效果图看这里，我是根据这里的代码继续往下写的
https://www.jianshu.com/p/a4b78f4cabd0
image.png
简单实现了view的复用，另外加载更多数据以后也能继续往上滚了。我也不知道到底咋判断属于加载更多数据，就简单按照滚动的距离大于0来判断的
import android.content.res.Resources;
import android.graphics.Rect;
import android.support.v7.widget.RecyclerView;
import android.util.SparseArray;
import android.view.View;
public class CustomLayoutManager extends RecyclerView.LayoutManager {
private int mFirstVisiPos;//屏幕可见的第一个View的Position
private int mLastVisiPos;//屏幕可见的最后一个View的Position
private int verticalScrollOffset;
private int offsetH = 0;//
private int leftMargin, rightMargin;
private int smallWidth = 0;//1/3的宽
private SparseArray<Rect> mItemRects = new SparseArray<>();//key 是View的position，保存View的bounds 和 显示标志，
@Override
public RecyclerView.LayoutParams generateDefaultLayoutParams() {
return new RecyclerView.LayoutParams(RecyclerView.LayoutParams.WRAP_CONTENT, RecyclerView.LayoutParams.WRAP_CONTENT);
}
@Override
public boolean isAutoMeasureEnabled() {
return super.isAutoMeasureEnabled();
}
@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
super.onLayoutChildren(recycler, state);
if (state.getItemCount() == 0) {
removeAndRecycleAllViews(recycler);
mItemRects.clear();
verticalScrollOffset=0;
return;
}
if (getChildCount() == 0 && state.isPreLayout()) {
return;
}
RecyclerView.LayoutParams params = (RecyclerView.LayoutParams)
recycler.getViewForPosition(0).getLayoutParams();
leftMargin = params.leftMargin;
rightMargin = params.rightMargin;
mFirstVisiPos = 0;
mLastVisiPos = getItemCount() - 1;
offsetH = getPaddingTop();
if(getChildCount()==0){
mItemRects.clear();
}
if(verticalScrollOffset>0){
addMore=true;//上滑加载更多数据以后，
offsetH=getDecoratedTop(getChildAt(0));
mFirstVisiPos=getPosition(getChildAt(0));
}
//先把所有item从RecyclerView中detach
detachAndScrapAttachedViews(recycler);
layoutItem(recycler);
}
private boolean addMore=false;
private void layoutItem(RecyclerView.Recycler recycler) {
layoutItem(recycler, 0);
}
private void layoutItem(RecyclerView.Recycler recycler, int dy) {
if (smallWidth == 0) {
smallWidth = (Resources.getSystem().getDisplayMetrics().widthPixels
- getRightDecorationWidth(recycler.getViewForPosition(0))
- getLeftDecorationWidth(recycler.getViewForPosition(0))
- leftMargin - rightMargin) / 3;
}
if (dy >= 0) {
//往上滑动，底部可能需要添加新的item
int minPosition = 0;
mLastVisiPos = getItemCount() - 1;
if(getChildCount()>0){
View lastChild = getChildAt(getChildCount() - 1);
int lastPosition = getPosition(lastChild) ;
minPosition=lastPosition+1;
if(lastPosition!=getItemCount()-1&&!addMore){
minPosition = lastPosition + 1;
offsetH = getDecoratedBottom(lastChild);//测试发现快速滑动可能出现问题，因为最后一个显示的child的index=6，下边要添加7和8的时候，getoffsetH就不对了，所以得判断下
if(minPosition%3!=0){
offsetH=getDecoratedTop(lastChild);
if(minPosition%6==5){
offsetH=getDecoratedTop(lastChild)-lastChild.getHeight();
}
}
}
}
//移除顶部即将不可见的item,要移除一次就是3个
View child;
while (getChildCount() > 2 && getDecoratedBottom(child = getChildAt(2)) - dy < getPaddingTop()-child.getHeight()) {
System.out.println("remove child=====3个==" + getPosition(child)+"=="+getDecoratedBottom(child)+"/"+child.getHeight());
removeAndRecycleView(child, recycler);
removeAndRecycleView(getChildAt(1), recycler);
removeAndRecycleView(getChildAt(0), recycler);
}
if(addMore){
addMore=false;
minPosition=mFirstVisiPos;
}
System.out.println("dy=== " + dy + " ========" + minPosition + "/" + mLastVisiPos + "=========" + offsetH+ "/" + getHeight());
for (int i = minPosition; i <= mLastVisiPos; i++) {
if (offsetH - dy > getHeight() - getPaddingBottom()) {
mLastVisiPos = i;
System.out.println("dy>0 break========" + mLastVisiPos + "====" + offsetH + "/" + dy + "/" + getHeight());
break;
}
addViewBottom(recycler, i);
}
} else {
//顶部可能需要添加新的item
int maxPosition = getItemCount() - 1;
mFirstVisiPos = 0;
if (getChildCount() > 0) {
