Updated to Android Studio 3.0
Please share missing items in comments.
A late answer but this alternative answer was not right for us ...
So, here's our gitignore file:
#built application files
*.apk
*.ap_
*.aab
# files for the dex VM
*.dex
# Java class files
*.class
# generated files
bin/
gen/
# Local configuration file (sdk path, etc)
local.properties
# Windows thumbnail db
Thumbs.db
# OSX files
.DS_Store
# Android Studio
*.iml
.idea
#.idea/workspace.xml - remove # and delete .idea if it better suit your needs.
.gradle
build/
.navigation
captures/
output.json
#NDK
obj/
.externalNativeBuild
Since Android Studio 2.2 and up to 3.0, new projects are created with this gitignore file:
*.iml
.gradle
/local.properties
/.idea/workspace.xml
/.idea/libraries
.DS_Store
/build
/captures
.externalNativeBuild
Deprecated - for older project format, add this section to your gitignore file:
/*/out
/*/*/build
/*/*/production
*.iws
*.ipr
*~
*.swp
This file should be located in the project's root folder and not inside the project's module folder.
Edit Notes:
Since version 0.3+ it seems you can commit and push *.iml and build.gradle files. If your project is based on Gradle: in the new open/import dialog, you should check the "use auto import" checkbox and mark the "use default gradle wrapper (recommended)" radio button. All paths are now relative as @George suggested.
Updated answer according to @128KB attached source and @Skela suggestions
Short Answer
Gradle is a build system.
Long Answer
Before Android Studio you were using Eclipse for your development purposes, and, chances are, you didn't know how to build your Android APK without Eclipse.
You can do this on the command line, but you have to learn what each tool (dx and AAPT) does in the SDK.
Eclipse saved us all from these low-level, but important, fundamental details by giving us their own build system.
Now, have you ever wondered why the res folder is in the same directory as your src folder?
This is where the build system enters the picture. The build system automatically takes all the source files (.java or .xml), then applies the appropriate tool (e.g., takes .java class files and converts them to .dex files), and groups all of them into one compressed file - our beloved APK.
This build system uses some conventions: an example of one is to specify the directory containing the source files (in Eclipse it is \src folder) or resources files (in Eclipse it is \res folder).
Now, in order to automate all these tasks, there has to be a script; you can write your own build system using shell scripting in Linux or batch files syntax in Windows. Got it?
Gradle is another build system that takes the best features from other build systems and combines them into one. It is improved based off of their shortcomings. It is a JVM-based build system. That means you can write your own script in Java, which Android Studio makes use of.
One cool thing about Gradle is that it is a plugin-based system. This means if you have your own programming language and you want to automate the task of building some package (output like a JAR file for Java) from sources, then you can write a complete plugin in Java or Groovy (or Kotlin, see here), and distribute it to the rest of the world.
Why did Google use it?
Google saw one of the most advanced build systems on the market and realized that you could write scripts of your own with little-to-no learning curve, and without learning Groovy or any other new language. So they wrote the Android plugin for Gradle.
You must have seen build.gradle file(s) in your project. That is where you can write scripts to automate your tasks. The code you saw in these files is Groovy code. If you write System.out.println("Hello Gradle!"); then it will print on your console.
What can you do in a build script?
A simple example is that you have to copy some files from one directory to another before the actual build process happens. A Gradle build script can do this.
Best Answer
Restarting logcat helps me always.