android中listview仿qq群组向上滚动特效

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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