Android studio import Intelij idea projects => Migrate Project to Gradle? This project does not use the Gradle build system...

Migrate Project to Gradle?
This project does not use the Gradle build system. We recommend that you migrate to using the Gradle build system.
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http://stackoverflow.com/questions/21606504/cant-migrate-project-to-gradle-in-android-studio

The project thinks it's still a non-Gradle based project; it's not the presence of the build.gradle file that makes it Gradle-based, but it's how the project was set up in the first place. You'll need to re-import your project to finish the conversion to Gradle.

First, though, it looks like you don't have a settings.gradle file; it looks like you need one. Since you've set up your project as a single-module project, then you can put the file in your project's root directory, next to build.gradle. It should contain this:

import ':'

In the future if you add more modules to your project you may want to convert it to a multi-module directory structure, but you don't need to worry about that now. In any event, now you need to do the re-import in Android Studio:

1. Close your project
2. Back up your project
3. Delete the .idea folder in the root directory of the project
4. Delete all the .iml files in your project
5. Import your project in Android Studio, and in the dialog that prompts you for a file, choose thebuild.gradle file.
6. After this you should be good to go.

I followed yellow highlighted and open android studio then import project, open the root folder it prompt me the following screen:

Just click "Next"

Click "Finish"

It imported with some warnings, but I still can run the entire project successfully.