原文：Android——RecyclerView入門學(xué)習(xí)之ItemDecoration

image.png

簡單效果：水平方向第一個(gè)和最后一個(gè)加間距

項(xiàng)目里有一個(gè)水平滑動(dòng)的RecyclerView,第一個(gè)和最后一個(gè)距離手機(jī)兩邊間距大一點(diǎn),其他的間距都靠加的背景圖帶了點(diǎn)距離撐開
以前的我都是在item里左右都放一個(gè)View,判斷第0個(gè)的時(shí)候顯示左邊的View,最后一個(gè)顯示右邊的View,其他的兩個(gè)View都隱藏,方法很笨,但是也實(shí)現(xiàn)了
但是強(qiáng)大的RecyclerView會(huì)教你優(yōu)雅的實(shí)現(xiàn)間距,就是 ItemDecoration

看了文章寫了一個(gè)可以實(shí)現(xiàn)上述效果的一個(gè)簡單ItemDecoration,這里記錄一下

/**
 *水平滑動(dòng)的RecyclerView：第0個(gè)和第size-1個(gè)加間距尔许，其他的不加
 *垂直滑動(dòng)的RecyclerView：每個(gè)底部加36的間距
 */
public class RecyclerViewLeftRightAddPadding extends RecyclerView.ItemDecoration {

    private int drawPadding = 36;
    private int orientation;
    private Paint paint;

    public RecyclerViewLeftRightAddPadding(Context context, int orientation) {

        paint = new Paint();
        paint.setAntiAlias(true);
        paint.setColor(context.getResources().getColor(R.color.white));

        this.orientation = orientation;
    }

     @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        //加一個(gè)偏移量

        RecyclerView.LayoutManager manager = parent.getLayoutManager();
        int index = parent.getChildAdapterPosition(view);
        int listSize = state.getItemCount();

        if (manager instanceof LinearLayoutManager) {
            if (orientation == LinearLayoutManager.VERTICAL) {
                //垂直
                outRect.set(0, 0, 0, drawPadding);
            } else {
                //水平
                if (index == 0) {
                    outRect.set(drawPadding, 0, 0, 0);
                } else if (index == listSize - 1) {
                    outRect.set(0, 0, drawPadding, 0);
                } else {
                    outRect.set(0, 0, 0, 0);
                }
            }
        }
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDraw(c, parent, state);

        int listSize = state.getItemCount();
//        LogUtil.d("listSize = " + listSize);
        int childCount = parent.getChildCount();
//        LogUtil.d("childCount = " + childCount);

        for (int i = 0; i < childCount; i++) {
            View view = parent.getChildAt(i);
            int index = parent.getChildAdapterPosition(view);
//            LogUtil.d("index = " + index);

            if (orientation == LinearLayoutManager.VERTICAL) {
                //垂直
                float top = view.getBottom();
                float bottom = view.getBottom() + drawPadding;
                float left = view.getLeft();
                float right = view.getRight();
                c.drawRect(left, top, right, bottom, paint);

            } else {
                //水平
                if (index == 0) {
                    c.drawRect(view.getLeft() - drawPadding, view.getTop(), view.getLeft(), view.getBottom(), paint);
//                    LogUtil.d("left = " + (view.getLeft() - drawPadding) + ",top = " + top + ",right = " + view.getRight() + ",bottom = " + bottom);
                } else if (index == listSize - 1) {
                    c.drawRect(view.getRight(), view.getTop(), view.getRight() + drawPadding, view.getBottom(), paint);
//                    LogUtil.d("left = " + view.getLeft() + ",top = " + top + ",right = " + (view.getRight() + drawPadding) + ",bottom = " + bottom);
                } else {
                    c.drawRect(view.getLeft(), view.getTop(), view.getLeft(), view.getBottom(), paint);
//                    LogUtil.d("left = " + view.getLeft() + ",top = " + top + ",right = " + view.getRight() + ",bottom = " + bottom);
                }
            }
        }
 
    }

調(diào)用

        manager.setOrientation(LinearLayoutManager.HORIZONTAL);
        recyclerView.addItemDecoration(new RecyclerViewLeftRightAddPadding(this, LinearLayoutManager.HORIZONTAL));
        horizontalAdapter = new RecyclerViewHorizontalAdapter(this, list);
        recyclerView.setAdapter(horizontalAdapter);