/ 前言 /
还是老套路, 先来看看实现的成果!
在写这个成果之前, 须要相熟 Rv 的回收复用机制, 因为实现这个成果, 须要自定义 LayoutManager()…
家喻户晓,RecyclerView 是一个可滑动的 View, 那么他的回收 / 复用入口肯定是在 onTouchEvent()事件中
滑动过程中响应的是 MotionEvent.ACTION_MOVE 事件, 所以间接来这里找找看!!
/ 缓存机制 /
onTouchEvent()入口
#RecyclerView.java
@Override
public boolean onTouchEvent(MotionEvent e) {final int action = e.getActionMasked();
switch (action) {
........................................
........ 只展现代码思路, 细节请自行查看........
........................................
case MotionEvent.ACTION_MOVE: {if (mScrollState == SCROLL_STATE_DRAGGING) {mLastTouchX = x - mScrollOffset[0];
mLastTouchY = y - mScrollOffset[1];
// 要害代码 1
if (scrollByInternal(
canScrollHorizontally ? dx : 0,
canScrollVertically ? dy : 0,
vtev)) {getParent().requestDisallowInterceptTouchEvent(true);
}
if (mGapWorker != null && (dx != 0 || dy != 0)) {mGapWorker.postFromTraversal(this, dx, dy);
}
}
}
break;
}
} 接着找 scrollByInternal(int x, int y, MotionEvent ev)办法
#RecyclerView.java
boolean scrollByInternal(int x, int y, MotionEvent ev) {if (mAdapter != null) {
........................................
........ 只展现代码思路, 细节请自行查看........
........................................
if (x != 0) {
// 要害代码 2 去到 LinearLayoutManager 执行 fill 办法
consumedX = mLayout.scrollHorizontallyBy(x, mRecycler, mState);
unconsumedX = x - consumedX;
}
if (y != 0) {
// 要害代码 2 去到 LinearLayoutManager 执行 fill 办法
consumedY = mLayout.scrollVerticallyBy(y, mRecycler, mState);
unconsumedY = y - consumedY;
}
}
....
} 当初走到了 mLayout.scrollHorizontallyBy(x, mRecycler, mState);
接着去 LinearLayoutManager() 中去找 scrollHorizontallyBy() 办法
#LinearLayoutManager.java
@Override
public int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler,
RecyclerView.State state) {if (mOrientation == HORIZONTAL) {return 0;}
// 要害代码 3
return scrollBy(dy, recycler, state);
} scrollBy()->
#LinearLayoutManager.java
int scrollBy(int dy, RecyclerView.Recycler recycler, RecyclerView.State state) {
........................................
........ 只展现代码思路, 细节请自行查看........
........................................
final int consumed = mLayoutState.mScrollingOffset
// 要害代码 4
+ fill(recycler, mLayoutState, state, false);
} 接着找到 fill()办法
#LinearLayoutManager.java
int fill(RecyclerView.Recycler recycler, LayoutState layoutState,
RecyclerView.State state, boolean stopOnFocusable) {if (layoutState.mScrollingOffset != LayoutState.SCROLLING_OFFSET_NaN) {
// 要害代码 19 缓存 ViewHolder
recycleByLayoutState(recycler, layoutState);
}
// 循环调用
while ((layoutState.mInfinite || remainingSpace > 0) && layoutState.hasMore(state)) {// 要害代码 5 [用来 4 级复用]
layoutChunk(recycler, state, layoutState, layoutChunkResult);
........................................
........ 只展现代码思路, 细节请自行查看........
........................................
}
} 看到这里只须要记住以下两点即可:
- recycleByLayoutState(recycler, layoutState); 缓存 ViewHolder
- layoutChunk(recycler, state, layoutState, layoutChunkResult); 四级复用
有人可能会问, 这里为什么是四级? 不是说的三级嘛?
