如何在 Android 中的 RecyclerView 末尾添加一个加号图像作为按钮？ [复制]

Question

我想要一个 add 按钮，我的所有锻炼项目如下：

Image of the RecyclerView I want

我尝试在我的CustomAdapter 中像这样实现它：

class CustomAdapterExercise(val exerciseList: ArrayList<Exercise>) : RecyclerView.Adapter<CustomAdapterExercise.ViewHolder>() {

val typeAdd = 0
val typeExercise = 1

//this method is returning the view for each item in the list
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CustomAdapterExercise.ViewHolder {

    if (viewType == typeAdd) {
        val itemView = LayoutInflater.from(parent.context).inflate(R.layout.exercise_layout, parent, false)
        return ViewHolder(itemView)
    } else if (viewType == typeExercise) {
        val itemView = LayoutInflater.from(parent.context).inflate(R.layout.add_layout, parent, false)
        return ViewHolder(itemView)
    }
    else{
        val itemView = LayoutInflater.from(parent.context).inflate(R.layout.add_layout, parent, false)
        return ViewHolder(itemView)
    }

}

//this method is binding the data on the list
override fun onBindViewHolder(holder: CustomAdapterExercise.ViewHolder, position: Int) {
    holder.bindItems(exerciseList[position])
}

override fun getItemViewType(position: Int): Int {
    if (position <= exerciseList.size) {
        return typeExercise
    } else if (position == exerciseList.size + 1) {
        return typeAdd
    }
    else{
        return typeAdd
    }
}

//this method is giving the size of the list
override fun getItemCount(): Int {
    return exerciseList.size + 1
}

//the class is hodling the list view
class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {

    fun bindItems(Exercise: Exercise) {

        val exerciseAmount = itemView.findViewById<TextView>(R.id.exerciseAmount)
        val exerciseName  = itemView.findViewById<TextView>(R.id.exerciseName)
        val exerciseWeight = itemView.findViewById<TextView>(R.id.exerciseWeight)
        val exerciseSets  = itemView.findViewById<TextView>(R.id.exerciseSets)
        exerciseAmount.text = Exercise.exAmount
        exerciseName.text = Exercise.exName
        exerciseWeight.text = Exercise.weight
        exerciseSets.text = Exercise.sets
    }
}
}

但是当我进入该视图时它会崩溃，并给我这个错误：

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
                      at abyte.fitness.fitnessbyte.CustomAdapterExercise$ViewHolder.bindItems(CustomAdapterExercise.kt:67)

我知道这是因为我正在为我的添加按钮分配文本，但我不知道如何以不同的方式执行此操作并使其正常工作。

当我整天搜索时，我已经看到了“重复”的问题，但对于像我这样的初学者来说，它并没有得到很好的解释......

Answer 1

你需要在onBindViewHolder中开启viewType。

override fun onBindViewHolder(holder: CustomAdapterExercise.ViewHolder, position: Int) {
    if (holder.itemViewType == typeAdd) {
        // Bind the add button
    else {
        holder.bindItems(exerciseList[position])
    }
}

旁注：

您以错误的方式使用 ViewHolder，ViewHolders 的好处之一是不会在每次更新 View 时都强制执行findByView。