当前,我有一个要填充的列表,但是列表项可以具有不同的数据。我有两个数据类,为了适应RecyclerView,我有两个不同的ViewHolder扩展了基本的基本ViewHolder。需要不同的ViewHolders,因为不同的布局用于不同的数据类。
我已将视图持有人转换为Kotlin,但是适配器存在问题。
Kotlin中的基本ViewHolder:
abstract class BaseViewHolder<T> internal constructor(view: View) : RecyclerView.ViewHolder(view) {
abstract fun bind(item: T)
}
在Kotlin中实现基本ViewHolder的ViewHolder:
class StandardViewHolder(view: View): BaseViewHolder<Standard>(view) {
private val _eventView : TextView = view.findViewById(R.id.eventTextView)
private val _dateView : TextView = view.findViewById(R.id.dateTextView)
override fun bind(item: Standard) {
_eventView.text = item.event
_dateView.text = item.date.toString()
}
}
在Java中,我可以创建一个使用以下ViewHolders的适配器:
public class ListAdapter extends RecyclerView.Adapter<BaseViewHolder> {
private List<Object> _items;
private Context _context;
public ListAdapter(List<Object> items, Context context){
_items = items;
_context = context;
}
@NonNull
@Override
public BaseViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
if(viewType == R.layout.item_standard){
return new StandardViewHolder(LayoutInflater.from(_context).inflate(
R.layout.item_standard, parent, false));
}
return new AdvancedViewHolder(LayoutInflater.from(_context).inflate(
R.layout.item_advanced, parent, false));
}
@Override
@SuppressWarnings("unchecked")
public void onBindViewHolder(@NonNull BaseViewHolder holder, int position) {
holder.bind(_items.get(position));
}
@Override
public int getItemCount() {
return _items.size();
}
@Override
public int getItemViewType(int position) {
if(_items.get(position) instanceof Standard){
return R.layout.item_standard;
}
return R.layout.item_advanced;
}
}
但是,如果将其转换为Kotlin,则会在 holder.bind 上出现错误,即:
投影类型'BaseViewHolder <*>'禁止使用'public 抽象有趣的bind(item:T)'
class ListAdapter(private val _items: List<Any>, private val _context: Context) : RecyclerView.Adapter<BaseViewHolder<*>>() {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): BaseViewHolder<*> {
return if (viewType == R.layout.item_standard) {
StandardViewHolder(LayoutInflater.from(_context).inflate(
R.layout.item_standard, parent, false))
} else {
AdvancedViewHolder(LayoutInflater.from(_context).inflate(
R.layout.item_advanced, parent, false))
}
}
override fun onBindViewHolder(holder: BaseViewHolder<*>, position: Int) = holder.bind(_items[position])
override fun getItemCount() = _items.size
override fun getItemViewType(position: Int): Int {
return if (_items[position] is Standard) {
R.layout.item_standard
} else {
R.layout.item_advanced
}
}
}
如何在Kotlin中使用这些通用ViewHolders?
答案 0 :(得分:3)
问题是,即使您知道绑定的项目与为其创建的ViewHolder的类型匹配,您也无法在编译时证明它,因此编译器会对您大吼大叫。您不能在bind
上调用BaseViewHolder<*>
,因为那样的话,该参数必须为*
类型,这是不可能发生的。您在那里BaseViewHolder<Any>
所需要的东西,但是您无法制造适配器RecyclerView.Adapter<BaseViewHolder<Any>>
,因为那样会破坏onCreateViewHolder
。而且我已经尝试过BaseViewHolder<out Any>
,但这也不起作用。
因此,您可以执行以下操作:使用BaseViewHolder<*>
,然后在onBindViewHolder
内部将其强制转换为BaseViewHolder<Any>
。编译器会抱怨“ 嘿!这是未经检查的强制转换!您不应该这样做!”,因此告诉它使用@Suppress("UNCHECKED_CAST")
关闭。
class ListAdapter(
private val _items: List<Any>,
private val _context: Context
) : RecyclerView.Adapter<BaseViewHolder<*>>() {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): BaseViewHolder<*> {
return if (viewType == R.layout.item_standard) {
StandardViewHolder(LayoutInflater.from(_context).inflate(
R.layout.item_standard, parent, false))
} else {
AdvancedViewHolder(LayoutInflater.from(_context).inflate(
R.layout.item_advanced, parent, false))
}
}
@Suppress("UNCHECKED_CAST")
override fun onBindViewHolder(holder: BaseViewHolder<*>, position: Int) {
(holder as BaseViewHolder<Any>).bind(_items[position])
}
override fun getItemCount() = _items.size
override fun getItemViewType(position: Int): Int {
return if (_items[position] is Standard) {
R.layout.item_standard
} else {
R.layout.item_advanced
}
}
}
答案 1 :(得分:0)
好人……实际上,我对此进行了一些修改,看看我做了什么。 我使它成为有史以来最动态的适配器。
https://medium.com/@sandipsavaliya/tired-with-adapters-4240e5f45c24
答案 2 :(得分:0)
对于通用回收站视图,请使用以下代码:
第1步:使用RecyclerView.Adapter()扩展适配器 例如
class MyAdapter(private val recentList: ArrayList<CollectionModel>) :
RecyclerView.Adapter<**RecyclerView.ViewHolder**>() {
}
步骤2:为所有视图设置视图类型 例如
override fun getItemViewType(position: Int): Int {
return if (recentList[position].type == 0) CollectionModel.COLLECTION_HEADER else CollectionModel.COLLECTION_DETAIL
}
第3步:在onCreateViewHolder内部定义正确的视图和ViewHolder 例如
if (viewType == CollectionModel.COLLECTION_HEADER) {
val view = LayoutInflater.from(parent.context).inflate(R.layout.signle_row_header, parent, false)
return HeaderCollectionHolder(view)
} else {
val view = LayoutInflater.from(parent.context).inflate(R.layout.single_row_collection_history, parent, false)
return DetailHolder(view)
}
第4步:在内部onBindViewHolder中,根据视图类型绑定数据,并使用 as 关键字类型强制转换视图持有者 例如
val collectionModel = recentList[position]
if (recentList[position].type == CollectionModel.COLLECTION_HEADER) {
(holder as HeaderCollectionHolder).apply {
header.text = collectionModel.date
}
} else {
(holder as DetailHolder).apply {
name.text = collectionModel.name
phone.text = collectionModel.phone
collectedAmount.text = collectionModel.lastCollectAmount.toInt().toString()
balanceAmount.text = collectionModel.pendingBalance.toInt().toString()
Utils.setImage(collectionModel.picUrl, imageView)
}
}
第5步:创建两个视图持有人类,如下所示:
inner class DetailHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
var name: TextView = itemView.findViewById(R.id.name)
var phone: TextView = itemView.findViewById(R.id.phone)
var collectedAmount: TextView = itemView.findViewById(R.id.total_amount)
var balanceAmount: TextView = item`enter code here`View.findViewById(R.id.balance_amount)
var imageView: CircularImageView = itemView.findViewById(R.id.user_image)
}
inner class HeaderCollectionHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
val header: TextView = itemView.findViewById(R.id.text)
}
就这样。