其实三级和四级都无所谓, 知识点是不会变的, 只是层级越多, 了解就越粗浅, 越细罢了
间接进入到缓存的代码:
#LinearLayoutManager.java
private void recycleByLayoutState(RecyclerView.Recycler recycler, LayoutState layoutState) {if (layoutState.mLayoutDirection == LayoutState.LAYOUT_START) {
// 要害代码 21 缓存底部
recycleViewsFromEnd(recycler, layoutState.mScrollingOffset);
} else {
// 要害代码 20 缓存头部
recycleViewsFromStart(recycler, layoutState.mScrollingOffset);
}
} 这里如果是向下滑动, 就会缓存头部那么就会执行到
recycleViewsFromStart()
如果是向上滑动, 就会缓存尾部那么就会执行到 recycleViewsFromEnd()
recycleViewsFromStart() 和 recycleViewsFromEnd() 轻易点开一个看看, 外面代码都差不多一样.
#LinearLayoutManager.java
private void recycleViewsFromStart(RecyclerView.Recycler recycler, int dt) {if (mShouldReverseLayout) {for (int i = childCount - 1; i >= 0; i--) {
...
// 要害代码 22
recycleChildren(recycler, childCount - 1, i);
return;
}
} else {for (int i = 0; i < childCount; i++) {
...
// 要害代码 23
recycleChildren(recycler, 0, i);
return;
}
}
}这里无论走哪一个 if() 都会走到 recycleChildren()办法
#LinearLayoutManager.java
private void recycleChildren(RecyclerView.Recycler recycler, int startIndex, int endIndex) {if (startIndex == endIndex) {return;}
if (endIndex > startIndex) {for (int i = endIndex - 1; i >= startIndex; i--) {// 移除 View 要害代码 23 [执行到 RecyclerView.removeAndRecycleViewAt()]
removeAndRecycleViewAt(i, recycler);
}
} else {for (int i = startIndex; i > endIndex; i--) {removeAndRecycleViewAt(i, recycler);
}
}
} 接着这里会执行到 RecyclerView 的 removeAndRecycleViewAt()办法
#RecyclerView.java
// 要害代码 24
public void removeAndRecycleViewAt(int index, Recycler recycler) {final View view = getChildAt(index);
removeViewAt(index);
// 要害代码 25
recycler.recycleView(view);
} 持续往下执行
#RecyclerView.java
public void recycleView(View view) {
.......
ViewHolder holder = getChildViewHolderInt(view);
// 缓存
recycleViewHolderInternal(holder);
} 接着继续执行 recycleViewHolderInternal()
#RecyclerView.java
void recycleViewHolderInternal(ViewHolder holder) {
........................................
........ 只展现代码思路, 细节请自行查看........
........................................
boolean cached = false;
if (forceRecycle || holder.isRecyclable()) {
// mViewCacheMax = 缓存的最大值
// mViewCacheMax = 2
// 如果 viewHolder 是有效、未被移除、未被标记的
if (mViewCacheMax > 0
&& !holder.hasAnyOfTheFlags(ViewHolder.FLAG_INVALID
| ViewHolder.FLAG_REMOVED
| ViewHolder.FLAG_UPDATE
| ViewHolder.FLAG_ADAPTER_POSITION_UNKNOWN)) {int cachedViewSize = mCachedViews.size();
// 要害代码 24
// mViewCacheMax = 2
if (cachedViewSize >= mViewCacheMax && cachedViewSize > 0) {
// 如果 viewholder 存满 2 个则移除第 0 个地位
// 保障 mCachedViews 最多能缓存 2 个 ViewHolder
recycleCachedViewAt(0);
cachedViewSize--;
}
....
// 保留 ViewHolder 数据 [mCachedViews 数据不会超过 2 个]
mCachedViews.add(targetCacheIndex, holder);
cached = true;
}
if (!cached) {// 当 ViewHolder 不扭转时候(只有一个 ViewHolder) 就会间接存到缓存池中
addViewHolderToRecycledViewPool(holder, true);
recycled = true;
}
........................................
