Type script - angular : static injector error

问题

Hi i am trying to use socket.io in my angular project. there are three files which i am going to show which are component file and one service file and one module file. when ever i use service in my component file i get the static injector error. which is:

Error: StaticInjectorError(AppModule)[AppComponent -> WrappedSocket]: StaticInjectorError(Platform: core)[AppComponent -> WrappedSocket]:
NullInjectorError: No provider for WrappedSocket!

Here is the Component file:

import { Component } from '@angular/core';   
import {  cheema2 } from './practice.service';
import { Injectable } from '@angular/core';
import { Socket } from 'ng-socket-io';

@Component
({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})

 @Injectable()    
 export class AppComponent  
 {   
     constructor(private socket: Socket) { }

     sendMessage(msg: string){
     this.socket.emit("message", msg);
   }

   getMessage() 
   {
     console.log( this.socket.fromEvent("message"));
   }

}

Here is the Module file

import { BrowserModule } from '@angular/platform-browser';   
import { NgModule } from '@angular/core';
import { SocketIoModule, SocketIoConfig } from 'ng-socket-io';

const config: SocketIoConfig = { url: 'http://localhost:4200', options: {}    
};       
import { AppComponent } from './app.component';

@NgModule
({  
declarations:
 [
   AppComponent
 ],
 imports: [
   BrowserModule
  ],
 providers: [],
 bootstrap: [AppComponent]
})

export class AppModule { }

Here is the service file

import { Injectable } from '@angular/core';  
import { Socket } from 'ng-socket-io';

@Injectable()
export class cheema2  
{
    constructor(private socket: Socket) { console.log("adil"); }

    sendMessage(msg: string){
       console.log("sharif");
       this.socket.emit("message", msg);
    }

    getMessage() {
      console.log( this.socket.fromEvent("message"));              
    }
}

any one who can solve this error.

回答1:

You're missing an import in your AppModule:

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { SocketIoModule, SocketIoConfig } from 'ng-socket-io';
const config: SocketIoConfig = { 
  url: 'http://localhost:4200', options: {}
};

import { AppComponent } from './app.component';

@NgModule ({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    SocketIoModule.forRoot(config) <<< ADD THIS
  ],
  providers: [],
  bootstrap: [AppComponent] })
export class AppModule { }

来源：https://stackoverflow.com/questions/50233403/type-script-angular-static-injector-error