简介
鸿蒙OS 开发SDK中对于长列表的实现ListContainer的实现较为简单，没法想RecyclerView一样通过应用不同的LayoutManager来实现简单布局因而没法疾速实现瀑布流成果。
但鸿蒙OS也都反对控件的Measure（onEstimateSize），layout（onArrange) 和事件的解决。齐全能够在鸿蒙OS中自定义一个布局来实现RecyclerView+LayoutManager的成果，以此来实现瀑布流等简单成果。
自定义布局
对于鸿蒙OS自定义布局在官网上有介绍，次要实现onEstimateSize来测量控件大小和onArrange实现布局，这里咱们将子控件的确定和测量摆放齐全交LayoutManager来实现。同时咱们要反对滑动，这里用Component.DraggedListener实现。因而咱们的布局容器非常简略，调用LayoutManager进行测量布局，同时对于滑动事件，确定滑动后的视窗，调用LayoutManager的fill函数确定填满视窗的子容器汇合，而后触发从新绘制。外围代码如下
public class SpanLayout extends ComponentContainer implements ComponentContainer.EstimateSizeListener, ComponentContainer.ArrangeListener, Component.CanAcceptScrollListener, Component.ScrolledListener, Component.TouchEventListener, Component.DraggedListener { private BaseItemProvider mProvider; public SpanLayout(Context context) { super(context); setEstimateSizeListener(this); setArrangeListener(this); setDraggedListener(DRAG_VERTICAL,this); } @Override public boolean onEstimateSize(int widthEstimatedConfig, int heightEstimatedConfig) { int width = Component.EstimateSpec.getSize(widthEstimatedConfig); int height = Component.EstimateSpec.getSize(heightEstimatedConfig); setEstimatedSize( Component.EstimateSpec.getChildSizeWithMode(width, widthEstimatedConfig, EstimateSpec.UNCONSTRAINT), Component.EstimateSpec.getChildSizeWithMode(height, heightEstimatedConfig, EstimateSpec.UNCONSTRAINT)); mLayoutManager.setEstimateSize(widthEstimatedConfig,heightEstimatedConfig);// measureChild(widthEstimatedConfig,heightEstimatedConfig); return true; } @Override public boolean onArrange(int left, int top, int width, int height) { //第一次fill，从item0开始始终到leftHeight和rightHeight都大于height为止。 if(mRecycler.getAttachedScrap().isEmpty()){ mLayoutManager.fill(left,top,left+width,top+height,DIRECTION_UP); }// removeAllComponents(); //调用removeAllComponents的话会始终登程从新绘制。 for(RecyclerItem item:mRecycler.getAttachedScrap()){ item.child.arrange(item.positionX+item.marginLeft,scrollY+item.positionY+item.marginTop,item.width,item.height); } return true; } @Override public void onDragStart(Component component, DragInfo dragInfo) { startY = dragInfo.startPoint.getPointYToInt(); } @Override public void onDragUpdate(Component component, DragInfo dragInfo) { int dt = dragInfo.updatePoint.getPointYToInt() - startY; int tryScrollY = dt + scrollY; startY = dragInfo.updatePoint.getPointYToInt(); mDirection = dt<0?DIRECTION_UP:DIRECTION_DOWN; mChange = mLayoutManager.fill(0, -tryScrollY,getEstimatedWidth(),-tryScrollY+getEstimatedHeight(),mDirection); if(mChange){ scrollY = tryScrollY; postLayout(); } }}瀑布流LayoutManager
LayoutManager次要是用来确定子控件的布局，重点是要实现fill函数，用于确认对于一个视窗内的子控件。
咱们定义一个Span类，来记录某一列瀑布以后startLine和endLine状况，对于spanNum列的瀑布流，咱们创立Span数组来记录状况。
例如向上滚动，当一个子控件满足bottom小于视窗top时须要回收，当一个子控件的bottom小于视窗的bottom是阐明其下方需有子控件填充。因为瀑布流是多列的且每个子控件高度不同，因而咱们不能简略的判断以后显示的第一个子控件是否要回收，最初一个子控件下方是否须要填充来实现充斥视窗的工作。咱们用while循环+双端队列，通过保障所有的Span其startLine都小于视窗top，endLine都大于视窗bottom来实现充斥视窗的工作。外围fill函数实现如下：
public synchronized boolean fill(float left,float top,float right,float bottom,int direction){ int spanWidth = mWidthSize/mSpanNum; if(mSpans == null){ mSpans = new Span[mSpanNum]; for(int i=0;i<mSpanNum;i++){ Span span = new Span(); span.index = i; mSpans[i] = span; span.left = (int) (left + i*spanWidth); } } LinkedList<RecyclerItem> attached = mRecycler.getAttachedScrap(); if(attached.isEmpty()){ mRecycler.getAllScrap().clear(); int count = mProvider.getCount(); int okSpan = 0; for (int i=0;i<count;i++){ Span span = getMinSpanWithEndLine(); RecyclerItem item = fillChild(span.left,span.endLine,i); item.span = span; if(item.positionY>=top && item.positionY<=bottom+item.height){//在显示区域 mRecycler.addItem(i,item); mRecycler.attachItemToEnd(item); }else{ mRecycler.recycle(item); } span.endLine += item.height+item.marginTop+item.marginBottom; if(span.endLine>bottom){ okSpan++; } if(okSpan>=mSpanNum){ break; } } return true; }else{ if(direction == DIRECTION_UP){ RecyclerItem last = attached.peekLast(); int count = mProvider.getCount(); if(last.index == count-1 && last.getBottom()<=bottom){//曾经到底 return false; }else{ //先回收 RecyclerItem first = attached.peekFirst(); while(first != null && first.getBottom()<top){ mRecycler.recycle(first);//recycle自身会remove first.span.startLine += first.getVSpace(); first = attached.peekFirst(); } Span minEndLineSpan = getMinSpanWithEndLine(); int index = last.index+1; while(index<count && minEndLineSpan.endLine<=bottom){//须要填充 RecyclerItem item; if(mRecycler.getAllScrap().size()>index){ item = mRecycler.getAllScrap().get(index); mRecycler.recoverToEnd(item); }else{ item = fillChild(minEndLineSpan.left,minEndLineSpan.endLine,index); item.span = minEndLineSpan; mRecycler.attachItemToEnd(item); mRecycler.addItem(index,item); } item.span.endLine += item.getVSpace(); minEndLineSpan = getMinSpanWithEndLine(); index++; } return true; } }else if(direction == DIRECTION_DOWN){ RecyclerItem first = attached.peekFirst(); int count = mProvider.getCount(); if(first.index == 0 && first.getTop()>=top){//曾经到顶 return false; }else{ //先回收 RecyclerItem last = attached.peekLast(); while(last != null && last.getTop()>bottom){ mRecycler.recycle(last);//recycle自身会remove last.span.endLine -= last.getVSpace(); last = attached.peekFirst(); } Span maxStartLineSpan = getMaxSpanWithStartLine(); int index = first.index-1; while(index>=0 && maxStartLineSpan.startLine>=top){//须要填充 RecyclerItem item = mRecycler.getAllScrap().get(index); if(item != null){ mRecycler.recoverToStart(item); item.span.startLine -= item.getVSpace(); }else{ //实践上不存在 } maxStartLineSpan = getMaxSpanWithStartLine(); index--; } return true; } } } return true;}Item回收
对于长列表，必定要有相似于RecyclerView的回收机制。item的回收和还原在LayoutManager的fill函数中触发，通过Reycler实现。
简略的应用了mAttacthedScrap来保留以后视窗上显示的Item和mCacheScrap来保留被回收的控件。这里的设计就是对RecyclerView的回收机制的简化。
不同的是参考Flutter中三棵树的概念，定义了RecycleItem类，用来记录每个Item的左上角坐标和宽高值，只有在视窗上显示的Item会绑定组件。因为未绑定组件时的RecycleItem是非常轻量级的，因而内存的损耗根本能够疏忽。咱们用mAllScrap来按程序保留所有的RecycleItem对象，用来复用。当复原一个mAllScrap中存在的Item时，其坐标和宽高都曾经确定。
Recycler的实现外围代码如下：
public class Recycler { public static final int DIRECTION_UP = 0; public static final int DIRECTION_DOWN = 2; private ArrayList<RecyclerItem> mAllScrap = new ArrayList<>(); private LinkedList<RecyclerItem> mAttachedScrap = new LinkedList<>(); private LinkedList<Component> mCacheScrap = new LinkedList<Component>(); private BaseItemProvider mProvider; private SpanLayout mSpanLayout; private int direction = 0; public Recycler(SpanLayout layout, BaseItemProvider provider) { this.mSpanLayout = layout; this.mProvider = provider; } public ArrayList<RecyclerItem> getAllScrap() { return mAllScrap; } public LinkedList<RecyclerItem> getAttachedScrap() { return mAttachedScrap; } public void cacheItem(int index, RecyclerItem item) { mAllScrap.add(index, item); } public void attachComponent(RecyclerItem item) { mAttachedScrap.add(item); } public Component getView(int index, ComponentContainer container) { Component cache = mCacheScrap.poll(); return mProvider.getComponent(index, cache, container); } public void addItem(int index,RecyclerItem item) { mAllScrap.add(index,item); } public void attachItemToEnd(RecyclerItem item) { mAttachedScrap.add(item); } public void attachItemToStart(RecyclerItem item) { mAttachedScrap.add(0,item); } public void recycle(RecyclerItem item) { mSpanLayout.removeComponent(item.child); mAttachedScrap.remove(item); mCacheScrap.push(item.child); item.child = null; } public void recoverToEnd(RecyclerItem item) { Component child = mProvider.getComponent(item.index, mCacheScrap.poll(), mSpanLayout); child.estimateSize( Component.EstimateSpec.getSizeWithMode(item.width, Component.EstimateSpec.PRECISE), Component.EstimateSpec.getSizeWithMode(item.height, Component.EstimateSpec.PRECISE) ); item.child = child; mAttachedScrap.add(item); mSpanLayout.addComponent(child); } public void recoverToStart(RecyclerItem item) { Component child = mProvider.getComponent(item.index, mCacheScrap.poll(), mSpanLayout); child.estimateSize( Component.EstimateSpec.getSizeWithMode(item.width, Component.EstimateSpec.PRECISE), Component.EstimateSpec.getSizeWithMode(item.height, Component.EstimateSpec.PRECISE) ); item.child = child; mAttachedScrap.add(0,item); mSpanLayout.addComponent(child); }}总结
鸿蒙OS的开发SDK中根底能力都曾经提供全面了，齐全能够用来实现一些简单成果。这里实现的SpanLayout+LayoutManager+Recycler的根本是一个残缺的简单列表实现，其余布局成果也能够通过实现不同的LayoutManager来实现。
残缺代码在自己的码云我的项目上 ,在com.profound.notes.component包下，路过的请帮忙点个star。https://gitee.com/profound-la...
原文链接：https://developer.huawei.com/...
原作者：zjwujlei