Spannable String

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/textViewTwo"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="24dp"
        android:layout_marginTop="24dp"
        android:layout_marginEnd="24dp"
        android:text="Text Two"
        android:textColor="@color/black"
        android:textSize="22sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textViewOne" />

    <TextView
        android:id="@+id/textViewOne"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="24dp"
        android:layout_marginTop="24dp"
        android:layout_marginEnd="24dp"
        android:text="Text One"
        android:textColor="@color/black"
        android:textSize="22sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/textViewThree"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="24dp"
        android:layout_marginTop="24dp"
        android:layout_marginEnd="24dp"
        android:text="Text Three"
        android:textColor="@color/black"
        android:textSize="22sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textViewTwo" />

</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.kt

package com.sriyank.spannablestring

import android.graphics.Color
import android.graphics.Typeface
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.text.Spannable
import android.text.SpannableString
import android.text.SpannableStringBuilder
import android.text.TextPaint
import android.text.method.LinkMovementMethod
import android.text.style.*
import android.view.View
import android.widget.TextView
import android.widget.Toast
import kotlinx.android.synthetic.main.activity_main.*

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

        textOneSpan()
        textTwoSpan()
        textThreeSpan()
    }

    private fun textOneSpan() {
        val spannableStringBuilder = SpannableStringBuilder("Hi Sriyank Siddhartha.")

        val fColor = ForegroundColorSpan(Color.RED)
        spannableStringBuilder.setSpan(fColor, 0, 2, Spannable.SPAN_INCLUSIVE_EXCLUSIVE)

        val bColor = BackgroundColorSpan(Color.GREEN)
        spannableStringBuilder.setSpan(bColor, 3, 21, Spannable.SPAN_INCLUSIVE_EXCLUSIVE)

        spannableStringBuilder.append(" Welcome!")
        textViewOne.text = spannableStringBuilder
    }

    private fun textTwoSpan() {

        val spannableString = SpannableString("How are you?")

        val sizeSpan = RelativeSizeSpan(2f)
        spannableString.setSpan(sizeSpan, 0, 3, Spannable.SPAN_INCLUSIVE_EXCLUSIVE)

        val styleSpan = StyleSpan(Typeface.BOLD)
        spannableString.setSpan(styleSpan, 0, 3, Spannable.SPAN_INCLUSIVE_EXCLUSIVE)

        val underlineSpan = UnderlineSpan()
        spannableString.setSpan(underlineSpan, 8, 11, Spannable.SPAN_INCLUSIVE_EXCLUSIVE)

        textViewTwo.text = spannableString
    }

    private fun textThreeSpan() {

        val spannableString = SpannableString("Click to know")

        val clickableSpan = object : ClickableSpan() {
            override fun onClick(widget: View) {
                Toast.makeText(this@MainActivity, "I am great!", Toast.LENGTH_SHORT).show()
            }

            override fun updateDrawState(ds: TextPaint) {
                super.updateDrawState(ds)

                ds.color = Color.BLUE
                ds.isUnderlineText = false
            }
        }

        spannableString.setSpan(clickableSpan, 0, 13, Spannable.SPAN_INCLUSIVE_EXCLUSIVE)

        textViewThree.text = spannableString
        textViewThree.movementMethod = LinkMovementMethod.getInstance()
    }
}

Use it as GIST and source code too. Thanks