Error when trying to inject a service into an angular component EXCEPTION Can t resolve all parameters for component why

Question

I ve built a basic app in Angular  but I have encountered a strange issue where I cannot inject a service into one of my components  It injects fine into any of the three other components I have created  however  For starters  this is the service   import   Injectable   from   angular core     Injectable   export class MobileService     screenWidth  number    screenHeight  number     constructor         this screenWidth   window outerWidth      this screenHeight   window outerHeight       window addEventListener  quot resize quot   this onWindowResize bind this             onWindowResize ev  Event        var win    ev currentTarget as Window       this screenWidth   win outerWidth      this screenHeight   win outerHeight            And the component that it refuses to work with  import   Component    from   angular core   import   NgClass   from   angular common   import   ROUTER DIRECTIVES   from   angular router    import  MobileService  from          Component     moduleId  module id    selector   pm-header     templateUrl   header component html     styleUrls    header component css      directives   ROUTER DIRECTIVES  NgClass      export class HeaderComponent     mobileNav  boolean   false     constructor public ms  MobileService        console log ms           The error I get in the browser console is this   EXCEPTION  Can t resolve all parameters for HeaderComponent        I have the service in the bootstrap function so it has a provider  And I seem to be able to inject it into the constructor of any of my other components without issue

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In my case  I was exporting a Class and an Enum from the same component file   mComponent component ts   export class MyComponentClass      export enum MyEnum        Then  I was trying to use MyEnum from a child of MyComponentClass  That was causing the Can t resolve all parameters error   By moving MyEnum in a separate folder from MyComponentClass  that solved my issue   As G  nter Z  chbauer mentioned  this is happening because of a service or component is circularly dependent

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When using barrel imports - consider importing injectables first as a rule of thumb

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It happens when referring an interface as well   Changing interface for class fixed it  working with and without  Inject

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In my case  I took a dependency on a service that had no dependencies and therefore I did not add a constructor   function to the service class  I added a parameterless constructor to the dependent service class and everything started working

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This can be a really difficult issue to debug due to the lack of feedback in the error  If you are concerned about an actual cyclic dependency  here s the most important thing to look at in the stack trace a  the name of the service b  the constructor parameter in that service that has a question mark e g  if it looks like this      can t resolve all parameters for AuthService    object Object      object Object    object Object    object Object        then it means the 5th parameter is a service that also depend on AuthService  i e  question mark  means it wasn t resolved by DI   From there  you just need to decouple the 2 services by restructuring the code

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For the benefit of searchers  I got this error  It was simply a missing   symbol   I e  This produces the Can t resolve all parameters for MyHttpService error   Injectable   export class MyHttpService      Adding the missing   symbol fixes it    Injectable   export class MyHttpService

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If you try to inject an interface  this error occurs as well  Somewhere  export const MY SERVICE   new InjectionToken lt MyService gt   MY SERVICE     export interface MyService                Injectable   export class MyServiceImpl implements MyService               Incorrect    constructor      private myService  MyService         Correct    constructor       Inject MY SERVICE  private myService  MyService

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In my case fix was replacing relative path with absolute before  import  Service  from    service     after  import  Service  from  src app services service     Looks like typescript angular issue

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In my case it was because of the plugin Augury  disable it will work fine  Alternative option is aot  also works   all credits to  Boboss74   he posted the answer here  https   github com angular angular issues 23958

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In my case  the reason was the following    my injectable service A extended another class B B had a constructor which required an argument I hadn t defined any constructor in A   As a consequence  when trying to create an object A  the default constructor failed  I have no idea why this wasn t a compile error   I got it fixed by simply adding a constructor in A  which correctly called B s constructor

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As of Angular 2 2 3 there is now a forwardRef   utility function that allows you to inject providers that have not yet been defined   By not defined  I mean that the dependency injection map doesn t know the identifier  This is what happens during circular dependencies  You can have circular dependencies in Angular that are very difficult to untangle and see   export class HeaderComponent     mobileNav  boolean   false     constructor  Inject forwardRef      gt  MobileService   public ms  MobileService        console log ms            Adding  Inject forwardRef      gt  MobileService   to the parameter of the constructor in the original question s source code will fix the problem   References  Angular 2 Manual  ForwardRef  Forward references in Angular 2

