Error:FAILURE: Build failed with an exception. * What went wrong: Task '' not found in root projec

在使用Android studio的过程中，用gradle assembleRelease编译版本的时候，出现下列错误，无法编译

Error:FAILURE: Build failed with an exception.
* What went wrong:
Task '' not found in root project ''.
* Try:
Run gradle tasks to get a list of available tasks. Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

在网上找了好多方法，有两种说法最多的：

   1.直接在项目的目录下修改与项目名称同名的.iml文件，删除 ... ，这个方法试过，没什么卵用！

   2.在用mv命令移除方法：mv .idea .idea.bak    然后Import the project again   这种方法我没没试过 ；

   3.最后在stack overflow论坛的乱花从中发现一句话（红色的字体是关键）：

This happened to me recently when I close one Android Studio project and imported another Eclipse project. It seemed to be some bug in Android Studio where it preserves some gradle settings from previously open project and then get confused in the new project.

 The solution was extremely simple: Close the project and shut down Android Studio completely, before re-opening it and then import/open the new project. Everything goes smoothly from then on.

也就是说，解决的方法很简单，就是关闭项目并且完全关闭Android Studio这个软件，然后打开一个新项目import/open the new project，然后就正常了。经本人测试，方法有效。