RecycleView item 边框、阴影

DividerDecoration.java

private static class DividerDecoration extends RecyclerView.ItemDecoration {

        final int bottomOffset = DisplayUtil.dip2px(15);
        final int hOffset = DisplayUtil.dip2px(7);
        final ShadowHelper mShadowHelper;

        DividerDecoration(Context context) {
            mShadowHelper = new ShadowHelper(context);
        }

        @Override
        public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
            outRect.bottom = bottomOffset;
            final int position = parent.getChildAdapterPosition(view);
            if (position == 0) {
                return;
            }
            if (position % 2 == 0) {
                outRect.left = hOffset;
            } else {
                outRect.right = hOffset;
            }
        }

//        @Override
//        public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
//public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
//        }

        @Override
        public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
            RecyclerView.LayoutManager layoutManager = null;
            int firstVisibleItem = 0, lastVisibleItem = 0;
            if (parent.getLayoutManager() instanceof GridLayoutManager) {
                GridLayoutManager gridLayoutManager = (GridLayoutManager) parent.getLayoutManager();
                firstVisibleItem = gridLayoutManager.findFirstVisibleItemPosition();
                lastVisibleItem = gridLayoutManager.findLastVisibleItemPosition();
                if (firstVisibleItem != RecyclerView.NO_POSITION && lastVisibleItem != RecyclerView.NO_POSITION) {
                    layoutManager = gridLayoutManager;
                }
            } else if (parent.getLayoutManager() instanceof LinearLayoutManager) {
                LinearLayoutManager linearLayoutManager = (LinearLayoutManager) parent.getLayoutManager();
                firstVisibleItem = linearLayoutManager.findFirstVisibleItemPosition();
                lastVisibleItem = linearLayoutManager.findLastVisibleItemPosition();
                if (firstVisibleItem != RecyclerView.NO_POSITION && lastVisibleItem != RecyclerView.NO_POSITION) {
                    layoutManager = linearLayoutManager;
                }
            }
            if (layoutManager == null) {
                return;
            }

            View item;
            for (; firstVisibleItem <= lastVisibleItem; firstVisibleItem++) {
                item = layoutManager.findViewByPosition(firstVisibleItem);
                mShadowHelper.drawShadow(c, item);
            }
        }
    }
    private static class ShadowHelper {

        final int shadowStartColor = 0x37000000;
        final int shadowEndColor = 0x03000000;
        final int cornerRadius = (int) (DisplayUtil.dip2px(6) + .5f);
        final int shadowSize = DisplayUtil.dip2px(5);

        final Rect tmpRect = new Rect();

        Path cornerShadowPath;

        Paint cornerShadowPaint;
        Paint edgeShadowPaint;
        Paint testPaint;

        ShadowHelper(Context context) {
            cornerShadowPaint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.DITHER_FLAG);
            cornerShadowPaint.setStyle(Paint.Style.FILL);

            edgeShadowPaint = new Paint(cornerShadowPaint);
            edgeShadowPaint.setAntiAlias(false);


            RectF innerBounds = new RectF(-cornerRadius, -cornerRadius, cornerRadius, cornerRadius);
            RectF outerBounds = new RectF(innerBounds);
            outerBounds.inset(-shadowSize, -shadowSize);

            cornerShadowPath = new Path();
            cornerShadowPath.setFillType(Path.FillType.EVEN_ODD);
            cornerShadowPath.moveTo(-cornerRadius, 0);
            cornerShadowPath.rLineTo(-shadowSize, 0);
            // outer arc
            cornerShadowPath.arcTo(outerBounds, 180f, 90f, false);
            // inner arc
            cornerShadowPath.arcTo(innerBounds, 270f, -90f, false);
            cornerShadowPath.close();

//            final float startRatio = cornerRadius / (cornerRadius + shadowSize);
            cornerShadowPaint.setShader(new RadialGradient(0, 0, cornerRadius + shadowSize,
                    new int[]{shadowStartColor, shadowStartColor, shadowEndColor},
                    new float[]{0f, .6f, 1f}, Shader.TileMode.CLAMP));

            edgeShadowPaint.setShader(new LinearGradient(0, -cornerRadius + shadowSize,
                    0, -cornerRadius - shadowSize,
                    new int[]{shadowStartColor, shadowStartColor, shadowEndColor},
                    new float[]{0f, .5f, 1f}, Shader.TileMode.CLAMP));

            testPaint = new Paint();
            testPaint.setStyle(Paint.Style.FILL);
            testPaint.setColor(Color.RED);
//            testPaint.setStrokeWidth(2);
        }