........ 只展现代码思路, 细节请自行查看........
........................................
} 通过 要害代码 24 可知,mCachedViews 最多能保留 2 个 ViewHolder
如果第三个 ViewHolder 降临的时候, 就会先删除掉第 0 个, 而后在 mCachedViews.add(targetCacheIndex, holder);
而后再来看看 recycleCachedViewAt(0)的细节!
#RecyclerView.java
void recycleCachedViewAt(int cachedViewIndex) {
...
ViewHolder viewHolder = mCachedViews.get(cachedViewIndex);
// 要害代码 25
// 增加到 ViewPool 到缓存外面取
addViewHolderToRecycledViewPool(viewHolder, true);
// 将第 0 个 ViewHolder 移除
mCachedViews.remove(cachedViewIndex);
} 继续执行到 addViewHolderToRecycledViewPool()办法
将 mCachedViews.get(0)中的 ViewHolder 获取进去, 增加到缓存池中, 并删除
#RecyclerView.java
void addViewHolderToRecycledViewPool(ViewHolder holder, boolean dispatchRecycled) {
.....
// 向缓存池中 保留 ViewHolder 要害代码 28
getRecycledViewPool().putRecycledView(holder);
} 点进来看看 putRecycledView()办法
#RecyclerView.java
// SparseArray 相似与 HashMap<int,ScrapData>
// 特点: key 雷同会保留最初一个,
// 会依据 key 的 int 值排序(从小到大)
SparseArray<ScrapData> mScrap = new SparseArray<>();
public void putRecycledView(ViewHolder scrap) {
// 获取 ViewHolder 布局类型
final int viewType = scrap.getItemViewType();
// 依据布局类型来获取 ViewHolder
final ArrayList scrapHeap = getScrapDataForType(viewType).mScrapHeap;
// 判断缓存池的大小
// mScrap.get(viewType).mMaxScrap 默认为 5
// 同一种 ViewType 只保留 5 个 ViewHolder
if (mScrap.get(viewType).mMaxScrap <= scrapHeap.size()) {return;}
// 清空 ViewHolder 记录
scrap.resetInternal();
//add
scrapHeap.add(scrap);
}
// 清空 ViewHolder 记录
void resetInternal() {
mFlags = 0;
mPosition = NO_POSITION;
mOldPosition = NO_POSITION;
mItemId = NO_ID;
mPreLayoutPosition = NO_POSITION;
mIsRecyclableCount = 0;
mShadowedHolder = null;
mShadowingHolder = null;
clearPayload();
mWasImportantForAccessibilityBeforeHidden = View.IMPORTANT_FOR_ACCESSIBILITY_AUTO;
mPendingAccessibilityState = PENDING_ACCESSIBILITY_STATE_NOT_SET;
clearNestedRecyclerViewIfNotNested(this);
}
// 依据不同 viewType 获取 ViewHolder
private ScrapData getScrapDataForType(int viewType) {ScrapData scrapData = mScrap.get(viewType);
if (scrapData == null) {scrapData = new ScrapData();
mScrap.put(viewType, scrapData);
}
return scrapData;
} 能够看出, 缓存池, 中最多保留 5 个同一类型的 ViewHolder, 并且 ViewHolder 是空的 ViewHolder,
而且缓存池中保留的都是 mCachedViews 移除的数据!!
[](https://upload-images.jianshu…)
- 小结
mCachedViews 保留行将来到屏幕外的 2 个 ViewHolder
mRecyclerPool 缓存池中: 同一种 ItemViewType 类型可能默认最多保留 5 个空数据的 ViewHolder.
带入实战看看成果:
这里以单布局 (ItemViewType = 0) 为例
我的 layoutManger 为GridLayoutManager(content,7), 所以每次划出屏幕的时候, 就间接会划走 7 个 ViewHolder
能够看出, 划出去的一刹那, 前 5 个不会执行 onCreateViewHolder(), 后 2 个会执行 onCreateViewHolder()
⚠️:onCreateViewHolder() 是用来创立 ViewHolder 的, 前面复用的时候会说!
