class MainActivity : AppCompatActivity() {

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

        val textView: TextView = findViewById(R.id.tv_hello)
        val text = "Hello World!"
        val purple = getColor(R.color.purple_200)
        val teal = getColor(R.color.teal_200)
        val spannable = text.toSpannable()
        spannable[0..text.length] = LinearGradientSpan(text, text, purple, teal)
        textView.text = spannable
    }
}