RecyclerView 添加自定义分割线

默认的浅灰色的分割线在某些时候并不能满足我们的要求，这时就需要自定义分割线了。

我们可以通过两种方式来实现：调用 DividerItemDecoration.setDrawable 方法或者继承实现 RecyclerView.ItemDecoration 类来实现。

一、调用 DividerItemDecoration.setDrawable 方法

实现分割线只需要调用 setDrawable(@NonNull Drawable drawable)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>

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);

运行起来之后，就可以看到一条多彩的分割线了：

二、继承实现 RecyclerView.ItemDecoration 类

这块就不多赘述了，直接贴代码：

public class RecyclerViewDivider extends RecyclerView.ItemDecoration{
    private Paint mPaint;
    //分割线
    private Drawable mDivider;
    //分割线高度，默认是2px
    private int mDividerHeight = 2;
    //列表的方向：LinearLayoutManager.VERTICAL或LinearLayoutManager.HORIZONTAL
    private int mOrientation;
    
    private static final int[] ATTRS = new int[]{android.R.attr.listDivider};

    /**
     *
     * 默认分割线：高度为2px，颜色为灰色
     * 获取属性值，
     *
     * @param context
     * @param orientation  列表方向
     */

    public RecyclerViewDivider(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 array = context.obtainStyledAttributes(ATTRS);
        mDivider = array.getDrawable(0);
        array.recycle();
        mDividerHeight = mDivider.getIntrinsicHeight();
    }

    /**
     * 自定义分割线
     *
     * @param context
     * @param orientation 列表方向
     * @param drawableId  分割线图片
     */
    public RecyclerViewDivider(Context context, int orientation, int drawableId) {
        if (orientation != LinearLayoutManager.VERTICAL && orientation != LinearLayoutManager.HORIZONTAL) {
            throw new IllegalArgumentException("请输入正确的参数！");
        }
        mOrientation = 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 RecyclerViewDivider(Context context, int orientation, int dividerHeight, int dividerColor) {

        if (orientation != LinearLayoutManager.VERTICAL && orientation != LinearLayoutManager.HORIZONTAL) {
            throw new IllegalArgumentException("请输入正确的参数！");
        }
        mOrientation = 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) {
        
        if (mOrientation == LinearLayoutManager.VERTICAL) {
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        } else {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
        }

        outRect.set(0, 0, 0, mDividerHeight);
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDraw(c, parent, state);
        if(mOrientation==LinearLayoutManager.VERTICAL){
            drawVerticalLine(c,parent);
        }else{
            drawHorizontalLine(c,parent);
        }
    }

    //为横方向item, 画分割线
    private void drawHorizontalLine(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);
            }
        }
    }

    //为竖方向item, 画分割线
    private void drawVerticalLine(Canvas canvas, RecyclerView parent) {
        final int left = parent.getPaddingLeft();
        final int right = parent.getMeasuredWidth() - parent.getPaddingRight();
        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 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);
            }
        }
    }
}