kema

Kotlin Extension Methods for Android

dp to pixels conversion (my favourite)

val eightDpInPixels = 8.dp

// before (the simplest one, I've seen far more complicated)
val eightDpInPixels = (8 * Resources.getSystem().displayMetrics.density + 0.5f).toInt()

Arguments

Methods for Activity, Fragment and android.support.v4.app.Fragment:

• argument(key)

val arg = argument<ArgumentType>(KEY)

// before
val arg = intent.extras.get(KEY) as ArgumentType // for Activity
val arg = arguments.get(KEY) as ArgumentType // for Fragments

• lazyArgument(key)

val arg by lazyArgument<ArgumentType>(KEY)

// before
val arg: ArgumentType by lazy { intent.extras.get(KEY) as ArgumentType } // for Activity
val arg: ArgumentType by lazy { arguments.get(KEY) as ArgumentType } // for Fragments

Color

Properties for Context:

• colorAccent
• colorPrimary
• colorPrimaryDark

Property for String:

• asColor

val color = "#442288".asColor

Drawable

Property for Drawable

• tint

mDrawable.tint = mColor

// before
if (Build.VERSION.SDK_INT >= 21) {
    mDrawable.setTint(value)
} else {
    DrawableCompat.setTint(DrawableCompat.wrap(mDrawable), mColor)
}

Menu

Methods for Menu:

• forEach { }
• get operator for ids

val menuItem = menu[id]

// before
val menuItem = menu.findItem(id)

• tint(color)

menu.tint(color)

// before
for (i in 0..menu.size()-1) {
    val icon = menu.getItem(i).icon
    if (Build.VERSION.SDK_INT >= 21) icon.setTint(color)
    else DrawableCompat.setTint(DrawableCompat.wrap(icon), color)
}

Methods for Activity:

• inflate(menuResId, menu)

override fun onCreateOptionsMenu(menu: Menu) = inflate(R.menu.main, menu)

// before
override fun onCreateOptionsMenu(menu: Menu): Boolean {
    menuInflater.inflate(R.menu.main, menu)
    return true
}

System Bars

Properties for Context:

hasNavigationBar // Boolean
isNavigationBarHorizontal // Boolean
navigationBarCanChangeItsPosition // Boolean
statusBarHeight // Int
navigationBarHeight // Int
navigationBarWidth // Int

Methods for View:

setLightStatusBar()

System Services

They are all included as properties for Context. The name of the property is the name of the returned class with the first letter lower-cased. Examples:

val lm = locationManager
val js = jobScheduler

// before
val lm = getSystemService(Context.LOCATION_SERVICE) as LocationManager
val js = getSystemService(Context.JOB_SCHEDULER_SERVICE) as JobScheduler

Ternary operator

val v = (condition) % true / false  // not so useful, but there it is

// before 
val v = if (condition) true else false

View

Methods for View

• show()
• hide()
• showIf(condition)
• setPaddingStart(paddingStart)
• setPaddingEnd(paddingEnd)
• setPaddingTop(paddingTop)
• setPaddingBottom(paddingBottom)
• setPaddingDp(left, top, right, bottom)
• setMargins(left, top, right, bottom)
• setMarginsDp(left, top, right,)
• elevate(elevation)
• isAttachedToWindow()
• isInBounds(anotherView)
• onClick { }
• onLongClick { }

ViewGroup

• Properties
  • children: List
• Functions
  • inflate(layoutResId): View

val view = parent.inflate(layoutResId)

// before
val view = LayoutInflater.from(parent.context).inflate(parent, layoutResId, false);