如何在Android应用中实现一个列表悬浮效果

package com.xiaos.view;

import android.content.Context;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.ExpandableListAdapter;
import android.widget.ExpandableListView;
import android.widget.ExpandableListView.OnGroupClickListener;

public class PinnedHeaderExpandableListView extends ExpandableListView implements OnScrollListener,OnGroupClickListener {
 public PinnedHeaderExpandableListView(Context context, AttributeSet attrs, int defStyle) {
 super(context, attrs, defStyle);
 registerListener();
 }

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

 public PinnedHeaderExpandableListView(Context context) {
 super(context);
 registerListener();
 }

 /**
 * Adapter 接口 . 列表必须实现此接口 .
 */
 public interface HeaderAdapter {
 public static final int PINNED_HEADER_GONE = 0;
 public static final int PINNED_HEADER_VISIBLE = 1;
 public static final int PINNED_HEADER_PUSHED_UP = 2;
 
 /**
  * 获取 Header 的状态
  * @param groupPosition
  * @param childPosition
  * @return PINNED_HEADER_GONE,PINNED_HEADER_VISIBLE,PINNED_HEADER_PUSHED_UP 当中之中的一个
  */
 int getHeaderState(int groupPosition, int childPosition);

 /**
  * 配置 Header, 让 Header 知道显示的内容
  * @param header
  * @param groupPosition
  * @param childPosition
  * @param alpha
  */
 void configureHeader(View header, int groupPosition,int childPosition, int alpha);

 /**
  * 设置组按下的状态 
  * @param groupPosition
  * @param status
  */
 void setGroupClickStatus(int groupPosition, int status);

 /**
  * 获取组按下的状态
  * @param groupPosition
  * @return
  */
 int getGroupClickStatus(int groupPosition);

 }

 private static final int MAX_ALPHA = 255;

 private HeaderAdapter mAdapter;

 /**
 * 用于在列表头显示的 View,mHeaderViewVisible 为 true 才可见
 */
 private View mHeaderView;

 /**
 * 列表头是否可见
 */
 private boolean mHeaderViewVisible;

 private int mHeaderViewWidth;

 private int mHeaderViewHeight;

 public void setHeaderView(View view) {
 mHeaderView = view;
 AbsListView.LayoutParams lp = new AbsListView.LayoutParams(
 ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
 view.setLayoutParams(lp);

 if (mHeaderView != null) {
  setFadingEdgeLength(0);
 }

 requestLayout();
 }

 private void registerListener() {
 setOnScrollListener(this);
 setOnGroupClickListener(this);
 }

 /**
 * 点击 HeaderView 触发的事件
 */
 private void headerViewClick() {
 long packedPosition = getExpandableListPosition(this.getFirstVisiblePosition());
 
 int groupPosition = ExpandableListView.getPackedPositionGroup(packedPosition);
 
 if (mAdapter.getGroupClickStatus(groupPosition) == 1) {
  this.collapseGroup(groupPosition);
  mAdapter.setGroupClickStatus(groupPosition, 0);
 }
 else{
  this.expandGroup(groupPosition);
  mAdapter.setGroupClickStatus(groupPosition, 1);
 }
 
 this.setSelectedGroup(groupPosition);
 }

 private float mDownX;
 private float mDownY;

 /**
 * 假设 HeaderView 是可见的 , 此函数用于推断是否点击了 HeaderView, 并对做对应的处理 ,
 * 由于 HeaderView 是画上去的 , 所以设置事件监听是无效的 , 仅仅有自行控制 .
 */
 @Override
 public boolean onTouchEvent(MotionEvent ev) {
 if (mHeaderViewVisible) {
  switch (ev.getAction()) {
  case MotionEvent.ACTION_DOWN:
  mDownX = ev.getX();
  mDownY = ev.getY();
  if (mDownX <= mHeaderViewWidth && mDownY <= mHeaderViewHeight) {
   return true;
  }
  break;
  case MotionEvent.ACTION_UP:
  float x = ev.getX();
  float y = ev.getY();
  float offsetX = Math.abs(x - mDownX);
  float offsetY = Math.abs(y - mDownY);
  // 假设 HeaderView 是可见的 , 点击在 HeaderView 内 , 那么触发 headerClick()
  if (x <= mHeaderViewWidth && y <= mHeaderViewHeight
  && offsetX <= mHeaderViewWidth && offsetY <= mHeaderViewHeight) {
   if (mHeaderView != null) {
   headerViewClick();
   }

   return true;
  }
  break;
  default:
  break;
  }
 }

 return super.onTouchEvent(ev);

 }

 @Override
 public void setAdapter(ExpandableListAdapter adapter) {
 super.setAdapter(adapter);
 mAdapter = (HeaderAdapter) adapter;
 }

