Android | 一篇文章带你玩转RecyclerView.ItemDecoration类
RecyclerView GridLayoutManager 添加分割线
自定义实战详解小甜点，RecyclerView 之 ItemDecoration 讲解及高级特性实践
参考RecyclerView设置分隔线的三种方法
RecyclerView去除底部分割线
最简单的方法（布局划线）
在item.xml文件中在最下方指定一条分割线，例如：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="wrap_content">
<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<ImageView
android:id="@+id/image_view"
android:layout_gravity="center"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/text_view"
android:layout_gravity="center"
android:gravity="left"
android:layout_marginTop="10dp"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
<View
android:layout_width="match_parent"
android:layout_height="1dp"
android:layout_marginTop="10dp"
android:background="@color/colorPrimary"/>
</LinearLayout>
添加默认的分割线
现在我们就来添加分割线，首先来试试最简单的，也就是安卓自带的分割线。只需要加一行代码即可。
//添加Android自带的分割线
recyclerView.addItemDecoration(new DividerItemDecoration(this,DividerItemDecoration.VERTICAL));
addItemDecoration方法需要一个DividerItemDecoration的对象，而创建其对象时，我们需要传入上下文和分割线的方向。再运行一下，就可以看到分割线出现了：
image.png
自定义Drawable为分割线
有时候默认的浅灰色的分割线并不能满足我们的要求，这时我们就需要自己“写”一条分割线了，那应该怎么写呢？打开DividerItemDecoration看看它的源码，有这么一个函数：
public void setDrawable(@NonNull Drawable drawable) {
if (drawable == null) {
throw new IllegalArgumentException("Drawable cannot be null.");
}
mDivider = drawable;
}
我们只需要调用这个方法，然后传入一个Drawable函数对象就可以了。现在可以用shape来编写一个分割线样式:
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle">
<gradient
android:centerColor="#ff00ff00" //绿色
android:endColor="#ff0000ff" //蓝色
android:startColor="#ffff0000" //红色
android:type="linear" />
<size android:height="3dp" />
</shape>
我这里弄的是一条骚气的渐变色分割线。然后添加分割线的代码改为如下：
//添加自定义分割线
DividerItemDecoration divider = new DividerItemDecoration(this,DividerItemDecoration.VERTICAL);
divider.setDrawable(ContextCompat.getDrawable(this,R.drawable.custom_divider));
recyclerView.addItemDecoration(divider);
跑起来之后，就可以看到一条多彩的分割线了：
image.png
自定义分割线
RecyclerView不像ListView 那样有divider和dividerHeight属性，为了RecyclerView的高度自由性，我们还是可以自己去添加分割线，RecyclerView提供了一个抽象类ItemDecoration，它是item的装饰类，
public static abstract class ItemDecoration {
public void onDraw(Canvas c, RecyclerView parent, State state) {
onDraw(c, parent);
}
public void onDrawOver(Canvas c, RecyclerView parent, State state) {
onDrawOver(c, parent);
}
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, State state) {
getItemOffsets(outRect,((LayoutParams)view.getLayoutParams()).getViewLayoutPosition(),parent)
}
}
这三个方法中，onDraw（）和onDrawOver（）显然是用于绘制的，那么绘制分割线的逻辑可以放在这里面，它们二者的具体区别是：onDraw是在item view绘制之前调用，而onDrawOver是在item view绘制之后调用，因此我们一般选择重写其中一个方法即可。getItemOffsets，这个方法是告诉RecyclerView在绘制完一个item view的时候，应该留下多少空位，以便于绘制分割线。
万能分割线RecycleViewDivider.java
public class RecycleViewDivider extends RecyclerView.ItemDecoration {
private Paint mPaint;
private Drawable mDivider;
private int mDividerHeight = 2;//分割线高度，默认为1px
private int mOrientation;//列表的方向：LinearLayoutManager.VERTICAL或LinearLayoutManager.HORIZONTAL
private static final int[] ATTRS = new int[]{android.R.attr.listDivider};//使用系统自带的listDivider
/**
* 默认分割线：高度为2px，颜色为灰色
*
* @param context
* @param orientation 列表方向
*/
public RecycleViewDivider(Context context, int orientation) {