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In my case  it happened because I didn t declare the type for a constructor parameter   I had something like this   constructor private URL  private http  Http        and then changing it to the code below solved my problem   constructor private URL   string  private http  Http

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This answer might be very helpful for this problem  In addition  for my case  exporting the service as default was the cause   WRONG    Inject   export default class MobileService           CORRECT    Inject   export class MobileService

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In addition to the missing  Injectable   decorator  Missing  Injectable   decorator in abstract class produced the Can t resolve all parameters for service      The decorator needs be present in MyService as well as in the derived class BaseService    abstract class  Injectable   abstract class BaseService            MyService      Injectable   export class MyService extends BaseService

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You can try running the following command again   ng serve --open

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Im my case  add  quot emitDecoratorMetadata quot  and  quot esModuleInterop quot  solved the problem  https   github com thymikee jest-preset-angular issues 288

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for me it was just lack of    in  Injectable  Proper is  Injectable

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In my case passing wrong parameters to constructor generates this error  basic idea about this error is that you unknowingly passed some wrong args to any function   export class ProductComponent       productList  Array lt Product gt        constructor productList Product                 productList Product this arg was causing error of unresolved parameters           this productList                 I solved this by just removing that argument

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You have to add providers array in  Component decorator or in the module where your component is declared  Inside component you can do as below    Component     moduleId  module id    selector   pm-header     templateUrl   header component html     styleUrls    header component css      directives   ROUTER DIRECTIVES  NgClass     providers   MobileService

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For me this was because i stopped using the -aot flag whilst trying to make the compile time faster    ng serve -aot

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for angular 6 and newer versions  try   Injectable     providedIn   root         right above your service class with no other lines in between  advantages   no need to add the service to any module  will be  auto-discovered   service will be a singleton  since it will be injected into root     angular docs

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x000D   x000D  import  Injector  from   angular core   import  ServiceA  from    service-a     Component                class MyComp     constructor private injector  Injector         const serviceA   injector get ServiceA         x000D   x000D   x000D

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Well for me the issue was even more annoying  I was using a service within a service and forgot to add it as dependency in the appModule  Hope this helps someone save several hours breaking the app down only to build it back up again

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to me stopping the application and issuing ng serve fixed the problem

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In my case I missed to call the constructor of the class I inherited from   Before    Component          export class ComponentA extends ComponentParent                After    Component          export class ComponentA extends ComponentParent     constructor protected route  ActivatedRoute  protected store   Store lt AppState gt         super route  store

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I have encountered this error by mistyping the service s name  i e   constructor  private myService  MyService    For misspelled services  I was able to determine which service was the problem  I had several listed in the constructor  by inspecting the page in Chrome- Console  You will see as part of the message a  parameter  array list by displaying object Object  object Object     or something like that   Notice where the     is and that is the position of the service that is causing the problem

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Import it from the file where it is declared directly instead of the barrel   I don t know what exactly causes the issue but I saw it mentioned several times  probably some kind of circular dependency    It should also be fixable by changing the order of the exports in the barrel  don t know details  but was mentioned as well

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WRONG  1  Forgetting Decorator     Uncaught Error  Can t resolve all parameters for MyFooService       export class MyFooService           WRONG  2  Omitting     Symbol     Uncaught Error  Can t resolve all parameters for MyFooService       Injectable   export class MyFooService           WRONG  3  Omitting      Symbols     Uncaught Error  Can t resolve all parameters for TypeDecorator        Injectable export class MyFooService           WRONG  4  Lowercase  i      Uncaught ReferenceError  injectable is not defined  injectable export class MyFooService           WRONG  5  You forgot  import   Injectable   from   angular core      Uncaught ReferenceError  Injectable is not defined  Injectable export class MyFooService           CORRECT    Injectable   export class MyFooService

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For me  it was because I had an empty line between my  Component decorator and my Component class   This caused the decorator not to get applied to the class

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In addition to the previous answers given  it seems this error is thrown as well when your injectable service is missing the actual  Injectable   decorator  So before you debug the cyclic dependency thing and the order of your imports exports  do a simple check whether your service actually has  Injectable   defined   This applies to the current Angular latest  Angular 2 1 0   I opened an issue on this matter

