瀑布流系统是本身自带的，但在实际使用中会有诸多问题
比如：在底部刷新了之后，回到顶部，就参差不齐了，空白 item交换等。
造轮子是为了解决这个问题，提供实际问题的解决思路。相比系统自带完善的layoutManger 还差太远太远
效果
2017-11-29-10-16-12.gif
实现
- 自定义一个LayoutManager主要重写以下方法
- generateDefaultLayoutParams()
- onLayoutChildren
- scrollVerticallyBy canScrollVertically() 当然水平方向也有
- 核心是onLayoutChildren scrollVerticallyBy
@Override
public RecyclerView.LayoutParams generateDefaultLayoutParams() {
return new RecyclerView.LayoutParams(eachWidth, ViewGroup.LayoutParams.WRAP_CONTENT);
}
@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
if (state.getItemCount() == 0) {
detachAndScrapAttachedViews(recycler);
}
if (getChildCount() == 0 && state.isPreLayout()) {
return;
}
if (helper == null) {
helper = OrientationHelper.createHorizontalHelper(this);
helper2 = OrientationHelper.createVerticalHelper(this);
}
detachAndScrapAttachedViews(recycler);
/**
* 预计算位置
*/
init(recycler, state);
layout(recycler, state, 0);
}
private void init(final RecyclerView.Recycler recycler, RecyclerView.State state) {
offsets = new int[count];
attchedViews.clear();
eachWidth = helper.getTotalSpace() / count;
}
private void caculate(final RecyclerView.Recycler recycler, int dy) {
long start = System.currentTimeMillis();
A:
for (int i = layouts.size(); i < getItemCount(); i++) {
/**
* 之测量不同type的大小 计算位置
*/
View scrap = recycler.getViewForPosition(i);
addView(scrap);
measureChildWithMargins(scrap, eachWidth, 0);
int decoratedMeasuredHeight = getDecoratedMeasuredHeight(scrap);
removeAndRecycleView(scrap, recycler);
int rowNumber = getMinIndex();
Rect rect = layouts.get(i);
rect.set(rowNumber * eachWidth, offsets[rowNumber], (rowNumber + 1) * eachWidth, offsets[rowNumber] + decoratedMeasuredHeight);
offsets[rowNumber] = offsets[rowNumber] + rect.height();
/**
* 只多加载一屏幕的
*/
if (offsets[getMinIndex()] > dy + scrolls + getPaddingTop() + helper2.getTotalSpace()) {
break A;
}
}
maxHeight = getMaxHeight();
}
/**
* 获取最小的指针位置
*
* @return
*/
private int getMinIndex() {
int min = 0;
int minnum = offsets[0];
for (int i = 1; i < offsets.length; i++) {
if (minnum > offsets[i]) {
minnum = offsets[i];
min = i;
}
}
return min;
}
/**
* 获取最大的高度
*
* @return
*/
private int getMaxHeight() {
int max = offsets[0];
for (int i = 1; i < offsets.length; i++) {
if (offsets[i] > max) {
max = offsets[i];
}
}
return max;
}
public Rect getRect(RecyclerView.Recycler recycler, int position) {
Rect rectx = layouts.get(position);
return rectx;
}
/**
* dy 1 上滑 -1 下滑 0出初始
*
* @param recycler
* @param state
*/
private void layout(RecyclerView.Recycler recycler, RecyclerView.State state, int dy) {
Rect layoutRange = new Rect(getPaddingLeft(), getPaddingTop() + scrolls, helper.getTotalSpace() + getPaddingLeft(), helper2.getTotalSpace() + getPaddingTop() + scrolls);
int itemCount = state.getItemCount();
if (dy >= 0) {
dolayoutAndRecycler(recycler, layoutRange, itemCount);
} else {
dolayoutAndRecyclerDown(recycler, layoutRange, itemCount);
}
}
private void recyclerViews(RecyclerView.Recycler recycler,Rect layoutrect) {
// detachAndScrapAttachedViews(recycler);
int childCount = getChildCount();
for (int i = 0; i < childCount; i++) {
View childAt = getChildAt(i);
int position = getPosition(childAt);
Rect rect = layouts.get(position);
if(!Rect.intersects(rect,layoutrect)){
attchedViews.remove(position);
removeAndRecycleView(childAt,recycler);
childCount--;
}
}
}
private void dolayoutAndRecyclerDown(RecyclerView.Recycler recycler, Rect layoutRange, int itemCount) {
int childCount = getChildCount();
int max = getMax(childCount);
recyclerViews(recycler,layoutRange);
int xx = 0;
for (int i = max; i >= 0; i--) {
