自定义一个RV的分割线
/**
* Measure a child view using standard measurement policy, taking the padding
* of the parent RecyclerView and any added item decorations into account.
*
* <p>If the RecyclerView can be scrolled in either dimension the caller may
* pass 0 as the widthUsed or heightUsed parameters as they will be irrelevant.</p>
*
* @param child Child view to measure
* @param widthUsed Width in pixels currently consumed by other views, if relevant
* @param heightUsed Height in pixels currently consumed by other views, if relevant
*/
public void measureChild(@NonNull View child, int widthUsed, int heightUsed) {
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
1.//下面三行代码就是把分割线的距离增加到每个view上
final Rect insets = mRecyclerView.getItemDecorInsetsForChild(child);
widthUsed += insets.left + insets.right;
heightUsed += insets.top + insets.bottom;
final int widthSpec = getChildMeasureSpec(getWidth(), getWidthMode(),
getPaddingLeft() + getPaddingRight() + widthUsed, lp.width,
canScrollHorizontally());
final int heightSpec = getChildMeasureSpec(getHeight(), getHeightMode(),
getPaddingTop() + getPaddingBottom() + heightUsed, lp.height,
canScrollVertically());
if (shouldMeasureChild(child, widthSpec, heightSpec, lp)) {
child.measure(widthSpec, heightSpec);
}
Rect getItemDecorInsetsForChild(View child) {
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
if (!lp.mInsetsDirty) {
return lp.mDecorInsets;
}
if (mState.isPreLayout() && (lp.isItemChanged() || lp.isViewInvalid())) {
// changed/invalid items should not be updated until they are rebound.
return lp.mDecorInsets;
}
final Rect insets = lp.mDecorInsets;
insets.set(0, 0, 0, 0);
2.//拿到所有的Item
final int decorCount = mItemDecorations.size();
for (int i = 0; i < decorCount; i++) {
mTempRect.set(0, 0, 0, 0);
// 调用 getItemOffsets（）方法，给mTempRect赋值
mItemDecorations.get(i).getItemOffsets(mTempRect, child, this, mState);
insets.left += mTempRect.left;
insets.top += mTempRect.top;
insets.right += mTempRect.right;
insets.bottom += mTempRect.bottom;
}
lp.mInsetsDirty = false;
return insets;
}
绘制分割线:
final ArrayList<ItemDecoration> mItemDecorations = new ArrayList<>();
@Override
public void onDraw(Canvas c) {
super.onDraw(c);
final int count = mItemDecorations.size();
for (int i = 0; i < count; i++) {
1.//会回调分割线方法
mItemDecorations.get(i).onDraw(c, this, mState);
}
}
public abstract static class ItemDecoration {
//通过重写此onDraw方法绘制分割线
public void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull State state) {
onDraw(c, parent);
}
//此方法已过时
@Deprecated
public void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent) {
}
}
1.在getItemOffset()方法中，设置分割线的大小最终是加在itemView的宽高上。这会造成一个问题，就是每个itemView的大小可能不一致 2. 在确定了分割线大小后，在绘制itemView时，会调用分割线的onDraw()方法。我们可以重写分割线的onDraw()方法绘制分割线。
大致思路：定义三个变量(leftRight,topBottom,mColor)，然后根据不同的layoutManager使用不同的引擎确定分割线的大小和绘制分割线
public class NiceItemDecoration extends RecyclerView.ItemDecoration {
private int mColor;
private int leftRight;
private int topBottom;
private NiceItemDecorationEntrust mEntrust;
public NiceItemDecoration(int leftRight, int topBottom) {
this.leftRight = leftRight;
this.topBottom = topBottom;
}
public NiceItemDecoration(int leftRight, int topBottom, int mColor) {
this(leftRight, topBottom);
this.mColor = mColor;
}
//由不同的引擎确定分割线的大小
@Override
public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
