Angular Compilation Error: NG6001 - The specified class is included in the NgModule 'AppModule' declarations, however, it is not recognized as a directive, component, or pipe

My app is having trouble compiling and showing the error

Error NG6001: The class NavigationMenuItemComponent is included in the declarations of the NgModule AppModule, but it is not a directive, component, or pipe. You must either remove it from the NgModule's declarations or add an appropriate Angular decorator.

I noticed that the error disappears when I remove the constructor with parameters. However, I would like to keep the constructor with parameters because I want to use it to initialize a list of components without having to call set methods for each member in the list. How can I resolve this issue?

import {
    Component,
    OnInit
} from '@angular/core';

@Component({
    selector: 'app-navigation-menu-item',
    templateUrl: './navigation-menu-item.component.html',
    styleUrls: ['./navigation-menu-item.component.scss']
})
export class NavigationMenuItemComponent implements OnInit {
    static readonly ID_PREFIX: string = 'sidebar-menuitem-';
    static readonly ICON_CLASS_PREFIX: string = 'mdi mdi-';

    constructor(id: string, iconClass: string) {
        this._id = NavigationMenuItemComponent.ID_PREFIX + id;
        this._iconClass = NavigationMenuItemComponent.ICON_CLASS_PREFIX + iconClass;
    }
    //constructor() {}

    private _id: string;
    private _iconClass: string;

    get id() {
        return this._id;
    }

    get iconClass() {
        return this._iconClass;
    }

    set id(id: string) {
        this._id = NavigationMenuItemComponent.ID_PREFIX + id;
    }

    set iconClass(iconClass) {
        this._iconClass = NavigationMenuItemComponent.ID_PREFIX + iconClass;
    }

    ngOnInit(): void {}
}

Answer №1

Make sure to execute npm install after creating new components. It appears that hot reload cannot automatically include the new component.

Answer №2

If you encounter several error messages, this particular one could be the first to appear.
Remember to thoroughly review all other error messages as well.

For instance, in my situation, a mistake in the tempalteURL was identified (as indicated by another error message:

NG2008: Could not locate template file
)

Answer №3

I encountered a similar issue and found that removing the OnInit method from both the declaration part and inside the class solved the problem for me. This was necessary because it was causing all data-bound properties of the directive to be initialized unnecessarily. It's worth noting that this component may have been added in app.module.ts.

export class NavigationMenuItemComponent {
     ....
     ....
     set iconClass(iconClass) {
            this._iconClass = NavigationMenuItemComponent.ID_PREFIX + iconClass;
        }

        //ngOnInit(): void {}
    }

Answer №4

Include the following code in your component:

constructor() {};

ngOnInit(): void {};

I encountered a similar problem, and I believe the issue arose because Angular was not recognizing it as a complete component until I added both the constructor and ngOnInit.

Answer №5

It seems that Angular is structured to utilize a component's constructor for the Dependency Injection system, which operates on classes rather than primitives.

Essentially, you are unable to customize your own component and assign specific properties to its constructor.

Why? Because doing so would violate the Inversion of Control principle, leading to potential maintenance issues.

What can you do instead?

  1. Employ the @Input() decorator, purposefully created by the Angular development team to pass values to a component during runtime. These values can be modified later if needed. More information can be found here and here

  2. If you require global or hierarchical configuration options, you can establish your own Injector and supply it with a custom Token for components to utilize. Further details are available here

In essence, the preferred method is the first approach as it offers clarity in your code and aligns with common practices. The second approach is more complex and may be better suited for service-oriented tasks.


TL;DR

Opt for using @Input to efficiently pass properties to child components, adhering to standard practice.

Answer №6

Ensure that the paths specified in 'templateUrl' and 'styleUrls' actually exist,

@Component({
    selector: 'app-navigation-menu-item',
    templateUrl: './navigation-menu-item.component.html',
    styleUrls: ['./navigation-menu-item.component.scss']
})

This turned out to be the issue in my particular case.

Answer №7

Encountered a similar error message when attempting to relocate a component within a different directory using Resharper in Visual Studio. The issue stemmed from a problem with one of the imports that became corrupted, specifically:

import { Component, OnInit, Input, ViewChild } from '@angular/core/core';

Solved it by making the following adjustment:

import { Component, OnInit, Input, ViewChild } from '@angular/core';

Answer №8

During my recent project, I made updates to the component files but neglected to modify the templateUrl with the new file name. After rectifying this mistake, everything began functioning properly.

It's intriguing how a single oversight can cause such confusion, leading to errors that appear consistent despite varying root causes!

Answer №9

This issue may also arise from incorrect imports. In my case, the problem was caused by importing ViewEncapsulation.

To fix this, make the following change:

import { ViewEncapsulation } from '@angular/compiler';

Change it to:

import { Component, OnInit, ViewEncapsulation } from '@angular/core';

Answer №10

I found a solution that worked for me.

The issue was caused by missing quotation marks around a variable in the ngIf condition.

<div *ngIf=!loaded" id="loader "> </div>

Changing it to:

<div *ngIf="!loaded" id="loader "> </div>

Hopefully, this can be helpful for someone facing a similar problem.

Answer №11

The issue I encountered was due to declaring the component in multiple modules instead of just one.

It is important to ensure that components are only declared in a single module.

Answer №12

Encountering a similar issue, I tackled it by meticulously debugging the code step by step to pinpoint the underlying cause. Often, such errors arise when the selector name in the HTML file does not align with that used in the TypeScript file (.ts).

Another crucial aspect to scrutinize is the templateURL files – opt for string interpolation over using backticks with $ for variables. For instance, employ {{ title }} if the variable name is title. This precaution is vital since any compilation failure within the Ng Main module will trigger the same error.

If you encounter the error message stating "it's not a directive," the problem likely lies in the discrepancy between the selectors utilized in the HTML and those specified in the TS file.

Answer №13

None of the solutions provided worked in my case. I ended up deleting the component and used the command line interface to generate a new one with a slightly different name.

Answer №14

Give it a shot with ng serve. That should take care of the issue. If not, try running npm i once.

Answer №15

After encountering a problem in my ionic framework application, I found that running the following build command resolved the issue:

ionic cordova build android

Answer №16

It turns out, in my situation, this particular line was the root of all the issues

this.router.routeReuseStrategy.shouldReuseRoute = () => false;

Answer №17

I encountered a silent error in my component import statement :

The shorthand path was not functioning properly :

import { PageLabelsConfig } from '@core/_interfaces/page-labels.interface';

After changing it to the following, everything worked fine:

 import { PageLabelsConfig } from '../../../../core/_interfaces/page-labels.interface';

For more information on shorthand paths, you can visit: https://medium.com/@aleksanderkolata/angular-tips-01-get-rid-of-long-relative-import-paths-398c5926ecd4

Answer №18

After encountering the identical error message, I discovered that the root cause was located within my app.module.ts file. It turned out that I mistakenly included a service as a Provider and inadvertently declared it in both @NgModule declarations and providers. Once I removed it from declarations, the problem was resolved.

Answer №19

While I can't speak for the other responses, one common cause of this error is attempting to call modules within the declaration part of the AppModule. Instead, make sure to import any necessary modules in the appropriate section.

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