走到这里, 只是剖析了 RecyclerView 从 onTouchEvent()–>MOVE 事件滑动事件
最终会把 ViewHolder 保留 mCachedViews, mCachedViews 只能保留 2 个 ViewHolder
如果第三个 ViewHolder 降临的时候, 就保留到缓存池 (mRecyclerPool) 中
缓存池 (mRecyclerPool) 最多保留 5 个空的 ViewHolder…
这只是一种缓存的入口, 缓存还有另一种入口, 在 RecyclerView 的 onLayout()的时候
mAttachedScrap 和 mChangedScrap 会缓存屏幕内可见的 ViewHolder
onLayout()入口
#RecyclerView.java
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
// 入口
dispatchLayout();} 接着执行 dispatchLayout()
#RecyclerView.java
void dispatchLayout() {
.....
dispatchLayoutStep2();
......
} 接着执行 dispatchLayoutStep2()
#RecyclerView.java
private void dispatchLayoutStep2() {
......
// 在这里先缓存
mLayout.onLayoutChildren(mRecycler, mState);
.....
}接着走到 LinearLayoutManager.onLayoutChildren()办法
#LinearLayoutManager.java
@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
....
// 会执行到: RecyclerView.detachAndScrapAttachedViews()
detachAndScrapAttachedViews(recycler);
......
} 这里会走到 RecyclerView.detachAndScrapAttachedViews(),这行代码十分要害, 能够说是缓存屏幕内的 ViewHolder 的终点, 前面实现”探探“成果也须要用到!!
#RecyclerView.java
public void detachAndScrapAttachedViews(Recycler recycler) {final int childCount = getChildCount();
for (int i = childCount - 1; i >= 0; i--) {final View v = getChildAt(i);
// 回收机制要害代码 1
scrapOrRecycleView(recycler, i, v);
}
} 持续走 scrapOrRecycleView()
#RecyclerView.java
private void scrapOrRecycleView(Recycler recycler, int index, View view) {final ViewHolder viewHolder = getChildViewHolderInt(view);
...
if (viewHolder.isInvalid() && !viewHolder.isRemoved()
&& !mRecyclerView.mAdapter.hasStableIds()) {removeViewAt(index);
// 缓存机制要害代码 2 次要用来解决 cacheView ,RecyclerViewPool 的缓存
recycler.recycleViewHolderInternal(viewHolder);
} else {detachViewAt(index);
// 缓存机制要害代码 3
recycler.scrapView(view);
}
}这里有两个十分要害的点
- 缓存机制要害代码 2 次要用来解决 cacheView ,RecyclerViewPool 的缓存 recycler.recycleViewHolderInternal(viewHolder); // 这个关键点下面曾经剖析过了!!, 遗记的 ctrl+ F 搜寻看看看一看
- recycler.scrapView(view); // 缓存屏幕内的 ViewHolder
这里间接看看 recycler.scrapView(view); 的细节
void scrapView(View view) {final ViewHolder holder = getChildViewHolderInt(view);
// 如果标记没有移除, 或者生效等清空 就会缓存
if (holder.hasAnyOfTheFlags(ViewHolder.FLAG_REMOVED | ViewHolder.FLAG_INVALID)
|| !holder.isUpdated() || canReuseUpdatedViewHolder(holder)) {holder.setScrapContainer(this, false);
// 一级缓存地位点 1
mAttachedScrap.add(holder);
} else {if (mChangedScrap == null) {mChangedScrap = new ArrayList<ViewHolder>();
}
holder.setScrapContainer(this, true);
// 一级缓存地位点 2
mChangedScrap.add(holder);
}
} 走到这里 4 级缓存就完结了
总结一下:
参考 深刻了解 Android RecyclerView 的缓存机制：
https://segmentfault.com/a/11…
/ 复用机制 /
回到 fill()办法。ctrl + F 搜寻一下, 上边说过
#LinearLayoutManager.java
int fill(RecyclerView.Recycler recycler, LayoutState layoutState,
RecyclerView.State state, boolean stopOnFocusable) {
final int start = layoutState.mAvailable;
if (layoutState.mScrollingOffset != LayoutState.SCROLLING_OFFSET_NaN) {
.....
