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前言
Android中，大家都用过ListView，ExpandableListView等，或许你还用过PinnedHeaderListView，可是假设我说PinnedHeaderExpandableListView，你听过吗？还有可下拉的PinnedHeaderExpandableListView呢？没听过也不要紧，本文就是介绍这个东西的，为了让大家有更直观的了解。先上效果图。通过效果图能够看出，首先它是一个ExpandableListView，可是它的头部能够固定，其次。在它的上面另一个头部能够来回伸缩。恩，这就是本文要介绍的自己定义view。
为了提高复用性。这个效果我分成来了2个view来实现，第一个是PinnedHeaderExpandableListView来实现头部固定的ExpandableListView。第二个view是StickyLayout，这个view具有一个能够上下滑动的头部，最后将这2个view组合在一起，就达到了例如以下的效果。
PinnedHeaderExpandableListView的实现
关于ExpandableListView的用法请自己了解下，网上非常多。
关于这个view，它的实现方式是这种：
首先继承自ExpandableListView，然后再它滚动的时候我们要监听顶部的item是属于哪个group的，当知道是哪个group以后，我们就在view的顶部绘制这个group。这样就完毕了头部固定这个效果。当然过程远没有我描写叙述的这个简单，期间有一些问题须要正确处理。以下分别说明：
1.怎样知道顶部的item是哪个group，这个简单。略过；
2. 怎样在顶部绘制group，这个我们能够重写dispatchDraw这种方法。在这种方法里drawChild就可以。dispatchDraw是被draw方法用来绘制子元素的，和onDraw不同。onDraw是用来绘制自己的。我们要知道。view画图的过程是先背景再自己最后在绘制子元素；
3. 滑动过程中header的更新，当滑动的时候。要去推断最上面的group是否发生改变，假设改变了就须要又一次绘制group，这个非常easy。注意到有一个效果，就是当两个group接近的时候，以下的group会把上面的header推上去，这个效果就难处理一些，推动的效果能够用layout来实现，通过layout将上面的group的位置给改变就能够了；
4.header的点击，要知道固定的头部是绘制上去的，而且它也不是ExpandableListView的子元素。能够理解为我们凭空绘制的一个view，假设处理它的点击，这个貌似非常难。可是能够这么解决，当点击事件发生的时候，推断其区域是否落在header内部，假设落在了内部将能够处理点击事件了，处理后要讲事件消耗掉。
同一时候。我还提供了一个接口，OnHeaderUpdateListener，通过实现这个接口，PinnedHeaderExpandableListView就知道怎样绘制和更新header了。以下看代码：
/**
The MIT License (MIT)
Copyright (c) 2014 singwhatiwanna
https://github.com/singwhatiwanna
http://blog.csdn.net/singwhatiwanna
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/
package com.ryg.expandable.ui;
import android.content.Context;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.AbsListView;
import android.widget.ExpandableListView;
import android.widget.AbsListView.OnScrollListener;
public class PinnedHeaderExpandableListView extends ExpandableListView implements OnScrollListener {
private static final String TAG = "PinnedHeaderExpandableListView";
public interface OnHeaderUpdateListener {
/**
* 採用单例模式返回同一个view对象就可以
* 注意：view必须要有LayoutParams
*/
public View getPinnedHeader();
public void updatePinnedHeader(int firstVisibleGroupPos);
}
private View mHeaderView;
private int mHeaderWidth;
private int mHeaderHeight;
private OnScrollListener mScrollListener;
private OnHeaderUpdateListener mHeaderUpdateListener;
private boolean mActionDownHappened = false;
public PinnedHeaderExpandableListView(Context context) {
super(context);
initView();
}
public PinnedHeaderExpandableListView(Context context, AttributeSet attrs) {
super(context, attrs);
initView();
}
public PinnedHeaderExpandableListView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
initView();
}
private void initView() {
setFadingEdgeLength(0);
setOnScrollListener(this);
}
@Override
public void setOnScrollListener(OnScrollListener l) {
if (l != this) {
mScrollListener = l;
}
super.setOnScrollListener(this);
}
public void setOnHeaderUpdateListener(OnHeaderUpdateListener listener) {
mHeaderUpdateListener = listener;
if (listener == null) {
return;
}
mHeaderView = listener.getPinnedHeader();
int firstVisiblePos = getFirstVisiblePosition();
int firstVisibleGroupPos = getPackedPositionGroup(getExpandableListPosition(firstVisiblePos));
listener.updatePinnedHeader(firstVisibleGroupPos);
requestLayout();
postInvalidate();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
