定义了这个接口(interface):publicinterfaceIInputBoxService{boolShowDialog();TResult{get;}}为什么下面的代码有效:publicclassStringInputBoxService:IInputBoxService{...}...IInputBoxServiceservice=newStringInputBoxService();这不是吗？publicclassIntegerInputBoxService:IInputBoxService{...}...IInputBoxServiceservice=newInteg