// 要害代码 19 [用来 4 级缓存]
recycleByLayoutState(recycler, layoutState);
}
....
// 循环调用
while ((layoutState.mInfinite || remainingSpace > 0) && layoutState.hasMore(state)) {// 要害代码 5 [用来 4 级复用]
layoutChunk(recycler, state, layoutState, layoutChunkResult);
........................................
........ 只展现代码思路, 细节请自行查看........
........................................
}
} 缓存是进入的 recycleByLayoutState(recycler, layoutState); 办法
复用是进入的 layoutChunk()办法
执行到 layoutState.next(recycler); 办法
#LinearLayoutManager.java
void layoutChunk(RecyclerView.Recycler recycler, RecyclerView.State state,
LayoutState layoutState, LayoutChunkResult result) {
// 获取以后 view
// 要害代码 6
View view = layoutState.next(recycler);
// 测量 View
measureChildWithMargins(view, 0, 0);
.....
} 接着执行到 recycler.getViewForPosition(mCurrentPosition);
#LinearLayoutManager.java
View next(RecyclerView.Recycler recycler) {
.....
// 要害代码 7 [复用机制入口]
final View view = recycler.getViewForPosition(mCurrentPosition);
return view;
} 而后继续执行到 getViewForPosition()–> getViewForPosition()
#RecyclerView.java
public View getViewForPosition(int position) {
// 要害代码 8
return getViewForPosition(position, false);
}
View getViewForPosition(int position, boolean dryRun) {
// 要害代码 10 所有的复用都在这里
return tryGetViewHolderForPositionByDeadline(position, dryRun, FOREVER_NS).itemView;
} 最终会执行到 tryGetViewHolderForPositionByDeadline(), 所有的复用代码都在这里了!
#RecyclerView.java
ViewHolder tryGetViewHolderForPositionByDeadline(int position,
boolean dryRun, long deadlineNs) {
ViewHolder holder = null;
// 一级别复用 [mChangedScrap]
if (mState.isPreLayout()) {
// 要害代码 11
holder = getChangedScrapViewForPosition(position);
fromScrapOrHiddenOrCache = holder != null;
}
// 一级复用 [mAttachedScrap]
if (holder == null) {
// 通过地位
// 要害代码 12
holder = getScrapOrHiddenOrCachedHolderForPosition(position, dryRun);
}
// 二级复用 [mCachedViews]
if (holder == null) {
// 获取布局类型
final int type = mAdapter.getItemViewType(offsetPosition);
// 2) Find from scrap/cache via stable ids, if exists
// 2) 通过稳固 ID 从废料 / 缓存中查找（如果存在）if (mAdapter.hasStableIds()) {
// 要害代码 13 依据 Id 来复用
holder = getScrapOrCachedViewForId(mAdapter.getItemId(offsetPosition),
type, dryRun);
}
}
// 三级复用【自定义复用】if (holder == null && mViewCacheExtension != null) {
// 要害代码 14
// 自定义复用
final View view = mViewCacheExtension
.getViewForPositionAndType(this, position, type);
if (view != null) {holder = getChildViewHolder(view);
}
}
// 四级复用 [mRecyclerPool(缓存池复用)]
if (holder == null) {
// 要害代码 15 从缓存池获取 viewHolder
holder = getRecycledViewPool().getRecycledView(type);
}
// 最终, 如果走到这里,holder == 0, 示意没有缓存, 那么则创立 ViewHolder
if (holder == null) {
// 如果四级缓存都是 null, 那么就由适配器创立 ViewHolder
holder = mAdapter.createViewHolder(RecyclerView.this, type);
}
// 走到这了的时候,ViewHolder != null
// 绑定布局
if (mState.isPreLayout() && holder.isBound()) {.....} else if (!holder.isBound() || holder.needsUpdate() || holder.isInvalid()) {
......
