1、ItemDecoration简介
Recyclerview是我们日常开发中使用频率比较高的的控件，而其中的ItemDecoration作为布局装饰又能很方便的帮助我们定义分割线，列表排行效果以及设置布局悬浮置顶效果等，所以有必要去了解ItemDecoration的诸多细节。
2、基本原理
public class MyDecoration extends RecyclerView.ItemDecoration{
/**
* step1 相当于itemView外还有一个矩形，我们可以自由在itemview上下左右设置空余部分，
通过outRect 的left,top,right,bottom 来进行设置，我们可在这块控件进行绘制
* 目标针对每一个item个体
*/
@Override
public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
}
/**
* step2 在item间绘制 常用于绘制分割线
* 针对整个Recyclerview 绘制需要循环遍历item子布局 然后方能针对具体的item进行增加绘制
*/
@Override
public void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
super.onDraw(c, parent, state);
}
/**
* 在item上绘制
*/
@Override
public void onDrawOver(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
super.onDrawOver(c, parent, state);
}
}
2.1 getItemoffsets在RecyclerView源码中作用时机
manager#getItemDecorInsetsForChild
为指定view计算分割线矩形
Rect getItemDecorInsetsForChild(View child) {
RecyclerView.LayoutParams lp = (RecyclerView.LayoutParams)child.getLayoutParams();
if (!lp.mInsetsDirty) {
return lp.mDecorInsets;
} else if (this.mState.isPreLayout() && (lp.isItemChanged() || lp.isViewInvalid())) {
return lp.mDecorInsets;
} else {
Rect insets = lp.mDecorInsets;
insets.set(0, 0, 0, 0);
int decorCount = this.mItemDecorations.size();
for(int i = 0; i < decorCount; ++i) {
this.mTempRect.set(0, 0, 0, 0);
((RecyclerView.ItemDecoration)this.mItemDecorations.get(i)).getItemOffsets(this.mTempRect, child, this, this.mState);
insets.left += this.mTempRect.left;
insets.top += this.mTempRect.top;
insets.right += this.mTempRect.right;
insets.bottom += this.mTempRect.bottom;
}
lp.mInsetsDirty = false;
return insets;
}
}
// 测量的时候 当作padding值放入其中
public void measureChild(@NonNull View child, int widthUsed, int heightUsed) {
RecyclerView.LayoutParams lp = (RecyclerView.LayoutParams)child.getLayoutParams();
Rect insets = this.mRecyclerView.getItemDecorInsetsForChild(child);
widthUsed += insets.left + insets.right;
heightUsed += insets.top + insets.bottom;
int widthSpec = getChildMeasureSpec(this.getWidth(), this.getWidthMode(), this.getPaddingLeft() + this.getPaddingRight() + widthUsed, lp.width, this.canScrollHorizontally());
int heightSpec = getChildMeasureSpec(this.getHeight(), this.getHeightMode(), this.getPaddingTop() + this.getPaddingBottom() + heightUsed, lp.height, this.canScrollVertically());
if (this.shouldMeasureChild(child, widthSpec, heightSpec, lp)) {
child.measure(widthSpec, heightSpec);
}
}
manager#calculateItemDecorationsForChild
manager向外部提供的获取分割线矩形数据的api
public void calculateItemDecorationsForChild(@NonNull View child, @NonNull Rect outRect) {
if (this.mRecyclerView == null) {
outRect.set(0, 0, 0, 0);
} else {
Rect insets = this.mRecyclerView.getItemDecorInsetsForChild(child);
outRect.set(insets);
}
}
可解决问题：如何获取指定itemView的分割线的高度
Rect rect = new Rect();
View view = mRvConflict.getLayoutManager().findViewByPosition(1);
if (view != null){
mRvConflict.getLayoutManager().calculateItemDecorationsForChild(view,rect);
Log.e("decoration", "高度 = "+rect.height() );
}
3. 分割线使用
3.1无任何分割线的RecyclerView
private void initAdapter() {
mMyRecvAdapter = new MyRecvAdapter(mContext,mList);
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(mContext);
linearLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
mRecyclerView.setLayoutManager(linearLayoutManager);
mRecyclerView.setAdapter(mMyRecvAdapter);
}
相信大家对如何说些一个RecyclerView列表再熟悉不过了吧，不过推荐大家可以使用BRVAH出来蛮久的了，可以大大提升开发效率。
3.2 一行代码添加系统分割线
mRecyclerView.addItemDecoration(new DividerItemDecoration(this,DividerItemDecoration.VERTICAL));
运行效果:
分析一下: RecyclerView 为我们提供的DividerItemDecoration的用于添加分割线的类中 代码其实不多，主要是继承了ItemDecoration并实现了 getItemOffsets()和onDra()方法，这里的getItemOffsets( )实际上是在条目之间分配一块矩形区域用来放置我们的分割线,注意一下方法参数Rect outRect，而通过onDraw（ ）方法把条目画在刚刚申请的间隔矩形中。没错就是这么简单，有兴趣的可以对照着源码细看一下。
public class DividerItemDecoration extends RecyclerView.ItemDecoration {
......
