Collection of Extensions for String and SpannableString

CustomTypefaceSpan.kt

package com.collectiveidea.util.string

import android.graphics.Paint
import android.graphics.Typeface
import android.text.TextPaint
import android.text.style.MetricAffectingSpan

class CustomTypefaceSpan(private val typeface: Typeface) : MetricAffectingSpan() {
  override fun updateDrawState(drawState: TextPaint) = apply(drawState)
  override fun updateMeasureState(paint: TextPaint) = apply(paint)

  private fun apply(paint: Paint) {
    val oldTypeface = paint.typeface
    val oldStyle = oldTypeface?.style ?: 0
    val fakeStyle = oldStyle and typeface.style.inv()

    if (fakeStyle and Typeface.BOLD != 0) {
      paint.isFakeBoldText = true
    }

    if (fakeStyle and Typeface.ITALIC != 0) {
      paint.textSkewX = -0.25f
    }

    paint.typeface = typeface
  }
}

StringExt.kt

package com.collectiveidea.util.string

import android.content.Context
import android.support.v4.content.res.ResourcesCompat
import android.text.Html
import android.text.Spannable
import android.text.SpannableString
import android.text.Spanned
import android.text.style.AbsoluteSizeSpan
import android.text.style.ForegroundColorSpan
import android.text.style.StyleSpan
import android.text.style.TextAppearanceSpan
import com.collectiveidea.exampleapp.R
import timber.log.Timber

// Wrap a backwards compatible implementation of `Html.fromHtml()` as a string extension.
fun String.fromHtml(): Spanned {
  return if (android.os.Build.VERSION.SDK_INT < android.os.Build.VERSION_CODES.N) {
    @Suppress("DEPRECATION")
    Html.fromHtml(this)
  } else {
    Html.fromHtml(this, Html.FROM_HTML_MODE_LEGACY)
  }
}

// Return the string if it is not null or blank, otherwise return null.
// Example usage:
//   textView.text = nullableOrBlankOrValidString.presence() ?: "Default Filler Text"
fun String?.presence(): String? {
  return if (isNullOrBlank()) null else this
}

// Converts a regular `String` to a `SpannableString`
fun String.spannable(): SpannableString = SpannableString(this)

// Applies a `ForegroundColorSpan` to the receiver with the provided color at 
// the indices of the provided substring.
// If the receiver does not contain the matching substring, warn, and ignore.
// Returns the receiver to allow for chaining.
fun SpannableString.colorSpan(substring: String, color: Int): SpannableString {
  return applySpan(substring, ForegroundColorSpan(color))
}

// Applies a `TextAppearanceSpan` to the receiver with the provided `TextAppearance` 
// style at the indices of the provided substring.
// If the receiver does not contain the matching substring, warn, and ignore.
// Returns the receiver to allow for chaining.
fun SpannableString.textAppearanceSpan(
    context: Context,
    substring: String,
    style: Int
): SpannableString {
  val span = TextAppearanceSpan(context, style)
  return applySpan(substring, span).also {
    // Handle typeface being set by font resource
    val fontName = span.family
        ?.removePrefix("res/font/")
        ?.replaceAfter(".", "")
        ?.replace(".", "") ?: ""
    val res = fontName.presence()?.let { context.getResId(it, R.font::class.java) } ?: -1
    if (res != -1) { fontSpan(context, substring, res) }
  }
}

// Applies a `StyleSpan` to the receiver with the provided `Style` value 
// at the indices of the provided substring.
// If the receiver does not contain the matching substring, warn, and ignore.
// Returns the receiver to allow for chaining.
fun SpannableString.styleSpan(substring: String, style: Int): SpannableString {
  return applySpan(substring, StyleSpan(style))
}

// Applies a `AbsoluteSizeSpan` to the receiver with the provided size
// at the indices of the provided substring
fun SpannableString.sizeSpan(substring: String, size: Int): SpannableString {
  return applySpan(substring, AbsoluteSizeSpan(size))
}

// Applies a `CustomTypefaceSpan` to the receiver with the provided font resource
// at the indices of the provided substring.
// If the receiver does not contain the matching substring, warn, and ignore.
// Returns the receiver to allow for chaining.
fun SpannableString.fontSpan(context: Context, substring: String, fontRes: Int): SpannableString {
  if (fontRes == -1) {
    Timber.w("Font resource not found: -1")
    return this
  }
  val typeface = ResourcesCompat.getFont(context, fontRes)
  return typeface?.let { applySpan(substring, CustomTypefaceSpan(typeface)) } ?: this
}

// Applies the provided span to the recevier at the indices of the provided substring.
// If the receiver does not contain the matching substring, warn, and ignore.
// Returns the receiver to allow for chaining.
fun SpannableString.applySpan(substring: String, span: Any): SpannableString {
  val start = indexOf(substring, 0, true)
  if (start == -1) {
    Timber.w("Cannot apply span <$span>: <$this> does not contain substring <$substring>")
    return this
  }
  val end = start + substring.length
  setSpan(span, start, end, Spannable.SPAN_INCLUSIVE_INCLUSIVE)
  return this
}