DataBindingUtil.kt

/*
* ViewModel variable name must be {{viewModel}}.
*
* Binds the viewModel to the DataBinding and clears the observable subscription
* on view detached from window.
* */
fun <T : ViewDataBinding, V : BaseViewModel> T.bindViewModel(viewModel: V): Boolean {
    val bindSuccess = setVariable(BR.viewModel, viewModel)
    if (bindSuccess) {
        root.onAttachStateChanged(
                {
                    viewModel.onDetach()
                    viewModel.onAttach()
                },
                {
                    viewModel.onDetach()
                }
        )
    } else {
        throw IllegalStateException("Binding $this view model variable name should be `viewModel`")
    }
    return bindSuccess
}


/*
* Calls the corresponding method based on initial state on setting the listener.
* */
inline fun View.onAttachStateChanged(
    crossinline onAttach: () -> Unit,
    crossinline onDetach: () -> Unit
) {
    var isAttached = isAttachedToWindow
    if (isAttached) {
        onAttach()
    }
    addOnAttachStateChangeListener(object : View.OnAttachStateChangeListener {
        override fun onViewDetachedFromWindow(v: View?) {
            if (isAttached) {
                onDetach()
                isAttached = false
            }
        }

        override fun onViewAttachedToWindow(v: View?) {
            if (!isAttached) {
                onAttach()
                isAttached = true
            }
        }
    })
}