package mcxtzhang.recyclerviewdemo.zxt;
import android.graphics.Rect;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.util.SparseArray;
import android.view.View;
import android.view.ViewGroup;
/**
* 介绍：流式布局LayoutManager
* 作者：zhangxutong
* 邮箱：zhangxutong@imcoming.com
* 时间： 2016/10/26.
*/
public class FlowLayoutManager extends RecyclerView.LayoutManager {
private int mVerticalOffset;//竖直偏移量 每次换行时，要根据这个offset判断
private int mFirstVisiPos;
private int mLastVisiPos;
private SparseArray<Rect> mItemRects;//key 是View的position，保存View的bounds 和 显示标志，
/* private class FlowItem {
public Rect bounds;//View的边界
public boolean isShow;//View 是否显示
public FlowItem(Rect bounds, boolean isShow) {
this.bounds = bounds;
this.isShow = isShow;
}
}*/
public FlowLayoutManager() {
mItemRects = new SparseArray<>();
}
@Override
public RecyclerView.LayoutParams generateDefaultLayoutParams() {
return new RecyclerView.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
}
@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
if (getItemCount() == 0) {
detachAndScrapAttachedViews(recycler);
return;
}
if (getChildCount() == 0 && state.isPreLayout()) {
return;
}
//onLayoutChildren方法在RecyclerView 初始化时 会执行两边
detachAndScrapAttachedViews(recycler);
//初始化区域
mVerticalOffset = 0;
mFirstVisiPos = 0;
mLastVisiPos = getItemCount();
fill(recycler, state);
}
/**
* 初始化时调用 填充childView
*
* @param recycler
* @param state
*/
private void fill(RecyclerView.Recycler recycler, RecyclerView.State state) {
fill(recycler, state, 0);
}
/**
* 填充childView的核心方法,应该先填充，再移动。
* 在填充时，预先计算dy的在内，如果View越界，回收掉。
* 一般情况是返回dy，如果出现View数量不足，则返回修正后的dy.
*
* @param recycler
* @param state
* @param dy RecyclerView给我们的位移量,+,显示底端， -，显示头部
* @return 修正以后真正的dy（可能剩余空间不够移动那么多了 所以return <|dy|）
*/
private int fill(RecyclerView.Recycler recycler, RecyclerView.State state, int dy) {
int topOffset = getPaddingTop();
//回收越界子View
if (getChildCount() > 0) {//滑动时进来的
for (int i = getChildCount() - 1; i >= 0; i--) {
View child = getChildAt(i);
if (dy > 0) {//需要回收当前屏幕，上越界的View
if (getDecoratedBottom(child) - dy < topOffset) {
removeAndRecycleView(child, recycler);
mFirstVisiPos++;
continue;
}
} else if (dy < 0) {//回收当前屏幕，下越界的View
if (getDecoratedTop(child) - dy > getHeight() - getPaddingBottom()) {
removeAndRecycleView(child, recycler);
mLastVisiPos--;
continue;
}
}
}
//detachAndScrapAttachedViews(recycler);
}
int leftOffset = getPaddingLeft();
int lineMaxHeight = 0;
//布局子View阶段
if (dy >= 0) {
int minPos = mFirstVisiPos;
mLastVisiPos = getItemCount() - 1;
if (getChildCount() > 0) {
View lastView = getChildAt(getChildCount() - 1);
minPos = getPosition(lastView) + 1;//从最后一个View+1开始吧
topOffset = getDecoratedTop(lastView);
leftOffset = getDecoratedRight(lastView);
lineMaxHeight = Math.max(lineMaxHeight, getDecoratedMeasurementVertical(lastView));
}
//顺序addChildView
for (int i = minPos; i <= mLastVisiPos; i++) {
//找recycler要一个childItemView,我们不管它是从scrap里取，还是从RecyclerViewPool里取，亦或是onCreateViewHolder里拿。
View child = recycler.getViewForPosition(i);
addView(child);
measureChildWithMargins(child, 0, 0);
//计算宽度 包括margin
if (leftOffset + getDecoratedMeasurementHorizontal(child) <= getHorizontalSpace()) {//当前行还排列的下
layoutDecoratedWithMargins(child, leftOffset, topOffset, leftOffset + getDecoratedMeasurementHorizontal(child), topOffset + getDecoratedMeasurementVertical(child));
//保存Rect供逆序layout用
Rect rect = new Rect(leftOffset, topOffset + mVerticalOffset, leftOffset + getDecoratedMeasurementHorizontal(child), topOffset + getDecoratedMeasurementVertical(child) + mVerticalOffset);
mItemRects.put(i, rect);
//改变 left lineHeight
leftOffset += getDecoratedMeasurementHorizontal(child);