// 要害代码 17
// 在这里调 onBindViewHolder() 绑定数据
bound = tryBindViewHolderByDeadline(holder, offsetPosition, position, deadlineNs);
......
}
......
} 看一下 tryBindViewHolderByDeadline(), 绑定 ViewHolder 的具体绑定细节:
private boolean tryBindViewHolderByDeadline(ViewHolder holder, int offsetPosition,
int position, long deadlineNs) {
....
// 最终绑定地位
mAdapter.bindViewHolder(holder, offsetPosition);
...
} 复用机制比缓存机制简略很多, 因为复用入口就一个。看看流程图高深莫测!
/ 探探成果实战 /
⚠️: 为了全局性思考, 实战采纳 java, 底部附 java/kotlin 源码
要想实战, 那就得先实现最一般的成果, 这段代码没啥养分, 间接看成果!
自定义 LayoutManager
public class CardStack3LayoutManager extends RecyclerView.LayoutManager {
@Override
public RecyclerView.LayoutParams generateDefaultLayoutParams() {
return new RecyclerView.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT,
ViewGroup.LayoutParams.WRAP_CONTENT);
}
// 必须重写 在 RecyclerView->OnLayout()时候调用, 用来摆放 Item 地位
@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {super.onLayoutChildren(recycler, state);
}
} 须要重写 generateDefaultLayoutParams()办法, 咋们是仿造着 LinearLayoutManager()来写, 所以间接参考 LinearLayoutManager()就能够
留神: 这里的 onLayoutChildren() 须要手动重写!
次要性能都在 onLayoutChildren()中编写
#CardStack2LayoutManager.java
// 最开始显示个数
public static final int MAX_SHOW_COUNT = 4;
@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {super.onLayoutChildren(recycler, state);
// 调用 RecyclerView 的缓存机制 缓存 ViewHolder
detachAndScrapAttachedViews(recycler);
// 最上面图片下标
int bottomPosition = 0;
// 获取所有图片
int itemCount = getItemCount();
if (itemCount > MAX_SHOW_COUNT) {
// 获取到从第几张开始
bottomPosition = itemCount - MAX_SHOW_COUNT;
}
for (int i = bottomPosition; i < itemCount; i++) {
// 获取以后 view 宽高
View view = recycler.getViewForPosition(i);
addView(view);
// 测量
measureChildWithMargins(view, 0, 0);
// getWidth() RecyclerView 宽
// getDecoratedMeasuredWidth() View 的宽
int widthSpace = getWidth() - getDecoratedMeasuredWidth(view);
int heightSpace = getHeight() - getDecoratedMeasuredHeight(view);
// LinearLayoutManager#layoutChunk#layoutDecoratedWithMargins
// 绘制布局
layoutDecoratedWithMargins(view, widthSpace / 2,
heightSpace / 2,
widthSpace / 2 + getDecoratedMeasuredWidth(view),
heightSpace / 2 + getDecoratedMeasuredHeight(view));
}
} 这段代码就是获取所有的 ItemView, 而后全副布局到屏幕核心
先来看看以后的成果:
detachAndScrapAttachedViews()下面提到过, 是缓存的入口, 会间接调用到 RecyclerView.detachAndScrapAttachedViews()办法
测量布局, 摆放的代码参考自 LinearLayoutManager(), 思路就是吧以后 View 增加到 RecyclerView 中, 而后在测量 View, 最初在摆放(布局)View
最初让 View 摆放时候有缩放层级:
#CardStack2LayoutManager.java
// 最开始显示个数
public static final int MAX_SHOW_COUNT = 4;
// item 平移 Y 轴距
public static final int TRANSLATION_Y = 20;
// 缩放的大小
public static final float SCALE = 0.05f;
