This code is the utility for span the textview, modify textcolor, textstyle, textsize and clickable specific text as per you want in one textview. Copy and paste SpanTextUtility.kt file in the project and start using it.

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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/textHello"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

MainActivity.kt

package com.textspansample

import android.graphics.Color
import android.graphics.Typeface
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.text.TextUtils
import android.text.method.LinkMovementMethod
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)
      
        val helloMessage = spannable("Hello  ", {
            textColor = Color.BLUE
            textSize = 50F
            textStyle = Typeface.ITALIC
        })
        val worldMessage = spannable("World!", {
            textColor = Color.RED

            textSize = 75F

            textStyle = Typeface.BOLD

            clickableSpan = {
                Toast.makeText(this@MainActivity, "Clicked", Toast.LENGTH_SHORT).show()
            }

            // if you set clickable then you should add this
            textHello.movementMethod = LinkMovementMethod.getInstance()

            // set highlightColor for when text click this color set as background color
            textHello.highlightColor = Color.TRANSPARENT

            // set text link color, if this color is not set then it will take a ColorAccent by default
            textHello.setLinkTextColor(Color.RED)
        })

        textHello.text = TextUtils.concat(helloMessage, worldMessage)
    }
}

SpanTextUtility.kt

class SpanAttributes(context: Context) {
    private val mContext = context
    private val defaultTextView = TextView(mContext)
    var textSize = defaultTextView.textSize
    var textColor = defaultTextView.currentTextColor
    var textStyle = defaultTextView.typeface.style
    var clickableSpan: (() -> Unit)? = null
}

fun Context.spannable(text: String, func: SpanAttributes.() -> Unit): SpannableString {

    val sb = SpannableString(text)

    val spanAttributes = SpanAttributes(this).apply(func)


    // text size
    sb.setSpan(AbsoluteSizeSpan(spanAttributes.textSize.toInt()), 0, text.length, 0)

    // text color
    sb.setSpan(ForegroundColorSpan(spanAttributes.textColor), 0, text.length, 0)

    // text style
    sb.setSpan(StyleSpan(spanAttributes.textStyle), 0, text.length, 0)

    // click
    spanAttributes.clickableSpan?.let {
        sb.setSpan(object : ClickableSpan() {
            override fun onClick(widget: View?) {
                spanAttributes.clickableSpan?.invoke()
            }
        }, 0, text.length, 0)
    }

    return sb
}