class TestView(context: Context) : View(context) {

    private var testCallBack: TestCallback? = null
    fun setTestCallback(callback: TestCallback) {
        testCallBack = callback
    }

    interface TestCallback {
        fun test()
    }
}

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools">

    <android.support.constraint.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".application.home.HomeActivity">

        <com.test.TestView
            android:id="@+id/testView"
            android:layout_width="match_parent"
            android:layout_height="match_parent"/>

    </android.support.constraint.ConstraintLayout>
</layout>

class TestFragment : TiFragmentBase<TiPresenterHolder, TiView>(), TiView {
    override fun providePresenter(): TiPresenterHolder =
            TiPresenterHolder()

    override fun provideView(): TiView = this

    // Reference to the fragment's view binding
    private var viewBinding: FragmentTestBinding? = null

    override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        val _viewBinding = FragmentTestBinding.inflate(inflater ?: LayoutInflater.from(context))

        _viewBinding.testView.setTestCallback(object: TestView.TestCallback {
            override fun test() {
                return
            }
        })
    }
}

java.lang.NullPointerException: Attempt to invoke virtual method 'void com.test.TestView.setTestCallback(com.test.testview.TestViewCallback)' on a null object reference
at com.test.TestFragment.onCreateView(TestFragment.kt:52)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:2354)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1419)
at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1740)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1809)
at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:799)
at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2580)
at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2367)
at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2322)
at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:2199)
at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:651)
at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:167)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1236)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1084)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1614)
at android.view.View.measure(View.java:22002)
at android.support.constraint.ConstraintLayout.onMeasure(ConstraintLayout.java:1028)
at android.view.View.measure(View.java:22002)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
at android.view.View.measure(View.java:22002)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1514)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:806)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:685)
at android.view.View.measure(View.java:22002)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.view.View.measure(View.java:22002)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1514)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:806)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:685)
at android.view.View.measure(View.java:22002)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at com.android.internal.policy.DecorView.onMeasure(DecorView.java:721)
at android.view.View.measure(View.java:22002)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2410)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1498)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1751)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1386)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6733)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:911)
at android.view.Choreographer.doCallbacks(Choreographer.java:723)
at android.view.Choreographer.doFrame(Choreographer.java:658)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:897)
at android.os.Handler.handleCallback(Handler.java:789)
at android.os.Handler.dispatchMessage(Handler.java:98)
at android.os.Looper.loop(Looper.java:164)
10-21 15:31:38.731 20659-20659/? E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)