 /**
 * 
 * 点击了 Group 触发的事件 , 要依据依据当前点击 Group 的状态来
 */
 @Override
 public boolean onGroupClick(ExpandableListView parent,View v,int groupPosition,long id) {
 if (mAdapter.getGroupClickStatus(groupPosition) == 0) {
  mAdapter.setGroupClickStatus(groupPosition, 1);
  parent.expandGroup(groupPosition);
  //Header自己主动置顶
  //parent.setSelectedGroup(groupPosition);
  
 } else if (mAdapter.getGroupClickStatus(groupPosition) == 1) {
  mAdapter.setGroupClickStatus(groupPosition, 0);
  parent.collapseGroup(groupPosition);
 }

 // 返回 true 才干够弹回第一行 , 不知道为什么
 return true;
 }

 @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();
 }
 }

 private int mOldState = -1;

 @Override
 protected void onLayout(boolean changed, int left, int top, int right,int bottom) {
 super.onLayout(changed, left, top, right, bottom);
 final long flatPostion = getExpandableListPosition(getFirstVisiblePosition());
 final int groupPos = ExpandableListView.getPackedPositionGroup(flatPostion);
 final int childPos = ExpandableListView.getPackedPositionChild(flatPostion);
 int state = mAdapter.getHeaderState(groupPos, childPos);
 if (mHeaderView != null && mAdapter != null && state != mOldState) {
  mOldState = state;
  mHeaderView.layout(0, 0, mHeaderViewWidth, mHeaderViewHeight);
 }

 configureHeaderView(groupPos, childPos);
 }

 public void configureHeaderView(int groupPosition, int childPosition) {
 if (mHeaderView == null || mAdapter == null
 || ((ExpandableListAdapter) mAdapter).getGroupCount() == 0) {
  return;
 }

 int state = mAdapter.getHeaderState(groupPosition, childPosition);

 switch (state) {
  case HeaderAdapter.PINNED_HEADER_GONE: {
  mHeaderViewVisible = false;
  break;
  }
 
  case HeaderAdapter.PINNED_HEADER_VISIBLE: {
  mAdapter.configureHeader(mHeaderView, groupPosition,childPosition, MAX_ALPHA);
 
  if (mHeaderView.getTop() != 0){
   mHeaderView.layout(0, 0, mHeaderViewWidth, mHeaderViewHeight);
  }
 
  mHeaderViewVisible = true;
 
  break;
  }
 
  case HeaderAdapter.PINNED_HEADER_PUSHED_UP: {
  View firstView = getChildAt(0);
  int bottom = firstView.getBottom();
 
  // intitemHeight = 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.configureHeader(mHeaderView, groupPosition,childPosition, alpha);
 
  if (mHeaderView.getTop() != y) {
   mHeaderView.layout(0, y, mHeaderViewWidth, mHeaderViewHeight + y);
  }
 
  mHeaderViewVisible = true;
  break;
  }
 }
 }

 @Override
 /**
 * 列表界面更新时调用该方法(如滚动时)
 */
 protected void dispatchDraw(Canvas canvas) {
 super.dispatchDraw(canvas);
 if (mHeaderViewVisible) {
  //分组栏是直接绘制到界面中。而不是增加到ViewGroup中
  drawChild(canvas, mHeaderView, getDrawingTime());
 }
 }

 @Override
 public void onScroll(AbsListView view, int firstVisibleItem,int visibleItemCount, int totalItemCount) {
 final long flatPos = getExpandableListPosition(firstVisibleItem);
 int groupPosition = ExpandableListView.getPackedPositionGroup(flatPos);
 int childPosition = ExpandableListView.getPackedPositionChild(flatPos);
 
 configureHeaderView(groupPosition, childPosition);
 }

 @Override
 public void onScrollStateChanged(AbsListView view, int scrollState) {
 }
}

package com.xiaos.adapter;

import android.content.Context;
import android.util.SparseIntArray;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseExpandableListAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import com.xiaos.pinnedheaderexpandable.R;
import com.xiaos.view.PinnedHeaderExpandableListView;
import com.xiaos.view.PinnedHeaderExpandableListView.HeaderAdapter;

public class PinnedHeaderExpandableAdapter extends BaseExpandableListAdapter implements HeaderAdapter{
private String[][] childrenData;
private String[] groupData;
private Context context;
private PinnedHeaderExpandableListView listView;
private LayoutInflater inflater;

public PinnedHeaderExpandableAdapter(String[][] childrenData,String[] groupData
,Context context,PinnedHeaderExpandableListView listView){
this.groupData = groupData; 
this.childrenData = childrenData;
this.context = context;
this.listView = listView;
inflater = LayoutInflater.from(this.context);
}

@Override
public Object getChild(int groupPosition, int childPosition) {
return childrenData[groupPosition][childPosition];
}

@Override
public long getChildId(int groupPosition, int childPosition) {
return 0;
}

