android中listview仿qq群组向上滚动特效

非谢谢java豆子的修改方法，主要是计算分组内成员个数的逻辑有问题，已重新修改计算逻辑，并添加了注释，源码已重新上传

感谢kylin17和哟一嗨同学发现的bug，确实存在此问题，已修正

MySectionIndexer.java中public int getPositionForSection(int section)方法第一个判断有误，应该为大于等于，已修改

手机qq上有这样一个特效：当前分组的好友，向上滚动时，在顶部会出现一个透明的框，当下一个分组到达时，会把上一个分组慢慢顶上去，觉得这个特效蛮有意思，就研究了一下，android自带的通讯录分组就有这个特效，这里是自己仿写的一个，部分源码从通讯录中扣出来的

实现原理：

前提条件，假设所有的数据已经分好组

1.listview中每一个item都默认有一个分组标签，但是只显示此分组下面的第一个，其他的默认不显示

2.滚动的时候，判断每一个分组的状态，是向上滚动，还是完全显示，或者隐藏，主要是取当前item所在的分组跟(下一个分组-1=当前分组)相比，如果相等，说明是向上流动，否则是隐藏

3.获取当前分组的状态后，就可以放置分组的位置了，这里使用view.layout(int left,int top,int rigth,int bottom) ，其他left是0，right是分组标签的长度，top和bottom是需要计算的，用ViewGroup.getChileAt(0)获取listview中第一个孩子的view，然后用bottom=view.getBottom获取底部距离父窗口的位置，最后得到两者之差y=bottom-标题框的高度，用这个差就可以得出顶部和底部的位置，就是top和bottom的值。

关键类解析：

PinnedHeaderListView.java 这个是实现listview分组的关键，当然布局文件中的listview也要使用这个类，里面有个接口，adapter要实现此接口，是滚动时回调用，其中getPinnedHeaderState()是用来分组标签状态的，

它的3种状态都在此接口中定义，configurePinnedHeader()是用来设置分组标签的标题，也是相当于qq群组中的组名，此类中的configHeaderView()就是放置分组使用的，结合上面的分析跟这个方法研究这个类

/*
 * Copyright (C) 2010 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 com.demo.sectionlistview;

import android.content.Context;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.view.View;
import android.widget.ListAdapter;
import android.widget.ListView;

/**
 * A ListView that maintains a header pinned at the top of the list. The
 * pinned header can be pushed up and dissolved as needed.
 */
public class PinnedHeaderListView extends ListView {

    /**
     * Adapter interface.  The list adapter must implement this interface.
     */
    public interface PinnedHeaderAdapter {

        /**
         * Pinned header state: don't show the header.
         */
        public static final int PINNED_HEADER_GONE = 0;

        /**
         * Pinned header state: show the header at the top of the list.
         */
        public static final int PINNED_HEADER_VISIBLE = 1;

        /**
         * Pinned header state: show the header. If the header extends beyond
         * the bottom of the first shown element, push it up and clip.
         */
        public static final int PINNED_HEADER_PUSHED_UP = 2;

        /**
         * Computes the desired state of the pinned header for the given
         * position of the first visible list item. Allowed return values are
         * {@link #PINNED_HEADER_GONE}, {@link #PINNED_HEADER_VISIBLE} or
         * {@link #PINNED_HEADER_PUSHED_UP}.
         */
        int getPinnedHeaderState(int position);

        /**
         * Configures the pinned header view to match the first visible list item.
         *
         * @param header pinned header view.
         * @param position position of the first visible list item.
         * @param alpha fading of the header view, between 0 and 255.
         */
        void configurePinnedHeader(View header, int position, int alpha);
    }

    private static final int MAX_ALPHA = 255;

    private PinnedHeaderAdapter mAdapter;
    private View mHeaderView;
    private boolean mHeaderViewVisible;

    private int mHeaderViewWidth;

    private int mHeaderViewHeight;

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

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

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

    public void setPinnedHeaderView(View view) {
        mHeaderView = view;

        // Disable vertical fading when the pinned header is present
        // TODO change ListView to allow separate measures for top and bottom fading edge;
        // in this particular case we would like to disable the top, but not the bottom edge.
        if (mHeaderView != null) {
            setFadingEdgeLength(0);
        }
        requestLayout();
    }

