SRecyclerView：实现上拉加载下拉刷新的 Recyclerview

实现上拉加载下拉刷新的Recyclerview---SRecyclerview(非基于SwipeRefreshLayout)

原理：由于recyleview并不支持headview，所以传统listview用headveiw做刷新头的做法很显然不行，这里的做法参考了android著名的开源控件，PullToRefreshLayout的部分代码，原理相似，这里感谢作者的发明。SRecyclerview的做法就是将headerview和Recyleview放在同一个父容器里面，SRecyclerview其实是一个viewgroup，并不是一个view，实现刷新的过程就是，讲headview和Recyclerview同时使用addview的方式加入在viewgroup中，经过测量和onlayout方法只会将headveiw放在recyleview的上方，然后onlayout执行完成之后将viewgroup整体网上滑动让headview正好隐藏，然后下拉的时候在actionmove方法里面将偏移量减半，实现滑动的阻塞效果，并不能让headview一路滑到底，放开之后用Scroller类移动到到设置好的刷新的位置，刷新结束之后回到初始值

接下来我们分过程结合代码来解析一下Srecyleview的实现过程吧，

第一步：将子view装进viewgroup并进行测量和布局子view

初始化Scroller类

 <span class="hljs-keyword">*</span><span class="hljs-keyword">*</span>  <span class="hljs-keyword">*</span> 初始化操作  <span class="hljs-keyword">*</span>  <span class="hljs-keyword">*</span> <span class="hljs-comment">@param context</span>  <span class="hljs-keyword">*</span>/ void init(Context context) {     this.context = context;     mScroller = new Scroller(context);     addChildView(context); }  addview的操作，初始化Recyclerview `</pre>     /**  <pre>` * 增加子View  *  * <span class="hljs-annotation">@param</span> context  */ <span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">addChildView</span><span class="hljs-params">(Context context)</span> </span>{     ViewGroup.LayoutParams params = <span class="hljs-keyword">new</span> ViewGroup.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);     mHeaderView = <span class="hljs-keyword">new</span> FruitView(context);     mRecyclerView = <span class="hljs-keyword">new</span> RecyclerView(context);     addView(mHeaderView);     addView(mRecyclerView);     mLayoutManager = <span class="hljs-keyword">new</span> LinearLayoutManager(context);     mRecyclerView.setLayoutManager(mLayoutManager);     <span class="hljs-comment">// 设置Item增加、移除默认动画</span>     mRecyclerView.setItemAnimator(<span class="hljs-keyword">new</span> DefaultItemAnimator());     mRecyclerView.addOnScrollListener(onScrollListener);     mRecyclerView.setHasFixedSize(<span class="hljs-keyword">true</span>);     mRecyclerView.setLayoutParams(params); }  onMeasure测量  onLayout进行布局     <span class="hljs-annotation">@Override</span> <span class="hljs-function"><span class="hljs-keyword">protected</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onMeasure</span><span class="hljs-params">(<span class="hljs-keyword">int</span> widthMeasureSpec, <span class="hljs-keyword">int</span> heightMeasureSpec)</span> </span>{     <span class="hljs-keyword">int</span> width = MeasureSpec.getSize(widthMeasureSpec);     <span class="hljs-keyword">int</span> height = <span class="hljs-number">0</span>;     <span class="hljs-keyword">for</span> (<span class="hljs-keyword">int</span> i = <span class="hljs-number">0</span>; i < getChildCount(); i++) {         View child = getChildAt(i);         measureChild(child, widthMeasureSpec, heightMeasureSpec);         height += child.getMeasuredHeight();     }     setMeasuredDimension(width, height); }  <span class="hljs-annotation">@Override</span> <span class="hljs-function"><span class="hljs-keyword">protected</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onLayout</span><span class="hljs-params">(<span class="hljs-keyword">boolean</span> changed, <span class="hljs-keyword">int</span> l, <span class="hljs-keyword">int</span> t, <span class="hljs-keyword">int</span> r, <span class="hljs-keyword">int</span> b)</span> </span>{     <span class="hljs-keyword">int</span> left = getPaddingLeft();     <span class="hljs-keyword">int</span> top = getPaddingTop();     <span class="hljs-keyword">for</span> (<span class="hljs-keyword">int</span> i = <span class="hljs-number">0</span>; i < getChildCount(); i++) {         View child = getChildAt(i);         <span class="hljs-keyword">if</span> (i == <span class="hljs-number">0</span>) {<span class="hljs-comment">//当是header的时候居中显示</span>             <span class="hljs-keyword">int</span> headerLeft = getMeasuredWidth() / <span class="hljs-number">2</span> - child.getMeasuredWidth() / <span class="hljs-number">2</span>;             child.layout(headerLeft, top, headerLeft + child.getMeasuredWidth(), top + child.getMeasuredHeight());         } <span class="hljs-keyword">else</span>             child.layout(left, top, left + child.getMeasuredWidth(), top + child.getMeasuredHeight());         top += child.getMeasuredHeight();     }     mHeadviewHeight = getPaddingTop() + mHeaderView.getMeasuredHeight();     scrollTo(<span class="hljs-number">0</span>, mHeadviewHeight);<span class="hljs-comment">//移动到header下方以显示recyleview</span>     mFristScollerY = getScrollY(); }  在onmeasure方法里面主要测量子view的宽高，然后把headview和recyleview的高度相加得出Srecyleview的高度 OnLayout方法里面主要就是吧两个view的顺序排列一下，headview居中置顶现实，recyleview在headview的下面，最后布局结束之后呢，我们通过scrollto方法将viewgroup往上移动headview的高度，使其正好隐藏，到此，我们完成了整个界面的UI部分，这个时候是没有任何功能的  > 在我们的意识里，下拉刷新肯定是要等到下面的recyleview滑动到顶部，然后下拉的时候才出现headview，思考一下如何实现这个效果，我们这里肯定需要标志位的支持了，监听Recyleview的onscroll监听，滑动到顶部的时候我们设置mIsTop = <span class="hljs-keyword">true</span> ; 然后在mIsTop = <span class="hljs-keyword">true</span>的时候拦截触摸时间。，让recyleview无法响应触摸事件，往下滑动的时候解禁 `</pre>> <pre>`    recyleview的触摸事件， 

