当滑动到顶部和底部时，实现Item的分离效果的ListView

拉动ListView，Item之间的间距会变大，释放后恢复原样；

package cn.tangdada.tangbang.widget;

import android.annotation.TargetApi;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.drawable.BitmapDrawable;
import android.os.Build;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.animation.AccelerateInterpolator;
import android.widget.AbsListView;
import android.widget.ListView;
import cn.tangdada.tangbang.R;

import com.nineoldandroids.view.ViewPropertyAnimator;

/**
 * 当滑动到顶部和底部时，实现Item的分离效果。
 *
 * @author pythoner
 *
 */
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public class PullSeparateListView extends ListView
{
    /**
     * 最大滑动距离
     */
    private static final float MAX_DELTAY = 100;

    /**
     * 分离后恢复的动画时长
     */
    private static final long SEPARATE_RECOVER_DURATION = 200;

    /**
     * 摩擦系数
     */
    private static final float FACTOR = 0.25f;

    /**
     * 按下x的缩放比例
     */
    private static final float SCALEX = 1.0f;

    /**
     * 按下y的缩放比例
     */
    private static final float SCALEY = 1.0f;

    /**
     * 展开全部
     */
    private boolean separateAll;

    /**
     * 到达边界时，滑动的起始位置
     */
    private float startY;

    /**
     * 按下时的View
     */
    private View downView;

    private int touchSlop;

    private boolean separate = false;

    private boolean showDownAnim;

    /**
     * 原始按下位置(在所有Item中的位置)
     */
    private int originDownPosition;

    /**
     * 按下的位置(在屏幕中的位置)
     */
    private int downPosition;

    /**
     * 上次滑动的位置，用于判断方向
     */
    private float preY;

    private float deltaY;

    private boolean reachTop, reachBottom, move;

    private OnScrollListener mScrollListener;

    public PullSeparateListView(Context context, AttributeSet attrs)
    {
        super(context, attrs);
        TypedArray t = context.obtainStyledAttributes(attrs, R.styleable.PullSeparateListView);
        separateAll = t.getBoolean(R.styleable.PullSeparateListView_separate_all, false);
        showDownAnim = t.getBoolean(R.styleable.PullSeparateListView_showDownAnim, true);
        t.recycle();
        init();
    }

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

    public PullSeparateListView(Context context)
    {
        super(context);
        init();
    }

    @SuppressWarnings("deprecation")
    private void init()
    {
        // 不知道怎么让divider和selector和Item一起移动，所以去除，需要自己加分割线
        this.setDivider(null);
        this.setSelector(new BitmapDrawable());

        touchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
        super.setOnScrollListener(listener);
    }

    /**
     * 是否全部分离
     *
     * @param separateAll 如果为true,那么全部都会分离。否则的话，如果是顶部下拉，只有点击位置之前的Item会分离 如果是底部上拉，则只有点击位置之后的item会分离。默认为false
     */
    public void setSeparateAll(boolean separateAll)
    {
        this.separateAll = separateAll;
    }

    public boolean isSeparateAll()
    {
        return separateAll;
    }

    /**
     * 设置是否显示按下的Item的动画效果
     *
     * @param showDownAnim 默认为true
     */
    public void setShowDownAnim(boolean showDownAnim)
    {
        this.showDownAnim = showDownAnim;
    }

    public boolean isShowDownAnim()
    {
        return showDownAnim;
    }

    public void setOnScrollListener(OnScrollListener l)
    {
        mScrollListener = l;
    }

    // 核心代码
    @Override
    public boolean dispatchTouchEvent(MotionEvent ev)
    {
        float currentY = ev.getY();
        switch (ev.getAction())
        {
            case MotionEvent.ACTION_DOWN:
                float downX = ev.getX();
                float downY = ev.getY();
                // 记录按下位置，当isSeparateAll()返回false时，会用到
                originDownPosition = pointToPosition((int) downX, (int) downY);
                downPosition = originDownPosition - getFirstVisiblePosition();
                if (showDownAnim)
                {
                    performDownAnim(downPosition);
                }
                break;
            case MotionEvent.ACTION_MOVE:
                // 记录到达顶部或底部时手指的位置
                if (!separate)
                {
                    startY = currentY;
                }
                deltaY = currentY - startY;

                // 到达顶部
                if (reachTop)
                {
                    if (!separateFromTop(currentY))
                    {
                        return super.dispatchTouchEvent(ev);
                    }
                    return false;
                }
                // 到达底部
                if (reachBottom)
                {
                    if (!separateFromBottom(currentY))
                    {
                        return super.dispatchTouchEvent(ev);
                    }
                    return false;
                }
                preY = currentY;
                break;
            case MotionEvent.ACTION_CANCEL:
            case MotionEvent.ACTION_UP:
                preY = 0;
                recoverDownView();
                if (separate)
                {
                    separate = false;
                    recoverSeparate();
                    // 移动，不响应点击事件
                    if (move)
                    {
                        move = false;
                        return false;
                    }
                }
                break;
        }
        return super.dispatchTouchEvent(ev);
    }

    private boolean separateFromTop(float currentY)
    {
        // 不能放在外部，否则在顶部滑动没有Fling效果
        if (deltaY > touchSlop)
        {
            move = true;
        }
        separate = true;
        // 超过滑动允许的最大距离，则将起始位置向下移
        if (deltaY > MAX_DELTAY)
        {
            startY = currentY - MAX_DELTAY;
            // 超过最大距离时，出现overScroll效果//有问题
            // return super.dispatchTouchEvent(ev);
        }
        else if (deltaY < 0)
        { // 为负值时（说明反方向超过了起始位置startY）归0
            deltaY = 0;
            separate = false;
        }

