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

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
        }
    }

其他回答

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
        }
    }

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);
        }
    }

}

我使用ViewSwitcher

<ViewSwitcher
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/switcher"
    >

    <android.support.v7.widget.RecyclerView
        android:id="@+id/list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />

    <TextView android:id="@+id/text_empty"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="@string/list_empty"
        android:gravity="center"
        />

</ViewSwitcher>

在代码中,您将检查光标/数据集和切换视图。

void showItems(Cursor items) {
    if (items.size() > 0) {

        mAdapter.switchCursor(items);

        if (R.id.list == mListSwitcher.getNextView().getId()) {
            mListSwitcher.showNext();
        }
    } else if (R.id.text_empty == mListSwitcher.getNextView().getId()) {
        mListSwitcher.showNext();
    }
}

如果你愿意,你也可以用几行代码设置动画

mListSwitcher.setInAnimation(slide_in_left);
mListSwitcher.setOutAnimation(slide_out_right);

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);
            }
        });

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;