@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {super.onLayoutChildren(recycler, state);
// 缓存 ViewHolder
detachAndScrapAttachedViews(recycler);
// 最上面图片下标
int bottomPosition = 0;
// 获取所有图片
int itemCount = getItemCount();
// 如果所有图片 > 显示的图片
if (itemCount > MAX_SHOW_COUNT) {
// 获取到从第几张开始
bottomPosition = itemCount - MAX_SHOW_COUNT;
}
for (int i = bottomPosition; i < itemCount; i++) {
// 获取以后 view 宽高
View view = recycler.getViewForPosition(i);
addView(view);
// 测量
measureChildWithMargins(view, 0, 0);
// getWidth() RecyclerView 宽
// getDecoratedMeasuredWidth() View 的宽
int widthSpace = getWidth() - getDecoratedMeasuredWidth(view);
int heightSpace = getHeight() - getDecoratedMeasuredHeight(view);
// LinearLayoutManager#layoutChunk#layoutDecoratedWithMargins
// 绘制布局
layoutDecoratedWithMargins(view, widthSpace / 2,
heightSpace / 2,
widthSpace / 2 + getDecoratedMeasuredWidth(view),
heightSpace / 2 + getDecoratedMeasuredHeight(view));
/*
* 作者:android 超级兵
* TODO itemCount - 1 = 最初一个元素
最初一个元素 - i = 倒数的元素
*/
int level = itemCount - 1 - i;
if (level > 0) {int value = toDip(view.getContext(), TRANSLATION_Y);
// 如果不是最初一个才缩放
if (level < MAX_SHOW_COUNT - 1) {
// 平移
view.setTranslationY(value * level);
// 缩放
view.setScaleX(1 - SCALE * level);
view.setScaleY(1 - SCALE * level);
} else {// 最上面的 View 和前一个 View 布局一样(level - 1)
view.setTranslationY(value * (level - 1));
view.setScaleX(1 - SCALE * (level - 1));
view.setScaleY(1 - SCALE * (level - 1));
}
}
}
}
private int toDip(Context context, float value) {return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, value, context.getResources().getDisplayMetrics());
} 以后成果为:
到目前为止, 实现了 ItemView 的叠加摆放, 接下来只须要增加上滑动即可!
RecyclerView 拖拽滑动须要应用到 ItemTouchHelper.SimpleCallback
public class SlideCardStackCallBack2<T> extends ItemTouchHelper.SimpleCallback {
private final CardStackAdapter<T> mAdapter;
public SlideCardStackCallBack2(CardStackAdapter<T> mAdapter) {super(0, 15);
this.mAdapter = mAdapter;
}
// 拖拽应用, 不必管
@Override
public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder target) {return false;}
// 滑动完结后的解决
@Override
public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int direction) {}} 这里须要传递两个参数:
- 参数一:dragDirs 拖拽
- 参数二:swipeDirs 滑动
这里咋们不必拖拽, 间接给 0 就行, 次要说一下滑动 swipeDirs
#ItemTouchHelper.java
/**
* Up direction, used for swipe & drag control.
*/
public static final int UP = 1; //1
/**
* Down direction, used for swipe & drag control.
*/
public static final int DOWN = 1 << 1; //2
/**
* Left direction, used for swipe & drag control.
*/
public static final int LEFT = 1 << 2; //4
/**
* Right direction, used for swipe & drag control.
