OBJECT EXPRESSIONS
Object expressions allow for strict singleton definition so there’s no mistaking it for a class that can be instantiated. They also ensure that you do not have to store singletons somewhere like in the Application class or as a static class variable.
For example, if I have a utility class with static thread-related methods I want to access throughout the app:
import android.os.Handler
import android.os.Looper
// notice that this is object instead of class
object ThreadUtil {
fun onMainThread(runnable: Runnable) {
val handler = Handler(Looper.getMainLooper())
handler.post(runnable)
}
}
ThreadUtil is called later in the typical way you would call a static class method:
ThreadUtil.onMainThread(runnable)
This means there’s no more declaring a constructor as private, or having to figure out where the static instance is stored. Objects are essentially first class citizens of the language. In a similar way, we create objects instead of anonymous inner classes:
viewPager.addOnPageChangeListener(object : ViewPager.OnPageChangeListener {
override fun onPageScrollStateChanged(state: Int) {}
override fun onPageScrolled(position: Int, positionOffset: Float,
positionOffsetPixels: Int) {}
override fun onPageSelected(position: Int) {
bindUser(position)
}
})
Both of these do essentially the same thing — create a single instance of a class as a declared object.
Proud Geek 