if (mHeaderView == null) {
return;
}
measureChild(mHeaderView, widthMeasureSpec, heightMeasureSpec);
mHeaderWidth = mHeaderView.getMeasuredWidth();
mHeaderHeight = mHeaderView.getMeasuredHeight();
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
super.onLayout(changed, l, t, r, b);
if (mHeaderView == null) {
return;
}
mHeaderView.layout(0, 0, mHeaderWidth, mHeaderHeight);
}
@Override
protected void dispatchDraw(Canvas canvas) {
super.dispatchDraw(canvas);
if (mHeaderView != null) {
drawChild(canvas, mHeaderView, getDrawingTime());
}
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
int x = (int) ev.getX();
int y = (int) ev.getY();
Log.d(TAG, "dispatchTouchEvent");
int pos = pointToPosition(x, y);
if (y >= mHeaderView.getTop() && y <= mHeaderView.getBottom()) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
mActionDownHappened = true;
} else if (ev.getAction() == MotionEvent.ACTION_UP) {
int groupPosition = getPackedPositionGroup(getExpandableListPosition(pos));
if (groupPosition != INVALID_POSITION && mActionDownHappened) {
if (isGroupExpanded(groupPosition)) {
collapseGroup(groupPosition);
} else {
expandGroup(groupPosition);
}
mActionDownHappened = false;
}
}
return true;
}
return super.dispatchTouchEvent(ev);
}
protected void refreshHeader() {
if (mHeaderView == null) {
return;
}
int firstVisiblePos = getFirstVisiblePosition();
int pos = firstVisiblePos + 1;
int firstVisibleGroupPos = getPackedPositionGroup(getExpandableListPosition(firstVisiblePos));
int group = getPackedPositionGroup(getExpandableListPosition(pos));
if (group == firstVisibleGroupPos + 1) {
View view = getChildAt(1);
if (view.getTop() <= mHeaderHeight) {
int delta = mHeaderHeight - view.getTop();
mHeaderView.layout(0, -delta, mHeaderWidth, mHeaderHeight - delta);
}
} else {
mHeaderView.layout(0, 0, mHeaderWidth, mHeaderHeight);
}
if (mHeaderUpdateListener != null) {
mHeaderUpdateListener.updatePinnedHeader(firstVisibleGroupPos);
}
}
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
if (mHeaderView != null && scrollState == SCROLL_STATE_IDLE) {
int firstVisiblePos = getFirstVisiblePosition();
if (firstVisiblePos == 0) {
mHeaderView.layout(0, 0, mHeaderWidth, mHeaderHeight);
}
}
if (mScrollListener != null) {
mScrollListener.onScrollStateChanged(view, scrollState);
}
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
if (totalItemCount > 0) {
refreshHeader();
}
if (mScrollListener != null) {
mScrollListener.onScroll(view, firstVisibleItem, visibleItemCount, totalItemCount);
}
}
}下拉效果的实现
如今介绍第二个view，即StickyLayout，字面意思是黏性的layout。这个view内部分为2部分，header和content，而且header能够来回收缩。
至于怎样让header上下收缩。有几个看似可行的方案，我们分析下：
1.通过scrollTo/scrollBy来实现view的滚动，因为这两个api是对view内容的滚动，无论怎么滚动，内容都不会覆盖到别的view上去，除非你用了FrameLayout、RelativeLayout且经过精心布局，否则非常难实现将内容滚动到别的view上面，即便如此。假设将header展开和收缩也是一个非常大的问题，除非你动态地去调整header的布局。通过分析，这种方法不可行；
2. 通过动画来实现view的平移，从效果上来说。这个可行的，使用平移和缩放动画并结合手势的监听。能够实现这个效果。可是动画有一个问题。就是点击事件的处理，我们知道view动画。即使view区域发生了改变，可是事件点击区域仍然不变。而属性动画在3.0以下系统上根本不支持，就算採用兼容包。可是属性动画在3.0以下系统的点击事件区域仍然不会随着动画而改变。这更加证实了一个结论：动画是对view的显示发生作用，而不是view这个对象，也即是说动画并不影响view的区域（4个顶点）。
说了这么多，好像还挺晦涩的，直白来说，採用动画来实现的问题是：在3.0以下系统。尽管view已经看起来跑到新位置了。可是你在新位置点击是不会触发点击事件的，而老位置还是能够触发点击事件，这就意味着，content移动后，content无法点击了。基于此。动画不可行；
3.第三种方案，也就是本文所採用的方案：通过手势监听结合header高度的改变来实现整个动画效果，详细点就是。当手指滑动的时候，动态去调整header的高度并重绘。这个时候因为header的高度发生了改变。所以content中的内容就会挤上去。就实现了本文中的效果了。
