Android Studio 1.0 and error "Library projects cannot set applicationId"

Libraries can't set applicationId and if you are working in a multi-module project and picking up flavors from a separate file , none of the above answers will work. For a modularized app, you need the following steps -

Create a flavors.gradle file in project root directory

 ext.flavorConfig = { // 1
    
        flavorDimensions "pricing"
        productFlavors {
            free {
                dimension "pricing"
                ext.myApplicationIdSuffix = '.free' // 2
            }
            paid {
                dimension "pricing"
                ext.myApplicationIdSuffix = '.paid'
            }
        }
    
        productFlavors.all { flavor -> // 3
            if (flavor.hasProperty('myApplicationIdSuffix') && isApplicationProject()) {
                flavor.applicationIdSuffix = flavor.myApplicationIdSuffix
            }
        }
    
    }
    
    def isApplicationProject() { // 4
        return project.android.class.simpleName.startsWith('BaseAppModuleExtension')
     
    }

• In 1 we export a closure so that we can use it in our modules’ build.gradle files.
• In 2 we define a custom myApplicationIdSuffix property. We cannot simply have applicationIdSuffix as it is not possible to use it in library modules (build would fail if you did).
• In 3 we iterate over created flavors and set applicationIdSuffix if we detect that it’s an application module only.
• 4 is a way to check where this closure is being used.

All that’s left is to use this closure in our modules’ build.gradle files. E.g. in application module this would look like this:

apply plugin: 'com.android.application'
apply from: "${rootProject.projectDir}/flavors.gradle"

android {
    // other config...

    with flavorConfig
}

If this isn't clear, you can check out this article for better understanding.

Just incase it helps some one :

When i imported an eclipse project into android studio,i got an error ::

"Error:Application and test application id cannot be the same"

Strange though,but i looked into the build.gradle and found the two placeholders,one for the application and other for testapplication.

I removed the testApplicationId from that as is suggested in this post and this helped me resolve the issue.

Note: This explaination is not related to the errors posted in this question,but might help someone who is getting a similar error.

Thanks to Joel for his correct answer: I need to remove only 1 line from te .gradle file:

defaultConfig {
        applicationId "com.super.app"   <---- remove this line
        minSdkVersion 15
        targetSdkVersion 19
        versionCode 1
        versionName "1.0"
    }

becomes

defaultConfig {
        minSdkVersion 15
        targetSdkVersion 19
        versionCode 1
        versionName "1.0"
    }

and my AndroidManifest.xml

 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        package="com.super.app">
...

This is the right solution if you don't need to rename the package name of your app. To rename it you need to use "flavours":

android {
   ...
   productFlavors {
       flavor1 {
           applicationId 'com.super.superapp'
       }
   }

Based on this info:

ApplicationId in Library Projects

You cannot use applicationId to customize the package of a library project. The package name has to be fixed in library projects (and specified as packageName in the manifest). The Gradle plugin did not enforce this restriction earlier.

Removing applicationId variable from the library's build.gradle file should resolve the issue.