How can I add a linked source folder in Android Studio?

In Eclipse I can add a source folder to my Android project as a "linked source folder". How do I achieve the same thing in Android Studio?

Or is it possible to add an external folder to build in Gradle?

In your build.gradle file, add the following to the end of the Android node:

android {
    ....
    ....

    sourceSets {
        main.java.srcDirs += 'src/main/<YOUR DIRECTORY>'
    }

}

The right answer is:

android {
    ....
    ....

    sourceSets {
        main.java.srcDirs += 'src/main/<YOUR DIRECTORY>'
    }
}

Furthermore, if your external source directory is not under src/main, you could use a relative path like this:

sourceSets {
    main.java.srcDirs += 'src/main/../../../<YOUR DIRECTORY>'
}

You can add a source folder to the build script and then sync. Look for sourceSets in the documentation here: http://tools.android.com/tech-docs/new-build-system/user-guide#TOC-Basic-Project

I haven't found a good way of adding test source folders. I have manually added the source to the .iml file. Of course this means it will go away everytime the build script is synched.

While sourceSets allows you to include entire directory structures, there's no way to exclude parts of it in Android Studio (as of version 1.2), as described in https://stackoverflow.com/questions/16701256/android-studio-exclude-class-from-build.

Until Android Studio gets updated to support include/exclude directives for Android sources, symbolic links work quite well. If you're using Windows, native tools such as junction or mklink can accomplish the equivalent of symbolic links on Unix-like systems. Cygwin can also create these with a little coercion. See: https://stackoverflow.com/questions/5917249/git-symlinks-in-windows/30457566#30457566 and https://stackoverflow.com/questions/3648819/how-to-make-symbolic-link-with-cygwin-in-windows-7.

Here’s a complete Java module Gradle file that correctly generates and references the built artefacts within an Android multi-module application:

buildscript {
    repositories {
        maven {
            url "https://plugins.gradle.org/m2/"
        }
    }
    dependencies {
        classpath "net.ltgt.gradle:gradle-apt-plugin:0.15"
    }
}

apply plugin: "net.ltgt.apt"
apply plugin: "java-library"
apply plugin: "idea"

idea {
    module {
        sourceDirs += file("$buildDir/generated/source/apt/main")
        testSourceDirs += file("$buildDir/generated/source/apt/test")
    }
}

dependencies {

    // Dagger 2 and Compiler
    compile "com.google.dagger:dagger:2.15"
    apt "com.google.dagger:dagger-compiler:2.15"
    compile "com.google.guava:guava:24.1-jre"

}

sourceCompatibility = "1.8"
targetCompatibility = "1.8"

If you're not using Gradle (creating a project from an APK, for instance), this can be done through the Android Studio UI (as of version 3.3.2):

• Right-click the project root directory and pick Open Module Settings
• Hit the + Add Content Root button (center right)
• Add your path and hit OK

In my experience (with native code), as long as your .so files are built with debug symbols and from the same absolute paths, breakpoints added in source files will be automatically recognized.

This is for Kotlin DSL (build.gradle.kts):

android {
    sourceSets["main"].java.srcDirs("src/main/myDirectory/code/")
    sourceSets["main"].resources.srcDirs("src/main/myDirectory/resources/")

    // Another notation:
    // sourceSets {
    //     getByName("main") {
    //         java.srcDirs("src/main/myDirectory/code/")
    //         resources.srcDirs("src/main/myDirectory/resources/")
    //     }
    // }
}