Android webview-Android listView反弹效果实现，遇到params.bottomMargin遮盖了listview内容的问题

Question

当我下拉的时候，改变params.topMargin的值来进行滚动没有问题。 但是在滑到最下面，然后上啦的时候， 通过params.bottomMargin来改变，发生了listview 被遮盖的问题。 想要的结果是 listview 整体向上移动。
上图:

代码如下：

package com.scroll;

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.widget.AdapterView;
import android.widget.LinearLayout;
import android.widget.Scroller;

public class ScrollLinearLayout extends LinearLayout
{

    public static final int DETEN = 200;

    private float preY;
    private float delayY;
    private Scroller mScroller;
    private AdapterView<?> childView;
    private LayoutParams params;

    private int childTopMargin;
    private int childBottomMargin;
    private int childTop;
    private int childBottom;
    private int childPaddingTop;
    private int childHeight;

    private int parentTop;
    private int parentButtom;
    private int parentHeight;

    private View lastView;
    private int lastViewBottom;
    private int lastVisiblePosition;

    private int offsetTop;
    private int offsetBottom;

    private View firstView;
    private int firstViewTop;

    public ScrollLinearLayout(Context context, AttributeSet attrs)
    {
        super(context, attrs);
        mScroller = new Scroller(getContext());
    }

    @Override
    protected void onFinishInflate()
    {
        super.onFinishInflate();
        childView = (AdapterView<?>) getChildAt(0);
        params = (LayoutParams) childView.getLayoutParams();
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent event)
    {
        int action = event.getAction();
        float x = event.getX();
        float y = event.getY();

        updateParameter();

        switch (action)
        {
            case MotionEvent.ACTION_DOWN:
                preY = y;
                break;
            case MotionEvent.ACTION_MOVE:
                delayY = y - preY;
                preY = y;
                if (isUpPrepareState())
                {
                    return true;
                }
                if (isUpState())
                {
                    return true;
                }
                if (isDownPrepareState())
                {
                    return true;
                }
                if (isDownState())
                {
                    return true;
                }

            case MotionEvent.ACTION_UP:
                break;
        }
        return false;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event)
    {
        int action = event.getAction();
        float x = event.getX();
        float y = event.getY();

        updateParameter();

        switch (action)
        {
            case MotionEvent.ACTION_DOWN:
                break;
            case MotionEvent.ACTION_MOVE:
                if (!mScroller.isFinished())
                {
                    mScroller.abortAnimation();
                    return true;
                }
                delayY = y - preY;
                preY = y;
                if (isUpPrepareState())
                {
                    updateTopMargin(delayY);
                }
                if (isUpState())
                {
                    updateTopMargin(delayY);
                }
                if (isDownPrepareState())
                {
                    updateBottomMargin(-delayY);
                }
                if (isDownState())
                {
                    updateBottomMargin(-delayY);
                }
                childView.setLayoutParams(params);
                postInvalidate();
                break;
            case MotionEvent.ACTION_UP:

                if (isUpState())
                {
                    mScroller.startScroll(0, (int) y, 0, -(int) (offsetTop),
                            DETEN);
                    postInvalidate();
                }
                if (isDownState())
                {
                    mScroller.startScroll(0, (int) y, 0, -(int) (offsetBottom),
                            DETEN);
                    postInvalidate();
                }
                break;
        }

        return super.onTouchEvent(event);
    }

    public void computeScroll()
    {

        updateParameter();

        super.computeScroll();
        if (mScroller.computeScrollOffset())
        {
            float x = mScroller.getCurrX();
            float y = mScroller.getCurrY();
            delayY = y - preY;
            preY = y;
            if (isUpState())
            {
                updateTopMargin(delayY);

            }
            if (isDownState())
            {
                updateBottomMargin(-delayY);
            }
            childView.setLayoutParams(params);
            postInvalidate();
        }
    }

    private void updateParameter()
    {
        childTopMargin = params.topMargin;
        childBottomMargin = params.bottomMargin;

        childTop = childView.getTop();
        childBottom = childView.getBottom();
        childPaddingTop = childView.getPaddingTop();
        childHeight = childView.getHeight();

        parentTop = this.getTop();
        parentButtom = this.getBottom();
        parentHeight = this.getHeight();

        lastView = childView.getChildAt(childView.getChildCount() - 1);
        lastViewBottom = lastView.getBottom();
        lastVisiblePosition = childView.getLastVisiblePosition();
        firstView = childView.getChildAt(0);
        firstViewTop = firstView.getTop();

        offsetTop = childTop - parentTop;
        offsetBottom = childBottom - parentButtom;
    }

    private int getMaxChildIndex()
    {
        return childView.getCount() - 1;
    }

    private boolean isUpPrepareState()
    {
        return childView.getFirstVisiblePosition() == 0 && childTopMargin == 0
                && delayY > 0;
    }

    private boolean isUpState()
    {
        return childView.getFirstVisiblePosition() == 0 && childTopMargin > 0;
    }

    private boolean isDownPrepareState()
    {
        return lastViewBottom == parentHeight
                && lastVisiblePosition == getMaxChildIndex() && delayY < 0;
    }

    private boolean isDownState()
    {
        return childBottomMargin > 0;
    }

    private void updateTopMargin(float value)
    {
        params.topMargin += value;
        params.bottomMargin += -value;
        if (params.topMargin < 0)
        {
            params.topMargin = 0;
        }
    }

    private void updateBottomMargin(float value)
    {
        params.bottomMargin += value;
        params.topMargin += -value;
        if (params.bottomMargin < 0)
        {
            params.bottomMargin = 0;
        }
    }
}

Answer 1

params.topMargin也需要修改，params.topMargin的变化，ListView的高度也跟着改变；
你这个功能，我觉得你可以参考下下拉刷新ListView的实现。百度下很多。