Cast class to its subclass in Kotlin

Question

I have a list of a class called Opportunity, which is filled with objects that extend Opportunity. The list can have either CommunityOpportunites or SponsorshipOpportunities.

I override getItemViewType and assign a value to each item based on whichever subclass the object in the relevant postition, and have a different ViewHolder for each:

override fun getItemViewType(position: Int): Int {

    return if (opportunityList[position] is SponsorshipOpportunity){

        Log.i(TAG,"Item type is sponsorshipId")

        SPONSORSHIP

    } else{
        Log.i(TAG,"Item type is community")
        COMMUNITY

    }

}

    inner class CommunityViewHolder(var view: CommunityTileBinding):RecyclerView.ViewHolder(view.root)
    inner class SponsorshipViewHolder(var view: SponsorshipTileBinding):RecyclerView.ViewHolder(view.root)



companion object{
    private const val COMMUNITY = 0
    private const val SPONSORSHIP = 1
}

In onCreateViewHolder() I create the proper ViewHolder for the class of the item, and in onBindViewHolder() I attempt to cast the items in the list (of type Opportunity in the constructor) to the subclass of the item in the view:

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {


    val inflater = LayoutInflater.from(parent.context)

    return when (viewType){

        COMMUNITY->CommunityViewHolder(DataBindingUtil.inflate(inflater, R.layout.community_tile, parent, false))
        SPONSORSHIP-> SponsorshipViewHolder(DataBindingUtil.inflate(inflater, R.layout.sponsorship_tile, parent, false))

        else-> throw IllegalArgumentException()


    }
}

override fun getItemCount(): Int = opportunityList.size


override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {

  when(holder.itemViewType){
      COMMUNITY-> {

          (holder as CommunityViewHolder).view.communityOpportunity = opportunityList[position] as CommunityOpportunity
      }
      SPONSORSHIP->{
          (holder as SponsorshipViewHolder).view.sponsorship = opportunityList[position] as SponsorshipOpportunity
          holder.view.postActionText.text = context.resources.getString(R.string.watch_respond)

      }
  }

}

However, I get the following class cast exception

java.lang.ClassCastException: com.example.model.Opportunity cannot be cast to com.example.model.CommunityOpportunity

when I try at the relevant line in onBindViewHolder, even though the log statement confirming that the item is a CommunityOpportunity in getItemViewType() is printed.

Is there a better way to ask, or is there a better way for me to be displaying multiple ViewHolder/Object types in the RecyclerView?

Edit: Here are the relevant xml layouts:

xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">

<data>
    <variable
        name="sponsorship"
        type="com.example.weare8sample.model.SponsorshipOpportunity"/>
</data>

<LinearLayout

    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="10dp"
    android:elevation="2dp"
    android:orientation="vertical"
    android:background="@drawable/tile_background">

    <ImageView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:foreground="@drawable/tile_background"
        android:imageUrl="@{sponsorship.coverTileUri}">

    </ImageView>



    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:gravity="center_vertical"
        android:padding="10dp">

        <TextView
            android:id="@+id/postActionText"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:fontFamily="@font/lato_bold"
            tools:text="@string/watch_respond">

        </TextView>

        <ImageView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentRight="true"
            android:src="@drawable/ic_chevron_right_black_36dp">

        </ImageView>



    </RelativeLayout>

</LinearLayout>

xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">

<data>

    <variable
        name="communityOpportunity"
        type="com.example.weare8sample.model.CommunityOpportunity" />
</data>


<ImageView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="10dp"
    android:background="@drawable/tile_background"
    android:imageUrl="@{communityOpportunity.mediaImageUri}">

</ImageView>

Answer 1

Add an explicit type check for all types in getItemViewType and throw if it's an unknown type, to properly handle all cases.

As it is now, if there's a 3rd type of Opportunity, it will be assumed to be of COMMUNITY type.