if (mEntrust == null) {
mEntrust = getEntrust(parent);
}
mEntrust.getItemOffsets(outRect,view,parent,state);
}
//由不同的引擎绘制分割线
@Override
public void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
if (mEntrust == null) {
mEntrust = getEntrust(parent);
}
mEntrust.onDraw(c,parent,state);
super.onDraw(c, parent, state);
}
//根据layoutManager确定不同的引擎
private NiceItemDecorationEntrust getEntrust(RecyclerView parent) {
RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
if (layoutManager instanceof GridLayoutManager) {
mEntrust = new GridEntrust(leftRight, topBottom, mColor);
} else if (layoutManager instanceof StaggeredGridLayoutManager) {
mEntrust = new StaggeredGridEntrust(leftRight, topBottom, mColor);
} else if (layoutManager instanceof LinearLayoutManager) {
mEntrust = new LinearEntrust(leftRight, topBottom, mColor);
}
return mEntrust;
}
}
**注意：**在判断时，要先判断GridLayoutManager再判断LinearLayoutManager，因为GridLayoutManager是继承LinearLayoutManager。**getEntrust（）**方法根据不同的layoutManager分别生成LinearEntrust、GridEntrust、StaggeredGridEntrust引擎来确定分割线大小和绘制分割线。
####一些基础知识： 1.关于LinearLayoutManager 1、 在getItemOffsets()方法中，可以获得childView在设配器中的位置，和childView的数量
@Override
void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
LinearLayoutManager layoutManager = (LinearLayoutManager) parent.getLayoutManager();
//获得childView所在的位置
int position = parent.getChildAdapterPosition(view);
//获得itemView的数量
int ItemSize = layoutManager.getItemCount();
}
2、在onDraw()方法中 可以获得每个childView的分割线的上下的高度和左右的宽度
//获得itemView的数量
int itemSize = layoutManager.getChildCount();
for (int i = 0; i < itemSize - 1; i++) {
final View childView = parent.getChildAt(i);
//获得childView分割线左右的宽度
layoutManager.getLeftDecorationWidth(childView);
layoutManager.getRightDecorationWidth(childView);
//获得childView分割线上下的高度
layoutManager.getTopDecorationHeight(childView);
layoutManager.getBottomDecorationHeight(childView);
}
2.关于GridLayoutManager 1.可以知道每个childView所在的行数，在行里的位置，每行的chilView比重
GridLayoutManager.LayoutParams.getSpanSize() //childView所占的比重
GridLayoutManager.LayoutParams.getSpanIndex() //childView在所在行的第几个
GridLayoutManager.getSpanCount() //每行多少个childView
GridLayoutManager.getSpanSizeLookup().getSpanSize(i); //childView所占的比重
GridLayoutManager.getSpanSizeLookup().getSpanIndex(childPosition,spanCount); //childView在所在行的第几个
GridLayoutManager.getSpanSizeLookup().getSpanGroupIndex(childPosition,spanCount) //childPosition的view处于第几排或第几列
2.可以设置每个view的比重
mLayoutManager = new GridLayoutManager(this, 3, GridLayoutManager.VERTICAL, false);
final GridLayoutManager manager = (GridLayoutManager) mLayoutManager;
manager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
@Override
public int getSpanSize(int position) {
return position % (manager.getSpanCount() + 1) == 0 ? manager.getSpanCount() : 1;
}
});
###1.写一个抽象引擎，让它们共有属性和要重写的方法封装起来
public abstract class NiceItemDecorationEntrust {
protected int leftRight;
protected int topBottom;
protected Drawable mDivider;
public NiceItemDecorationEntrust(int leftRight, int topBottom, int mColor){
this.leftRight = leftRight;
this.topBottom = topBottom;
if (mColor != 0){
mDivider = new ColorDrawable(mColor);
}
}
abstract void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state);
abstract void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state);
}
