最近一直在看RecyclerView，較之ListView它確實(shí)是靈活多變，給予開發(fā)者更多自定義的空間，比如：需要添加頭部和尾部、item的點(diǎn)擊事件、自定義的LayoutManager，還有就是下面要說的自定義的分割線。

1、如何理解分割線

經(jīng)常聽到有人說自定義分割線麻煩，為什么不把分割線寫到item布局里，這樣不是更簡單嗎？有些情況把分割線寫到item布局里是很難達(dá)到我們想要的效果，例如RecyclerView里的GridLayoutManager,StaggeredGridLayoutManager和一些自定義的LayoutManager，不同位置的item需要畫的分割線并不相同，這時(shí)候應(yīng)用自定義的分割線就能很好的解決這個(gè)問題。

2、如何畫分割線

網(wǎng)上也有很多關(guān)于RecyclerView自定義分割線的寫法，很多都是通過獲取系統(tǒng)屬性中的listDivider來添加，在系統(tǒng)中的AppTheme中設(shè)置，但是如果我有兩種風(fēng)格的分割線，這就尷尬了呀，所以我希望像ListView一樣能傳入一個(gè)drawable來設(shè)置分割線，所以我們的思路就是最終能像下面這樣設(shè)置分割線：

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

3、具體代碼實(shí)現(xiàn)

由于RecyclerView的布局方式多種多樣，所以它的分割線也根據(jù)布局的不同有所差異，本文只針對(duì)LinearLayoutManager線性布局

• 繼承自RecyclerView.ItemDecoration
• 重寫getItemOffsets()、 onDraw()方法
  現(xiàn)在給出完整的類，代碼中關(guān)鍵地方都有注釋，就不再一一說明：

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;

    /**
     * 分割線縮進(jìn)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       分割線縮進(jìn)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();
        //最后一個(gè)item不畫分割線
        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也有寬高，每一個(gè)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、具體怎么用

• 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>

對(duì)應(yīng)的效果如下：

1.png

我們可以看到明顯的縮進(jìn)效果，設(shè)置成零就沒有縮進(jìn)了。

• 還是看看正常使用中是什么樣子吧

2.png

對(duì)應(yīng)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>

我們只需要修改下CustomDecoration中paint的顏色就可以讓縮進(jìn)的顏色和背景色一致了，默認(rèn)是白色。

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

• That's all。