for Xamarin :您必須加入組件 'System.Threading.Tasks, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' 的參考。

錯誤 CS0012 類型 'Task<>' 定義在未參考的組件中。您必須加入組件
'System.Threading.Tasks, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' 的參考。
TabHostWalkthrough C:\Users\John\Documents\TabHostWalkthrough\TabHostWalkthrough\DlgEditAccount.cs 78

Solution:

參考:

http://stackoverflow.com/questions/19439564/method-error-cannot-await-system-threading-tasks-task-from-await-and-async-pr

,中間那段:

What a Nightmare! I have found the problem.

Microsoft.Bcl

It appears in my case that the Microsoft.Bcl and Microsoft.Bcl.Async are in conflict. I removed the Microsoft.Bcl and Microsoft.Bcl.Async with the following commands:

uninstall-package Microsoft.Bcl.Async -force

then:

uninstall-package Microsoft.Bcl -force

and then install again:

install-package Microsoft.Bcl.Async

....