RecyclerView的详细使用-优快云博客

本文介绍如何在RecyclerView中实现指定位置项的置顶显示，并提供了将Bitmap转换为圆形图片的方法。针对RecyclerView置顶需求，通过LinearLayoutManager的scrollToPositionWithOffset方法结合setStackFromEnd设置可以实现。此外，还分享了自定义ViewHolder获取当前位置的方法。

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RecyclerView 相应的条目置顶

准确定位到指定位置，并且将指定位置的item置顶，

若直接调用scrollToPosition(…)方法，则不会置顶。

//1.获取manager
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(mActivity, LinearLayoutManager.VERTICAL, false);

//2.置顶到第一个
linearLayoutManager.scrollToPositionWithOffset(position, 0);
linearLayoutManager.setStackFromEnd(true);

获取当前条目的position，ViewHolder自带的方法

ViewHolder(final View view) {
    super(view);
    ButterKnife.bind(this, view);
    view.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            //获取当前条目的position，自带的方法
            int layoutPosition = getLayoutPosition();
            Toast.makeText(mActivity, layoutPosition, Toast.LENGTH_SHORT).show();
        }
    });
}

Bitmap切换成圆形

public static Bitmap makeRoundCorner(Bitmap bitmap) {
    int width = bitmap.getWidth();
    int height = bitmap.getHeight();
    int left = 0, top = 0, right = width, bottom = height;
    float roundPx = height / 2;
    if (width > height) {
        left = (width - height) / 2;
        top = 0;
        right = left + height;
        bottom = height;
    } else if (height > width) {
        left = 0;
        top = (height - width) / 2;
        right = width;
        bottom = top + width;
        roundPx = width / 2;
    }

    Bitmap output = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(output);
    int color = 0xff424242;
    Paint paint = new Paint();
    Rect rect = new Rect(left, top, right, bottom);
    RectF rectF = new RectF(rect);

    paint.setAntiAlias(true);
    canvas.drawARGB(0, 0, 0, 0);
    paint.setColor(color);
    canvas.drawRoundRect(rectF, roundPx, roundPx, paint);
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    canvas.drawBitmap(bitmap, rect, rect, paint);
    return output;
}