分析：在确定分割线大小时，分两种情况：垂直滑动：每个childView都有上左右，但最后一个childView时要下；水平滑动：每个childView都有上下右，但第一个又左。 在绘制分割线时只绘制ChildView的之间的距离，分两种情况：垂直滑动：每个childView画bottom,但最后一个不画（i<childCount - 1）；水平滑动：每个childView画right,但最后一个不画（i<childCount - 1）。
public class LinearEntrust extends NiceItemDecorationEntrust {
public LinearEntrust(int leftRight, int topBottom, int mColor) {
super(leftRight, topBottom, mColor);
}
@Override
void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
LinearLayoutManager layoutManager = (LinearLayoutManager) parent.getLayoutManager();
if (layoutManager.getOrientation() == LinearLayoutManager.VERTICAL) {
//垂直滑动
outRect.top = topBottom;
outRect.left = leftRight;
outRect.right = leftRight;
//最后一个子view需要bottom
if (parent.getChildAdapterPosition(view) == layoutManager.getItemCount() - 1) {
outRect.bottom = topBottom;
}
} else {
//横向滑动
outRect.top = topBottom;
outRect.right = leftRight;
outRect.bottom = topBottom;
if (parent.getChildAdapterPosition(view) == 0) {
outRect.left = leftRight;
}
}
}
@Override
void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
LinearLayoutManager layoutManager = (LinearLayoutManager) parent.getLayoutManager();
if (mDivider == null || layoutManager.getChildCount() == 0) {
return;
}
//只画item之间的间隙
int left, top, right, bottom;
int childCount = parent.getChildCount();
//垂直方向，第一排top不画，最后一排bottom不画，左右两边不画
if (layoutManager.getOrientation() == LinearLayoutManager.VERTICAL) {
for (int i = 0; i < childCount - 1; i++) {
final View childView = parent.getChildAt(i);
left = childView.getLeft();
right = childView.getRight();
top = childView.getBottom();
bottom = top + topBottom;
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(c);
}
} else {
//水平方向 第一个left不画，最后一个right不画，上下不画
for (int i = 0; i < childCount - 1; i++) {
final View childView = parent.getChildAt(i);
RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) childView.getLayoutParams();
left = childView.getRight();
right = left + layoutManager.getRightDecorationWidth(childView);
top = childView.getTop();
bottom = childView.getBottom();
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(c);
}
}
}
}
分析：确定分割线大小,分垂直和水平滑动。垂直滑动：每个childView都有下，但第一排有上。左右分两种情况：如果一个childView占满一行，则直接设置左右；如果不是，则按比例分配左右，因为分割线算在childView的区域，分割线分配不均会导致childView的大小不一样。 水平滑动：每个childView都有右，但第一列有左。上下分两种情况：如果一个childView占满一列，则直接设置上下，如果不是，则按比例分配上下，因为分割线算在childView的区域，分割线分配不均会导致childView的大小不一样。 绘制分割线,垂直滑动：画水平方向分割线：在不是第一个行，且childView在行的位置是0时，在chidView上方绘制一条分割线。画垂直方向:在不是最后列中，画childView右边的分割线。 水平滑动：画垂直方向分割线：在不是第一列中画ChildView的左边的垂直分割线。画水平方向分割线：在不是最后一行中，绘制每个childView的下方的分割线。
public class GridEntrust extends NiceItemDecorationEntrust {
public GridEntrust(int leftRight, int topBottom, int mColor) {
super(leftRight, topBottom, mColor);
}
@Override
void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
GridLayoutManager layoutManager = (GridLayoutManager) parent.getLayoutManager();
final GridLayoutManager.LayoutParams layoutParams = (GridLayoutManager.LayoutParams) view.getLayoutParams();
//在适配器中的位置
final int childPosition = parent.getChildAdapterPosition(view);
//每行或列的比重
final int spanCount = layoutManager.getSpanCount();
//垂直方向，第一排还有top，每排都有bottom，每列都有left,最后一列有right
if (layoutManager.getOrientation() == GridLayoutManager.VERTICAL) {
outRect.bottom = topBottom;
//是否在第一排
if (layoutManager.getSpanSizeLookup().getSpanGroupIndex(childPosition, spanCount) == 0) {
outRect.top = topBottom;
}
