Droidcon SF: Level up your extension game

PRESENTED AT:
Droidcon San Francisco
https://www.sf.droidcon.com/speaker/Aida-Issayeva

DATE:
November 26, 2019

DESCRIPTION:
In this talk I'll go over some good and bad practices about using extensions in Kotlin, as well as use cases for the Kotlin's standard and Android KTX extension functions.
Link to sample code: https://github.com/AidaIssayeva/Level-up-your-extension-game

MORE TALKS & ARTICLES FROM ME: https://cupsofcode.com/talks/

Transcript

1. Level up
   your extension
   game
   Aida Issayeva
   @aida_isay
   

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2. Why we need it?
   

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3. to make our lives
   easier
   

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4. Example:
   
   styling a text
   

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6. Without extensions:
   private fun spansWithoutExtensions(): SpannableStringBuilder {
   val firstPart = getString(R.string.what_is_android)
   val spannableStringBuilder = SpannableStringBuilder()
   spannableStringBuilder.append(firstPart)
   spannableStringBuilder.append("\n")
   spannableStringBuilder.setSpan(
   StyleSpan(Typeface.BOLD),
   0,
   firstPart.length,
   Spannable.SPAN_INCLUSIVE_INCLUSIVE
   )
   spannableStringBuilder.setSpan(
   RelativeSizeSpan(2f), 0,
   firstPart.length,
   Spannable.SPAN_INCLUSIVE_INCLUSIVE
   )
   spannableStringBuilder.setSpan(
   ForegroundColorSpan(Color.WHITE),
   0,
   firstPart.length,
   Spannable.SPAN_INCLUSIVE_INCLUSIVE
   )
   val secondPart = getString(R.string.what_is_android_answer)
   spannableStringBuilder.append(secondPart)
   spannableStringBuilder.setSpan(
   ForegroundColorSpan(
   ContextCompat.getColor(
   this@MainActivity,
   R.color.colorAccent
   )
   ),
   firstPart.length,
   firstPart.length + secondPart.length,
   Spannable.SPAN_EXCLUSIVE_INCLUSIVE
   )
   spannableStringBuilder.append("\n")
   val thirdPart = getString(R.string.faq)
   }
   spannableStringBuilder.append(thirdPart)
   spannableStringBuilder.setSpan(
   ForegroundColorSpan(
   ContextCompat.getColor(
   this@MainActivity,
   R.color.dirty_white
   )
   ),
   beginning,
   ending,
   Spannable.SPAN_EXCLUSIVE_INCLUSIVE
   )
   spannableStringBuilder.append(" ")
   val clickableText = "Android website."
   spannableStringBuilder.append(clickableText)
   spannableStringBuilder.setSpan(
   object : ClickableSpan() {
   override fun onClick(widget: View) {
   //open webview
   val url = getString(R.string.android_website)
   startActivity(Intent(Intent.ACTION_VIEW, Uri.parse(url)))
   }
   override fun updateDrawState(ds: TextPaint) {
   super.updateDrawState(ds)
   ds.isUnderlineText = true
   }
   }, spannableStringBuilder.length - clickableText.length,
   spannableStringBuilder.length,
   Spannable.SPAN_INCLUSIVE_INCLUSIVE
   )
   spannableStringBuilder.setSpan(
   ForegroundColorSpan(Color.GREEN),
   spannableStringBuilder.length - clickableText.length,
   spannableStringBuilder.length,
   Spannable.SPAN_INCLUSIVE_INCLUSIVE
   )
   return spannableStringBuilder
   }
   

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7. With extensions:
   private fun spansWithExtensions(): SpannedString {
   return buildSpannedString {
   bold { color(Color.WHITE) { scale(2f) { append(getString(R.string.what_is_android)) } } }
   lineBreak()
   color(ContextCompat.getColor(this@MainActivity, R.color.colorAccent)) {
   append(
   getString(R.string.what_is_android_answer)
   )
   }
   lineBreak()
   color(
   ContextCompat.getColor(
   this@MainActivity,
   R.color.dirty_white
   )
   ) { append(getString(R.string.faq)) }
   space()
   underline {
   inSpans(
   object : ClickableSpan() {
   override fun onClick(widget: View) {
   //open webview
   val url = getString(R.string.android_website)
   startActivity(Intent(Intent.ACTION_VIEW, Uri.parse(url)))
   }
   },
   ForegroundColorSpan(Color.GREEN)
   ) {
   append("Android website.")
   }
   }
   }
   }
   

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8. How to make extension?
   

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9. data class DomesticAnimal(
   val id: String,
   val name: String,
   val farmLocation: String,
   val type: Type,
   val logo: String,
   val longDescription: String,
   val shortDescription: String
   )
   

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10. data class DomesticAnimal(
    val id: String,
    val name: String,
    val farmLocation: String,
    val type: Type,
    val logo: String,
    val longDescription: String,
    val shortDescription: String
    )
    data class Animal(
    val id: String,
    val name: String,
    val isDomestic: Boolean,
    val inRedList: Boolean,
    val description: String,
    val logo: String
    )
    

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11. fun DomesticAnimal.toAnimal(): Animal {
    return Animal(
    id = id,
    name = name,
    logo = logo,
    isDomestic = true,
    description = shortDescription,
    inRedList = false
    )
    }
    

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12. override fun onCreate(savedInstanceState: Bundle?) {
    . . .
    val domesticAnimal = DomesticAnimal(
    name = "Bactrian Camel",
    . . .
    farmLocation = "Aral Sea"
    )
    val animal = domesticAnimal.toAnimal()
    }
    

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13. How to use extension in java classes?
    