        //        private void drawShadow(Canvas c, View item) {
//            final float edgeShadowTop = -cornerRadius - shadowSize;
//            final float inset = cornerRadius + shadowSize / 2;
//            tmpRect.set(item.getLeft(), item.getTop(), item.getRight(), item.getBottom());
//            // LT
//            int saved = c.save();
//            c.translate(tmpRect.left + inset, tmpRect.top + inset);
////            c.drawPath(cornerShadowPath, cornerShadowPaint);
//            testPaint.setColor(Color.RED);
//            c.drawPath(cornerShadowPath, testPaint);
//            // draw horizontal edge
////            c.drawRect(0, edgeShadowTop, tmpRect.width() - 2 * inset, -cornerRadius, edgeShadowPaint);
//            testPaint.setColor(Color.GREEN);
//            c.drawRect(0, edgeShadowTop, tmpRect.width() - 2 * inset, -cornerRadius, testPaint);
//            c.restoreToCount(saved);
//            // RB
////            saved = c.save();
////            c.translate(tmpRect.right - inset, tmpRect.bottom - inset);
////            c.rotate(180f);
//////            c.drawPath(cornerShadowPath, cornerShadowPaint);
////            testPaint.setColor(Color.RED);
////            c.drawPath(cornerShadowPath, testPaint);
////            // draw horizontal edge
//////            c.drawRect(0, edgeShadowTop, tmpRect.width() - 2 * inset, -cornerRadius + shadowSize, edgeShadowPaint);
////            testPaint.setColor(Color.GREEN);
////            c.drawRect(0, edgeShadowTop, tmpRect.width() - 2 * inset, -cornerRadius + shadowSize, testPaint);
////            c.restoreToCount(saved);
//            // LB
//            saved = c.save();
//            c.translate(tmpRect.left + inset, tmpRect.bottom - inset);
//            c.rotate(270f);
////            c.drawPath(cornerShadowPath, cornerShadowPaint);
//            testPaint.setColor(Color.RED);
//            c.drawPath(cornerShadowPath, testPaint);
//            // draw vertical edge
////            c.drawRect(0, edgeShadowTop, tmpRect.height() - 2 * inset, -cornerRadius, edgeShadowPaint);
//            testPaint.setColor(Color.GREEN);
//            c.drawRect(0, edgeShadowTop, tmpRect.height() - 2 * inset, -cornerRadius, testPaint);
//            c.restoreToCount(saved);
//            // RT
////            saved = c.save();
////            c.translate(tmpRect.right - inset, tmpRect.top + inset);
////            c.rotate(90f);
//////            c.drawPath(cornerShadowPath, cornerShadowPaint);
////            testPaint.setColor(Color.RED);
////            c.drawPath(cornerShadowPath, testPaint);
////            // draw vertical edge
//////            c.drawRect(0, edgeShadowTop, tmpRect.height() - 2 * inset, -cornerRadius, edgeShadowPaint);
////            testPaint.setColor(Color.GREEN);
////            c.drawRect(0, edgeShadowTop, tmpRect.height() - 2 * inset, -cornerRadius, testPaint);
////            c.restoreToCount(saved);
//        }
        private void drawShadow(Canvas c, View item) {
            final float edgeShadowTop = -cornerRadius - shadowSize;
            final float inset = cornerRadius + shadowSize / 2;
            tmpRect.set(item.getLeft(), item.getTop(), item.getRight(), item.getBottom());
            // LT
            int saved = c.save();
            c.translate(tmpRect.left + inset, tmpRect.top + inset);
            c.drawPath(cornerShadowPath, cornerShadowPaint);
            // draw horizontal edge
            c.drawRect(0, edgeShadowTop, tmpRect.width() - 2 * inset, -cornerRadius, edgeShadowPaint);
            c.restoreToCount(saved);
            // RB
            saved = c.save();
            c.translate(tmpRect.right - inset, tmpRect.bottom - inset);
            c.rotate(180f);
            c.drawPath(cornerShadowPath, cornerShadowPaint);
            // draw horizontal edge
            c.drawRect(0, edgeShadowTop, tmpRect.width() - 2 * inset, -cornerRadius + shadowSize, edgeShadowPaint);
            c.restoreToCount(saved);
            // LB
            saved = c.save();
            c.translate(tmpRect.left + inset, tmpRect.bottom - inset);
            c.rotate(270f);
            c.drawPath(cornerShadowPath, cornerShadowPaint);
            // draw vertical edge
            c.drawRect(0, edgeShadowTop, tmpRect.height() - 2 * inset, -cornerRadius, edgeShadowPaint);
            c.restoreToCount(saved);
            // RT
            saved = c.save();
            c.translate(tmpRect.right - inset, tmpRect.top + inset);
            c.rotate(90f);
            c.drawPath(cornerShadowPath, cornerShadowPaint);
            // draw vertical edge
            c.drawRect(0, edgeShadowTop, tmpRect.height() - 2 * inset, -cornerRadius, edgeShadowPaint);
            c.restoreToCount(saved);
        }
    }