*/
public static final int RIGHT = 1 << 3; //8 滑动次要以这几个位运算组
- 如果须要高低滑动 那么就是 UP+DOWN = 1+2 = 3
- 如果是高低左滑动就是 UP + DOWN + LEFT = 1 + 2 + 4 = 7
- 那么如果是上下左右滑动就是 UP + DOWN + LEFT + RIGHT = 15
所以这里间接填 15 就示意能够上下左右滑动
onSwiped()解决:
#SlideCardStackCallBack2.java
@Override
public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int direction) {
// 以后滑动的 View 下标
int layoutPosition = viewHolder.getLayoutPosition();
// 删除以后滑动的元素
CardStackBean<T> bean = mAdapter.getData().remove(layoutPosition);
// 增加到汇合第 0 个地位 造成循环滑动的成果
mAdapter.addData(0, bean);
mAdapter.notifyDataSetChanged();}这段代码很好了解, 先删除以后滑动的 View, 而后在增加到最初一个, 造成循环滑动的成果! 来看看成果:
当初看来, 还是有点僵硬, 增加一些滑动系数缩放: 这里间接贴出残缺代码: 看图谈话:
#SlideCardStackCallBack2.java
@Override
public void onChildDraw(@NonNull Canvas c, @NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
int maxDistance = recyclerView.getWidth() / 2;
// dx = 以后滑动 x 地位
// dy = 以后滑动 y 地位
//sqrt 开根号
double sqrt = Math.sqrt((dX * dX + dY * dY));
// 放大系数
double scaleRatio = sqrt / maxDistance;
// 系数最大为 1
if (scaleRatio > 1.0) {scaleRatio = 1.0;}
int childCount = recyclerView.getChildCount();
// 循环所有数据
for (int i = 0; i < childCount; i++) {View view = recyclerView.getChildAt(i);
int valueDip = toDip(view.getContext(), 20f);
/*
* 作者:android 超级兵
* TODO
* childCount - 1 = itemView 总个数
* childCount - 1 - i = itemView 总个数 - i = 从最初一个开始
*
* 假如 childCount - 1 = 7
* i 累加
* 那么 level = childCount - 1 - 0 = 7
* 那么 level = childCount - 1 - 1 = 6
* 那么 level = childCount - 1 - 2 = 5
* 那么 level = childCount - 1 - 3 = 4
* 那么 level = childCount - 1 - 4 = 3
*。。。。*/
int level = childCount - 1 - i;
if (level > 0) {
// 最大显示叠加个数:CardStack2LayoutManager.MAX_SHOW_COUNT = 4
if (level < CardStack2LayoutManager.MAX_SHOW_COUNT - 1) {
// 缩放比例: CardStack2LayoutManager.SCALE = 0.05
float scale = CardStack2LayoutManager.SCALE;
// valueDip * level = 原始平移间隔
// scaleRatio * valueDip = 平移系数
// valueDip * level - scaleRatio * valueDip = 手指滑动过程中的 Y 轴平移间隔
// 因为是 Y 轴, 所以向上平移是 - 号
view.setTranslationY((float) (valueDip * level - scaleRatio * valueDip));
// 1 - scale * level = 原始缩放大小
// scaleRatio * scale = 缩放系数
// 因为是须要放大, 所以这里是 + 号
view.setScaleX((float) ((1 - scale * level) + scaleRatio * scale));
view.setScaleY((float) ((1 - scale * level) + scaleRatio * scale));
}
}
}
}
private int toDip(Context context, float value) {return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, value, context.getResources().getDisplayMetrics());
} 滑动系数图解:
⚠️: 记得绑定 RecyclerView
// 创立拖拽
val slideCardStackCallBack = SlideCardStackCallBack2(cardStackAdapter)
val itemTouchHelper = ItemTouchHelper(slideCardStackCallBack)
// 绑定拖拽
itemTouchHelper.attachToRecyclerView(rootRecyclerView) 这里的正文比拟清晰, 来看看最终成果吧~
还有两个比拟好玩的参数
// 设置回弹间隔
@Override
public float getSwipeThreshold(@NonNull RecyclerView.ViewHolder viewHolder) {return 0.3f;}
// 设置回弹工夫
@Override
public long getAnimationDuration(@NonNull RecyclerView recyclerView, int animationType, float animateDx, float animateDy) {return 3000;} 很简略, 间接看成果
我的项目地址：https://gitee.com/lanyangyang…
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