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一样通过使用不同的LayoutManager来实现复杂布局因此没法快速实现瀑布流效果。
但鸿蒙OS也都支持控件的Measure（onEstimateSize），layout（onArrange) 和事件的处理。完全可以在鸿蒙OS中自定义一个布局来实现RecyclerView+LayoutManager的效果，以此来实现瀑布流等复杂效果。
自定义布局
对于鸿蒙OS自定义布局在官网上有介绍，主要实现onEstimateSize来测量控件大小和onArrange实现布局，这里我们将子控件的确定和测量摆放完全交LayoutManager来实现。同时我们要支持滑动，这里用Component.DraggedListener实现。因此我们的布局容器十分简单，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集合，然后触发重新绘制。核心代码如下
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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开始一直到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的话会一直出发重新绘制。
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();
}
}
}
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瀑布流LayoutManager
LayoutManager主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。
我们定义一个Span类，来记录某一列瀑布当前startLine和endLine情况，对于spanNum列的瀑布流，我们创建Span数组来记录情况。
例如向上滚动，当一个子控件满足bottom小于视窗top时需要回收，当一个子控件的bottom小于视窗的bottom是说明其下方需有子控件填充。由于瀑布流是多列的且每个子控件高度不同，因此我们不能简单的判断当前显示的第一个子控件是否要回收，最后一个子控件下方是否需要填充来完成充满视窗的工作。我们用while循环+双端队列，通过保证所有的Span其startLine都小于视窗top，endLine都大于视窗bottom来完成充满视窗的工作。核心fill函数实现如下：
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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){
//已经到底
return
false
;
}
else
{
//先回收
RecyclerItem first = attached.peekFirst();
while
(first !=
null
&& first.getBottom()<top){
mRecycler.recycle(first);
//recycle本身会remove
first.span.startLine += first.getVSpace();
first = attached.peekFirst();
}
Span minEndLineSpan = getMinSpanWithEndLine();
int
index = last.index+
1
;
while
(index<count && minEndLineSpan.endLine<=bottom){
//需要填充
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){
//已经到顶
return
false
;
}
else
{
//先回收
RecyclerItem last = attached.peekLast();
while
(last !=
null
&& last.getTop()>bottom){
mRecycler.recycle(last);
//recycle本身会remove
last.span.endLine -= last.getVSpace();
last = attached.peekFirst();
}
Span maxStartLineSpan = getMaxSpanWithStartLine();
int
index = first.index-
1
;
while
(index>=
0
&& maxStartLineSpan.startLine>=top){
//需要填充
RecyclerItem item = mRecycler.getAllScrap().get(index);
if
(item !=
null
){
mRecycler.recoverToStart(item);
item.span.startLine -= item.getVSpace();
}
else
{
//理论上不存在
}
maxStartLineSpan = getMaxSpanWithStartLine();
index--;
}
return
true
;
}
}
}
return
true
;
}
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Item回收
对于长列表，肯定要有类似于RecyclerView的回收机制。item的回收和复原在LayoutManager的fill函数中触发，通过Reycler实现。
简单的使用了mAttacthedScrap来保存当前视窗上显示的Item和mCacheScrap来保存被回收的控件。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。由于未绑定组件时的RecycleItem是十分轻量级的，因此内存的损耗基本可以忽略。我们用mAllScrap来按顺序保存所有的RecycleItem对象，用来复用。当恢复一个mAllScrap中存在的Item时，其坐标和宽高都已经确定。
Recycler的实现核心代码如下：
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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);
}
}
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总结
鸿蒙OS的开发SDK中基础能力都已经提供全面了，完全可以用来实现一些复杂效果。这里实现的SpanLayout+LayoutManager+Recycler的基本是一个完整的复杂列表实现，其他布局效果也可以通过实现不同的LayoutManager来实现。
完整代码在本人的码云项目上 ,在com.profound.notes.component包下，路过的请帮忙点个star。https://gitee.com/profound-lab/super-notes
原文链接：https://developer.huawei.com/consumer/cn/forum/topic/0202558139689270488?fid=0101303901040230869
原作者：zjwujlei