NullInjectorError: No provider for String! angular2开发

https://stackoverflow.com/questions/41882599/angular2-exception-no-provider-for-string

下面是回答摘抄

 

private my: string should not be injected in the constructor, but outside, here assuming it's a variable you want to use in your component.

 

 

@Whisher To cut things short and MUCH simplified, the @Component decorator tells that AppComponent is a not a "normal" class, but a Component. And in that case you would have to tell that string is a provider for your component, because it expects that what is in injected in the constructor should be a provider, and therefore declared in providers: [string] in your component or ngModule. "string" wouldn't work as it's no known angular 2 provider, unless you create a service (or whatever) that is named string and has Angular magic in it ;) As said this was just a simplified example.

 

虽然我还没理解到底为什么，也没找到具体的解释的地方，不过@component 主键中的construct 里确实不能带属性构造函数参数，会报错

实际上我在开发的时候打开 F12 有时候是看不到的，不同的浏览器看到的信息不同，下面的是ie edge 的返回的错误，才让我找到了上面的 回答。 有时候换一换思路是对的。

HTML1300: 进行了导航。
localhost:4200
当前窗口: localhost
ERROR Error: StaticInjectorError(AppModule)[HelloStep1Component -> String]: 
  StaticInjectorError(Platform: core)[HelloStep1Component -> String]: 
    NullInjectorError: No provider for String!
Function code (10) (5,3)
   "ERROR"
   {
      [functions]: ,
      __proto__: { },
      description: "NullInjectorError: No provider for String!",
      message: "StaticInjectorError(AppModule)[HelloStep1Component -> String]: 
  StaticInjectorError(Platform: core)[HelloStep1Component -> String]: 
    NullInjectorError: No provider for String!",
      name: "Error",
      ngDebugContext: { },
      ngTempTokenPath: null,
      ngTokenPath: [ ],
      stack: "Error: StaticInjectorError(AppModule)[HelloStep1Component -> String]: 
  StaticInjectorError(Platform: core)[HelloStep1Component -> String]: 
    NullInjectorError: No provider for String!
   at NullInjector.prototype.get (http://localhost:4200/vendor.js:30329:13)
   at resolveToken (http://localhost:4200/vendor.js:30566:9)
   at tryResolveToken (http://localhost:4200/vendor.js:30511:9)
   at StaticInjector.prototype.get (http://localhost:4200/vendor.js:30408:13)
   at resolveToken (http://localhost:4200/vendor.js:30566:9)
   at tryResolveToken (http://localhost:4200/vendor.js:30511:9)
   at StaticInjector.prototype.get (http://localhost:4200/vendor.js:30408:13)
   at resolveNgModuleDep (http://localhost:4200/vendor.js:37456:9)
   at NgModuleRef_.prototype.get (http://localhost:4200/vendor.js:38144:9)
   at resolveDep (http://localhost:4200/vendor.js:38509:5)"
   }