有了这个StickyLayout，想实现相似的效果，这要把能够收缩的内容放到header里。其它内容放到content里就可以。以下看代码：
/**
The MIT License (MIT)
Copyright (c) 2014 singwhatiwanna
https://github.com/singwhatiwanna
http://blog.csdn.net/singwhatiwanna
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/
package com.ryg.expandable.ui;
import java.util.NoSuchElementException;
import android.annotation.TargetApi;
import android.content.Context;
import android.os.Build;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewConfiguration;
import android.widget.LinearLayout;
public class StickyLayout extends LinearLayout {
private static final String TAG = "StickyLayout";
public interface OnGiveUpTouchEventListener {
public boolean giveUpTouchEvent(MotionEvent event);
}
private View mHeader;
private View mContent;
private OnGiveUpTouchEventListener mGiveUpTouchEventListener;
// header的高度 单位：px
private int mOriginalHeaderHeight;
private int mHeaderHeight;
private int mStatus = STATUS_EXPANDED;
public static final int STATUS_EXPANDED = 1;
public static final int STATUS_COLLAPSED = 2;
private int mTouchSlop;
// 分别记录上次滑动的坐标
private int mLastX = 0;
private int mLastY = 0;
// 分别记录上次滑动的坐标(onInterceptTouchEvent)
private int mLastXIntercept = 0;
private int mLastYIntercept = 0;
// 用来控制滑动角度，仅当角度a满足例如以下条件才进行滑动：tan a = deltaX / deltaY > 2
private static final int TAN = 2;
public StickyLayout(Context context) {
super(context);
}
public StickyLayout(Context context, AttributeSet attrs) {
super(context, attrs);
}
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public StickyLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
@Override
public void onWindowFocusChanged(boolean hasWindowFocus) {
super.onWindowFocusChanged(hasWindowFocus);
if (hasWindowFocus && (mHeader == null || mContent == null)) {
initData();
}
}
private void initData() {
int headerId= getResources().getIdentifier("header", "id", getContext().getPackageName());
int contentId = getResources().getIdentifier("content", "id", getContext().getPackageName());
if (headerId != 0 && contentId != 0) {
mHeader = findViewById(headerId);
mContent = findViewById(contentId);
mOriginalHeaderHeight = mHeader.getMeasuredHeight();
mHeaderHeight = mOriginalHeaderHeight;
mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
Log.d(TAG, "mTouchSlop = " + mTouchSlop);
} else {
throw new NoSuchElementException("Did your view with "header" or "content" exist?");
}
}
public void setOnGiveUpTouchEventListener(OnGiveUpTouchEventListener l) {
mGiveUpTouchEventListener = l;
}
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
int intercepted = 0;
int x = (int) event.getX();
int y = (int) event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
mLastXIntercept = x;
mLastYIntercept = y;
mLastX = x;
mLastY = y;
intercepted = 0;
break;
}
case MotionEvent.ACTION_MOVE: {
int deltaX = x - mLastXIntercept;
int deltaY = y - mLastYIntercept;
if (mStatus == STATUS_EXPANDED && deltaY <= -mTouchSlop) {
intercepted = 1;
} else if (mGiveUpTouchEventListener != null) {
if (mGiveUpTouchEventListener.giveUpTouchEvent(event) && deltaY >= mTouchSlop) {
intercepted = 1;
}
}
break;
}
case MotionEvent.ACTION_UP: {
intercepted = 0;
mLastXIntercept = mLastYIntercept = 0;
break;
}
default:
break;
}
Log.d(TAG, "intercepted=" + intercepted);
