最近由于项目需求，需要实现列表分组，并且头部悬浮。
于是这里是扩展ExpandableListView来实现，下面说一下思路：
重写onMeasure测量headerview的大小；
重写onLayout计算headerview位置；
-
为ExpandableListView设置滑动监听，在onScroll方法中，根据当前view所在的position位置判断headerview的状态：
- 如果position是当前组内的最后一个位置，headerview需上滑，即headerview处于上滑状态，headerview的y值为当前view的bottom-headerviewHeight，更新headerview的位置；
代码如下：
1、扩展ExpandableListView ：
package com.northking.dayrecord.common_views;
import android.content.Context;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.ExpandableListAdapter;
import android.widget.ExpandableListView;
import com.northking.dayrecord.common_utils.NLog;
public class LevitateHeaderExpandListView extends ExpandableListView implements AbsListView.OnScrollListener {
public LevitateHeaderExpandListView(Context context) {
super(context);
iniView();
}
public LevitateHeaderExpandListView(Context context, AttributeSet attrs) {
super(context, attrs);
iniView();
}
private void iniView() {
registerListener();
}
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;
LayoutParams lp = new LayoutParams(
ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
view.setLayoutParams(lp);
if (mHeaderView != null) {
setFadingEdgeLength(0);
}
requestLayout();
}
private void registerListener() {
setOnScrollListener(this);
}
/**
* 重写onMeasure计算悬浮条的大小
* @param widthMeasureSpec
* @param heightMeasureSpec
*/
@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);
if(mAdapter != null) {
int state = mAdapter.getHeaderState(groupPos, childPos);
if (mHeaderView != 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，而不是加入到ViewGroup中
drawChild(canvas, mHeaderView, getDrawingTime());
}
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
NLog.i("LevitateHeaderExpandListView:onScroll ");
//获取该item在listview中的原始position
// (the raw position of an item (child or group) in the list)
final long flatPos = getExpandableListPosition(firstVisibleItem);
//返回经过包装后的group的position，即当前的group在所有group中的第几个(从0开始)。
// 参数是getExpandableListPosition()的返回值
int groupPosition = ExpandableListView.getPackedPositionGroup(flatPos);
//返回经过包装后的child的position，即在该group中该child的下标(从0开始)。
// 如果该group中没有child或者显示的是group界面，那么返回的是-1
int childPosition = ExpandableListView.getPackedPositionChild(flatPos);
configureHeaderView(groupPosition, childPosition);
}
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
NLog.i("LevitateHeaderExpandListView:onScrollStateChanged ");
}
@Override
public void setAdapter(ExpandableListAdapter adapter) {
super.setAdapter(adapter);
mAdapter = (HeaderAdapter) adapter;
}
/**
* 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 其中之一
*/
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);
}
}
2、为ExpandableListView设置一个headerview用来显示悬浮条：
@Bind(R.id.lv_message)
LevitateHeaderExpandListView lv_message;
lv_message.setHeaderView(getLayoutInflater().inflate(R.layout.item_header_msg_listview,lv_message, false));
这个headerview并非listView中的headerview，它只是普通的一个布局文件，item_header_msg_listview.xml 如下：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<TextView
android:id="@+id/tv_msg_listview_label"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@color/gray_color"
android:padding="15dp"
android:textSize="@dimen/text_14"
android:textStyle="bold" />
</LinearLayout>
3、适配器除了继承BaseExpandableListAdapter之外实现LevitateHeaderExpandListView.HeaderAdapter并实现其方法：
@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 = getGroup(groupPosition).getUpdateDate();//悬浮条的显示信息
((TextView) header.findViewById(R.id.tv_msg_listview_label)).setText(groupData);
}
在onScroll方法中涉及到ExpandableListView的几个方法具体介绍有兴趣看下面链接
ExpandableListView常用方法介绍
欢迎各位矫正！
