监听ListView是否滚动到顶部

package com.example.propertyanimation;

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.widget.ListView;

/**
 * @类名:MyListView.java 

 * @功能描述: 监听ListView滚动到顶部

 * @作者:XuanKe'Huang 

 * @时间:2015-6-5 下午8:25:02 

 * @Copyright @2015 

 */

public class MyListView extends ListView {

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

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

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

    private int startY = 0;
    private int distanceY = 0;

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        if (listener != null)
            switch (ev.getAction()) {
            case MotionEvent.ACTION_DOWN:
                startY = (int) ev.getRawY();
                distanceY = 0;
                break;
            case MotionEvent.ACTION_MOVE:
                distanceY = (int) (ev.getRawY() - startY);
                break;
            case MotionEvent.ACTION_UP:
                if (getTop() == getChildAt(0).getTop() && distanceY > 50) {
                    listener.onScrollBottomListener(distanceY);
                }
                startY = 0;
                distanceY = 0;
                break;
            }
        return super.onTouchEvent(ev);
    }

    /**
     * 方法名: setOnScrollToHeadLintener
     * 
     * 功能描述:设置监听
     * 
     * @param listener
     * @param layout
     *            ScrollView包含的Layout
     * @return void
     * 
     *         throws
     */
    public void setOnScrollToHeadLintener(OnScrollToBottomListener listener) {
        this.listener = listener;
    }

    public interface OnScrollToBottomListener {
        // 当前滑动的距离
        public void onScrollBottomListener(int top);
    }

    private OnScrollToBottomListener listener;

}