Kotlin Android Studio Warning "Do not concatenate text displayed with setText. Use resource string with placeholders."

Question

I made a simple program to learn about concatenation in android studio with Kotlin. So, I tried to get a string value from resources in strings.xml as shown below and concatenate with a value

<string name="txt_show">Your lucky number is %1$s</string>

I got warning "Do not concatenate text..." from getString

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    val firstNumber = numEditText.text

    processButton.setOnClickListener {
        val result = concatText(firstNumber.toString().toDouble())
        resultView.text = getString(R.string.txt_show, " ") + result.format(2)

    }
}

private fun concatText(myNumber: Double): Double {
    val luckyNumber = 1.79
    return luckyNumber * myNumber
}
private fun Double.format(digits: Int) = java.lang.String.format("%.${digits}f", this)} 

By replacing

resultView.text = getString(R.string.txt.show, " ") + result.format(2)

with

val finalResult =  result.toInt()<p>
resultView.text = getString(R.string.txt_show, finalResult)<p>

And replace %1$s to %1$d in resources of strings.xml

The warning is gone but I got problems, first the result is integer which is not what I expected. It should be double. Second, adding the function format in getString will stop the program with "Unexpected Error..." message on the screen.

How can I solve this problem?

Answer 1

If you have string with some placeholders like:

<string name="price_string">Your price: %d</string>

First you have to read this value and next fill it

JAVA

String text = getString(R.string.price_string, 2.5);

KOTLIN

val text = getString(R.string.price_string, 2.5)

.

or in "longer" way:

JAVA:

// Read text
String priceString = getString(R.string.price_string);

// Fill it
String output = String.format(priceString, 2.5);

KOTLIN

// Read text
val priceString = getString(R.string.price_string)

// Fill it
val output = String.format(priceString, 2.5)
// or
val output = priceString.format(2.5)

If you have %s you have to fill it with String. Here you have more info: https://developer.android.com/guide/topics/resources/string-resource#formatting-strings

Answer 2

first the result is integer which is not what I expected. It should be double.

Then why did you call toInt? Just use

resultView.text = getString(R.string.txt_show, result) 

and %1$.2f (or just %.2f) in the string instead of %1$d to format to two digits fractional number. You can see it's specified the same as in the format function in your code. The documentation for format strings (what all of these %d etc. mean) is at https://developer.android.com/reference/java/util/Formatter.html.