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Level up
your extension
game
Aida Issayeva
@aida_isay
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Why we need it?
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to make our lives
easier
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Example:
styling a text
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No content
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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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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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How to make extension?
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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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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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fun DomesticAnimal.toAnimal(): Animal {
return Animal(
id = id,
name = name,
logo = logo,
isDomestic = true,
description = shortDescription,
inRedList = false
)
}
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override fun onCreate(savedInstanceState: Bundle?) {
. . .
val domesticAnimal = DomesticAnimal(
name = "Bactrian Camel",
. . .
farmLocation = "Aral Sea"
)
val animal = domesticAnimal.toAnimal()
}
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How to use extension in java classes?
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@InlineOnly
When can you not use extensions in java?
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Common practices
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some sad…
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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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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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Modifying members of a class
fun MainActivity.showWhiteLoadingIndicator() {
mNumActiveLoadingIndicators++
runOnUiThread {
. . .
}
}
class MainActivity : AppCompatActivity() {
var mNumActiveLoadingIndicators: Int = 0
}
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Make a member function instead
class MainActivity : AppCompatActivity() {
var mNumActiveLoadingIndicators: Int = 0
fun showWhiteLoadingIndicator() {
mNumActiveLoadingIndicators++
runOnUiThread {
. . .
}
}
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Using the same name as member function
fun View.setBackgroundColor(colorResId: Int) {
setBackgroundColor(
ContextCompat.getColor(
context, colorResId
)
)
}
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Use different name instead
fun View.setBackgroundColorResId(colorId: Int) {
setBackgroundColor(
ContextCompat.getColor(
context, colorId
)
)
}
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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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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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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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Extend classes that being passed
fun Activity.showDialog(message: String) {
if (!isFinishing) {
MaterialDialog.Builder(this)
.content(message)
.positiveText("Ok")
.show()
}
}
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some good…
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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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Interface conversion
public fun Map.asSequence():
Sequence> {
return entries.asSequence()
}
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Missing iterators
inline fun Menu.forEach(action: (item: MenuItem) -> Unit) {
for (index in 0 until size()) {
action(getItem(index))
}
}
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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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Kotlin standard library is full examples of extension functions
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core-ktx comes out of box in recent versions of Android Studio
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References:
https://kotlinlang.org/api/latest/jvm/stdlib
https://developer.android.com/kotlin/ktx
https://jakewharton.com/android-ktx
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Thank you!
Aida Issayeva
@aida_isay