Set Package Name

Your package name is your app’s unique ID, like com.yourname.yourapp. Android and Google Play use it to tell your app apart from every other app.

The sample uses dev.jahir.blueprint.app. You have to change it, because Google Play only allows one app per package name and that one is already taken.

This is the step people struggle with the most, so it’s worth going slowly. Follow the steps in order and your app will build at the end. 💪

Caution

Once you publish your app, you can’t change its package name. Google Play treats a new package name as a completely different app.

What you’re going to change

The package name lives in two places, and both have to be exactly the same:

1. The app ID in buildSrc/src/main/java/MyApp.kt. This is what Android and Google Play see.
2. The Kotlin package of the 4 files in app/src/main/kotlin/. This is the folder they live in, plus the package line at the top of each file.

If they don’t match, the app either doesn’t build, or it builds and then crashes as soon as you open it. That’s because:

• AndroidManifest.xml points to .MainActivity and .MyApplication. Android completes the leading . with your app ID, so it looks for com.yourname.yourapp.MainActivity. If the file is still in the old package, Android can’t find it.
• Android Studio generates the BuildConfig and R classes in your app ID’s package. Your Kotlin files can only use them without an import if they’re in that same package.

Before you start

• Pick your package name. It should look like com.yourname.yourapp:
  • It needs at least two parts separated by dots.
  • Each part must start with a letter.
  • Use only lowercase letters, numbers and underscores.
  • Don’t use dev.jahir. That one belongs to the sample.
• Run the sample once without changing anything (see Get Started). If the untouched sample doesn’t build, the problem is your setup, not this step.
• If you use Git, commit now, so you can go back if something goes wrong.

In the steps below, replace com.yourname.yourapp with your own package name.

Step 1: Show the real folders

By default, Android Studio’s Project panel (on the left) uses the Android view, which hides and merges some folders. You need to see the real ones.

1. At the top of the Project panel, click the dropdown that says Android and choose Project.
2. Open the panel’s options menu (the ⋮ or gear icon at the top of the panel), go to Appearance, and make sure Compact Middle Packages is unchecked.

Now app/src/main/kotlin/dev/jahir/blueprint/app shows as separate nested folders, which you’ll need in the next steps.

Step 2: Create your package

1. In the Project panel, expand app/src/main/.
2. Right-click the kotlin folder and select New → Package.
3. Type your package name, for example com.yourname.yourapp, and press Enter.

You should now see a new folder structure next to dev: kotlin/com/yourname/yourapp.

Step 3: Move the 4 files

1. Expand app/src/main/kotlin/dev/jahir/blueprint/app. Inside are 4 files:
   • MainActivity.kt
   • MuzeiService.kt
   • MyApplication.kt
   • NotificationServiceExtension.kt
2. Select all 4 (click the first one, then Shift + click the last one).
3. Drag them onto your new yourapp folder.
4. A Move dialog opens. Click Refactor.

Important

Move the files inside Android Studio, not with Finder or File Explorer. When Android Studio moves a file, it also updates the package line inside it. Your file manager doesn’t.

Step 4: Check the package line

Open each of the 4 files. The very first line should be your package name:

package com.yourname.yourapp

If any file still says package dev.jahir.blueprint.app, change it by hand.

Step 5: Delete the old folder

The dev/jahir/blueprint/app folder should now be empty. Right-click the dev folder (inside app/src/main/kotlin) and select Delete.

If Android Studio warns that something inside is still in use, stop and check step 3 again. Something didn’t move.

Step 6: Set the app ID

Open buildSrc/src/main/java/MyApp.kt and set appId to the exact same package name:

object MyApp {
    const val appId = "com.yourname.yourapp"
    const val version = 1
    const val versionName = "1.0.0"
}

While you’re here, you can also set your version. See Set App Version.

Note

You don’t need to edit AndroidManifest.xml. Older versions of this guide asked you to change a package="..." line there. Current versions don’t have it: the app takes the package name from appId automatically.

Step 7: Fix leftover imports

Some files may still import BuildConfig or R from the old package. Find them all at once:

1. Open Edit → Find → Find in Files (Ctrl + Shift + F on Windows and Linux, Cmd + Shift + F on Mac).
2. Search for import dev.jahir.

You’ll get a few results. Only change the ones that end in .app.R or .app.BuildConfig, for example:

import dev.jahir.blueprint.app.R

Either delete that line, or change it to use your package:

import com.yourname.yourapp.R

In the Blueprint sample, NotificationServiceExtension.kt imports dev.jahir.kuper.app.R. That’s wrong for your app too, so change it to your package as well.

Leave every other dev.jahir. import alone, like dev.jahir.blueprint.ui.activities.... Those come from the Blueprint library itself, not from your app.

Note

Some of these imports are inside comments, in code that’s turned off until you set up notifications. Fix them now anyway, so notifications work later without surprises.

Step 8: Sync and build

1. Click File → Sync Project with Gradle Files and wait until it finishes.
2. Click Build → Clean Project, then Build → Rebuild Project. If your version of Android Studio doesn’t show these options, skip this part. The next step builds the app anyway.
3. Press the green Run button to install the app on your emulator or phone.

If the app opens, you’re done. 🎉

Quick check

Everything in this table should show your package name:

Where	What it should say
buildSrc/src/main/java/MyApp.kt	const val appId = "com.yourname.yourapp"
The folder of your Kotlin files	app/src/main/kotlin/com/yourname/yourapp/
First line of each of the 4 files	package com.yourname.yourapp
Imports of R or BuildConfig	None, or com.yourname.yourapp.R / com.yourname.yourapp.BuildConfig

Common problems

• “Unresolved reference: BuildConfig” or “Unresolved reference: R”

  The package line of that file doesn’t match appId, or the file still imports the old package. Go back to steps 4 and 7, then sync again.

• The app installs, but closes as soon as you open it

  Open Logcat at the bottom of Android Studio and look for ClassNotFoundException. It means your Kotlin files are in a different package than appId. Compare both against the table above.

• You still see a dev.jahir.blueprint.app folder

  The Project panel is probably back in the Android view, or Compact Middle Packages is on. Repeat step 1.

• Everything matches the table, but Android Studio still shows errors

  Android Studio’s cache is out of date. Click File → Invalidate Caches, check Clear file system cache and local history, and click Invalidate and Restart.

Still stuck? Ask in the Discord server. Include a screenshot of your Project panel and the error message, so people can help you faster.