lineMaxHeight = Math.max(lineMaxHeight, getDecoratedMeasurementVertical(child));
} else {//当前行排列不下
//改变top left lineHeight
leftOffset = getPaddingLeft();
topOffset += lineMaxHeight;
lineMaxHeight = 0;
//新起一行的时候要判断一下边界
if (topOffset - dy > getHeight() - getPaddingBottom()) {
//越界了 就回收
removeAndRecycleView(child, recycler);
mLastVisiPos = i - 1;
} else {
layoutDecoratedWithMargins(child, leftOffset, topOffset, leftOffset + getDecoratedMeasurementHorizontal(child), topOffset + getDecoratedMeasurementVertical(child));
//保存Rect供逆序layout用
Rect rect = new Rect(leftOffset, topOffset + mVerticalOffset, leftOffset + getDecoratedMeasurementHorizontal(child), topOffset + getDecoratedMeasurementVertical(child) + mVerticalOffset);
mItemRects.put(i, rect);
//改变 left lineHeight
leftOffset += getDecoratedMeasurementHorizontal(child);
lineMaxHeight = Math.max(lineMaxHeight, getDecoratedMeasurementVertical(child));
}
}
}
//添加完后，判断是否已经没有更多的ItemView，并且此时屏幕仍有空白，则需要修正dy
View lastChild = getChildAt(getChildCount() - 1);
if (getPosition(lastChild) == getItemCount() - 1) {
int gap = getHeight() - getPaddingBottom() - getDecoratedBottom(lastChild);
if (gap > 0) {
dy -= gap;
}
}
} else {
/**
* ## 利用Rect保存子View边界
正序排列时，保存每个子View的Rect，逆序时，直接拿出来layout。
*/
int maxPos = getItemCount() - 1;
mFirstVisiPos = 0;
if (getChildCount() > 0) {
View firstView = getChildAt(0);
maxPos = getPosition(firstView) - 1;
}
for (int i = maxPos; i >= mFirstVisiPos; i--) {
Rect rect = mItemRects.get(i);
if (rect.bottom - mVerticalOffset - dy < getPaddingTop()) {
mFirstVisiPos = i + 1;
break;
} else {
View child = recycler.getViewForPosition(i);
addView(child, 0);
measureChildWithMargins(child, 0, 0);
layoutDecoratedWithMargins(child, rect.left, rect.top - mVerticalOffset, rect.right, rect.bottom - mVerticalOffset);
}
}
}
Log.d("TAG", "count= [" + getChildCount() + "]" + ",[recycler.getScrapList().size():" + recycler.getScrapList().size() + ", dy:" + dy + ", mVerticalOffset" + mVerticalOffset);
return dy;
}
@Override
public boolean canScrollVertically() {
return true;
}
@Override
public int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler, RecyclerView.State state) {
//位移0、没有子View 当然不移动
if (dy == 0 || getChildCount() == 0) {
return 0;
}
int realOffset = dy;//实际滑动的距离， 可能会在边界处被修复
//边界修复代码
if (mVerticalOffset + realOffset < 0) {//上边界
realOffset = -mVerticalOffset;
} else if (realOffset > 0) {//下边界
//利用最后一个子View比较修正
View lastChild = getChildAt(getChildCount() - 1);
if (getPosition(lastChild) == getItemCount() - 1) {
int gap = getHeight() - getPaddingBottom() - getDecoratedBottom(lastChild);
if (gap > 0) {
realOffset = -gap;
} else if (gap == 0) {
realOffset = 0;
} else {
realOffset = Math.min(realOffset, -gap);
}
}
}
realOffset = fill(recycler, state, realOffset);//先填充，再位移。
mVerticalOffset += realOffset;//累加实际滑动距离
offsetChildrenVertical(-realOffset);//滑动
return realOffset;
}
//模仿LLM Horizontal 源码
/**
* 获取某个childView在水平方向所占的空间
*
* @param view
* @return
*/
public int getDecoratedMeasurementHorizontal(View view) {
final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams)
view.getLayoutParams();
return getDecoratedMeasuredWidth(view) + params.leftMargin
+ params.rightMargin;
}
/**
* 获取某个childView在竖直方向所占的空间
*
* @param view
* @return
*/
public int getDecoratedMeasurementVertical(View view) {
final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams)
view.getLayoutParams();
return getDecoratedMeasuredHeight(view) + params.topMargin
+ params.bottomMargin;
}
public int getVerticalSpace() {
return getHeight() - getPaddingTop() - getPaddingBottom();
}
public int getHorizontalSpace() {
return getWidth() - getPaddingLeft() - getPaddingRight();
}
}