owin - No conversion available between HelloWorldComponent and System.Func`2[System.Collections.Generic.IDictionary`2 // Parameter name: signature -

i working through scott allen's mvc 5 fundamentals course on pluralsight

i error @ "using (webapp.start(uri)) " in code below.

the error

an unhandled exception of type 'system.argumentexception' occurred in microsoft.owin.dll   system.argumentexception unhandled   hresult=-2147024809   message=no conversion available between consoleapplication1.helloworldcomponent , system.func`2[system.collections.generic.idictionary`2[system.string,system.object],system.threading.tasks.task]. parameter name: signature   source=microsoft.owin   paramname=signature   stacktrace:        @ microsoft.owin.builder.appbuilder.convert(type signature, object app)        @ microsoft.owin.builder.appbuilder.buildinternal(type signature)        @ microsoft.owin.builder.appbuilder.build(type returntype)        @ microsoft.owin.hosting.serverfactory.serverfactoryadapter.create(iappbuilder builder)        @ microsoft.owin.hosting.engine.hostingengine.startserver(startcontext context)        @ microsoft.owin.hosting.engine.hostingengine.start(startcontext context)        @ microsoft.owin.hosting.starter.directhostingstarter.start(startoptions options)        @ microsoft.owin.hosting.starter.hostingstarter.start(startoptions options)        @ microsoft.owin.hosting.webapp.startimplementation(iserviceprovider services, startoptions options)        @ microsoft.owin.hosting.webapp.start(startoptions options)        @ microsoft.owin.hosting.webapp.start[tstartup](startoptions options)        @ microsoft.owin.hosting.webapp.start[tstartup](string url)        @ consoleapplication1.program.main(string[] args) in e:\eshared\dev2015\webappscottallen\consoleapplication1\consoleapplication1\program.cs:line 16        @ system.appdomain._nexecuteassembly(runtimeassembly assembly, string[] args)        @ system.appdomain.executeassembly(string assemblyfile, evidence assemblysecurity, string[] args)        @ microsoft.visualstudio.hostingprocess.hostproc.runusersassembly()        @ system.threading.threadhelper.threadstart_context(object state)        @ system.threading.executioncontext.runinternal(executioncontext executioncontext, contextcallback callback, object state, boolean preservesyncctx)        @ system.threading.executioncontext.run(executioncontext executioncontext, contextcallback callback, object state, boolean preservesyncctx)        @ system.threading.executioncontext.run(executioncontext executioncontext, contextcallback callback, object state)        @ system.threading.threadhelper.threadstart()   innerexception:  

the code is

using system; using system.collections.generic; using system.io; using system.threading.tasks; using microsoft.owin.hosting; using owin; namespace consoleapplication1 {     using appfunc = func<idictionary<string, object>, task>;     class program     {         static void main(string[] args)         {             string uri = "http://localhost:8080";             using (webapp.start<startup>(uri))   // katana please start, using configuration startup class , listening on port given uri             {                 console.writeline("started!");                 console.readkey();                 console.writeline("stopping!");             }         }     }      public class startup     {         public void configuration(iappbuilder app)         {             app.use<helloworldcomponent>();         }     }      public class helloworldcomponent     {         appfunc _next;         public helloworldcomponent(appfunc next)         {             _next = next;         }          // katana uses reflection find invoke function matches appfunc signature         public task invoke(idictionary<string, object> environment)         {              var response = environment["owin.responsebody"] stream;              using (var writer = new streamwriter(response))             {                 return writer.writeasync("hello");             }         }     } } 

packages.config is

<?xml version="1.0" encoding="utf-8"?> <packages>   <package id="microsoft.owin" version="3.0.1" targetframework="net451" />   <package id="microsoft.owin.diagnostics" version="3.0.1" targetframework="net451" />   <package id="microsoft.owin.host.httplistener" version="3.0.1" targetframework="net451" />   <package id="microsoft.owin.host.systemweb" version="3.0.1" targetframework="net451" />   <package id="microsoft.owin.hosting" version="3.0.1" targetframework="net451" />   <package id="owin" version="1.0" targetframework="net451" /> </packages> 

i wonder did not use message, wonder have changed

there new way write our middlewares components, looks this:

public class helloworldcomponent : owinmiddleware {     public helloworldcomponent(owinmiddleware next) : base(next) { }      public override task invoke(iowincontext context)     {         return context.response.writeasync("hello, world!");     } } 

specifically, the constructor must accept owinmiddleware reference first parameter, otherwise error because ctor signature not match expected current owin implementation.

further, consider following parameterized usage:

    var param1 = "hello, world!";     appbuilder.use<helloworldcomponent>(param1) 

to support want modified constructor signature:

public class helloworldcomponent : owinmiddleware {     public helloworldcomponent(owinmiddleware next) : base(next) { }      public override task invoke(iowincontext context, string param1)     {         return context.response.writeasync(param1);     } } 

thus, allowing parameterize our middleware via use()'s params array.