RecyclerView没有像之前ListView提供divider属性，而是提供了方法
recyclerView.addItemDecoration()
这时候我们需要去定制自己的ItemDecoration
ItemDecoration类主要是三个方法：
public void onDraw(Canvas c, RecyclerView parent, State state)
public void onDrawOver(Canvas c, RecyclerView parent, State state)
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, State state)
- 重写getItemOffsets()，可以实现类似padding的效果
- 重写onDraw，可以实现类似绘制背景的效果，用来绘制分隔线
- 重写onDrawOver，可以在View上覆盖内容
padding
直接传递dp
class SpaceItemDecoration(
private var left: Int = 0,
private var top: Int = 0,
private var right: Int = 0,
private var bottom: Int = 0
) : RecyclerView.ItemDecoration() {
override fun getItemOffsets(
outRect: Rect,
view: View,
parent: RecyclerView,
state: RecyclerView.State
) {
super.getItemOffsets(outRect, view, parent, state)
outRect.left = ScreenUtils.dpToPx(left.toFloat())
outRect.right = ScreenUtils.dpToPx(right.toFloat())
outRect.top = ScreenUtils.dpToPx(top.toFloat())
outRect.bottom = ScreenUtils.dpToPx(bottom.toFloat())
}
}
grid列表间隔设置
class GridSpaceItemDecoration(@Px val space: Int) : RecyclerView.ItemDecoration() {
override fun getItemOffsets(
outRect: Rect,
view: View,
parent: RecyclerView,
state: RecyclerView.State
) {
super.getItemOffsets(outRect, view, parent, state)
if (parent.layoutManager is GridLayoutManager) {
val spanCount = (parent.layoutManager as GridLayoutManager?)?.spanCount ?: return
val layoutParams = view.layoutParams as GridLayoutManager.LayoutParams
outRect.top = space / 2
outRect.bottom = space / 2
when (layoutParams.spanIndex) {
0 -> {
//第一列左边全部 右边一半
outRect.left = space
outRect.right = space / 2
}
spanCount - 1 -> {
//最后一列左边一半右边全部
outRect.left = space / 2
outRect.right = space
}
else -> {
//中间列 左右各一半
outRect.right = space / 2
outRect.left = space / 2
}
}
}
}
}
分割线
要实现分割线效果需要 getItemOffsets()和 onDraw()2个方法，首先用 getItemOffsets给item下方空出一定高度的空间（例子中是1dp），然后用onDraw绘制这个空间
public class SimpleDividerDecoration extends RecyclerView.ItemDecoration {
private int dividerHeight;
private Paint dividerPaint;
public SimpleDividerDecoration(Context context) {
dividerPaint = new Paint();
dividerPaint.setColor(context.getResources().getColor(R.color.colorAccent));
dividerHeight = context.getResources().getDimensionPixelSize(R.dimen.divider_height);
}
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
outRect.bottom = dividerHeight;
}
@Override
public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
int childCount = parent.getChildCount();
int left = parent.getPaddingLeft();
int right = parent.getWidth() - parent.getPaddingRight();
for (int i = 0; i < childCount - 1; i++) {
View view = parent.getChildAt(i);
float top = view.getBottom();
float bottom = view.getBottom() + dividerHeight;
c.drawRect(left, top, right, bottom, dividerPaint);
}
}
}
标签
使用onDrawOver()来实现“推荐”，”热卖“，“秒杀“
public class LeftAndRightTagDecoration extends RecyclerView.ItemDecoration {
private int tagWidth;
private Paint leftPaint;
private Paint rightPaint;
public LeftAndRightTagDecoration(Context context) {
leftPaint = new Paint();
leftPaint.setColor(context.getResources().getColor(R.color.colorAccent));
rightPaint = new Paint();
rightPaint.setColor(context.getResources().getColor(R.color.colorPrimary));
tagWidth = context.getResources().getDimensionPixelSize(R.dimen.tag_width);
}
@Override
public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDrawOver(c, parent, state);
int childCount = parent.getChildCount();
for (int i = 0; i < childCount; i++) {
View child = parent.getChildAt(i);
int pos = parent.getChildAdapterPosition(child);
boolean isLeft = pos % 2 == 0;
if (isLeft) {
float left = child.getLeft();
float right = left + tagWidth;
float top = child.getTop();
float bottom = child.getBottom();
c.drawRect(left, top, right, bottom, leftPaint);
} else {
float right = child.getRight();
float left = right - tagWidth;
float top = child.getTop();
float bottom = child.getBottom();
c.drawRect(left, top, right, bottom, rightPaint);
}
}
}
}
分组、StickyHeader
@Override
public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDrawOver(c, parent, state);
int itemCount = state.getItemCount();
int childCount = parent.getChildCount();
int left = parent.getPaddingLeft();
int right = parent.getWidth() - parent.getPaddingRight();
float lineHeight = textPaint.getTextSize() + fontMetrics.descent;
long preGroupId, groupId = -1;
for (int i = 0; i < childCount; i++) {
View view = parent.getChildAt(i);
int position = parent.getChildAdapterPosition(view);
preGroupId = groupId;
groupId = callback.getGroupId(position);
if (groupId < 0 || groupId == preGroupId) continue;
String textLine = callback.getGroupFirstLine(position).toUpperCase();
if (TextUtils.isEmpty(textLine)) continue;
int viewBottom = view.getBottom();
float textY = Math.max(topGap, view.getTop());
if (position + 1 < itemCount) { //下一个和当前不一样移动当前
long nextGroupId = callback.getGroupId(position + 1);
if (nextGroupId != groupId && viewBottom < textY ) {//组内最后一个view进入了header
textY = viewBottom;
}
}
c.drawRect(left, textY - topGap, right, textY, paint);
c.drawText(textLine, left, textY, textPaint);
}
}
自定义的功能就结束了，详细可了解RecyclerView之ItemDecoration由浅入深
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