我习惯于在布局文件中放置一个特殊的视图，如ListActivity文档中所述，在没有数据时显示。这个视图的id为“android:id/empty”。
<TextView
android:id="@android:id/empty"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/no_data" />
我想知道这如何能与新的RecyclerView?
当前回答
另一种方法是使用addOnChildAttachStateChangeListener来处理RecyclerView中出现/消失的子视图。
recyclerView.addOnChildAttachStateChangeListener(new RecyclerView.OnChildAttachStateChangeListener() {
@Override
public void onChildViewAttachedToWindow(@NonNull View view) {
forEmptyTextView.setVisibility(View.INVISIBLE);
}
@Override
public void onChildViewDetachedFromWindow(@NonNull View view) {
forEmptyTextView.setVisibility(View.VISIBLE);
}
});
其他回答
在适配器的getItemViewType上检查适配器是否有0个元素，如果是，则返回不同的viewType。
然后在onCreateViewHolder上检查viewType是否为之前返回的视图，并膨胀一个不同的视图。在这种情况下，布局文件与该TextView
编辑
如果这仍然不能工作，那么你可能想通过编程来设置视图的大小，就像这样:
Point size = new Point();
((WindowManager)itemView.getContext().getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay().getSize(size);
然后当你膨胀你的视图调用:
inflatedView.getLayoutParams().height = size.y;
inflatedView.getLayoutParams().width = size.x;
下面是一种解决方案，它仅使用一个自定义适配器，为空情况使用不同的视图类型。
public class EventAdapter extends
RecyclerView.Adapter<EventAdapter.ViewHolder> {
private static final int VIEW_TYPE_EVENT = 0;
private static final int VIEW_TYPE_DATE = 1;
private static final int VIEW_TYPE_EMPTY = 2;
private ArrayList items;
public EventAdapter(ArrayList items) {
this.items = items;
}
@Override
public int getItemCount() {
if(items.size() == 0){
return 1;
}else {
return items.size();
}
}
@Override
public int getItemViewType(int position) {
if (items.size() == 0) {
return VIEW_TYPE_EMPTY;
}else{
Object item = items.get(position);
if (item instanceof Event) {
return VIEW_TYPE_EVENT;
} else {
return VIEW_TYPE_DATE;
}
}
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View v;
ViewHolder vh;
if (viewType == VIEW_TYPE_EVENT) {
v = LayoutInflater.from(parent.getContext()).inflate(
R.layout.item_event, parent, false);
vh = new ViewHolderEvent(v);
} else if (viewType == VIEW_TYPE_DATE) {
v = LayoutInflater.from(parent.getContext()).inflate(
R.layout.item_event_date, parent, false);
vh = new ViewHolderDate(v);
} else {
v = LayoutInflater.from(parent.getContext()).inflate(
R.layout.item_event_empty, parent, false);
vh = new ViewHolder(v);
}
return vh;
}
@Override
public void onBindViewHolder(EventAdapter.ViewHolder viewHolder,
final int position) {
int viewType = getItemViewType(position);
if (viewType == VIEW_TYPE_EVENT) {
//...
} else if (viewType == VIEW_TYPE_DATE) {
//...
} else if (viewType == VIEW_TYPE_EMPTY) {
//...
