error “activity class does not exist” when launching android app with adb shell am start

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Watch out for applicationIdSuffix!!

When using applicationIdSuffix in build.gradle the suffix only applies to your application id, not to the actual package structure in the generated .apk, meaning that referencing your activity the short way (.MainActivity, instead of using its fully qualified name) will add the application id suffix to the path of the activity too and hence AS will fail to locate it. E.g.:

My application’s package name is my.application.package, and I have this in my app module’s build.gradle:

buildTypes {
           
    someBuildType {
        [...]
        applicationIdSuffix ".dev"
    }
}

When trying to execute, let’s say MainActivity (which is located in the root package) from the command line:

$ adb shell am start -n my.application.package.dev/.MainActivity

actually resolves to

$ adb shell am start -n my.application.package.dev/my.application.package.dev.MainActivity

But MainActivity is actually located in my.application.package.MainActivity, not in my.application.package.dev.MainActivity, because applicationIdSuffix changes only the application id, not the actual package structure, so it will fail to locate it.

Therefore, you should use the activity’s fully qualified name:

$ adb shell am start -n my.application.package.dev/my.application.package.MainActivity

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