? Current link is broken. – Satinet

@BhavikShah Thanks for the hint! Updated. – Arcuation

Answer 2

I've the same error, when run test for ParentComponent. Inside was ChildComponent component with @Input property: string;. Both components were also declared inside app.module.ts.

I've fixed this like that (parent component test file):

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [ParentComponent, ChildComponent]// added child component declaration here
    })
      .compileComponents();
  }));

Dorcia

Answer 3

As The Aelfinn pointed out if you are using your Component across Modules you need to export it. BUT you should not import, export and declare it in the Module you want to use it, since its not part of this Module !!!
So suppose you have a TreeViewStuffModule which declares the TreeViewComponent and a DoSomethingWithTreeViewModule where the TreeViewComponent is used in, your declarations would be as follows:

@NgModule({
  declarations: [
    TreeViewComponent
  ],
  exports: [
    TreeViewComponent
  ]
})
export class TreeViewStuffModule { }

@NgModule({
  imports: [
    TreeViewStuffModule
  ]
})
export class DoSomethingWithTreeViewModule

Implosive

Answer 4

If you are using TreeViewComponent in another module, you will need to import the component into the @NgModule as follows:

@NgModule({
    imports: [TreeViewComponent],
    // This says that all components in this module can import TreeViewComponent
    exports: [ThisModulesComponents],
    declarations: [ThisModulesComponents]
})
export class ModuleDependentOnTreeViewComponent

Langevin

You should not import export and declare the Component in some other Module it is not part of – Implosive