Kotlin's simple layout trick

initial_layout.kt

LinearLayout(this).apply {

    orientation = LinearLayout.VERTICAL

    addView(TextView(context).apply {
        text = "Hello"
    })

    addView(TextView(context).apply {
        text = "click me"
        setOnClickListener {
            // ...
        }
    })
}

initialization_with_invoke.kt

LinearLayout(this) layout {
    +TextView(context) {

    }
}

class Layout<V : ViewGroup>(val layout: V) : ViewManager by layout, ViewParent by layout {
    
    // ...

    operator fun <V : View> V.invoke(block: V.() -> Unit): V =
            also(block)

}

unary_plus.kt

LinearLayout(this) layout {
    +TextView(context)
}

class Layout<V : ViewGroup>(val layout: V) : ViewManager by layout, ViewParent by layout {

    val context = layout.context

    operator fun <V : View> V.unaryPlus(): V =
            also(layout::addView)

}

view_extensions.kt

LinearLayout(this) layout {
    +textView {
        text = "Hello"
    }
}

val Layout<*>.textView: TextView get() = TextView(context)
val Layout<*>.button: Button get() = Button(context)

viewgroup_dsl.kt

LinearLayout(this) layout {
 // ...
}

infix fun <V : ViewGroup> V.layout(block: Layout<V>.() -> Unit): V =
        also { Layout(it).run(block) }

class Layout<V : ViewGroup>(val layout: V) : ViewManager by layout, ViewParent by layout {}