        if (deltaY <= MAX_DELTAY)
        {
            for (int index = 0; index < getChildCount(); index++)
            {
                View child = getChildAt(index);
                int multiple = index;
                if (!separateAll)
                {
                    if (index > downPosition)
                    {
                        multiple = Math.max(1, downPosition);
                    }
                }
                float distance = multiple * deltaY * FACTOR;
                child.setTranslationY(distance);
            }
            // 向分离方向的反方向滑动，但位置还未复原时
            if (deltaY != 0 && currentY - preY < 0)
            {
                return true;
            }
            // deltaY=0，说明位置已经复原，然后交给父类处理
        }
        if (deltaY == 0)
        {
            return false;
        }
        return true;
    }

    private boolean separateFromBottom(float currentY)
    {
        if (Math.abs(deltaY) > touchSlop)
        {
            move = true;
        }
        separate = true;
        // 超过滑动允许的最大距离，则将起始位置向上移
        if (Math.abs(deltaY) > MAX_DELTAY)
        {
            startY = currentY + MAX_DELTAY;
            // 超过最大距离时，出现overScroll效果
            // return super.dispatchTouchEvent(ev);
        }
        else if (deltaY > 0)
        { // 为正值时（说明反方向移动超过起始位置startY），归0
            deltaY = 0;
            separate = false;
        }
        if (Math.abs(deltaY) <= MAX_DELTAY)
        {
            int visibleCount = getChildCount();
            for (int inedex = 0; inedex < visibleCount; inedex++)
            {
                View child = getChildAt(inedex);
                int multiple = visibleCount - inedex - 1;
                if (!separateAll)
                {
                    if (inedex < downPosition)
                    {
                        multiple = Math.max(1, visibleCount - downPosition - 1);
                    }
                }
                float distance = multiple * deltaY * FACTOR;
                child.setTranslationY(distance);
            }
            // 向分离方向的反方向滑动，但位置还未复原时
            if (deltaY != 0 && currentY - preY > 0)
            {
                return true;
            }
            // deltaY=0，说明位置已经复原，然后交给父类处理
            if (deltaY == 0)
            {
                return false;
            }
        }
        return true;
    }

    /**
     * 恢复
     */
    private void recoverSeparate()
    {
        for (int i = 0; i < getChildCount(); i++)
        {
            View child = getChildAt(i);
            ViewPropertyAnimator.animate(child).translationY(0).setDuration(SEPARATE_RECOVER_DURATION).setInterpolator(new AccelerateInterpolator());
        }
    }

    /**
     * 按下的动画
     *
     * @param downPosition 在屏幕中的位置
     */
    private void performDownAnim(int downPosition)
    {
        downView = getChildAt(downPosition);
        if (downView != null)
        {
            ViewPropertyAnimator.animate(downView).scaleX(SCALEX).scaleY(SCALEY).setDuration(50).setInterpolator(new AccelerateInterpolator());
        }
    }

    /**
     * 恢复点击的View
     */
    private void recoverDownView()
    {
        if (showDownAnim && downView != null)
        {
            ViewPropertyAnimator.animate(downView).scaleX(1f).scaleY(1f).setDuration(separate ? SEPARATE_RECOVER_DURATION : 100)
                    .setInterpolator(new AccelerateInterpolator());
        }
    }

    private OnScrollListener listener = new OnScrollListener()
    {
        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState)
        {
            if (mScrollListener != null)
            {
                mScrollListener.onScrollStateChanged(view, scrollState);
            }
        }

        @Override
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount)
        {
            if (mScrollListener != null)
            {
                mScrollListener.onScroll(view, firstVisibleItem, visibleItemCount, totalItemCount);
            }

            // 是否到达顶部
            if (firstVisibleItem == 0)
            {
                View firstView = getChildAt(firstVisibleItem);
                if (firstView != null && (firstView.getTop() + getPaddingTop()) >= 0)
                {
                    downPosition = originDownPosition;
                    reachTop = true;
                }
                else
                {
                    reachTop = false;
                }
            }
            else
            {
                reachTop = false;
            }
            // 是否到达底部
            if (firstVisibleItem + visibleItemCount == getCount())
            {
                View lastView = getChildAt(visibleItemCount - 1);
                if (lastView != null && (lastView.getBottom() + getPaddingBottom()) <= getHeight() && getCount() > getChildCount())
                {
                    downPosition = originDownPosition - firstVisibleItem;
                    reachBottom = true;
                }
                else
                {
                    reachBottom = false;
                }
            }
            else
            {
                reachBottom = false;
            }
        }
    };

    /**
     * 是否到达顶部
     *
     * @return
     */
    @Deprecated
    protected boolean isReachTopBound()
    {
        int firstVisPos = getFirstVisiblePosition();
        if (firstVisPos == 0)
        {
            View firstView = getChildAt(firstVisPos);
            if (firstView != null && firstView.getTop() >= 0)
            {
                return true;
            }
            else
            {
                return false;
            }
        }
        return false;
    }

    /**
     * 是否到达底部
     *
     * @return
     */
    @Deprecated
    protected boolean isReachBottomBound()
    {
        int lastVisPos = getLastVisiblePosition();
        if (lastVisPos == getCount() - 1)
        {
            View lastView = getChildAt(getChildCount() - 1);
            if (lastView != null && lastView.getBottom() <= getHeight() && getCount() > getChildCount())
            {
                return true;
            }
            else
            {
                return false;
            }
        }
        return false;
    }

}

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="PullSeparateListView">
        <attr name="separate_all" format="boolean"/>
        <attr name="showDownAnim" format="boolean"/>
    </declare-styleable>
</resources>

http://gundumw100.iteye.com/blog/2178560