Unresolved Reference using Kotlin for android

Question

I am getting Unresolved Reference when compiling

Error:(42, 26) Unresolved reference: r1 Error:(42, 36) Unresolved reference: ds

in the onClick method variables r1, and ds are shown to be in errors. in kotlin all varibales are final. so how come it is not accepting it. please advice following is the script

class MainActivity : AppCompatActivity(), View.OnClickListener {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val b1: Button = findViewById(R.id.add)

        val a1: EditText = findViewById(R.id.opr1)
        val a2: EditText = findViewById(R.id.opr2)

        val d1: Int = (a1.getText().toString().toInt())
        val d2: Int = (a2.getText().toString().toInt())

      var r1: TextView = findViewById(R.id.res)
        var ds :Int =d1+d2


    }

    override fun onClick(v: View?) {

        when (v?.id) {

            R.id.add ->  r1.text= (ds).toString()

        }
    }
}

As to your next question: Are you sure you want to compute d1 + d2 only once at the beginning? You should probably move reading current values to the click listener. (Do what CrazyApple says.) — Eugen Pechanec
– Eugen Pechanec, Commented Oct 22, 2017 at 11:57

CrazyApple · Accepted Answer · 2017-10-22 12:07:15Z

1

ds is local variable that can only be accessed within the function onCreate(). If you want to sum up the numbers of the EditText, you should put your addition logic inside the onClick() method:

override fun onClick(v: View) {
    when (v.id) {
        R.id.add -> {
            val d1: Int = et1.text.toString().toInt()
            val d2: Int = et2.text.toString().toInt()
            val ds = d1 + d2
            r1.text = ds.toString()
        }
    }
}

Also, you should declare r1 and other view reference as class member so that they can be accessed within your Activity class but not only onCreate().

edited Oct 22, 2017 at 12:07

answered Oct 22, 2017 at 11:57

CrazyApple

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2 Comments

Eugen Pechanec Over a year ago

I think it's safe to say that v is never null.

reader Over a year ago

what you are suggesting is correct, but some times we want same variable in the main and in the methods so this will create a confilct it is better to define it outside the on create as suggested by eugen pechanec ,thank you

Eugen Pechanec · Accepted Answer · 2017-10-22 11:52:36Z

0

r1 is a local variable in onCreate so it's not accessible outside of this function.

Declare it outside of the function like so:

private lateinit var r1: TextView

Assign it in onCreate like so:

r1 = findViewById(R.id.res)

Then you can access it as you expect:

r1.text= ds.toString()

The same rule applies for other variables you want to access outside of onCreate.

Why lateinit

onCreate is not a constructor so r1 is uninitialized before that. But you know that onCreate is the first thing called in the activity lifecycle so when you initialize the variable here it will always be non-null.

Otherwise you'd have to declare the variable like this:

private var r1: TextView?

and access it with the !! operator, for example:

r1!!.setText(...)

answered Oct 22, 2017 at 11:52

Eugen Pechanec

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2 Comments

Eugen Pechanec Over a year ago

Unrelated: While at it, please, give your variables more meaningful names. When you look at the code in a few weeks you're going to ask yourself "What the hell does r1 mean?".

reader Over a year ago

thank you for the detailed explanation.i did forgot to declare it outside the oncreate. you are right the variable names should be easy to understand i will definitely follow it from the next tutorial.

Sergio · Accepted Answer · 2017-10-22 11:52:54Z

0

The variable ds only exists into the first function. You must declare it outside to access it from the second.

answered Oct 22, 2017 at 11:52

Sergio

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1 Comment

reader Over a year ago

yes sir u r right , i missed this point. thank you for the reply

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