prebuilts/gradle/XYZTouristAttractions/Application/src/main/java/com/example/android/xyztouristattractions/ui/AttractionsRecyclerView.java

/*
 * Copyright 2015 Google Inc. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.xyztouristattractions.ui;

import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.view.View;

/**
 * Simple RecyclerView subclass that supports providing an empty view (which
 * is displayed when the adapter has no data and hidden otherwise).
 */
public class AttractionsRecyclerView extends RecyclerView {
    private View mEmptyView;

    private AdapterDataObserver mDataObserver = new AdapterDataObserver() {
        @Override
        public void onChanged() {
            super.onChanged();
            updateEmptyView();
        }
    };

    public AttractionsRecyclerView(Context context) {
        super(context);
    }

    public AttractionsRecyclerView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public AttractionsRecyclerView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    /**
     * Designate a view as the empty view. When the backing adapter has no
     * data this view will be made visible and the recycler view hidden.
     *
     */
    public void setEmptyView(View emptyView) {
        mEmptyView = emptyView;
    }

    @Override
    public void setAdapter(RecyclerView.Adapter adapter) {
        if (getAdapter() != null) {
            getAdapter().unregisterAdapterDataObserver(mDataObserver);
        }
        if (adapter != null) {
            adapter.registerAdapterDataObserver(mDataObserver);
        }
        super.setAdapter(adapter);
        updateEmptyView();
    }

    private void updateEmptyView() {
        if (mEmptyView != null && getAdapter() != null) {
            boolean showEmptyView = getAdapter().getItemCount() == 0;
            mEmptyView.setVisibility(showEmptyView ? VISIBLE : GONE);
            setVisibility(showEmptyView ? GONE : VISIBLE);
        }
    }
}