小编Sag*_*gar的帖子

我是棱角分明的新人.我使用vs2015和最新的角度包创建了一个web应用程序.当我尝试从按钮单击事件上的组件调用我的服务时,我在浏览器控制台窗口中收到以下错误.

错误: -

ERROR Error: Uncaught (in promise): Error: StaticInjectorError[ViewCountService]: 
  StaticInjectorError[ViewCountService]: 
    NullInjectorError: No provider for ViewCountService!
Error: StaticInjectorError[ViewCountService]: 
  StaticInjectorError[ViewCountService]: 
    NullInjectorError: No provider for ViewCountService!
    at _NullInjector.get (injector.js:31)
    at resolveToken (injector.js:387)
    at tryResolveToken (injector.js:330)
    at StaticInjector.get (injector.js:170)
    at resolveToken (injector.js:387)
    at tryResolveToken (injector.js:330)
    at StaticInjector.get (injector.js:170)
    at resolveNgModuleDep (ng_module.js:103)
    at NgModuleRef_.get (refs.js:1037)
    at resolveDep (provider.js:455)
    at _NullInjector.get (injector.js:31)
    at resolveToken (injector.js:387)
    at tryResolveToken (injector.js:330)
    at StaticInjector.get (injector.js:170)
    at resolveToken (injector.js:387)
    at tryResolveToken (injector.js:330)
    at StaticInjector.get (injector.js:170)
    at resolveNgModuleDep (ng_module.js:103)
    at NgModuleRef_.get …

我有一个基类Base和一个Derived1类,它派生自Base类,另一个派生类Derived2派生自derived1.

下面我提到了几个对象创建的例子(后面是类的多级继承).有人可以帮助我理解那些无法创建对象的情况以及为什么在C#中无法实现对象？

Base b1 = new Base() //Possible 
Base b1 = new derived1() // Possible 
Derived1 d1 = new Base() // Not Possible 
Derived1 d1 = new Derived1() // Possible 
Derived2 d2 = new Derived1() // ---- 
Derived1 d1 = new Derived2() // ---- 
Derived2 d2 = new Derived2() // Possible
Derived2 d2 = new Base() // ---- 
Base b1 = new Derived2() // ----