学习Android实现可折叠ListView（ExpandableListView）

<ExpandableListView
android:id="@+id/expendableListview"
android:layout_width="match_parent"
android:layout_height="wrap_content" />

class MyAdapter(
private var mContext : Context,
/** group 数据 */
private var groupList: ArrayList<String>,
/** child 数据 */
private var childList : ArrayList<ArrayList<String>>) : BaseExpandableListAdapter() {

override fun getGroup(groupPosition: Int): Any {
return groupPosition
}

override fun isChildSelectable(p0: Int, p1: Int): Boolean {
return true
}

override fun hasStableIds(): Boolean {
return true
}

@SuppressLint("SetTextI18n")
override fun getGroupView(groupPosition: Int, isExpanded: Boolean, convertView: View?, parent: ViewGroup?): View {
val groupView = View.inflate(mContext, R.layout.item_group, null)

/** 分组名字 */
val groupName = groupView.findViewById<TextView>(R.id.groupTvName)
groupName.text = groupList[groupPosition]
/** 子元素个数 */
val count = groupView.findViewById<TextView>(R.id.groupTvCount)
count.text = "${childList[groupPosition].size} 个"

return groupView
}

/**
* 这个返回的一定要是对应的item里面的List集合的size
*/
override fun getChildrenCount(groupPosition: Int): Int {
return childList[groupPosition].size
}

override fun getChild(groupPosition: Int, childPosition: Int): Any {
return childList[groupPosition][childPosition]
}

override fun getGroupId(groupPosition: Int): Long {
return groupPosition.toLong()
}

override fun getChildView(groupPosition: Int, childPosition: Int, isLastChild: Boolean, view: View?, viewGroup: ViewGroup?): View {
val childView = View.inflate(mContext, R.layout.item_child, null)
val username = childView.findViewById<TextView>(R.id.childTvUserName)
username.text = childList[groupPosition][childPosition]
return childView
}

override fun getChildId(groupPosition: Int, childPosition: Int): Long {
return childPosition.toLong()
}

override fun getGroupCount(): Int {
return groupList.size
}

}

val adapter = MyAdapter(this, groupList, childList)

expendableListview.setAdapter(adapter)