View firstChild = getChildAt(0);
maxPosition = getPosition(firstChild) - 1;
}
//移除底部不可见的,
View child;
while (true) {
if(getChildCount()==0){
break;
}
int topPre= getDecoratedTop(child = getChildAt(getChildCount() - 1))-dy;
int removeTop=getHeight() - getPaddingBottom()+child.getHeight();
System.out.println("remove child=======" + getPosition(child)+"==="+topPre+"==="+getHeight()+"=="+child.getHeight());
if(topPre>removeTop){
removeAndRecycleView(child, recycler);
}else{
break;
}
}
for (int i = maxPosition; i >= mFirstVisiPos; i = i - 3) {//如果顶部要添加，那么一次至少3个
Rect rect = mItemRects.get(i);
if (rect.bottom - verticalScrollOffset - dy < getPaddingTop()) {
mFirstVisiPos = i + 1;
return;
}
addViewTop(recycler, i);
addViewTop(recycler, i - 1);
addViewTop(recycler, i - 2);
}
}
}
private void addViewTop(RecyclerView.Recycler recycler, int i) {
if (i < 0) {
return;
}
View child = recycler.getViewForPosition(i);
addView(child, 0);//将View添加至RecyclerView中，childIndex为1，但是View的位置还是由layout的位置决定
measureChildWithMargins(child, 0, 0);
Rect rect = mItemRects.get(i);
layoutDecoratedWithMargins(child, rect.left, rect.top - verticalScrollOffset, rect.right, rect.bottom - verticalScrollOffset);
}
private void addViewBottom(RecyclerView.Recycler recycler, int i) {
if (i > getItemCount() - 1) {
return;
}
View view = recycler.getViewForPosition(i);
addView(view);
measureChildWithMargins(view, 0, 0);
int height = getDecoratedMeasuredHeight(view) + getBottomDecorationHeight(view);
System.out.println("addViewBottom=======" + i + "/verticalScrollOffset=" + verticalScrollOffset + "======" + offsetH + "====" + height + "====" + getHeight());
Rect rect = new Rect();
switch (i % 6) {
case 0:
rect.set(0, offsetH, 2 * smallWidth, offsetH + height);
layoutDecoratedWithMargins(view, 0, offsetH, 2 * smallWidth, offsetH + height);
break;
case 1:
rect.set(2 * smallWidth, offsetH,
3 * smallWidth, offsetH + height / 2);
layoutDecoratedWithMargins(view, 2 * smallWidth, offsetH,
3 * smallWidth, offsetH + height / 2);
break;
case 2:
rect.set(2 * smallWidth, offsetH + height / 2,
3 * smallWidth, offsetH + height);
layoutDecoratedWithMargins(view, 2 * smallWidth, offsetH + height / 2,
3 * smallWidth, offsetH + height);
this.offsetH = this.offsetH + height;
break;
case 3:
rect.set(0, offsetH,
smallWidth, offsetH + height / 2);
layoutDecoratedWithMargins(view, 0, offsetH,
smallWidth, offsetH + height / 2);
break;
case 4:
rect.set(0, offsetH + height / 2,
smallWidth, offsetH + height);
layoutDecoratedWithMargins(view, 0, offsetH + height / 2,
smallWidth, offsetH + height);
break;
case 5:
rect.set(smallWidth, offsetH,
3 * smallWidth, offsetH + height);
layoutDecoratedWithMargins(view, smallWidth, offsetH,
3 * smallWidth, offsetH + height);
this.offsetH = this.offsetH + height;
break;
}
rect.offset(0, verticalScrollOffset);
mItemRects.put(i, rect);
}
@Override
public boolean canScrollVertically() {
return true;
}
@Override
public int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler, RecyclerView.State state) {
if (getChildCount() == 0 || dy == 0) {
return 0;
}
//手指往上滑dy为正，手指往下滑dy为负
layoutItem(recycler, dy);//先添加布局，再位移
if (dy<0) {
View firstChild = getChildAt(0);
if (getPosition(firstChild) == 0 && getDecoratedTop(firstChild) - dy > 0) {
//第一个child的position是0，并且top即将大于0，那就不能移动
dy=getDecoratedTop(firstChild);
}
}else { //判断最后一个child的底部是否即将跑到屏幕底部的上边
int bottom=getDecoratedBottom(getChildAt(getChildCount()-1));
if(bottom- dy < getHeight() - getPaddingBottom()){
dy=bottom-getHeight()+getPaddingBottom();
}
}
//将竖直方向的偏移量+travel
verticalScrollOffset += dy;
// 调用该方法通知view在y方向上移动指定距离
offsetChildrenVertical(-dy);
System.out.println("scrollvertical===========" + dy + "=====" + verticalScrollOffset+"==offsetH===="+offsetH);
return dy;
}
}
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