Develop Reference

Android Studio Gradle dependency doesn't show up in External Libraries

I'm using Android Studio 3.0.1 and I'm trying to add an online dependency and while Gradle initially syncs without a problem it doesn't show my dependency in External Libraries and my code that references the dependency doesn't work.
Here's a snippet of what my build.gradle file looks like:
repositories {
mavenCentral()
maven { url 'https://oss.sonatype.org/content/groups/public/' }
}
dependencies {
compile group: 'com.fortysevendeg.android', name: 'swipelistview', version: '1.0-SNAPSHOT'
}
I'm pretty new to android development (took over an existing project from a dev who quit without leaving any documentation) so I'm not sure if this is a mistake with how to add a project dependency or if there is a problem with the dependency that I'm trying to add. Any help would be greatly appreciated!

I was able to get this to work by changing the dependency declaration to:
compile group: 'com.fortysevendeg.android', name: 'swipelistview', version: '1.0-SNAPSHOT', classifier: 'jar-with-dependencies'
The library artifacts up on the repository include an apklib and a JAR with a special classifier. The apklib format is not supported by Android Studio, and unfortunately the classifier on the JAR means that it's not accessible simply using the group-name-version format when declaring dependencies.

Your build.gradle file seems fine. If you want to keep the library specified as an external library, you can try and define the dependency using the alternative notation, replace:
compile group: 'com.fortysevendeg.android', name: 'swipelistview', version: '1.0-SNAPSHOT'
with:
compile 'com.fortysevendeg.android:swipelistview:1.0-SNAPSHOT'
The alternative approach is to download the jar file yourself and use it as a local dependency. If you navigate to the maven repository you can inspect the package which is included as a dependency and download the jar directly. Place the jar file in the libs folder of your project and add the following to your build.gradle file:
compile fileTree(dir: 'libs', include: ['*.jar'])
For further details on how to configure the dependencies of your gradle project, check out the Android Studio documentation here.
Based on the information you have provided, this should fix your issues. If this does not solve the error then there may be other issues with the project.

Your dependencies should not placed in the top-level build.gradle file where the repositories are defined. There is even a comment in that file that says so, by default.
You app dependencies should be the module's build.gradle along with the others like android-support
Additionally, that library is very old, and is a SNAPSHOT build, meaning it isn't meant to be generally used in a release environment. You should find an alternative... And there are plenty of other ListView swiping ones

Android can't find the third library on AAR

My AAR includes a picasso library, but in my java code can't find picasso.
Here is my build.gradle:
and here is my multi-image-selector AAR gradle:

Why you not using only
compile 'com.squareup.picasso:picasso:2.5.2'

The aar file doesn't contain the nested dependencies and doesn't have a pom file which describes the dependencies used by the library.
It means that, if you are importing a aar file using a flatDir repo you have to specify the dependencies also in your project.
In your case you have to add in your app (not the library):
compile 'com.android.support:appcompat-v7:23.0.1'
compile 'com.squareup.picasso:picasso:2.5.2'

If you use the gradle maven plugin to deploy the aar to a local repo, then you can get transitive dependencies to work. Here's how to do that:
How to use maven plugin to publish a library as an aar
How to enable transitive dependencies on the library dependency

Assume that you have one app and one library module. In your library module you use Picasso as dependency.
Let me explain step by step, with possible scenarios.
1- If you add your library module to your app module as the following :
implementation(project(":myLibrary"))
Your library works correctly.
2- If you add your library module to your app module as the following :
implementation files('../libs/mainLibrary-debug.aar')
You may get a crash if you don't put Picasso dependency to your app module. You have two options to get rid of this crash.
2.a.First option is to add Picasso library to your app module.
2.b.The second option is to compile you aar using any fat aar plugin. If you use a fat aar plugin, when you generate aar, it automatically downloads Picasso library and put it in aar. In this way, you don't need to add Picasso dependency into your app module. There are several fat aar plugins available, here is one of them : https://github.com/kezong/fat-aar-android

How is "libs" created and maintained in a gradle android project?

I currently am not using the "libs" folder for my third party dependencies (it seems they are added automatically to build/intermediates/pre-dexed/) but noticed that it may help static code analysis so I would like to add it to the project.
Note: I'm using maven dependencies.
My question: Are people using custom scripts to generate this folder? I hardly think that this is generated once and then manually maintained when there is a newer version available.
Please enlighten me!

