Kotlin: How to call getSupportFragmentManager() in RecyclerView.Adapter

user_7307194 0
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I would like to call the Support Fragment Manager in my RecyclerView.Adapter after the click event in order to move to a different fragment. My approach:

(context as MainActivity).supportFragmentManager
                            .beginTransaction()
                            .replace(MainActivity.FRAGMENT_CONTAINER, TextScreen())
                            .commit()

But I get the following error:

kotlin.TypeCastException: null cannot be cast to non-null type

Can you help me?

kotlin android
4 Answers

Updated for 2021 - Kotlin Answer

If you want to call "supportFragmentManager" in Fragment

activity.supportFragmentManager
user_84717980

This is because your Context instance in the adapter is not guaranteed to be an Activity. It could potentially be a ContextWrapper holding the Activity as a base Context. Attempting to unwrap this would be fragile.

Instead, I would recommend that you define an interface in your adapter. From your Activity, provide an implementation of this interface to your adapter that will perform the FragmentTransaction. For example:

class MyAdapter : RecyclerView.Adapter<MyType> {
    private var listener: (() -> Unit)? = null

    fun setListener(listener: (() -> Unit)?) {
        this.listener = listener
    }

    // wherever your onClick is handled:
    listener?.invoke()
}

Then, in the Activity that's initializing MyAdapter:

myAdapter.setListener {
    supportFragmentManager
        .beginTransaction()
        .replace(MainActivity.FRAGMENT_CONTAINER, TextScreen())
        .commit()
}
user_3216970

I suggest you handle your fragment transaction in your fragment/activity. This would help you to have cleaner code and using context in fragment/activity is much easier. Try to define the interface between your adapter and fragment and call your interface method in the adapter and implement the interface in activity/fragment. There you can access context easily.

user_52306820

get the activity or fragment as argument in your adapter.

class ArticleAdapter(private val articleActivity: ArticleActivity, private val docs: List<ArticleResult.ArticleDoc>) : RecyclerView.Adapter<ArticleAdapter.Holder>() {
    override fun onCreateViewHolder(p0: ViewGroup, p1: Int): Holder = Holder(LayoutInflater.from(p0.context).inflate(R.layout.row_general2, p0, false))
    override fun getItemCount(): Int = docs.size

    override fun onBindViewHolder(holder: Holder, position: Int) {
        articleActivity.supportFragmentManager
    }

    class Holder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val textViewTitleRow = itemView.findViewById<TextView>(R.id.textViewTitleRow)!!
        val textView1Row = itemView.findViewById<TextView>(R.id.textView1Row)!!
        val textView2Row = itemView.findViewById<TextView>(R.id.textView2Row)!!
        val imageViewDownloadRow = itemView.findViewById<ImageView>(R.id.imageViewDownloadRow)!!
        val textViewMoreRow = itemView.findViewById<TextView>(R.id.textViewMoreRow)!!
        val imageViewBookRow = itemView.findViewById<ImageView>(R.id.imageViewBookRow)!!
    }
}
user_89406300
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