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent,
RecyclerView.State state) {
if (mOrientation == VERTICAL) {
outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
} else {
outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
}
// 设置矩形区域
// set（left,top,right,bottom） = outRect.left = left ...
}
@Override
public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
if (parent.getLayoutManager() == null) {
return;
}
if (mOrientation == VERTICAL) {
drawVertical(c, parent);
} else {
drawHorizontal(c, parent);
}
}
.......
}
getitemOffset可依据混排的条目数 设置间距效果
View view = null;
GridLayoutManager.LayoutParams layoutParams = (GridLayoutManager.LayoutParams) view.getLayoutParams();
int spanSize = layoutParams.getSpanSize();
// 获得每行的下标 0,1
int spanIndex = layoutParams.getSpanIndex();
3.3 不用系统的分割线，自己设定分割线的宽度和颜色
看下面只需要知己设置drawable就可以了，你想要什么形状就可以添加什么样的形状。
DividerItemDecoration dividerItemDecoration = new DividerItemDecoration(this, DividerItemDecoration.VERTICAL); dividerItemDecoration.setDrawable(ContextCompat.getDrawable(this,R.drawable.shape_devider_line_red)); mRecyclerView.addItemDecoration(dividerItemDecoration);
如上右图所示
3. 4 扩展
前面已经分析了DeivderItemDecoration的实现了，我们也可以自己手动撸一个来实现不是嘛，我们可以发现前面虽然是可以设置drawable进去，那么每次还需要写一个drawable文件或者弄张.9图进去，但通常的业务环境是只需要带颜色的线条就可以了吧，所以基于此我们可以自己手写一个。
直接上代码了额:
/**
* @author zxl on 2018/7/14.
* discription: 自定义分割线支持水平和垂直布局 设置默认,图片和颜色为分割线
*/
public class MyRecyclerViewDivider extends RecyclerView.ItemDecoration {
private Paint mPaint;
private Drawable mDivider;
private int mDividerHeight;
private int mOrientation;
/**
* 系统默认的分割线
* */
private static final int[] ATTRS = new int[]{android.R.attr.listDivider};
/**
* 设置默认的分割线
* @param orientation 指代分割线的方向
* */
public MyRecyclerViewDivider(Context context, int orientation) {
this.mDividerHeight = 2;
if(orientation != 1 && orientation != 0) {
throw new IllegalArgumentException("请输入正确的参数！");
} else {
this.mOrientation = orientation;
TypedArray a = context.obtainStyledAttributes(ATTRS);
this.mDivider = a.getDrawable(0);
a.recycle();
}
}
/**
* 设置图片资源为分割线
* */
public MyRecyclerViewDivider(Context context, int orientation, int drawableId) {
this(context, orientation);
this.mDivider = ContextCompat.getDrawable(context, drawableId);
this.mDividerHeight = this.mDivider.getIntrinsicHeight();
}
/**
* 设置线条颜色和高度给分割线
* */
public MyRecyclerViewDivider(Context context, int orientation, int dividerHeight, int dividerColor) {
this(context, orientation);
this.mDividerHeight = dividerHeight;
this.mPaint = new Paint(1);
this.mPaint.setColor(dividerColor);
this.mPaint.setStyle(Paint.Style.FILL);
}
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
outRect.set(0, 0, 0, this.mDividerHeight);
}
@Override
public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDraw(c, parent, state);
if(this.mOrientation == 1) {
this.drawVertical(c, parent);
} else {
this.drawHorizontal(c, parent);
}
}
private void drawHorizontal(Canvas canvas, RecyclerView parent) {
canvas.save();
final int left;
final int right;
// 判断RecyclerView是否要裁剪padding值
if (parent.getClipToPadding()){
// 需要裁剪那么就进行裁剪