@Override
public View getChildView(int groupPosition, int childPosition,
boolean isLastChild, View convertView, ViewGroup parent) {
View view = null; 
if (convertView != null) { 
view = convertView; 
} else { 
view = createChildrenView(); 
} 
TextView text = (TextView)view.findViewById(R.id.childto);
text.setText(childrenData[groupPosition][childPosition]); 
return view; 
}

@Override
public int getChildrenCount(int groupPosition) {
return childrenData[groupPosition].length;
}

@Override
public Object getGroup(int groupPosition) {
return groupData[groupPosition];
}

@Override
public int getGroupCount() {
return groupData.length;
}

@Override
public long getGroupId(int groupPosition) {
return 0;
}

@Override
public View getGroupView(int groupPosition, boolean isExpanded,
View convertView, ViewGroup parent) {
View view = null; 
if (convertView != null) { 
view = convertView; 
} else { 
view = createGroupView(); 
}

ImageView iv = (ImageView)view.findViewById(R.id.groupIcon);

if (isExpanded) {
iv.setImageResource(R.drawable.btn_browser2);
}
else{
iv.setImageResource(R.drawable.btn_browser);
}

TextView text = (TextView)view.findViewById(R.id.groupto);
text.setText(groupData[groupPosition]); 
return view; 
}

@Override
public boolean hasStableIds() {
return true;
}

@Override
public boolean isChildSelectable(int groupPosition, int childPosition) {
return true;
}

private View createChildrenView() {
return inflater.inflate(R.layout.child, null);
}

private View createGroupView() {
return inflater.inflate(R.layout.group, null);
}

@Override
public int getHeaderState(int groupPosition, int childPosition) {
final int childCount = getChildrenCount(groupPosition);
if (childPosition == childCount - 1) {
return PINNED_HEADER_PUSHED_UP;
} else if (childPosition == -1
&& !listView.isGroupExpanded(groupPosition)) {
return PINNED_HEADER_GONE;
} else {
return PINNED_HEADER_VISIBLE;
}
}

@Override
public void configureHeader(View header, int groupPosition,
int childPosition, int alpha) {
String groupData = this.groupData[groupPosition];
((TextView) header.findViewById(R.id.groupto)).setText(groupData);

}

private SparseIntArray groupStatusMap = new SparseIntArray();

@Override
public void setGroupClickStatus(int groupPosition, int status) {
groupStatusMap.put(groupPosition, status);
}

@Override
public int getGroupClickStatus(int groupPosition) {
if (groupStatusMap.keyAt(groupPosition)>=0) {
return groupStatusMap.get(groupPosition);
} else {
return 0;
}
}
}

package com.xiaos.pinnedheaderexpandable;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.ExpandableListView;
import android.widget.ExpandableListView.OnGroupClickListener;

import com.xiaos.adapter.PinnedHeaderExpandableAdapter;
import com.xiaos.view.PinnedHeaderExpandableListView;

public class MainActivity extends Activity{
 private PinnedHeaderExpandableListView explistview;
 private String[][] childrenData = new String[10][10];
 private String[] groupData = new String[10];
 private int expandFlag = -1;//控制列表的展开 
 private PinnedHeaderExpandableAdapter adapter;
 
 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.layout_main);
 initView();
 initData();
 }
 
 /**
 * 初始化VIEW
 */
 private void initView() {
 explistview = (PinnedHeaderExpandableListView)findViewById(R.id.explistview);
 }

 /**
 * 初始化数据
 */
 private void initData() {
 for(int i=0;i<10;i++){
  groupData[i] = "分组"+i;
 }
 
 for(int i=0;i<10;i++){
  for(int j=0;j<10;j++){
  childrenData[i][j] = "好友"+i+"-"+j;
  }
 }
 //设置悬浮头部VIEW
 explistview.setHeaderView(getLayoutInflater().inflate(R.layout.group_head,
  explistview, false));
 adapter = new PinnedHeaderExpandableAdapter(childrenData, groupData, getApplicationContext(),explistview);
 explistview.setAdapter(adapter);
 
 //设置单个分组展开
 //explistview.setOnGroupClickListener(new GroupClickListener());
 }
 
 class GroupClickListener implements OnGroupClickListener{
 @Override
 public boolean onGroupClick(ExpandableListView parent, View v,
  int groupPosition, long id) {
  if (expandFlag == -1) {
  // 展开被选的group
  explistview.expandGroup(groupPosition);
  // 设置被选中的group置于顶端
  explistview.setSelectedGroup(groupPosition);
  expandFlag = groupPosition;
  } else if (expandFlag == groupPosition) {
  explistview.collapseGroup(expandFlag);
  expandFlag = -1;
  } else {
  explistview.collapseGroup(expandFlag);
  // 展开被选的group
  explistview.expandGroup(groupPosition);
  // 设置被选中的group置于顶端
  explistview.setSelectedGroup(groupPosition);
  expandFlag = groupPosition;
  }
  return true;
 }
 }
}

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