    /<span class="hljs-keyword">*</span><span class="hljs-keyword">*</span>  <span class="hljs-keyword">*</span> 屏蔽Recyclerview的触摸事件（下拉刷新的时候）  <span class="hljs-keyword">*</span>/ float lastY; `</pre> <pre>`@<span class="hljs-function">Override <span class="hljs-keyword">public</span> boolean <span class="hljs-title">onInterceptTouchEvent</span><span class="hljs-params">(MotionEvent ev)</span> </span>{     final <span class="hljs-keyword">int</span> action = MotionEventCompat.getActionMasked(ev);     <span class="hljs-keyword">switch</span> (action) {         <span class="hljs-keyword">case</span> MotionEvent.ACTION_DOWN:             lastY = ev.getRawY();             <span class="hljs-keyword">break</span>;         <span class="hljs-keyword">case</span> MotionEvent.ACTION_UP:         <span class="hljs-keyword">case</span> MotionEvent.ACTION_CANCEL:             <span class="hljs-keyword">return</span> <span class="hljs-keyword">false</span>;         <span class="hljs-keyword">case</span> MotionEvent.ACTION_MOVE:             <span class="hljs-keyword">if</span> (mHasRefresh && mIsTop && ev.getRawY() > lastY)                 <span class="hljs-keyword">return</span> <span class="hljs-keyword">true</span>;             <span class="hljs-keyword">break</span>; 

    }     <span class="hljs-keyword">return</span> <span class="hljs-keyword">false</span>; }  <span class="hljs-keyword">float</span> offsetY = <span class="hljs-number">0</span>;  @<span class="hljs-function">Override <span class="hljs-keyword">public</span> boolean <span class="hljs-title">onTouchEvent</span><span class="hljs-params">(MotionEvent <span class="hljs-keyword">event</span>)</span> </span>{     <span class="hljs-keyword">switch</span> (<span class="hljs-keyword">event</span>.getAction()) {         <span class="hljs-keyword">case</span> MotionEvent.ACTION_MOVE:             offsetY = Math.abs(<span class="hljs-keyword">event</span>.getRawY() - lastY); <span class="hljs-comment">//Y差值绝对值</span>             <span class="hljs-keyword">if</span> (offsetY > <span class="hljs-number">0</span>)                 scrollToOffset(offsetY);             <span class="hljs-keyword">else</span> {                 mIsTop = <span class="hljs-keyword">false</span>;             }             <span class="hljs-keyword">break</span>;         <span class="hljs-keyword">case</span> MotionEvent.ACTION_UP:             <span class="hljs-keyword">if</span> (getScrollY() <= <span class="hljs-number">0</span>) {                 doRefresh();             } <span class="hljs-function"><span class="hljs-keyword">else</span> <span class="hljs-title">complete</span><span class="hljs-params">()</span></span>;             <span class="hljs-keyword">break</span>;     }     <span class="hljs-keyword">return</span> super.onTouchEvent(<span class="hljs-keyword">event</span>); }  在onTouchEvent里面的ACTION_MOVE里面我们判断如果是往下拉的时候就执行scrollToOffset方法，这个方法里主要执行频繁的scrollto操作，实现一个连贯的下拉动画效果  <span class="hljs-comment">/**  * 滚动这个view到手滑动的位置  *  * @param offsetY Y轴偏移量  */</span> <span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">scrollToOffset</span><span class="hljs-params">(<span class="hljs-keyword">float</span> offsetY)</span> </span>{     <span class="hljs-comment">//假如正在刷新并且现在的scrolly和初始值一样的时候，代表准备下拉开始刷新，并执行一次only</span>     <span class="hljs-keyword">if</span> (getScrollY() == mFristScollerY && mRecyclerChangeListener != <span class="hljs-keyword">null</span>)         mRecyclerChangeListener.startRefresh();     <span class="hljs-keyword">int</span> <span class="hljs-keyword">value</span> = Math.round(offsetY / <span class="hljs-number">2.0</span>F);     <span class="hljs-keyword">value</span> = mFristScollerY - <span class="hljs-keyword">value</span>;     scrollTo(<span class="hljs-number">0</span>, <span class="hljs-keyword">value</span>); }  <span class="hljs-comment">/**  * 执行刷新操作,移动到header刚出来的位置  */</span> <span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">doRefresh</span><span class="hljs-params">()</span> </span>{     mStatus = STATUS_REFRESH;     <span class="hljs-keyword">int</span> currentY = getScrollY();     mScroller.startScroll(<span class="hljs-number">0</span>, currentY, <span class="hljs-number">0</span>, (mFristScollerY - mHeadviewHeight) - currentY);     invalidate();     <span class="hljs-keyword">if</span> (mRecyclerChangeListener != <span class="hljs-keyword">null</span>) mRecyclerChangeListener.onRefresh();     handler.sendEmptyMessageDelayed(<span class="hljs-number">0</span>, <span class="hljs-number">1000</span>); }  Handler handler = <span class="hljs-keyword">new</span> Handler() {     @<span class="hljs-function">Override     <span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">handleMessage</span><span class="hljs-params">(Message msg)</span> </span>{         super.handleMessage(msg);         complete();     } };