    @Override
    public void setAdapter(ListAdapter adapter) {
        super.setAdapter(adapter);
        mAdapter = (PinnedHeaderAdapter)adapter;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (mHeaderView != null) {
            measureChild(mHeaderView, widthMeasureSpec, heightMeasureSpec);
            mHeaderViewWidth = mHeaderView.getMeasuredWidth();
            mHeaderViewHeight = mHeaderView.getMeasuredHeight();
        }
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);
        if (mHeaderView != null) {
            mHeaderView.layout(0, 0, mHeaderViewWidth, mHeaderViewHeight);
            configureHeaderView(getFirstVisiblePosition());
        }
    }

    public void configureHeaderView(int position) {
        if (mHeaderView == null) {
            return;
        }

        int state = mAdapter.getPinnedHeaderState(position);
        switch (state) {
            case PinnedHeaderAdapter.PINNED_HEADER_GONE: {
                mHeaderViewVisible = false;
                break;
            }

            case PinnedHeaderAdapter.PINNED_HEADER_VISIBLE: {
                mAdapter.configurePinnedHeader(mHeaderView, position, MAX_ALPHA);
                if (mHeaderView.getTop() != 0) {
                    mHeaderView.layout(0, 0, mHeaderViewWidth, mHeaderViewHeight);
                }
                mHeaderViewVisible = true;
                break;
            }

            case PinnedHeaderAdapter.PINNED_HEADER_PUSHED_UP: {
                View firstView = getChildAt(0);
                int bottom = firstView.getBottom();
//                int itemHeight = firstView.getHeight();
                int headerHeight = mHeaderView.getHeight();
                int y;
                int alpha;
                if (bottom < headerHeight) {
                    y = (bottom - headerHeight);
                    alpha = MAX_ALPHA * (headerHeight + y) / headerHeight;
                } else {
                    y = 0;
                    alpha = MAX_ALPHA;
                }
                mAdapter.configurePinnedHeader(mHeaderView, position, alpha);
                if (mHeaderView.getTop() != y) {
                    mHeaderView.layout(0, y, mHeaderViewWidth, mHeaderViewHeight + y);
                }
                mHeaderViewVisible = true;
                break;
            }
        }
    }

    @Override
    protected void dispatchDraw(Canvas canvas) {
        super.dispatchDraw(canvas);
        if (mHeaderViewVisible) {
            drawChild(canvas, mHeaderView, getDrawingTime());
        }
    }
}

MySectionIndexer.java类，主要是用来提供分组的数据的，主要包括，String[] mSections-->所有的组名，int[] mPositions-->每一个组名在listivew中的位置，当然，他们的长度应该是相同的。

package com.demo.sectionlistview;

import java.util.Arrays;

import android.widget.SectionIndexer;

public class MySectionIndexer implements SectionIndexer{
    private final String[] mSections;//
    private final int[] mPositions;
    private final int mCount;
    
    /**
     * @param sections
     * @param counts
     */
    public MySectionIndexer(String[] sections, int[] counts) {
        if (sections == null || counts == null) {
            throw new NullPointerException();
        }
        if (sections.length != counts.length) {
            throw new IllegalArgumentException(
                    "The sections and counts arrays must have the same length");
        }
        this.mSections = sections;
        mPositions = new int[counts.length];
        int position = 0;
        for (int i = 0; i < counts.length; i++) {
            if(mSections[i] == null) {
                mSections[i] = "";
            } else {
                mSections[i] = mSections[i].trim(); 
            }
            
            mPositions[i] = position;
            position += counts[i];
        }
        mCount = position;
    }
    
    @Override
    public Object[] getSections() {
        // TODO Auto-generated method stub
        return mSections;
    }

    @Override
    public int getPositionForSection(int section) {
        //change by lcq 2012-10-12 section > mSections.length以为>= 
        if (section < 0 || section >= mSections.length) {
            return -1;
        }
System.out.println("lcq:section:"+section);
        return mPositions[section];
    }

    @Override
    public int getSectionForPosition(int position) {
        if (position < 0 || position >= mCount) {
            return -1;
        }
        //注意这个方法的返回值，它就是index<0时，返回-index-2的原因
        //解释Arrays.binarySearch，如果搜索结果在数组中，刚返回它在数组中的索引，如果不在，刚返回第一个比它大的索引的负数-1
        //如果没弄明白，请自己想查看api
        int index = Arrays.binarySearch(mPositions, position);
        return index >= 0 ? index : -index - 2; //当index小于0时，返回-index-2，
        
    }

}

　　当然，adapter也灰常重要，这里简单分析下，因为具体使用时，会根据情况使用不同的adapter，比如说，有数据库的，可以使用SimpleCursorAdapter，也可以使用SimpleAdapter等等，这里使用的原始的listAdapter，比较麻烦，这里要实现上面提到的PinnedHeaderAdapter，还要实现SectionIndexer,主要是用来根据实际位置查找分组的索引，以及根据索引返回组名在实际listview中的位置（这里有点不太好讲，不太懂的，仔细看源码和api）

其他的就是一些adapter的基本应用以及一些android 的基本知识，这里不在讲述，不懂的请提问。

源码下载地址：qq群组向上滚动DemoSectionListView_Plus