if (orientation != LinearLayoutManager.VERTICAL && orientation != LinearLayoutManager.HORIZONTAL) {
throw new IllegalArgumentException("请输入正确的参数！");
}
mOrientation = orientation;
final TypedArray a = context.obtainStyledAttributes(ATTRS);//使用TypeArray加载该系统资源
mDivider = a.getDrawable(0);
a.recycle();//缓存
}
/**
* 自定义分割线
*
* @param context
* @param orientation 列表方向
* @param drawableId 分割线图片
*/
public RecycleViewDivider(Context context, int orientation, int drawableId) {
this(context, orientation);
mDivider = ContextCompat.getDrawable(context, drawableId);
mDividerHeight = mDivider.getIntrinsicHeight();
}
/**
* 自定义分割线
*
* @param context
* @param orientation 列表方向
* @param dividerHeight 分割线高度
* @param dividerColor 分割线颜色
*/
public RecycleViewDivider(Context context, int orientation, int dividerHeight, int dividerColor) {
this(context, orientation);
mDividerHeight = dividerHeight;
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setColor(dividerColor);
mPaint.setStyle(Paint.Style.FILL);
}
//获取分割线尺寸
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
//设置偏移的高度是mDivider.getIntrinsicHeight，该高度正是分割线的高度
outRect.set(0, 0, 0, mDividerHeight);
}
//绘制分割线
@Override
public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDraw(c, parent, state);
if (mOrientation == LinearLayoutManager.VERTICAL) {
drawVertical(c, parent);
} else {
drawHorizontal(c, parent);
}
}
//绘制横向 item 分割线
private void drawHorizontal(Canvas canvas, RecyclerView parent) {
final int left = parent.getPaddingLeft();//获取分割线的左边距，即RecyclerView的padding值
final int right = parent.getMeasuredWidth() - parent.getPaddingRight();//分割线右边距
final int childSize = parent.getChildCount();
//遍历所有item view，为它们的下方绘制分割线
for (int i = 0; i < childSize; i++) {
final View child = parent.getChildAt(i);
RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) child.getLayoutParams();
final int top = child.getBottom() + layoutParams.bottomMargin;
final int bottom = top + mDividerHeight;
if (mDivider != null) {
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(canvas);
}
if (mPaint != null) {
canvas.drawRect(left, top, right, bottom, mPaint);
}
}
}
//绘制纵向 item 分割线
private void drawVertical(Canvas canvas, RecyclerView parent) {
final int top = parent.getPaddingTop();
final int bottom = parent.getMeasuredHeight() - parent.getPaddingBottom();
final int childSize = parent.getChildCount();
for (int i = 0; i < childSize; i++) {
final View child = parent.getChildAt(i);
RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) child.getLayoutParams();
final int left = child.getRight() + layoutParams.rightMargin;
final int right = left + mDividerHeight;
if (mDivider != null) {
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(canvas);
}
if (mPaint != null) {
canvas.drawRect(left, top, right, bottom, mPaint);
}
}
}
}
使用方法
//添加默认分割线：高度为2px，颜色为灰色
mRecyclerView.addItemDecoration(new RecycleViewDivider(mContext, LinearLayoutManager.HORIZONTAL));
//添加自定义分割线：可自定义分割线drawable
mRecyclerView.addItemDecoration(new RecycleViewDivider(
mContext, LinearLayoutManager.HORIZONTAL, R.drawable.divider_mileage));
//添加自定义分割线：可自定义分割线高度和颜色
mRecyclerView.addItemDecoration(new RecycleViewDivider(
mContext, LinearLayoutManager.HORIZONTAL, 10, getResources().getColor(R.color.divide_gray_color)));
