适配RecycleView的 ItemDecoration 的封装

ItemDecoration 的封装

1. ItemDecoration类的定义

ItemDecoration–>RecycleView的item系统间距以及系统item绘制封装类

/**
 * ItemDecoration允许程序对适配器的数据源中的特殊的条目      
 * view 添加一些特别的图形和布局的偏移，这被用于在条目之      
 * 间画间隔线，高亮显示，视觉分组界限和更多。
 * 所有的ItemDecorations
 * <p>所有的ItemDecorations都是按照它们添加的顺序绘制的, 
 * 在所有的条目view绘制之前
*  (in {@link ItemDecoration#onDraw(Canvas, RecyclerView, RecyclerView.State) onDraw()}
 * 在所有的条目view绘制之后 (in {@link ItemDecoration#onDrawOver(Canvas, RecyclerView,
 * RecyclerView.State)}.</p>
 */
public abstract static class ItemDecoration {
   ...
   ...
}

2. ItemDecoration的方法分析

此类下的六个方法有三个为过时方法，只需要复写另外三个未过时的方法即可，谷歌对这三个方法的定义如下：

在提供给RecyclerView的Canvas中绘制任何适当的装饰。此方法绘制的任何内容将在绘制项目视图之前绘制，因此将被视图覆盖.
```
public void onDraw(Canvas c, RecyclerView parent, State state{
    onDraw(c, parent);
}
```
在提供给RecyclerView的Canvas中绘制任何适当的装饰。此方法绘制的任何内容将在绘制项目视图之后绘制，因此将覆盖视图
```
public void onDrawOver(Canvas c, RecyclerView parent, State state) {
      onDrawOver(c, parent);
}
```
检索给定条目的所有偏移量， outRect 的每个字段指定条目视图应该被插入的像素大小，类似于填充或边距。默认实现将outRect的边界设置为0并返回。

public void getItemOffsets(Rect outRect, View view, RecyclerView parent, State state) { getItemOffsets(outRect, ((LayoutParams)view.getLayoutParams()).getViewLayoutPosition(), parent); }

注：onDraw 和 onDrawOver的区别在于，若未规定条目视图的左上右下的偏移量，在条目视图的基础上，使用canvas 所做的任何装饰，前者会被条目视图所覆盖，而后者方法则会在条目视图的基础上作画。

3. 封装 getItemOffsets

通过构造函数传入左上右下的间距

private int mSpaceHorizontal; private int mSpaceVertical; private Paint mPaint;

DividerDecoration(Activity activity, int spaceHorizontal, int spaceVertical) { mSpaceHorizontal = spaceHorizontal; mSpaceVertical = spaceVertical; mPaint = new Paint(); mPaint.setStyle(Paint.Style.FILL); mPaint.setAntiAlias(true); mPaint.setColor(ContextCompat.getColor(activity, android.R.color.transparent)); }

DividerDecoration(Activity activity, int color, int spaceHorizontal, int spaceVertical) { mSpaceHorizontal = spaceHorizontal; mSpaceVertical = spaceVertical; mPaint = new Paint(); mPaint.setStyle(Paint.Style.FILL); mPaint.setAntiAlias(true); mPaint.setColor(ContextCompat.getColor(activity, color)); }
筛选RecycleView的布局管理器，对应做单独处理

@Override public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) { super.getItemOffsets(outRect, view, parent, state); RecyclerView.LayoutManager layoutManager = parent.getLayoutManager(); if (layoutManager instanceof GridLayoutManager) { layoutGridItem(outRect, view, parent, (GridLayoutManager) layoutManager); } else if (layoutManager instanceof LinearLayoutManager) { layoutLinearItem(outRect, view, parent, (LinearLayoutManager) layoutManager); } else if (layoutManager instanceof StaggeredGridLayoutManager) { layoutStaggeredItem(outRect, view, parent, (StaggeredGridLayoutManager) layoutManager); } }

LinearLayoutManager 的布局偏移封装

private void layoutLinearItemSpace(Rect outRect, View view, RecyclerView parent, LinearLayoutManager linearManager) { int viewPosition = parent.getChildAdapterPosition(view);

  if (linearManager.getOrientation() == LinearLayoutManager.VERTICAL) {
      outRect.left = mSpaceHorizontal;
      outRect.right = mSpaceHorizontal;
      if (viewPosition == 0) {
          outRect.top = mSpaceVertical;
          outRect.bottom = mSpaceVertical / 2;
      } else if (viewPosition == linearManager.getItemCount() - 1) {
          outRect.top = mSpaceVertical / 2;
          outRect.bottom = mSpaceVertical;
      } else {
          outRect.top = mSpaceVertical / 2;
          outRect.bottom = mSpaceVertical / 2;
      }
  } else {
      outRect.top = mSpaceVertical;
      outRect.bottom = mSpaceVertical;

      if (viewPosition == 0) {
          outRect.left = mSpaceHorizontal;
          outRect.right = mSpaceHorizontal / 2;
      } else if (viewPosition == linearManager.getItemCount() - 1) {
          outRect.left = mSpaceHorizontal / 2;
          outRect.right = mSpaceHorizontal;
      } else {
          outRect.left = mSpaceHorizontal / 2;
          outRect.right = mSpaceHorizontal / 2;
      }
  }   }

