How can I fix this? cant put setError to my editText

Question

I make my first android app with Android Studio, and now I want to make a setError on my editText, but I cant, I only can put a toast here is my code:

class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)
        binding.calculateButton.setOnClickListener { calculateTip() }
    }

    private fun calculateTip() {
        val stringInTextField = binding.costOfProduct.text.toString()
        val stringInTextField1 = binding.amountOfProduct.text.toString()
        if (stringInTextField.isEmpty()) {
            Toast.makeText(this, "this cant be empty", Toast.LENGTH_SHORT).show()
            return
        }
        val cost = stringInTextField.toDouble() / stringInTextField1.toDouble()
        val tipPercentage = when (binding.productOptions.checkedRadioButtonId) {
            R.id.option_normal -> 1.5
            R.id.option_60 -> 1.6
            R.id.option_70 -> 1.7
            else -> 2.0
        }
        var product = tipPercentage * cost
        val roundUp = binding.IVA.isChecked
        if (roundUp) {
            product = (tipPercentage * cost) * 1.21
        }
        val formattedTip = NumberFormat.getCurrencyInstance().format(product)
        binding.result.text = getString(R.string.resultado, formattedTip)
    }
}

Answer 1

You should use to setError()

Like this: stringInTextField.setError("this cant be empty")

For more information: Show Error on the tip of the Edit Text Android

Answer 2

you can use this following code according to your code:

if (stringInTextField.isEmpty()) { stringInTextField.setError("this cant be empty") return; }