RecyclerView自定义分割线

最近一直在看RecyclerView，较之ListView它确实是灵活多变，给予开发者更多自定义的空间，比如：需要添加头部和尾部、item的点击事件、自定义的LayoutManager，还有就是下面要说的自定义的分割线。

1、如何理解分割线

经常听到有人说自定义分割线麻烦，为什么不把分割线写到item布局里，这样不是更简单吗？有些情况把分割线写到item布局里是很难达到我们想要的效果，例如RecyclerView里的GridLayoutManager,StaggeredGridLayoutManager和一些自定义的LayoutManager，不同位置的item需要画的分割线并不相同，这时候应用自定义的分割线就能很好的解决这个问题。

2、如何画分割线

网上也有很多关于RecyclerView自定义分割线的写法，很多都是通过获取系统属性中的listDivider来添加，在系统中的AppTheme中设置，但是如果我有两种风格的分割线，这就尴尬了呀，所以我希望像ListView一样能传入一个drawable来设置分割线，所以我们的思路就是最终能像下面这样设置分割线：

rvStore.addItemDecoration(new CustomDecoration(context,CustomDecoration.VERTICAL_LIST,R.drawable.divider_love,UnitHelper.dip2px(this,15)))

3、具体代码实现

由于RecyclerView的布局方式多种多样，所以它的分割线也根据布局的不同有所差异，本文只针对LinearLayoutManager线性布局

• 继承自RecyclerView.ItemDecoration
• 重写getItemOffsets()、 onDraw()方法
  现在给出完整的类，代码中关键地方都有注释，就不再一一说明：

public class CustomDecoration extends RecyclerView.ItemDecoration {

    public static final int HORIZONTAL_LIST = LinearLayoutManager.HORIZONTAL;

    public static final int VERTICAL_LIST = LinearLayoutManager.VERTICAL;

    private Drawable mDivider;

    private int mOrientation;

    /**
     * 分割线缩进值
     */
    private int inset;

    private Paint paint;

    /**
     * @param context
     * @param orientation layout的方向
     * @param drawable    引入的drawable的ID
     * @param inset       分割线缩进值
     */
    public CustomDecoration(Context context, int orientation, int drawable, int inset) {
        mDivider = context.getResources().getDrawable(drawable);
        this.inset = inset;
        paint = new Paint();
        paint.setColor(context.getResources().getColor(R.color.white));
        paint.setStyle(Paint.Style.FILL);
        paint.setAntiAlias(true);
        setOrientation(orientation);
    }

    public void setOrientation(int orientation) {
        if (orientation != HORIZONTAL_LIST && orientation != VERTICAL_LIST) {
            throw new IllegalArgumentException("invalid orientation");
        }
        mOrientation = orientation;
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent) {
        if (mOrientation == VERTICAL_LIST) {
            drawVertical(c, parent);
        } else {
            drawHorizontal(c, parent);
        }
    }

    private void drawVertical(Canvas c, RecyclerView parent) {
        final int left = parent.getPaddingLeft();
        final int right = parent.getWidth() - parent.getPaddingRight();

        final int childCount = parent.getChildCount();
        //最后一个item不画分割线
        for (int i = 0; i < childCount - 1; i++) {
            final View child = parent.getChildAt(i);
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
            final int top = child.getBottom() + params.bottomMargin;
            final int bottom = top + mDivider.getIntrinsicHeight();
            if (inset > 0) {
                c.drawRect(left, top, right, bottom, paint);
                mDivider.setBounds(left + inset, top, right - inset, bottom);
            } else {
                mDivider.setBounds(left, top, right, bottom);
            }
            mDivider.draw(c);
        }
    }

    private void drawHorizontal(Canvas c, RecyclerView parent) {
        final int top = parent.getPaddingTop();
        final int bottom = parent.getHeight() - parent.getPaddingBottom();

        final int childCount = parent.getChildCount();
        for (int i = 0; i < childCount - 1; i++) {
            final View child = parent.getChildAt(i);
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
            final int left = child.getRight() + params.rightMargin;
            final int right = left + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }

    //由于Divider也有宽高，每一个Item需要向下或者向右偏移
    @Override
    public void getItemOffsets(Rect outRect, int itemPosition, RecyclerView parent) {
        if (mOrientation == VERTICAL_LIST) {
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        } else {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
        }
    }
}

4、具体怎么用

• RecyclerView的三部曲

recyclerView.setLayoutManager(new LinearLayoutManager(this));
recyclerView.addItemDecoration(new CustomDecoration(this, CustomDecoration.VERTICAL_LIST, R.drawable.divider_love, UnitHelper.dip2px(this, 15)));
recyclerView.setAdapter(adapter);

- R.drawable.divider_love
```xml
<shape xmlns:android="http://schemas.android.com/apk/res/android"
   android:shape="rectangle">
   <solid android:color="#CB8589"/>
   <size android:height="15dp"/>
</shape>

对应的效果如下：

我们可以看到明显的缩进效果，设置成零就没有缩进了。

• 还是看看正常使用中是什么样子吧

对应的 R.drawable.divider_love

<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <solid android:color="#CD3131"/>
    <size android:height="1dp"/>
</shape>

我们只需要修改下CustomDecoration中paint的颜色就可以让缩进的颜色和背景色一致了，默认是白色。

paint.setColor(Color.parseColor("#ECF0F1"));

• That's all。