package com.mcxtzhang.cstnorecyclelistview;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
/**
* 介绍：换一种思路实现LM:一个普通的竖直列表(ListView)
* 支持不同大小的View
* 显示底端更多的，就从上往下排列，
* 显示头部更多的，就从下往上排.
* 作者：zhangxutong
* 邮箱：zhangxutong@imcoming.com
* 时间： 2016/10/20.
*/
public class ZxtCstLM2 extends RecyclerView.LayoutManager {
private final static int LAYOUT_FROM_TOP = 1;//从top->bottom布局子child
private final static int LAYOUT_FROM_BOTTOM = 2;//从bottom->top布局子child
private int mLayoutDirection;//layout child的方向
private int mFirstVisiblePosition;//记录第一个可见的postion 不太好算啊
private int mLastVisiblePosition; //记录最后一个可见的position
private int mVerticalScrollOffset = 0;//竖直滑动了多少距离
@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;
}
detachAndScrapAttachedViews(recycler);
//初始化postion和布局方向
mFirstVisiblePosition = 0;
mLastVisiblePosition = getItemCount() - 1;
/* int leftOffset = getPaddingLeft();
int topOffset = getPaddingTop();*/
mLayoutDirection = LAYOUT_FROM_TOP;
//布局子View
fill(recycler, state);
}
/**
* 核心布局子View函数
*
* @param recycler
* @param state
*/
private void fill(RecyclerView.Recycler recycler, RecyclerView.State state) {
//布局 offset初始化
int topOffset = getPaddingTop();
int leftOffset = getPaddingLeft();
int bottomOffset = getBottomBorder();//
//没有变化的View的下标 - View
//SparseArray<View> unChangedIndexView = new SparseArray<View>();
if (getChildCount() > 0) {
//有子View topOffset终于找到了 感动到哭，遍历一遍找到基准的Top Bottom
if (mLayoutDirection == LAYOUT_FROM_TOP) {
View topView = getChildAt(0);
topOffset = getDecoratedTop(topView);
//leftOffset = getDecoratedLeft(topView);
} else {
View bottomView = getChildAt(getChildCount() - 1);
bottomOffset = getDecoratedBottom(bottomView);
//leftOffset = getDecoratedLeft(bottomView);
}
//先将屏幕上不显示的移除掉，并且累加offset
int beforeRemoveFirstPosition = mFirstVisiblePosition;
for (int i = getChildCount() - 1; i >= 0; i--) {
//step1 recycle回收越界的View
View child = getChildAt(i);
//View下边超出上界 回收,isSHowDown true
if (getDecoratedBottom(child) < getPaddingTop()) {
removeAndRecycleView(child, recycler);
mFirstVisiblePosition++;
topOffset += getDecoratedMeasuredHeight(child);
continue;
}
//View上边超过下界 回收,isshowDOwn false
if (getDecoratedTop(child) > getBottomBorder()) {
removeAndRecycleView(child, recycler);
mLastVisiblePosition--;
bottomOffset -= getDecoratedMeasuredHeight(child);
continue;
}
//step2 将没越界的View不做任何处理
//unChangedIndexView.put(beforeRemoveFirstPosition + i, child);
}
//recycle掉不可见的后，detach所有可见的view
detachAndScrapAttachedViews(recycler);
}
//理论上不会 不过还是做个边界修正
if (mFirstVisiblePosition < 0) {
mFirstVisiblePosition = 0;
}
if (mLastVisiblePosition > getItemCount() - 1) {
mLastVisiblePosition = getItemCount() - 1;
}
if (mLayoutDirection == LAYOUT_FROM_TOP) {//从上往下显示
mLastVisiblePosition = getItemCount() - 1;
for (int i = mFirstVisiblePosition; i <= mLastVisiblePosition; i++) {
View child = recycler.getViewForPosition(i);
addView(child);
measureChildWithMargins(child, 0, 0);
