Android自定义FlowLayoutManager

package com.dongnao.layoutmanagerflow; import android.graphics.Rect; import android.support.v7.widget.RecyclerView; import android.util.SparseArray; import android.view.View; import android.view.ViewGroup; //自定义流式布局管理器 //这个Demo主要是为了演示自定义LayoutManager //很多代码都做了简化处理，在性能上并不够好 public class FlowLayoutManager extends RecyclerView.LayoutManager { //保存所有item偏移量信息，所有数据高度和 int totalHeight = 0; SparseArray<Rect> itemBounds = new SparseArray<>(); //滑动偏移量 int verticalScrollOffset = 0; @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) { //摆放 if (getItemCount() <= 0) return; //布局动画 if (state.isPreLayout()) return; //将视图分离放入scrap缓存中，以准备重新对view进行排版 detachAndScrapAttachedViews(recycler); int offsetY = 0; int offsetX = 0; int itemHeight = 0; for (int i = 0; i < getItemCount(); i++) { View view = recycler.getViewForPosition(i); addView(view); measureChildWithMargins(view, 0, 0); int w = getDecoratedMeasuredWidth(view); int h = getDecoratedMeasuredHeight(view); itemHeight = h; Rect bound = itemBounds.get(i); if (bound == null) bound = new Rect(); //需要换行 if (offsetX + w > getWidth()) { //换行的View的值 offsetY += h; offsetX = w; bound.set(0, offsetY, w, offsetY + h); } else { //不需要换行 bound.set(offsetX, offsetY, offsetX + w, offsetY + h); offsetX += w; } //计算前View的布局区域，然后放到allItemframs数组 itemBounds.put(i, bound); } totalHeight = offsetY + itemHeight; //回收不可见的元素 recyclerViewFillView(recycler, state); } @Override public int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler, RecyclerView.State state) { detachAndScrapAttachedViews(recycler); //实际滑动距离 int trval = dy; if (verticalScrollOffset + dy < 0) { trval = -verticalScrollOffset; } else if (verticalScrollOffset + dy > totalHeight - getHeight()) { trval = totalHeight - getHeight() - verticalScrollOffset; } //边界值判断 verticalScrollOffset += trval; //平移容器内的item offsetChildrenVertical(trval); recyclerViewFillView(recycler, state); return trval; } @Override public boolean canScrollVertically() { return true; } protected void recyclerViewFillView(RecyclerView.Recycler recycler, RecyclerView.State state) { //清空RecyclerView的子View detachAndScrapAttachedViews(recycler); Rect phoneFrame = new Rect(0, verticalScrollOffset, getWidth(), verticalScrollOffset + getHeight()); //将滑出屏幕的view进行回收 Rect childRect = new Rect(); for (int i = 0; i < getChildCount(); i++) { View childView = getChildAt(i); Rect child = itemBounds.get(i); if (!Rect.intersects(phoneFrame, child)) removeAndRecycleView(childView, recycler); } //可见区域出现在屏幕上的子view for (int j = 0; j < getItemCount(); j++) if (Rect.intersects(phoneFrame, itemBounds.get(j))) { //scrap回收池里面拿的 View scrap = recycler.getViewForPosition(j); measureChildWithMargins(scrap, 0, 0); addView(scrap); Rect frame = itemBounds.get(j); layoutDecorated(scrap, frame.left, frame.top - verticalScrollOffset, frame.right, frame.bottom - verticalScrollOffset); } } }