【茶包射手日記】Delegate 'System.Action' does not take 1 arguments
[Abstract]
I got a wired "Delegate 'System.Action' does not take 1 arguments" error while using Telerik().ScriptRegistrar().OnDocumentReady(@<text>alert("YES");</text>) in my project, but it works fine in the Telerik.Web.Mvc.Examples project on the same box. After hours of trouble-shooting, I found the root cause, the remaining System.Web.WebPages.dll in the bin folder, which is left by a tracing of MVC source, caused reference conflict. After removing it, the issue disappeared.
照著程式庫文件說明的範例，在程式中試圖使用Razor語法@<text></text>當作Telerik的參數，卻發生錯誤:
@{ Html.Telerik().ScriptRegistrar().OnDocumentReady(@<text>alert("YES");</text>); }
傳回Compilation Error:
Compiler Error Message: CS1593: Delegate 'System.Action' does not take 1 arguments
透過錯誤畫面的【Show Complete Compilation Source:】鈕檢視Razor View實際轉換的程式碼，原來@<text></text>會被Razor翻譯成item => new new System.Web.WebPages.HelperResult...的寫法:
Line 70: Html.Telerik().ScriptRegistrar()
Line 71: .OnDocumentReady(item =>
new System.Web.WebPages.HelperResult(__razor_template_writer => {
Line 72:
Line 73:
Line 74: #line default
Line 75: #line hidden
Line 76:
Line 77: WriteLiteralTo(@__razor_template_writer, "alert(\"YES\");");
Line 78:
Line 79:
Line 80:
Line 81: #line 10 "X:\WorkRoom\MVCWeb\Views\Home\Index.cshtml"
Line 82: }));
Line 83:
但詭異的是，同樣寫法在Telerik的範例網站中可順利執行無誤，Google爬文也找不到類似個案，比對兩個網站的設定看來也都相同，但就算將範例網站的cshtml移到我的網站也會出錯。經過一番摸索掙扎，決定再鑽深一點，追進Telerik的OnDocumentReady是如何做到支援@<text></text>當成參數，在範例專案中，透過VS2010好用的Go To Definition功能，我找到了它對應的Method:
public virtual ScriptRegistrarBuilder OnDocumentReady(Func<object, object> onDocumentReadyFunc)
換句話說，@<text></text>在Razor View Engine中被轉換成item => new System.Web.WebPages.HelperResult(...)，吻合Func<object, object>參數型別而適用此Overloading。這麼說來，在我的專案中是否因型別不吻合套不到Overloading才導致問題? 在我自己的專案裡，試著對cshtml中的OnDocumentReady做Go To Definition，卻傳回"Cannot navigate to function"，這印證了我的猜測。於是將範圍縮小，在cshtml寫了一段Func<object, object> x = @<text>AAA</text>做測試，結果:
Compiler Error Message: CS0433: The type 'System.Web.WebPages.HelperResult' exists in both 'c:\Windows\Microsoft.NET\assembly\GAC_MSIL\System.Web.WebPages\v4.0_1.0.0.0__31bf3856ad364e35\System.Web.WebPages.dll' and 'c:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\root\4dd28e84\bd0ec915\assembly\dl3\4f17bd54\d1ab414f_c0f5cb01\System.Web.WebPages.DLL'
哈!! 感覺好像在濃霧瀰漫的草原胡亂摸索了兩個鐘頭，忽然間一轉頭變成陽光普照，一眺千里，這才發現眼前的山頭聚集了滿滿一群羚羊...
想起來了，上週玩了Debug MVC Source Code，後來雖然將Reference改回正式System.Web.Mvc.dll，但bin目錄下卻殘留了System.Web.WebPages.DLL，實際執行時就引用了它而非GAC中的版本，造成參考來源不一致。
一邊在山頭奔跑驅趕，一邊刪除多餘的DLL檔案，羚羊群四處逃竄，錯誤訊息頓時消散，本次的懸疑茶包也終告結案。