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For me  I got this error when I mistakenly disabled this import in the polyfills ts file   you need to ensure it is imported to avoid that error       Evergreen browsers require these         Used for reflect-metadata in JIT  If you use AOT  and only Angular decorators   you can remove  import  core-js es7 reflect

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Sometimes this happens when you declared Angular s inbuilt module HttpClientModule  HttpErrorResponse etc  in app module js  I also faced the same issue but resolved now   The mistake I did was mention HttpClientModule into Providers instead of Import of angular Module

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Although the ordering of exported classes from within barrels may have been mentioned  the following scenario may also produce the same effect  Suppose you have classes A  B  and C exported from within the same file where A depends on B and C   Injectable   export class A           dependencies injected        constructor private b  B  private c  C         Injectable   export class B         Injectable   export class C        Since the dependent classes  i e  in this case classes B and C  are not yet known to Angular   probably at run-time during Angular s dependency injection process on class A  the error is raised  Solution The solution is to declare and export the dependent classes before the class where the DI is done  i e  in the above case the class A is declared right after its dependencies are defined   Injectable   export class B         Injectable   export class C         Injectable   export class A           dependencies injected        constructor private b  B  private c  C

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Anuglar import paths are case sensitive Check if your service paths are correct everywhere you use service and also check the letter cases to be correct and identical everywhere

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In my case  I needed to add import  core-js es7 reflect   to my application to make  Injectable work

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As already stated  the issue is caused by the export ordering within the barrel which is caused by circular dependencies   A more detailed explanation is here  https   stackoverflow com a 37907696 893630

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Removing parameters from injectable constructor   method solved it for my case

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In my case it was a circular reference  I had MyService calling Myservice2 And MyService2 calling MyService   Not good

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You get this error if you have service A that depends on a static property   method of service B and the service B itself depends on service A trough dependency injection  So it s a kind of a circular dependency  although it isn t since the property   method is static  Probably a bug that occurs in combination with AOT

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I also encountered this by injecting service A into service B and vice versa   I think it s a good thing that this fails fast as it should probably be avoided anyway  If you want your services to be more modular and re-usable  it s best to avoid circular references as much as possible  This post highlights the pitfalls surrounding that    Therefore  I have the following recommendations    If you feel the classes are interacting too often  I m talking about feature envy   you might want to consider merging the 2 services into 1 class  If the above doesn t work for you  consider using a 3rd service   an EventService  which both services can inject in order to exchange messages

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In my case  that was the TypeScript version that I upgraded to a major version and assignation assertions that I added to some Class properties   Reverting the changes solved this for me   details here

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Another possibility is not having emitDecoratorMetadata set to true in tsconfig json       compilerOptions                     emitDecoratorMetadata   true

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In my case I was trying to extend  NativeDateAdapter  in order to override  format date  Date  displayFormat  Object   method    In AngularMaterial-2 DatePicker    So basically I forgot to add  Injectable anotation   After I add this to my  CustomDateAdapter  class    Injectable     providedIn   root       Error has gone

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Gotcha   If none of the above answers helped you  maybe you are importing some element from the same file where a component is injecting the service   I explain better   This is the service file      your-service-file ts import   helloWorld    from  your-component-file ts    Injectable   export class CustomService       helloWorld       This is the component file    Component       export class CustomComponent     constructor service  CustomService         export function helloWorld       console log  hello world        So it causes problems even if the symbol isn t inside the same component  but just inside the same file  Move the symbol  it can be a function  a constant  a class and so on     elsewhere and the error will fade away

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In may case the error was caused by upgrading the  angular-devkit build-angular to  0 803    See https   github com angular angular-cli issues 15892 for the details

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If your service is defined in the same file as a component  that consumes it  and the service is defined after the component in the file you may get this error  This is due to the same  forwardRef  issue others have mentioned  At this time VSCode isn t great about showing you this error and the build compiles successfully   Running the build with --aot can mask this problem due to the way the compiler works  probably related to tree shaking     Solution  Make sure the service is defined in another file or before the component definition   I m not sure if forwardRef can be used in this case  but it seems clumsy to do so    If I have a very simple service that is very strongly tied to a component  sort of like a view model  - eg  ImageCarouselComponent  I may name it ImageCarouselComponent service ts so it doesn t get all mixed up with my other services

[angular] Error when trying to inject a service into an angular component "EXCEPTION: Can't resolve all parameters for component", why?

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