What is the best way to define log TAG constant in Kotlin?

Question

I\'m creating my first Kotlin classes in my Android application. Usually for logging purposes I have a constant with name TAG. What I would do in Java is:

Answer 1

Declare of TAG variable with val

class YourClass {
   companion object {
      //if use java and kotlin both in project
      //private val TAG = MyClass::class.java.simpleName

      //if use only kotlin in project
      private val TAG = YourClass::class.simpleName
   }
}

Use the variable like

Log.d(YourClass.TAG, "Your message");
//or 
Log.e(TAG, "Your message");

Answer 2

You can try this:

companion object {
    val TAG = ClearCacheTask::class.java.simpleName as String
}

Answer 3

This extension allows us to use TAG in any class

val Any.TAG: String
    get() {
        val tag = javaClass.simpleName
        return if (tag.length <= 23) tag else tag.substring(0, 23)
    }

//usage
Log.e(TAG,"some value")

It it also validated to work as an Android valid Log tag.

Answer 4

The best way to log (imho) is using Timber: https://github.com/JakeWharton/timber

But if you don't want to use library then

TAG can be defined as an inlined extension property (e.g. in Extensions.kt):

inline val <reified T> T.TAG: String
    get() = T::class.java.simpleName

Some more extensions to not to write TAG all the time in Log.d(TAG, ""):

inline fun <reified T> T.logv(message: String) = Log.v(TAG, message)
inline fun <reified T> T.logi(message: String) = Log.i(TAG, message)
inline fun <reified T> T.logw(message: String) = Log.w(TAG, message)
inline fun <reified T> T.logd(message: String) = Log.d(TAG, message)
inline fun <reified T> T.loge(message: String) = Log.e(TAG, message)

And then you can use them in any class:

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    logd("Activity created")
}

Answer 5

You can define your TAG by @JvmField as below:

companion object {
    @JvmField val TAG: String = MyClass::class.java.simpleName
}

For more details, you can read this article : Kotlin's hidden costs

Answer 6

Updated answer with Kotlin 1.2.20

class MyClass {
    companion object {

        @JvmField
        public val FOO = 1
    }
}

uses

MyClass.FOO