Rect layout = getRect(recycler, i);
if (Rect.intersects(layout, layoutRange)&&attchedViews.get(i)==null) {
View viewForPosition = recycler.getViewForPosition(i);
addView(viewForPosition);
attchedViews.put(i,viewForPosition);
measureChildWithMargins(viewForPosition, eachWidth, 0);
layoutDecoratedWithMargins(viewForPosition, layout.left, layout.top - scrolls, layout.right, layout.bottom - scrolls);
}
if (layout.bottom <= layoutRange.top) {
xx++;
if (xx >= count) {
break;
}
}
}
}
private int getMax(int childCount) {
int max = 0;
if (childCount != 0) {
max = getPosition(getChildAt(0));
for (int i = 1; i < childCount; i++) {
int position = getPosition(getChildAt(i));
if (position > max) {
max = position;
}
}
}
return max;
}
/**
* 出初始layout
*
* @param recycler
* @param layoutRange
* @param itemCount
*/
private void dolayoutAndRecycler(RecyclerView.Recycler recycler, Rect layoutRange, int itemCount) {
int childCount = getChildCount();
int min = getMin(childCount);
recyclerViews(recycler,layoutRange);
int xx = 0;
A:
for (int i = min; i < itemCount; i++) {
if (getRect(recycler, i).isEmpty()) {
layouts.getArray().remove(i);
caculate(recycler, 0);
}
final Rect layout = getRect(recycler, i);
if (Rect.intersects(layout, layoutRange)&&attchedViews.get(i)==null) {
View viewForPosition = recycler.getViewForPosition(i);
addView(viewForPosition);
attchedViews.put(i,viewForPosition);
measureChildWithMargins(viewForPosition, eachWidth, 0);
layoutDecoratedWithMargins(viewForPosition, layout.left, layout.top - scrolls, layout.right, layout.bottom - scrolls);
}
if (layout.top >= layoutRange.bottom) {
xx++;
if (xx >= count) {
break;
}
}
}
}
private int getMin(int childCount) {
int min = 0;
if (childCount != 0) {
min = getPosition(getChildAt(0));
for (int i = 1; i < childCount; i++) {
int position = getPosition(getChildAt(i));
if (position < min) {
min = position;
}
}
}
return min;
}
@Override
public boolean canScrollVertically() {
return true;
}
@Override
public boolean canScrollHorizontally() {
//返回true表示可以横向滑动
return false;
}
@Override
public int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler, RecyclerView.State state) {
System.out.println(getChildCount() + "------------");
if (layouts.size() < getItemCount() && maxHeight <= dy + scrolls + getPaddingTop() + helper2.getTotalSpace()) {
caculate(recycler, dy);
}
if (maxHeight < helper2.getTotalSpace()) {
return 0;
}
if (scrolls + dy > maxHeight - helper2.getTotalSpace()) {
dy = maxHeight - helper2.getTotalSpace() - scrolls;
}
if (scrolls + dy < 0) {
dy = -scrolls;
}
offsetChildrenVertical(-dy);
scrolls += dy;
if (dy > 0) {
layout(recycler, state, 1);
} else if (dy < 0) {
layout(recycler, state, -1);
}
return dy;
}
@Override
public void scrollToPosition(int position) {
int temp = position;
if (position > getItemCount()) {
temp = getItemCount();
} else if (position < 0) {
temp = 0;
}
int top = layouts.get(temp).top;
if (top > maxHeight - helper2.getTotalSpace()) {
top = maxHeight - helper2.getTotalSpace();
}
scrolls = top;
requestLayout();
}
@Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {//平滑的移动到某一项
int top = layouts.get(position).top;
int needscroll = top - scrolls;
recyclerView.smoothScrollBy(0, needscroll);
}
private static class Pool<T> {
SparseArray<T> array;
Factory<T> tnew;
public Pool(Factory<T> tnew) {
array = new SparseArray<>();
this.tnew = tnew;
}
public int size() {
return array.size();
}
public SparseArray<T> getArray() {
return array;
}
public T get(int key) {
T t = array.get(key);
if (t == null) {
t = tnew.get();
array.put(key, t);
}
return t;
}
public interface Factory<T> {
T get();
}
}
