How to detect the last string of a TextView contains 0 to 9

Issue

I'm a beginner in Android software development. I'm making a calculator app to test my skills. In a calculator there are 0-9 numeric and some others operators like +, -, *, / etc. In the time of Equal functionality, I have to make sure that the last string of the TextView has any number (0-9), not any operators.

My equal fun is like that:

fun onEqual(view: View) {
    if (tv_input.text.contains("0-9")) {
        Toast.makeText(this, "Last string is a number, not operator", Toast.LENGTH_SHORT).show()
    }
}

Solution

You need to use Kotlin regular expression matches

val lastString = "573" // input
val pattern = "-?\\d+(\\.\\d+)?".toRegex()
/**
-?         allows zero or more - for negative numbers in the string.
\\d+       checks the string must have at least 1 or more numbers (\\d).
(\\.\\d+)? allows zero or more of the given pattern (\\.\\d+) 
           In which \\. checks if the string contains . (decimal points) or not
           If yes, it should be followed by at least one or more number \\d+.
**/
val isLastString = pattern.matches(lastString)

Answered By - Vidyesh Churi