With Android Studio AND Gradle, there is no need to use libs folder (except for old .jar library).
In fact you can develop Android app whitout Android Studio as in your build.gradle there is already a apply plugin: 'com.android.application'
Gralde is using Maven or jCenter via gradle dependencies to import libraries. Gradle and Android Gradle plugin will automaticly download the libs as you sayed in a build/ folder. It is not static and can be clean with the Clean projet on Android Studio. Also, Android Studio will add a warning when a new library version is available automaticly in your build.gradle.
Dont miss the old libs folder used to import .jar library

I currently am not using the "libs" folder for my third party dependencies (it seems they are added automatically to build/intermediates/pre-dexed/) but noticed that it may help static code analysis so I would like to add it to the project. Note: I'm using maven dependencies.
Don't confuse the libs folder with build/intermediates/pre-dexed/ folder.
Currently the gradle plugin for Android manages the build process and create these "internal" and intermediates folders.
My question: Are people using custom scripts to generate this folder?
I hardly think that this is generated once
You don't have to create this folder. The Gradle plugin for Android manage it for your. Also it will be deleted and recreated when your run a gradlew clean command.
and then manually maintained when there is a newer version available.
No. Your dependencies are defined in your build.gradle file.
When you define a new version, Gradle downloads the new dependency and updates the intermediate folders.
You can define your dependencies in many ways:
dependencies{
//You can create a folder and put jar files inside. You can use your favorite name, usually it is libs.
compile fileTree(dir: 'libs', include: ['*.jar'])
//The support libraries dependencies are in a local maven managed by SDK
compile 'com.android.support:appcompat-v7:23.0.0'
// A Maven dependency
compile 'com.squareup.picasso:picasso:2.5.2'
//A local library
compile project(':mylibrary')
//An aar file. It requires to define a repository.
//repositories{
// flatDir{
// dirs 'libs'
// }
//}
compile(name:'nameOfYourAARFileWithoutExtension', ext:'aar')
}

Local AAR file doesn't manage dependencies

I have worked on an Android library (an API client) that uses Retrofit and Joda DateTime.
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
compile 'com.android.support:appcompat-v7:22.2.0'
compile 'com.squareup.retrofit:retrofit:1.9.0'
compile 'joda-time:joda-time:2.8.1'
}
Now that the library is completed I compiled it into an AAR file and I want to use it in an application, so I added it to the libs folder of the application and included it in the build.gradle file like so :
dependencies {
compile(name:'s3papiandroidclient', ext:'aar')
//Some other things
}
However, when I try to initialize the API client from the library, the application crashes when it comes to calling objects from RetroFit or DateTime (For instance, retrofit.RestAdapter). It looks like Gradle does not read the dependencies from the AAR library, thus doesn't install Retrofit and DateTime in my application. I tried to use the transitive=true parameter on my AAR file, does not help.
Other point that might help, I tried to generate a POM file, and the dependencies don't appear in it either. It looks like there's really something going on with these and I am completely stuck on that.
The only workaround I could find is to add manually the dependencies from the AAR file to the app's build.gradle file but it doesn't make sense, I assume Gradle can import dependencies on its own !
Regards,
Gyoo.

It looks like Gradle does not read the dependencies from the AAR library
That is because there are no dependencies in an AAR file.
I tried to generate a POM file, and the dependencies don't appear in it either
Then there is a problem in how you are generating the POM file. Plus, AFAIK, you would need to put the AAR and its POM file in a repository, in order for Gradle to recognize the POM and use the dependency information inside of it.

Android AAR third party jars

I have made an AAR using Android Studio and I can successfully use it in any app. Problem is I have to add all the dependencies it needs manually to the app build.gradle (like compile 'org.slf4j:slf4j-android:1.7.10').
I want the AAR to actually include all these third-party dependencies it requires so I won't have to add them manually in the app. Is there a way you would know of?

If you use
compile fileTree(dir: 'libs', include: ['*.jar'])
and put a jar in libs folder, this jar will be included in the AAR.
But you have to put the jar yourself.
As far as I know, there is no way to put a repository dependency inside an AAR.