如何在RecyclerView元素中更改标题背景颜色onClick？

Question

I have a RecyclerView with two ViewHolder . One for a header and one for the actual item. Now I want to change the background color in the header (it's an ImageView ) depending on what list item was clicked. I tried this but got:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setBackgroundColor(int)' on a null object reference

This is my code:

case class MyItemHolder(view: View, items: Array[Entry]) extends RecyclerView.ViewHolder(view) with MyHolder with View.OnClickListener{
    view.setOnClickListener(this)
    lazy val currentItem = items(getAdapterPosition - 1)
    val textView: TextView = view.findViewById(R.id.textView).asInstanceOf[TextView]
    val imageView: ImageView = view.findViewById(R.id.imageView).asInstanceOf[ImageView]
    def bind(e: Entry): Unit = textView.setText(e.name)

    override def onClick(view: View): Unit = {
      Toast.makeText(getApplicationContext, s"You clicked ${currentItem.name}!", Toast.LENGTH_SHORT).show()
      imageView.setBackgroundColor(Color.parseColor(currentItem.color)) // crashed with NPE
    }
  }

The ImageView of the header is actually in its own ViewHolder :

case class MyHeaderHolder(view: View) extends RecyclerView.ViewHolder(view) with MyHolder {
    val imageView: ImageView = view.findViewById(R.id.imageView).asInstanceOf[ImageView]
    val image = ContextCompat.getDrawable(getApplicationContext, R.drawable.title)
    def bind(): Unit = imageView.setImageDrawable(image)
  }

How can I access it from my MyItemHolder ?

Answer 1

Try to access the imageview from within the listener :

    override def onClick(view: View): Unit = {
            Toast.makeText(getApplicationContext, s"You clicked ${currentItem.name}!", Toast.LENGTH_SHORT).show()
            val imageView: ImageView = view.findViewById(R.id.imageView).asInstanceOf[ImageView]
            imageView.setBackgroundColor(Color.parseColor(currentItem.color)) // crashed with NPE
    }