ANDROID中LISTVIEW仿QQ群组向上滚动特效

转自：  http://www.cnblogs.com/xiaoQLu/archive/2011/12/20/2293732.html

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。

?

packagecom.demo.sectionlistview;

 

importjava.util.Arrays;

 

importandroid.widget.SectionIndexer;

 

publicclass MySectionIndexer implementsSectionIndexer{

    privatefinal String[] mSections;//

    privatefinal int[] mPositions;

    privatefinal int mCount;

     

    /**

     * @param sections

     * @param counts

     */

    publicMySectionIndexer(String[] sections, int[] counts) {

        if(sections == null|| counts == null) {

            thrownew NullPointerException();

        }

        if(sections.length != counts.length) {

            thrownew IllegalArgumentException(

                    "The sections and counts arrays must have the same length");

        }

        this.mSections = sections;

        mPositions = newint[counts.length];

        intposition = 0;

        for(inti = 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

    publicObject[] getSections() {

        // TODO Auto-generated method stub

        returnmSections;

    }

 

    @Override

    publicint getPositionForSection(intsection) {

        if(section < 0|| section > mSections.length) {

            return-1;

        }

        returnmPositions[section];

    }

 

    @Override

    publicint getSectionForPosition(intposition) {

        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

        intindex = Arrays.binarySearch(mPositions, position);

        returnindex >= 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：http://files.cnblogs.com/xiaoQLu/DemoSectionListView_Plus.rar