left = parent.getPaddingLeft();
right = parent.getWidth()-parent.getPaddingRight();
// 裁剪rv可视区域, 限制视图在该区域内是可见的，很重要的，这里
canvas.clipRect(left,parent.getPaddingTop(),right,parent.getHeight()-parent.getPaddingBottom());
}else {
// 不裁剪则宽贼为rv的宽
left = 0;
right = parent.getWidth();
}
int childSize = parent.getChildCount();
for(int i = 0; i < childSize; ++i) {
View child = parent.getChildAt(i);
// 获得item的信息包
RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams)child.getLayoutParams();
// 分割线顶部 = item的底部 + item到底部的距离 + 动画偏移
int top = child.getBottom() + layoutParams.bottomMargin + Math.round(ViewCompat.getTranslationY(child));
// 分割线底部 = 分割线底部 + 高度
int bottom = top + this.mDividerHeight;
if(this.mDivider != null) {
this.mDivider.setBounds(left, top, right, bottom);
this.mDivider.draw(canvas);
}
if(this.mPaint != null) {
canvas.drawRect((float)left, (float)top, (float)right, (float)bottom, this.mPaint);
}
}
canvas.restore();
}
private void drawVertical(Canvas canvas, RecyclerView parent) {
canvas.save();
final int top;
final int bottom;
if (parent.getClipToPadding()){
top = parent.getPaddingTop();
bottom = parent.getHeight() - parent.getPaddingBottom();
canvas.clipRect(parent.getPaddingLeft(),top,parent.getWidth()-parent.getPaddingRight(),bottom);
}else {
top = 0;
bottom = parent.getHeight();
}
int childSize = parent.getChildCount();
for(int i = 0; i < childSize; ++i) {
View child = parent.getChildAt(i);
RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams)child.getLayoutParams();
int left = child.getRight() + layoutParams.rightMargin + Math.round(ViewCompat.getTranslationX(child));
int right = left + this.mDividerHeight;
if(this.mDivider != null) {
this.mDivider.setBounds(left, top, right, bottom);
this.mDivider.draw(canvas);
}
if(this.mPaint != null) {
canvas.drawRect((float)left, (float)top, (float)right, (float)bottom, this.mPaint);
}
}
canvas.restore();
}
}
用法如下也是很简单,优点不用多说既囊括了系统提供的也支持drawable设置而且支持简易的线条颜色等，用途很大对的吧。
mRecyclerView.addItemDecoration(new MyRecyclerViewDivider(this, LinearLayoutManager.HORIZONTAL,2,ContextCompat.getColor(this,R.color.colorAccent)));
效果我下方左图所示
弄个表格出来
以下为 addItemDecoration的源码，可以发现的是可以设置多条分割线,哈哈,那么我们不就能画表格了嘛,6666
public void addItemDecoration(ItemDecoration decor, int index) {
if (mLayout != null) {
mLayout.assertNotInLayoutOrScroll("Cannot add item decoration during a scroll or"
+ " layout");
}
if (mItemDecorations.isEmpty()) {
setWillNotDraw(false);
}
if (index < 0) {
mItemDecorations.add(decor);
} else {
mItemDecorations.add(index, decor);
}
markItemDecorInsetsDirty();
requestLayout();
}
activity中的代码如下:
mMyRecvAdapter = new MyRecvAdapter(mContext,mList);
mRecyclerView.addItemDecoration(new MyRecyclerViewDivider(this, LinearLayoutManager.HORIZONTAL,2,ContextCompat.getColor(this,R.color.colorAccent)));
mRecyclerView.addItemDecoration(new MyRecyclerViewDivider(this,LinearLayoutManager.VERTICAL,2,ContextCompat.getColor(this,R.color.colorAccent)));
mRecyclerView.setLayoutManager(new GridLayoutManager(this,3));
mRecyclerView.setAdapter(mMyRecvAdapter);
原创文章，作者：ItWorker，如若转载，请注明出处：https://blog.ytso.com/291842.html