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?
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;
RVEmptyObserver
而不是使用自定义的RecyclerView,扩展AdapterDataObserver是一个更简单的解决方案,允许设置一个自定义视图,当列表中没有项目时显示:
使用示例:
RVEmptyObserver observer = new RVEmptyObserver(recyclerView, emptyView)
rvAdapter.registerAdapterDataObserver(observer);
类:
public class RVEmptyObserver extends RecyclerView.AdapterDataObserver {
private View emptyView;
private RecyclerView recyclerView;
public RVEmptyObserver(RecyclerView rv, View ev) {
this.recyclerView = rv;
this.emptyView = ev;
checkIfEmpty();
}
private void checkIfEmpty() {
if (emptyView != null && recyclerView.getAdapter() != null) {
boolean emptyViewVisible = recyclerView.getAdapter().getItemCount() == 0;
emptyView.setVisibility(emptyViewVisible ? View.VISIBLE : View.GONE);
recyclerView.setVisibility(emptyViewVisible ? View.GONE : View.VISIBLE);
}
}
public void onChanged() { checkIfEmpty(); }
public void onItemRangeInserted(int positionStart, int itemCount) { checkIfEmpty(); }
public void onItemRangeRemoved(int positionStart, int itemCount) { checkIfEmpty(); }
}
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);
}
对于我的项目,我做了这个解决方案(RecyclerView与setEmptyView方法):
public class RecyclerViewEmptySupport extends RecyclerView {
private View emptyView;
private AdapterDataObserver emptyObserver = new AdapterDataObserver() {
@Override
public void onChanged() {
Adapter<?> adapter = getAdapter();
if(adapter != null && emptyView != null) {
if(adapter.getItemCount() == 0) {
emptyView.setVisibility(View.VISIBLE);
RecyclerViewEmptySupport.this.setVisibility(View.GONE);
}
else {
emptyView.setVisibility(View.GONE);
RecyclerViewEmptySupport.this.setVisibility(View.VISIBLE);
}
}
}
};
public RecyclerViewEmptySupport(Context context) {
super(context);
}
public RecyclerViewEmptySupport(Context context, AttributeSet attrs) {
super(context, attrs);
}
public RecyclerViewEmptySupport(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
@Override
public void setAdapter(Adapter adapter) {
super.setAdapter(adapter);
if(adapter != null) {
adapter.registerAdapterDataObserver(emptyObserver);
}
emptyObserver.onChanged();
}
public void setEmptyView(View emptyView) {
this.emptyView = emptyView;
}
}
你应该使用它来代替RecyclerView类:
<com.maff.utils.RecyclerViewEmptySupport android:id="@+id/list1"
android:layout_height="match_parent"
android:layout_width="match_parent"
/>
<TextView android:id="@+id/list_empty"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Empty"
/>
and
RecyclerViewEmptySupport list =
(RecyclerViewEmptySupport)rootView.findViewById(R.id.list1);
list.setLayoutManager(new LinearLayoutManager(context));
list.setEmptyView(rootView.findViewById(R.id.list_empty));
因为凯文的答案不完整。
如果你使用RecyclerAdapter的notifyItemInserted和notifyItemRemoved来更新数据集,这是更正确的答案。
请参阅下面添加的另一个用户的Kotlin版本。
Java:
mAdapter.registerAdapterDataObserver(new RecyclerView.AdapterDataObserver() {
@Override
public void onChanged() {
super.onChanged();
checkEmpty();
}
@Override
public void onItemRangeInserted(int positionStart, int itemCount) {
super.onItemRangeInserted(positionStart, itemCount);
checkEmpty();
}
@Override
public void onItemRangeRemoved(int positionStart, int itemCount) {
super.onItemRangeRemoved(positionStart, itemCount);
checkEmpty();
}
void checkEmpty() {
mEmptyView.setVisibility(mAdapter.getItemCount() == 0 ? View.VISIBLE : View.GONE);
}
});
科特林
adapter.registerAdapterDataObserver(object : RecyclerView.AdapterDataObserver() {
override fun onChanged() {
super.onChanged()
checkEmpty()
}
override fun onItemRangeInserted(positionStart: Int, itemCount: Int) {
super.onItemRangeInserted(positionStart, itemCount)
checkEmpty()
}
override fun onItemRangeRemoved(positionStart: Int, itemCount: Int) {
super.onItemRangeRemoved(positionStart, itemCount)
checkEmpty()
}
fun checkEmpty() {
empty_view.visibility = (if (adapter.itemCount == 0) View.VISIBLE else View.GONE)
}
})