GridView cannot be cast to ViewPager in Kotlin Custom Calendar - kotlin

Question

Working on the custom calendar in Kotlin.
On tapping the DateText, this custom calendar widget will be opened in a new fragment.
I used Grid Views to display the dates and I'm getting ClassCastException on navigating to the Calendar Screen(GridView cannot be cast to ViewPager).
Error:
Caused by: java.lang.ClassCastException: com.daimler.myfinance.payment.paymentdate.extensions.CalendarGridView cannot be cast to com.daimler.myfinance.payment.paymentdate.extensions.CalendarViewPager
at com.payment.paymentdate.CalendarView.initUiElements(CalendarView.kt)
CalendarView.kt
open class CalendarView : LinearLayout {
private var mViewPager: CalendarViewPager? = null
private fun initUiElements() {
mViewPager = findViewById<ViewPager>(R.id.calendarViewPager) as CalendarViewPager
}
}
CalendarViewPager.kt
class CalendarViewPager : ViewPager {
constructor(context: Context?) : super(context!!) {
}
constructor(context: Context?, attrs: AttributeSet?) : super(context!!, attrs) {
}
override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
var heightMeasureSpec = heightMeasureSpec
var height = 0
for (i in 0 until getChildCount()) {
val child: View = getChildAt(i)
child.measure(widthMeasureSpec, MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED))
val h = child.measuredHeight
if (h > height) {
height = h
}
}
if (height != 0) {
heightMeasureSpec = MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY)
}
super.onMeasure(widthMeasureSpec, heightMeasureSpec)
}
}
calendar_view.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#android:color/white"
android:orientation="vertical">
<!-- date toolbar -->
<androidx.constraintlayout.widget.ConstraintLayout
android:id="#+id/calendarHeader"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:background="#color/jumio_white"
app:layout_constraintBottom_toTopOf="#+id/abbreviationsBar">
<ImageButton
android:id="#+id/previousButton"
style="#style/Widget.AppCompat.Button.Borderless.Colored"
android:layout_width="30dp"
android:layout_height="match_parent"
android:src="#drawable/ic_chevron_left"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<com.uikit.widgets.textviews.MBBody2TextView
android:id="#+id/currentDateLabel"
android:layout_width="wrap_content"
android:layout_height="56dp"
android:gravity="center"
android:textColor="#color/jumio_black"
android:textSize="18sp"
app:layout_constraintLeft_toRightOf="#id/previousButton"
app:layout_constraintRight_toLeftOf="#id/forwardButton"
app:layout_constraintTop_toTopOf="parent"
android:text="April 2020" />
<ImageButton
android:id="#+id/forwardButton"
style="#style/Widget.AppCompat.Button.Borderless.Colored"
android:layout_width="30dp"
android:layout_height="match_parent"
android:src="#drawable/ic_chevron_right"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
<!-- eventDays header -->
<LinearLayout
android:id="#+id/abbreviationsBar"
android:layout_width="match_parent"
android:layout_height="40dp"
android:gravity="center_vertical"
android:orientation="horizontal"
app:layout_constraintTop_toBottomOf="#+id/calendarHeader">
<com.\uikit.widgets.textviews.MBBody2TextView
android:id="#+id/mondayLabel"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:gravity="center_horizontal"
android:text="#string/material_calendar_monday"
android:textColor="#color/jumio_black" />
<com.uikit.widgets.textviews.MBBody2TextView
android:id="#+id/tuesdayLabel"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:gravity="center_horizontal"
android:text="#string/material_calendar_tuesday"
android:textColor="#color/jumio_black" />
<com.uikit.widgets.textviews.MBBody2TextView
android:id="#+id/wednesdayLabel"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:gravity="center_horizontal"
android:text="#string/material_calendar_wednesday"
android:textColor="#color/jumio_black" />
<com.uikit.widgets.textviews.MBBody2TextView
android:id="#+id/thursdayLabel"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:gravity="center_horizontal"
android:text="#string/material_calendar_thursday"
android:textColor="#color/jumio_black" />
<com.uikit.widgets.textviews.MBBody2TextView
android:id="#+id/fridayLabel"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:gravity="center_horizontal"
android:text="#string/material_calendar_friday"
android:textColor="#color/jumio_black" />
<com.uikit.widgets.textviews.MBBody2TextView
android:id="#+id/saturdayLabel"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:gravity="center_horizontal"
android:text="#string/material_calendar_saturday"
android:textColor="#color/jumio_black" />
<com.uikit.widgets.textviews.MBBody2TextView
android:id="#+id/sundayLabel"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:gravity="center_horizontal"
android:text="#string/material_calendar_sunday"
android:textColor="#color/jumio_black" />
</LinearLayout>
<ScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/gridScroll"
app:layout_constraintTop_toBottomOf="#+id/abbreviationsBar">
<com.payment.paymentdate.extensions.CalendarGridView
android:id="#+id/calendarViewPager"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</ScrollView>
</LinearLayout>

Answer 1

Because in your xml you have defined com.payment.paymentdate.extensions.CalendarGridView which is subclassof GridView and you are assigning it to ViewPager wich is type of ViewPager
<com.payment.paymentdate.extensions.CalendarViewPager
android:id="#+id/calendarViewPager"
android:layout_width="match_parent"
android:layout_height="wrap_content" />