layoutDecoratedWithMargins(child, leftOffset, topOffset, leftOffset + getDecoratedMeasuredWidth(child), topOffset + getDecoratedMeasuredHeight(child));
//}
topOffset += getDecoratedMeasuredHeight(child);
if (/*getDecoratedBottom(child)*/topOffset > (getBottomBorder())) {
//下越界 不再add
mLastVisiblePosition = i;
}
}
} else {//从下往上显示
mFirstVisiblePosition = 0;//从下往上看，上面最小应该是0
for (int i = mLastVisiblePosition; i >= mFirstVisiblePosition; i--) {
View child = recycler.getViewForPosition(i);
addView(child, 0);
measureChildWithMargins(child, 0, 0);
layoutDecoratedWithMargins(child, leftOffset, bottomOffset - getDecoratedMeasuredHeight(child), leftOffset + getDecoratedMeasuredWidth(child), bottomOffset);
//}
bottomOffset -= getDecoratedMeasuredHeight(child);
if (bottomOffset < getPaddingTop()) {//达到上届 不再add
mFirstVisiblePosition = i;
}
}
}
Log.d("TAG", "count= [" + getChildCount() + "]" + ",[recycler.getScrapList().size():" + recycler.getScrapList().size());
}
@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 offset = dy;
//边界处理 和滑动距离处理
if (offset > 0) {
View bottomView = getChildClosestToEnd();
//最后一个子View隐藏起来的距离,一般情况下它的取值是，0~bottomView的Height，但是当滑动到最后一个ItemCount的时候，它才可能为负值
int bottomViewHeightHind = (getDecoratedBottom(bottomView) - getBottomBorder());
/* if (bottomViewHeightHind == 0) {
//offset 随意吧
Log.w("TAG", "不设置限制:bottomViewHeightHind == 0]");
} else if (bottomViewHeightHind > 0) {//
if (offset > bottomViewHeightHind) {//下边界 bottom , 拉的太大 要留白了
Log.d("TAG", "scrollVerticallyBy() called with: offset = [" + offset + "], getDecoratedBottom(bottomView()) = [" + getDecoratedBottom(bottomView) + "], getBottomBorder() = [" + getBottomBorder() + "]");
//offset = bottomViewHeightHind;//这里还是正值
}
} else {//反常了 你赶紧给我修正！
Log.e("TAG", "//反常了，只有最后一个VIew越界才会出现 你赶紧给我修正！],下面的代码修正");
}*/
//这里很重要，获取bottomView的postion
int bottomPosition = getPosition(bottomView);
//如果是最后一个子View 而且没有隐藏的距离了
if (bottomPosition == getItemCount() - 1 && bottomViewHeightHind <= 0) {
offset = bottomViewHeightHind;//滑动的太嗨了，需要回弹
}
} else {//,offset 负
if (mVerticalScrollOffset + offset < 0) {//处理上边界 top
offset = -mVerticalScrollOffset;//这里还是负值
}
}
//平移childView,传入负值向上平移View，正值向下平移View
offsetChildrenVertical(-offset);
mVerticalScrollOffset += offset;
//根据位移方向 设置布局子View方向
if (offset > 0) {
mLayoutDirection = LAYOUT_FROM_TOP;
} else if (offset < 0) {
mLayoutDirection = LAYOUT_FROM_BOTTOM;
}
fill(recycler, state);
return offset;// 边界效果和fling
}
/**
* 模仿源码的
*
* @return
*/
private View getChildClosestToStart() {
return getChildAt(false ? getChildCount() - 1 : 0);
}
private View getChildClosestToEnd() {
return getChildAt(false ? 0 : getChildCount() - 1);
//return findViewByPosition(mLastVisiblePosition);
}
public int getVerticalSpace() {
return getHeight() - getPaddingTop() - getPaddingBottom();
}
public int getHorizontalSpace() {
return getWidth() - getPaddingLeft() - getPaddingRight();
}
/**
* 返回下边界
*
* @return
*/
public int getBottomBorder() {
return getHeight() - getPaddingBottom();
}
}