GridLayoutManager 的布局偏移封装

private void layoutGridItemSpace(Rect outRect, View view, RecyclerView parent, GridLayoutManager gridManager) { int viewPosition = parent.getChildAdapterPosition(view); int spanCount = gridManager.getSpanCount(); int index = viewPosition % spanCount;

  if (viewPosition < spanCount) {//第一行
      outRect.top = mSpaceVertical;
      outRect.bottom = mSpaceVertical / 2;
  } else if (viewPosition / spanCount == (gridManager.getItemCount() - 1) / spanCount) {//多宫格如何判断最后一行？
      outRect.top = mSpaceVertical / 2;
      outRect.bottom = mSpaceVertical;
  } else {
      outRect.top = mSpaceVertical / 2;
      outRect.bottom = mSpaceVertical / 2;
  }


  if (index == 0) {//第一列
      outRect.left = mSpaceHorizontal;
      outRect.right = mSpaceHorizontal / 2;

  } else if (index == spanCount - 1) {//最后一列
      outRect.left = mSpaceHorizontal / 2;
      outRect.right = mSpaceHorizontal;

  } else {
      outRect.left = mSpaceHorizontal / 2;
      outRect.right = mSpaceHorizontal / 2;
  }

}

StaggeredGridLayoutManager的布局偏移封装

private void layoutStaggeredItemSpace(Rect outRect, View view, RecyclerView parent, StaggeredGridLayoutManager staggeredManager) {

}

LinearLayoutManager 的布局偏移颜色封装

private void drawLinearItemSpace(Canvas c, RecyclerView parent, LinearLayoutManager linearManager) {

  if (linearManager.getOrientation() == LinearLayoutManager.VERTICAL) {
      for (int viewPosition = 0; viewPosition < linearManager.getItemCount(); viewPosition++) {
          View childView = parent.getChildAt(viewPosition);

          if (childView == null) {
              continue;
          }

          RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) childView.getLayoutParams();

          int left;
          int top;
          int right;
          int bottom;
          left = childView.getLeft() - params.leftMargin;
          right = childView.getRight() + params.rightMargin;
          top = childView.getBottom() + params.bottomMargin;
          bottom = top + mSpaceVertical;
          c.drawRect(left, top, right, bottom, mPaint);
          if (viewPosition == 0) {
              top = childView.getTop() - params.topMargin - mSpaceVertical;
              bottom = top + mSpaceVertical;
              c.drawRect(left, top, right, bottom, mPaint);
          }
      }
  } else {


      for (int viewPosition = 0; viewPosition < linearManager.getItemCount(); viewPosition++) {
          View childView = parent.getChildAt(viewPosition);

          if (childView == null) {
              continue;
          }

          RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) childView.getLayoutParams();

          int left;
          int top;
          int right;
          int bottom;


          left = childView.getRight() + params.rightMargin;
          top = childView.getTop() - params.topMargin;
          right = left + mSpaceHorizontal;
          bottom = childView.getBottom() + params.bottomMargin;
          c.drawRect(left, top, right, bottom, mPaint);

          if(viewPosition == 0) {
              left = childView.getLeft() - params.leftMargin - mSpaceHorizontal;
              top = childView.getTop() - params.topMargin;
              right = left + mSpaceHorizontal;
              bottom = childView.getBottom() + params.bottomMargin;
              c.drawRect(left, top, right, bottom, mPaint);
          }
      }
  }   }

GridLayoutManager 的布局颜色填充封装

private void drawGridItemSpace(Canvas c, RecyclerView parent, GridLayoutManager gridManager) { for (int viewPosition = 0; viewPosition < gridManager.getItemCount(); viewPosition++) { View childView = parent.getChildAt(viewPosition);

      if (childView == null) {
          continue;
      }

      final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) childView.getLayoutParams();

      int spanCount = gridManager.getSpanCount();
      int index = viewPosition % spanCount;

      int left;
      int top;
      int right;
      int bottom;

      left = childView.getLeft() - params.leftMargin;
      right = childView.getRight() + params.rightMargin + mSpaceHorizontal;
      if (viewPosition < spanCount) {//第一行
          top = childView.getTop() - params.topMargin - mSpaceVertical;
          bottom = top + mSpaceVertical;
          c.drawRect(left, top, right, bottom, mPaint);

          top = childView.getBottom() + params.bottomMargin;
          bottom = top + mSpaceVertical;
          c.drawRect(left, top, right, bottom, mPaint);
      } else {
          top = childView.getBottom() + params.bottomMargin;
          bottom = top + mSpaceVertical;
          c.drawRect(left, top, right, bottom, mPaint);
      }


      if (index == 0) {//第一列
          top = childView.getTop() - params.topMargin;
          bottom = childView.getBottom() + params.bottomMargin + mSpaceVertical;
          left = childView.getLeft() - params.leftMargin - mSpaceHorizontal;
          right = left + mSpaceHorizontal;
          c.drawRect(left, top, right, bottom, mPaint);

          top = childView.getTop() - params.topMargin;
          bottom = childView.getBottom() + params.bottomMargin;
          left = childView.getRight() + params.rightMargin;
          right = left + mSpaceHorizontal;
          c.drawRect(left, top, right, bottom, mPaint);

          if (viewPosition == 0) {
              top = childView.getTop() - params.topMargin - mSpaceVertical;
              bottom = top + mSpaceVertical;
              left = childView.getLeft() - params.leftMargin - mSpaceHorizontal;
              right = left + mSpaceHorizontal;
              c.drawRect(left, top, right, bottom, mPaint);
          }

      } else {
          top = childView.getTop() - params.topMargin;
          bottom = childView.getBottom() + params.bottomMargin;
          left = childView.getRight() + params.rightMargin;
          right = left + mSpaceHorizontal;
          c.drawRect(left, top, right, bottom, mPaint);
      }
  }   }

StaggeredGridLayoutManager的布局偏移颜色填充封装

StaggeredGridLayoutManager 相关的目前正在研究，后面会补充完善