Kotlin getString() exepects an Int? Why?

Question

I'm going through https://developer.android.com/codelabs/basic-android-kotlin-training-project-lemonade. Here, while trying to make "else" do nothing, I've stumbled upon "Type mismatch" errors.
Regarding setting the view elements, this is what I've come up with so far:

private fun setViewElements() {
        val textAction: TextView = findViewById(R.id.text_action)
        val text = when (lemonadeState) {
            SELECT -> R.string.lemon_select
            SQUEEZE -> R.string.lemon_squeeze
            DRINK -> R.string.lemon_drink
            RESTART -> R.string.lemon_empty_glass
            else -> null
        }
        textAction.text = getString(text)

I've tried all workarounds for "doing nothing": {}, Unit, null, empty string (and even data types like String, Int, Double...) but all I get is a "Type mismatch: inferred type is Any but Int was expected" (or "...inferred type is Int?...") error. So much so that an Int does makes the error disapear, as in:

...
else -> 0

According to the docs, both versions of getString(), single and double paramater, work stritcly with strings: parameter(s) and return type. So why on Earth is it saying this function expects an Int?
Also, writing text as an instance of Int (text: Int), doesn't affect anything, meaning it is in fact an Int. I am missing something big here: aren't those R.string.<name> supposed to be strings?

Btw, I did try this:

private fun setViewElements() {
        val textAction: TextView = findViewById(R.id.text_action)
        val text = when (lemonadeState) {
            SELECT -> R.string.lemon_select
            SQUEEZE -> R.string.lemon_squeeze
            DRINK -> R.string.lemon_drink
            else -> R.string.lemon_empty_glass
        }
        textAction.text = getString(text)

which is errorless and looks better. However, I wanted to keep the specificity, if possible (and it doesn't answer my question).

"According to the docs, both versions of getString(), single and double paramater, work stritcly with strings" – Where are you seeing that? All of those `R.string` values are `Int`s, if you inspect them. — Mike M., Dec 16 '21 at 12:59
https://developer.android.com/reference/kotlin/android/os/BaseBundle#getstring_1 @MikeM. — 101is5, Dec 16 '21 at 13:00
Aren't the generated `R.` resource values all `int`s, and something like `getString` is what does the lookup against the XML etc? — msbit, Dec 16 '21 at 13:00
Wrong one. You're dealing with [`Context#getString()`](https://developer.android.com/reference/android/content/Context#getString(int)). — Mike M., Dec 16 '21 at 13:02
@msbit this is what makes no sense to me. Aren't they Strings? — 101is5, Dec 16 '21 at 13:03
Ok, so probably what is expecting something here isn't getString(), but the variable text. Then, although e.g. R.string. refer to a string, they actually point to an Int first before returning the string. Is that it? — 101is5, Dec 16 '21 at 13:09
`R.string.*` are not strings. They are integers that identify strings. Note that you can have for example a multilingual application and then the same `R.string.something` points at different strings depending on the language. `getString()` looks through the resources for the proper string identified by the provided integer. — broot, Dec 16 '21 at 13:14
If they were already strings you wouldn't have to call ``getString`` with them ;) — cactustictacs, Dec 16 '21 at 17:48

score 3 · Answer 1 · answered Dec 16 '21 at 14:00

As the comments pointed out, getString takes a Int, which is a resource ID. This identifies one of the strings you have written in your XML files. This way, you can easily have e.g. multiple versions of the string, one for each localisation for your app, and getString will figure out which string to use based on the device locale. R.string.lemon_select, R.string.lemon_squeeze etc are those identifiers.

One way to do nothing, is to return just evaluate to null - you just have to handle the null value yourself. This will cause text to be of type Int?.

val text = when (lemonadeState) {
    SELECT -> R.string.lemon_select
    SQUEEZE -> R.string.lemon_squeeze
    DRINK -> R.string.lemon_drink
    RESTART -> R.string.lemon_empty_glass
    else -> null
}

if (text != null) {
    textAction.text = getString(text)
}

From your last code snippet though, it seems like you want to set it to lemon_empty_glass when the else branch is reached. If that is the case, then you can do:

val text = when (lemonadeState) {
    SELECT -> R.string.lemon_select
    SQUEEZE -> R.string.lemon_squeeze
    DRINK -> R.string.lemon_drink
    RESTART -> R.string.lemon_empty_glass
    else -> null
}
textAction.text = getString(text ?: R.string.lemon_empty_glass)

Kotlin getString() exepects an Int? Why?

1 Answers1