}
}
public static class ViewHolder extends ParentViewHolder {
public ViewHolder(View v) {
super(v);
}
}
public static class ViewHolderDate extends ViewHolder {
public ViewHolderDate(View v) {
super(v);
}
}
public static class ViewHolderEvent extends ViewHolder {
public ViewHolderEvent(View v) {
super(v);
}
}
}
这是如何显示空视图，同时过滤和更新RecyclerView使用LiveData
ViewModel.getInstance().getCustomers?.observe(viewLifecycleOwner, {customerList ->
//assign your adapter with your list then
listAdapter?.notifyDataSetChanged()
isListItemEmpty(customerList?.isEmpty())
}
创建一个接口来在适配器和片段之间通信，并在适配器中注册它
interface EmptyListener {
fun isListEmpty(isEmpty: Boolean)
}
然后在publishResults中调用它:
dataList?.isEmpty()?.let { mListener?.isListEmpty(it) }
最后在Fragment中实现你的接口:
override fun isListEmpty(isEmpty: Boolean) {
if (isEmpty) {
your_list?.visibility = View.GONE
empty_view?.visibility = View.VISIBLE
} else {
empty_view?.visibility = View.GONE
your_list?.visibility = View.VISIBLE
}
}
最简单的解决方案是使用RecyclerView。AdapterDataObserver并在适配器初始化后将其注册到recyclerview中。
val emptyDataObserver = EmptyDataObserver(recycler_view, empty_data_parent)
yourAdapter.registerAdapterDataObserver(emptyDataObserver)
其中，recycler_view & empty_data_parent是布局在你的活动，约束这些视图，你想要的，使其可见性消失。然后用图像和文本创建自己的空数据集视图。
<include
android:id="@+id/empty_data_parent"
layout="@layout/item_empty_dataset"
android:layout_width="match_parent"
android:visibility="gone"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintTop_toBottomOf="parent"
android:layout_height="match_parent"
android:layout_gravity="center" />
下面是empty_data_set_view.xml的示例
<?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"
android:orientation="vertical"
android:layout_gravity="center"
android:gravity="center"
android:paddingTop="10dp"
android:paddingBottom="10dp"
tools:ignore="RtlHardcoded">
<ImageView
android:id="@+id/imageView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.498"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.422"
android:src="@drawable/ic_empty_dataset_1" />
<TextView
android:id="@+id/title"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="Title is called when title is placed"
android:padding="10dp"
android:fontFamily="@font/normal"
android:textStyle="bold"
android:gravity="center"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/imageView2" />
<TextView
android:id="@+id/sub_title"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text=" Subtitle is called when title is placed. Subtitle is called when title is placed"
android:padding="5dp"
android:fontFamily="@font/normal"
android:gravity="center"
android:layout_marginStart="10dp"
android:layout_marginEnd="10dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/title" />
</androidx.constraintlayout.widget.ConstraintLayout>
和这个EmptyDataObserver类来做这项工作。
import android.view.View
import androidx.recyclerview.widget.RecyclerView
class EmptyDataObserver constructor(rv: RecyclerView?, ev: View?): RecyclerView.AdapterDataObserver() {
private var emptyView: View? = null
private var recyclerView: RecyclerView? = null
init {
recyclerView = rv
emptyView = ev
checkIfEmpty()
}
private fun checkIfEmpty() {
if (emptyView != null && recyclerView!!.adapter != null) {
val emptyViewVisible = recyclerView!!.adapter!!.itemCount == 0
emptyView!!.visibility = if (emptyViewVisible) View.VISIBLE else View.GONE
recyclerView!!.visibility = if (emptyViewVisible) View.GONE else View.VISIBLE
}
}
override fun onChanged() {
super.onChanged()
checkIfEmpty()
}
override fun onItemRangeChanged(positionStart: Int, itemCount: Int) {
super.onItemRangeChanged(positionStart, itemCount)
}
}
在定义了RecyclerView的相同布局上，添加TextView:
<android.support.v7.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scrollbars="vertical" />
<TextView
android:id="@+id/empty_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:visibility="gone"
android:text="@string/no_data_available" />
在onCreate或适当的回调中，您检查提供RecyclerView的数据集是否为空。 如果数据集为空，那么RecyclerView也是空的。在这种情况下，消息将显示在屏幕上。 如果不是，改变它的可见性:
private RecyclerView recyclerView;
private TextView emptyView;
// ...
recyclerView = (RecyclerView) rootView.findViewById(R.id.recycler_view);
emptyView = (TextView) rootView.findViewById(R.id.empty_view);
// ...
if (dataset.isEmpty()) {
recyclerView.setVisibility(View.GONE);
emptyView.setVisibility(View.VISIBLE);
}
else {
recyclerView.setVisibility(View.VISIBLE);
emptyView.setVisibility(View.GONE);
}