if (layoutParams.getSpanSize() == spanCount) {
//一个item占满一行
outRect.left = leftRight;
outRect.right = leftRight;
} else {
outRect.left = (int)
(((float) (spanCount - layoutParams.getSpanIndex())) / spanCount * leftRight);
outRect.right = (int)
(((float) leftRight * (spanCount + 1) / spanCount) - outRect.left);
}
} else {
//水平 第一列有left，全部列有right, 全部有top，最后一个有bottom
outRect.right = leftRight;
if (layoutManager.getSpanSizeLookup().getSpanGroupIndex(childPosition, spanCount) == 0) {
outRect.left = leftRight;
}
if (layoutParams.getSpanSize() == spanCount) {//占满
outRect.top = topBottom;
outRect.bottom = topBottom;
} else {
outRect.top = (int) (((float) (spanCount - layoutParams.getSpanIndex())) / spanCount * topBottom);
outRect.bottom = (int) (((float) topBottom * (spanCount + 1) / spanCount) - outRect.top);
}
}
}
@Override
void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
GridLayoutManager layoutManager = (GridLayoutManager) parent.getLayoutManager();
final GridLayoutManager.SpanSizeLookup spanSizeLookup = layoutManager.getSpanSizeLookup();
if (mDivider == null || layoutManager.getChildCount() == 0) {
return;
}
int spanCount = layoutManager.getSpanCount();
int chileCount = layoutManager.getChildCount();
int left, top, right, bottom;
//垂直方向，每排画bottom，但最后一排不画bottom，只画right，但最后一列不画right
if (layoutManager.getOrientation() == GridLayoutManager.VERTICAL) {
for (int i = 0; i < chileCount; i++) {
final View childView = parent.getChildAt(i);
int childPosition = parent.getChildAdapterPosition(childView);
RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) childView.getLayoutParams();
int spanSize = spanSizeLookup.getSpanSize(i);
int spanIndex = spanSizeLookup.getSpanIndex(childPosition, spanCount);
//画水平方向，除了最后一排，每排都画bottom边的
boolean isLast = spanSizeLookup.getSpanGroupIndex(childPosition, spanCount) == 0;
if (!isLast && spanIndex == 0) {
left = childView.getLeft();
right = parent.getWidth() - leftRight;
top = childView.getTop() - topBottom;
bottom = top + layoutManager.getBottomDecorationHeight(childView);
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(c);
}
//画垂直方向，每列都有right ，除了最右边
boolean isRight = spanIndex + spanSize == spanCount;
if (!isRight) {
left = childView.getRight();
right = left + leftRight;
top = childView.getTop();
bottom = parent.getBottom() - layoutManager.getBottomDecorationHeight(childView);
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(c);
}
}
} else {
//水平方向
for (int i = 0; i < chileCount; i++) {
final View childView = parent.getChildAt(i);
int childPosition = parent.getChildAdapterPosition(childView);
int spanSize = spanSizeLookup.getSpanSize(childPosition);
int spanIndex = spanSizeLookup.getSpanIndex(childPosition, spanCount);
//垂直
boolean isFirst = spanSizeLookup.getSpanGroupIndex(childPosition, spanCount) == 0;
if (!isFirst && spanIndex == 0) {
left = childView.getLeft() - leftRight;
right = left + leftRight;
top = layoutManager.getTopDecorationHeight(childView);
bottom = parent.getHeight() - layoutManager.getTopDecorationHeight(childView);
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(c);
}
//画水平
boolean isRight = spanIndex + spanSize == spanCount;
if (!isRight) {
left = childView.getLeft();
right = childView.getRight();
top = childView.getBottom();
bottom = top + leftRight;
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(c);
}
}
}
}
}