Android：如何将 R.string 值从 strings.xml 设置为 Z539A3A5859D24EFB74 中的全局常量

Question

I'm new to Kotlin so maybe I'm missing something obvious, but I couldn't find an answer through Google.

How can I set the value of a Kotlin constant to a strings.xml resource value? I've tried to do it like below but it's throwing the following error:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference

This is my code, the first val declaration fails:

class MainActivity: AppCompatActivity() {

        private val STATUS_PREP = getString(R.string.status_prep) //THIS LINE FAILS
        private val STATUS_FIGHT = "fight" //res.getString(R.string.status_fight)
        private val STATUS_REST = "rest" //res.getString(R.string.status_rest)
        private val STATUS_COMPLETE = "complete" //res.getString(R.string.status_complete)
        private val STATUS_PAUSED = "paused" //res.getString(R.string.status_paused)

Answer 1

Do this instead.

class MainActivity : AppCompatActivity() {

    private val STATUS_PREP: String by lazy {
        getString(R.string.status_prep_2) 
    }

    // OR

    private lateint var STATUS_PREP: String

    override fun onCreate(savedInstanceState: Bundle?) {
        // snip
        initString()
    }

    private fun initString() {
        STATUS_PREP = getString(R.string.status_prep) 
        // Init all your string here
    }
}

You are getting the exception because context is not initialized right after an instance of an activity is created.

Answer 2

You can create a class that inherits Application class and create inside it static field that will keep reference to application context like this:

class MyApplication: Application() {
    companion object {
         var context: Context? = null; private set
    }

     override fun onCreate() {
        super.onCreate()
        context = applicationContext
     }
}

after that put it's name in AndroidManifest.xml like this:

<application
    android:name="com.yourpackage.MyApplication"
    ...
    // many other tags>
<application>

And then you can simply use it in everywhere in your app like this:

class MainActivity : AppCompatActivity() {
     private val STATUS_PREP = MyApplication.context!!.getString(R.string.status_prep)
}