Question

无参数构造函数可以工作，但是当我尝试注入任何内容时，页面返回运行时错误：

无法解析AppComponent的所有参数：（？）

知道问题可能是什么？这是代码：

app.module.ts ：

www.example.com

app.component.ts ：

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { AppComponent } from './app.component';
import { AngularFireModule } from 'angularfire2';
import { AngularFireDatabaseModule, AngularFireDatabase } from 'angularfire2/database';
import { environment } from '../environments/environment';
import { MyService } from './my.service';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    AngularFireDatabaseModule,
    AngularFireModule.initializeApp(environment.firebase)
  ], 
  //providers:[],  
  providers: [MyService],
  bootstrap: [AppComponent]
})
export class AppModule { }

my.service.ts ：

import { Component, Inject, Injectable, HostListener } from '@angular/core';
import { AngularFireDatabaseModule, AngularFireDatabase } from 'angularfire2/database';
import { Observable } from 'rxjs/Observable';
import { VendingMachineService } from './vending-machine.service';

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

/*
    constructor()
    {
    }
*/  

    constructor(ms)         
    {
        var x = vms;
    }
}

Answer 1

重写

app.component.ts:

import { Component } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import { VendingMachineService } from './vending-machine.service';

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

export class AppComponent {

//please check vendingMachineService, this is not the name of the service you provided in code
    constructor(private vendingMachineService: VendingMachineService){}

/*
    constructor(ms)     what is ms????? remove
    {
        var x = vms;
    }
*/
}

为什么要导入已在应用模块中导入的模块？如果你想这样做，我不这么认为，你需要申报另一个模块

您可能想考虑将服务重命名为my-service.service.ts，看起来更好

Answer 2

如果要将MyService注入组件，那么构造函数应如下所示：

import { Component, Inject, Injectable, HostListener } from '@angular/core';
import { AngularFireDatabaseModule, AngularFireDatabase } from 'angularfire2/database';
import { Observable } from 'rxjs/Observable';
import { VendingMachineService } from './vending-machine.service';

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


    // CLASS as type is required for Angular to match to your service
    // otherwise angular doesn't know what to inject
    // Also I have added the access modifier private
    // which creates an field so you can access via this.myservice
    constructor(private myService: MyService){
    }

    // Example usage in a method:
    someMethod(){
       this.service.doSth();
    }
}

无法注入组件？

2 个答案: