The system cannot find the file specified. Confirm that the declaration is correct, that the assembly and all its dependencies are available, and that the task contains a public class that implements Microsoft.Build.Framework.ITask.

今天碰到了一個新的專案快樂按下Build然後就炸掉了，我原本想說這常見的問題可能是有引用到一些本地端的參考，把它手動加上去就好了，結果原來是需要回頭去Visual Studio 2017補安裝個別元件，算是又上了一課了。

---

錯誤訊息：The system cannot find the file specified. Confirm that the <UsingTask> declaration is correct, that the assembly and all its dependencies are available, and that the task contains a public class that implements Microsoft.Build.Framework.ITask.

---

一開始我以為到參考去補上缺少的Microsoft.Build.Framework 結果這是錯誤的做法

---

結果正確做法是要到去安裝Visual Studio 2017安裝程序的“個別元件”中有“Windows Workflow Foundation”組件。安裝完這個組件後，就解決了這個問題了。

PS.可以參考這片Visual Studio 2017  template is installation 模組安裝 補安裝

---

參考文件

https://social.msdn.microsoft.com/Forums/vstudio/en-US/cf2b26ba-d007-48ac-aa36-1eaf23f61f07/after-installing-vs2017-build-tools-on-ci-server-project-containing-workflow-foundation-components?forum=msbuild

https://docs.microsoft.com/zh-tw/dotnet/framework/windows-workflow-foundation/whats-new