return intercepted != 0;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
int x = (int) event.getX();
int y = (int) event.getY();
Log.d(TAG, "x=" + x + " y=" + y + " mlastY=" + mLastY);
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
break;
}
case MotionEvent.ACTION_MOVE: {
int deltaX = x - mLastX;
int deltaY = y - mLastY;
Log.d(TAG, "mHeaderHeight=" + mHeaderHeight + " deltaY=" + deltaY + " mlastY=" + mLastY);
mHeaderHeight += deltaY;
setHeaderHeight(mHeaderHeight);
break;
}
case MotionEvent.ACTION_UP: {
// 这里做了下推断，当松开手的时候。会自己主动向两边滑动。详细向哪边滑，要看当前所处的位置
int destHeight = 0;
if (mHeaderHeight <= mOriginalHeaderHeight * 0.5) {
destHeight = 0;
mStatus = STATUS_COLLAPSED;
} else {
destHeight = mOriginalHeaderHeight;
mStatus = STATUS_EXPANDED;
}
// 慢慢滑向终点
this.smoothSetHeaderHeight(mHeaderHeight, destHeight, 500);
break;
}
default:
break;
}
mLastX = x;
mLastY = y;
return true;
}
public void smoothSetHeaderHeight(final int from, final int to, long duration) {
final int frameCount = (int) (duration / 1000f * 30) + 1;
final float partation = (to - from) / (float) frameCount;
new Thread("Thread#smoothSetHeaderHeight") {
@Override
public void run() {
for (int i = 0; i < frameCount; i++) {
final int height;
if (i == frameCount - 1) {
height = to;
} else {
height = (int) (from + partation * i);
}
post(new Runnable() {
public void run() {
setHeaderHeight(height);
}
});
try {
sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
}.start();
}
private void setHeaderHeight(int height) {
Log.d(TAG, "setHeaderHeight height=" + height);
if (height < 0) {
height = 0;
} else if (height > mOriginalHeaderHeight) {
height = mOriginalHeaderHeight;
}
if (mHeaderHeight != height || true) {
mHeaderHeight = height;
mHeader.getLayoutParams().height = mHeaderHeight;
mHeader.requestLayout();
}
}
}关于这个view还须要说明的是滑动冲突，假设content里是个listview，因为两者都能竖向滑动，这就会有冲突。怎样解决滑动冲突一直是一个难点，我的解决思路是这种：首先StickyLayout默认不拦截事件，假设子元素不处理事件。它就会上下滑动。假设子元素处理了事件，它就不会滑动。所以在最外层我们须要知道子元素何时处理事件、何时不处理事件，为了解决问题。提供了一个接口OnGiveUpTouchEventListener，当子元素不处理事件的时候，StickyLayout就能够处理滑动事件。详细请參看代码中的onInterceptTouchEvent和onTouchEvent。以下看一下activity对这2个接口的实现。
Activity的实现
因为Activity中大部分代码都是环绕ExpandableListAdapter，是比較普通的代码，这里要介绍的是activity对上述2个view中接口的实现，分别为PinnedHeaderExpandableListView中怎样绘制和更新固定的头部以及StickyLayout中content何时放弃事件处理。
@Override
public View getPinnedHeader() {
if (mHeaderView == null) {
mHeaderView = (ViewGroup) getLayoutInflater().inflate(R.layout.group, null);
mHeaderView.setLayoutParams(new LayoutParams(
LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));
}
return mHeaderView;
}
@Override
public void updatePinnedHeader(int firstVisibleGroupPos) {
Group firstVisibleGroup = (Group) adapter.getGroup(firstVisibleGroupPos);
TextView textView = (TextView) getPinnedHeader().findViewById(R.id.group);
textView.setText(firstVisibleGroup.getTitle());
}
@Override
public boolean giveUpTouchEvent(MotionEvent event) {
if (expandableListView.getFirstVisiblePosition() == 0) {
View view = expandableListView.getChildAt(0);
if (view != null && view.getTop() >= 0) {
return true;
}
}
return false;
}总结
demo效果上还是不错的，在4.x和2.x上都经过測试，完美执行，市面上不少android应用有相似的效果，欢迎大家fork代码。欢迎大家交流。
代码地址
https://github.com/singwhatiwanna/PinnedHeaderExpandableListView
须要注意的是：该项目採用MIT共享协议公布，意味着假设你要使用或改动它，必须在源码中保留头部的版权声明，这个要求够不够低啊，哈哈！