如何从适配器类更改 TextView 文本？

Question

I need to change text according to my click listener function. I used findViewById method to get textview and I use setText to change text of textview but in here I get an error which is nullexception . I am quite new at Kotlin with no Java experience. I did research about that I saw Interface method to change text I tried it but it wasn't work. How can I solve it?

Here my code which is from Adapter Class:

var dd = holder.customView.findViewById<TextView>(R.id.toplamSayi)!!
dd.setText(tt)

Also I tried dd.text = tt but it wasn't work also.

Edit:

My Adapter Class:

private class DetailPageAdapterForSepetPage: RecyclerView.Adapter<DetailPageViewHolderForSepetPage>() {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): DetailPageViewHolderForSepetPage {
        val layoutInflater = LayoutInflater.from(parent?.context)
        val customDetailView = layoutInflater.inflate(R.layout.sepet_sayfasi_list_row_detail, parent,false)
        return DetailPageViewHolderForSepetPage(customDetailView)
    }

    override fun onBindViewHolder(holder: DetailPageViewHolderForSepetPage, position: Int) {
        var urunDb = sepetArr.get(position)

        holder.customView.urun_text.text = urunDb.eklenenUrun
        holder.customView.fiyat_text.text = urunDb.eklenenFiyat
        holder.customView.adet_text.text = "x" + urunDb.eklenenAdet

        var addedCount = urunDb.eklenenAdet.toInt()

        // ekleme butonu fonksiyonu
        holder.customView.imageButton4.setOnClickListener {
            addedCount += 1
            holder.customView.adet_text.text = "x$addedCount"

            // BURADA COUNT U BİR ARTTIRACAGIZ VE ARKADAN DIGER İKİLİ (URUN VE FIYAT) TUTAN ARRAYE DE EKLEME YAPACAGIZ.. YADA CIKARMASINI ASAGIDA..

            var urun = holder.customView.urun_text.text
            var fiyat = holder.customView.fiyat_text.text
            var adet = holder.customView.adet_text.text
            var addedData = SepeteGidenUrunlerModel(
                urunEklenen = urun.toString(),
                fiyatEklenen = fiyat.toString()
            )

            var fiyatStr = fiyat.toString()
            var droped = fiyatStr.dropLast(2)
            var doubleEklenecek = droped.toDouble()

            toplamTutar += doubleEklenecek
            var tt = toplamTutar.toString()

            holder.customView.toplamSayi.setText(tt)
            FirstDetailActivity.sepeteEklenenUrunler.add(addedData)
        }

        // cikarma butonu fonksiyonu
        holder.customView.imageButton5.setOnClickListener {

            if (addedCount > 1) {
                addedCount -= 1
                holder.customView.adet_text.text = "x$addedCount"

                var urun = holder.customView.urun_text.text
                var fiyat = holder.customView.fiyat_text.text

                var cikarilan = SepeteGidenUrunlerModel(
                    urunEklenen = urun.toString(),
                    fiyatEklenen = fiyat.toString()
                )

                FirstDetailActivity.sepeteEklenenUrunler.remove(cikarilan)

            }else if (addedCount == 1) {

                var urun = holder.customView.urun_text.text
                var fiyat = holder.customView.fiyat_text.text
                var adet = holder.customView.adet_text.text
                var cikarilan = SepeteGidenUrunlerModel(
                    urunEklenen = urun.toString(),
                    fiyatEklenen = fiyat.toString()
                )

                FirstDetailActivity.sepeteEklenenUrunler.remove(cikarilan)

                var sepetteData = SepetModel(
                    eklenenUrun = urun.toString(),
                    eklenenFiyat = fiyat.toString(),
                    eklenenAdet = adet.toString()
                )

                sepetArr.removeAt(position)
                notifyDataSetChanged()
            }
        }
    }

    override fun getItemCount(): Int {
        return sepetArr.size
    }
}

private class DetailPageViewHolderForSepetPage(val customView: View): RecyclerView.ViewHolder(customView){
}

And XML :

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".SepetSayfasi">


    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/sepet_recycler_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/toplamText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="24dp"
        android:layout_marginLeft="24dp"
        android:layout_marginTop="24dp"
        android:text="TextView"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/sepet_recycler_view" />

    <TextView
        android:id="@+id/topalmTutar"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TextView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@+id/toplamText"
        app:layout_constraintTop_toTopOf="@+id/toplamText" />

    <TextView
        android:id="@+id/textToplam"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:text="TextView"
        app:layout_constraintStart_toStartOf="@+id/toplamText"
        app:layout_constraintTop_toBottomOf="@+id/toplamText" />

    <TextView
        android:id="@+id/toplamSayi"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TextView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@+id/textToplam"
        app:layout_constraintTop_toTopOf="@+id/textToplam" />
</androidx.constraintlayout.widget.ConstraintLayout>

Answer 1

1. You need to pass to your adapter the list of elements that are gonna populate the view

2. You need to declare the views of your RecyclerView layout in your ViewHolder , then you can access it in onBindViewHolder

Try to use this code as the base of your Adapter and complete it as needed

private class DetailPageAdapterForSepetPage(
    private val activity: <the-class-of-your-activity>,
    private val sepetArr: List<the-type-of-your-list>
) : RecyclerView.Adapter<DetailPageViewHolderForSepetPage>() {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): DetailPageViewHolderForSepetPage {
        val customDetailView = LayoutInflater.from(parent.context).inflate(R.layout.sepet_sayfasi_list_row_detail, parent, false)
        return DetailPageViewHolderForSepetPage(customDetailView)
    }

    override fun onBindViewHolder(holder: DetailPageViewHolderForSepetPage, position: Int) 
    {
        val urunDb = sepetArr[position]

        holder.btn.setOnClickListener {
            activity.updateText("Your text")
        }
        
        // -- Put the rest of your initializazion code here --
    }

    override fun getItemCount(): Int = sepetArr.size

    inner class DetailPageViewHolderForSepetPage(customView: View): RecyclerView.ViewHolder(customView) {
        val btn: Button = customView.findViewById(<your-button-id>)

        // -- Put the other views in your recycler view item here --
    }
}

In your parent activity declare a public method

updateText(text: String) {
    // Update the text view
}