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20. @InlineOnly
    When can you not use extensions in java?
    

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21. Common practices
    

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22. some sad…
    

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23. Business logic on android and java common types
    fun CharSequence.toAnimal(): Animal {
    return Animal(
    id = this.toString(),
    name = this.toString(),
    logo = "",
    isDomestic = false,
    inRedList = false,
    description = this.toString()
    )
    }
    

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24. Do business to business or
    common to common instead
    fun WildAnimal.toAnimal(): Animal {
    return Animal(
    id = id,
    name = name,
    logo = logo,
    isDomestic = false,
    description =
    shortDescription,
    inRedList = inRedList
    )
    }
    @kotlin.internal.InlineOnly
    public inline fun String.toPattern(flags: Int = 0):
    java.util.regex.Pattern {
    return java.util.regex.Pattern.compile(this,
    flags)
    }
    

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25. Modifying members of a class
    fun MainActivity.showWhiteLoadingIndicator() {
    mNumActiveLoadingIndicators++
    runOnUiThread {
    . . .
    }
    }
    class MainActivity : AppCompatActivity() {
    var mNumActiveLoadingIndicators: Int = 0
    }
    

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26. Make a member function instead
    class MainActivity : AppCompatActivity() {
    var mNumActiveLoadingIndicators: Int = 0
    fun showWhiteLoadingIndicator() {
    mNumActiveLoadingIndicators++
    runOnUiThread {
    . . .
    }
    }
    

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27. Using the same name as member function
    fun View.setBackgroundColor(colorResId: Int) {
    setBackgroundColor(
    ContextCompat.getColor(
    context, colorResId
    )
    )
    }
    

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28. Use different name instead
    fun View.setBackgroundColorResId(colorId: Int) {
    setBackgroundColor(
    ContextCompat.getColor(
    context, colorId
    )
    )
    }
    

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29. Extending Context on every occasion
    fun Context.showGif(imageView: ImageView, url: String) {
    Glide.with(this)
    .asGif()
    .listener(object : RequestListener {
    override fun onLoadFailed(
    e: GlideException?,
    model: Any?,
    target: Target?,
    isFirstResource: Boolean
    ) = false
    override fun onResourceReady(
    resource: GifDrawable?,
    model: Any?,
    target: Target?,
    dataSource: DataSource?,
    isFirstResource: Boolean
    ): Boolean {
    resource?.setLoopCount(1)
    return false
    }
    })
    .load(url)
    .into(imageView)
    }
    

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30. Extend views that being passed
    fun ImageView.asGif(url: String) {
    Glide.with(this.context)
    .asGif()
    .listener(object : RequestListener {
    override fun onLoadFailed(
    e: GlideException?,
    model: Any?,
    target: Target?,
    isFirstResource: Boolean
    ) = false
    override fun onResourceReady(
    resource: GifDrawable?,
    model: Any?,
    target: Target?,
    dataSource: DataSource?,
    isFirstResource: Boolean
    ): Boolean {
    resource?.setLoopCount(1)
    return false
    }
    })
    .load(url)
    .into(this)
    }
    

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31. Extending Context on every occasion
    fun Context.showDialog(message: String, activity: Activity?) {
    if (activity != null && !activity.isFinishing) {
    MaterialDialog.Builder(this)
    .content(message)
    .positiveText("Ok")
    .show()
    }
    }
    

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32. Extend classes that being passed
    fun Activity.showDialog(message: String) {
    if (!isFinishing) {
    MaterialDialog.Builder(this)
    .content(message)
    .positiveText("Ok")
    .show()
    }
    }
    

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33. some good…
    

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34. Type conversion
    public fun Map.toList(): List> {
    if (size == 0)
    return emptyList()
    val iterator = entries.iterator()
    if (!iterator.hasNext())
    return emptyList()
    val first = iterator.next()
    if (!iterator.hasNext())
    return listOf(first.toPair())
    val result = ArrayList>(size)
    result.add(first.toPair())
    do {
    result.add(iterator.next().toPair())
    } while (iterator.hasNext())
    return result
    }
    

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35. Interface conversion
    public fun Map.asSequence():
    Sequence> {
    return entries.asSequence()
    }
    

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36. Missing iterators
    inline fun Menu.forEach(action: (item: MenuItem) -> Unit) {
    for (index in 0 until size()) {
    action(getItem(index))
    }
    }
    

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37. Nullable receiver
    public actual fun String?.equals(other: String?, ignoreCase: Boolean = false): Boolean {
    if (this === null)
    return other === null
    return if (!ignoreCase)
    (this as java.lang.String).equals(other)
    else
    (this as java.lang.String).equalsIgnoreCase(other)
    }
    

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38. Kotlin standard library is full examples of extension functions
    

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39. core-ktx comes out of box in recent versions of Android Studio
    

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40. References:
    https://kotlinlang.org/api/latest/jvm/stdlib
    https://developer.android.com/kotlin/ktx
    https://jakewharton.com/android-ktx
    

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41. Thank you!
    Aida Issayeva
    @aida_isay
    

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