/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * 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 android.widget;

import android.database.DataSetObservable;
import android.database.DataSetObserver;
import android.view.View;
import android.view.ViewGroup;

/**
 * 用于 {@link ListView} (实现了 {@link ListAdapter} 接口)和 {@link Spinner}
 * (实现了 {@link SpinnerAdapter} 接口)的共同实现的一个公共基类.
 * @author translate by 德罗德
 * @author review by cnmahj
 * @author convert by cnmahj
 */
public abstract class BaseAdapter implements ListAdapter, SpinnerAdapter {
    private final DataSetObservable mDataSetObservable = new DataSetObservable();

    public boolean hasStableIds() {
        return false;
    }
    
    public void registerDataSetObserver(DataSetObserver observer) {
        mDataSetObservable.registerObserver(observer);
    }

    public void unregisterDataSetObserver(DataSetObserver observer) {
        mDataSetObservable.unregisterObserver(observer);
    }
    
    /**
     * 通知关联的视图，后台数据已经改变，视图需要刷新.
     */
    public void notifyDataSetChanged() {
        mDataSetObservable.notifyChanged();
    }

    /**
     * 通知关联的观察器，底层数据不再有效或存在.一旦调用，该适配器将不再有效，
     * 应该也不会再发生数据集变更事件.
     */
    public void notifyDataSetInvalidated() {
        mDataSetObservable.notifyInvalidated();
    }

    public boolean areAllItemsEnabled() {
        return true;
    }

    public boolean isEnabled(int position) {
        return true;
    }

    public View getDropDownView(int position, View convertView, ViewGroup parent) {
        return getView(position, convertView, parent);
    }

    public int getItemViewType(int position) {
        return 0;
    }

    public int getViewTypeCount() {
        return 1;
    }
    
    public boolean isEmpty() {
        return getCount() == 0;
    }
}