在鸿蒙中实现类似瀑布流效果

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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

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();
        }

    }
}

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:

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;

}

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:

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。

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