一、实现LinearLayoutManager下的ItemDecoration的自定义
核心就是重写Itemdecoration下的 getItemOffsets方法和onDraw方法
1、getItemOffsets方法主要控制itemview的边距代码实现如下
@Override
void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
LinearLayoutManager linearLayoutManager = (LinearLayoutManager) parent.getLayoutManager();
if (linearLayoutManager.getOrientation() == LinearLayoutManager.VERTICAL) {
if (parent.getChildAdapterPosition(view) !=0) {
outRect.top =topBottom;
}
outRect.left =leftRight;
}else {
if (parent.getChildAdapterPosition(view) !=0) {
outRect.left =leftRight;
}
outRect.top =topBottom;
}
}
2、onDraw方法负责在空白区域绘制（该方法绘制的内容在itemview的下方 注意避免过度绘制）代码实现如下
@Override
void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
int left =0;
int right =0;
int top =0;
int bottom =0;
if (mColor ==0 || parent.getChildCount() ==0) {
return;
}
LinearLayoutManager layoutManager = (LinearLayoutManager) parent.getLayoutManager();
if (layoutManager.getOrientation() == LinearLayoutManager.VERTICAL) {
for (int i =0; i < parent.getChildCount(); i++) {
View itemView = parent.getChildAt(i);
left = parent.getLeft() + parent.getPaddingLeft();
right = parent.getRight() - parent.getPaddingRight();
top = itemView.getTop() -topBottom;
bottom = itemView.getTop();
if (parent.getChildAdapterPosition(itemView) !=0) {
c.drawRect(left, top, right, bottom, mPaint);
}
}
}else {
for (int i =0; i < parent.getChildCount(); i++) {
View itemView = parent.getChildAt(i);
left = itemView.getLeft() -leftRight;
right = itemView.getLeft();
top = parent.getTop() + parent.getPaddingTop();
bottom = parent.getBottom() - parent.getPaddingBottom();
if (parent.getChildAdapterPosition(itemView) !=0) {
c.drawRect(left, top, right, bottom, mPaint);
}
}
}
}
二、 实现GridLayoutManager下的ItemDecoration的自定义
@Override
void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
int left;
int top;
int right;
int bottom;
GridLayoutManager layoutManager = (GridLayoutManager) parent.getLayoutManager();
int childCount = layoutManager.getChildCount();
for (int i =0; i < childCount; i++) {
View child = parent.getChildAt(i);
left = child.getLeft();
top = child.getBottom();
right = child.getRight();
bottom = top +topBottom;
c.drawRect(left, top, right, bottom, mPaint);
left = child.getRight();
top = child.getTop();
right = left +leftRight;
bottom = child.getBottom() +topBottom;
c.drawRect(left, top, right, bottom, mPaint);
}
}
@Override
void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
GridLayoutManager layoutManager = (GridLayoutManager) parent.getLayoutManager();
GridLayoutManager.LayoutParams layoutParams =
(GridLayoutManager.LayoutParams) view.getLayoutParams();
int childPosition = parent.getChildAdapterPosition(view);
totalSpans =totalSpans + layoutParams.getSpanSize();
if (layoutManager.getOrientation() == GridLayoutManager.VERTICAL) {
if (layoutParams.getSpanIndex() !=0) {
outRect.left =leftRight;
}
if (childPosition > layoutManager.getSpanCount() -1) {
outRect.top =topBottom;
}
}else {
if (childPosition > layoutManager.getSpanCount() -1) {
outRect.left =leftRight;
}
outRect.bottom =topBottom;
}
}
参考链接： 小甜点，RecyclerView 之 ItemDecoration 讲解及高级特性实践 - frank 的专栏 - CSDN博客
