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RecyclerView系列之二:从源码中分析为RecyclerView添加分割线

来源：互联网 发布：mac如何运行java程序 编辑：程序博客网 时间：2024/05/21 07:07
  • 今天来解决RecyclerView第二个问题,就是分割线的问题:原生的RecyclerView并没有像ListView那样提供默认的分割线,我们需要自己处理分割线
  • 处理方式为继承RecyclerView的内部类ItemDecoration类,并且复写getItemOffsets()和onDraw()方法.
  • 文章内容包括:
  1. 效果图

  3. 从源码分析RecyclerView分割线的实现方式
  4. 列表和网格分割线的实现
  5. 网格分割线的边界处理
  • 先看对比效果
  •  查看源码RecyclerView中分割线的实现和RecyclerView的内部类ItemDecoration类
  1. public class RecyclerView extends ViewGroup implements ScrollingView, NestedScrollingChild {
  2.     public RecyclerView(Context context) {
  3.         this(context, null);
  4.     }
  6.     public RecyclerView(Context context, @Nullable AttributeSet attrs) {
  7.         this(context, attrs, 0);
  8.     }
  10.     public RecyclerView(Context context, @Nullable AttributeSet attrs, int defStyle) {
  11.         super(context, attrs, defStyle);
  12.         ...
  13.     }
  14. }
  • 可以知道RecyclerView是ViewGroup的子类
      1.     public static abstract class ItemDecoration {
      1.         public void onDraw(Canvas c, RecyclerView parent, State state) {
      2.             onDraw(c, parent);
      3.         }
      1.         public void onDrawOver(Canvas c, RecyclerView parent, State state) {
      2.             onDrawOver(c, parent);
      3.         }
      1.         public void getItemOffsets(Rect outRect, View view, RecyclerView parent, State state) {
      2.             getItemOffsets(outRect, ((LayoutParams) view.getLayoutParams()).getViewLayoutPosition(),
      3.                     parent);
      4.         }
      5.     }
  • 通过源码的继承类发现:
  1. ItemDecoration没有默认的分割线实现类,只有一个ItemTouchHelper类继承(这个类后面分析Item交互时会讲解到)
  2. 该类内部的几个方法的作用(该文章源码等级为24,过时方法不分析):
  3. getItemOffsets()方法作用是获取每个条目的偏移量,具体值放在参数outRect中,要获取具体的条目位置可通过方法RecyclerView.getChildAdapterPosition(view)获取
  4. onDraw()的作用是分割线的绘制,在传入的参数Canvas中绘制
  5. onDrawOver()分割线绘制完调用的方法(一般没用到)
  • 现在来分析RecyclerView的源码->找出他是如何来绘制分割线的
  1. RecyclerView继承自ViewGroup,自然要看他的三个主要方法onMeasure(),onLayout(),onDraw()和ViewGroup独有的方法measureChild().
  2. 通过查看方法onMeasure()和onLayout()没有发现分割线的影子,而在onDraw()中发现调用了ItemDecoration类的onDraw()方法.
    1.     @Override
    2.     public void onDraw(Canvas c) {
    3.         super.onDraw(c);
    5.         final int count = mItemDecorations.size();
    6.         for (int i = 0; i < count; i++) {
    7.             mItemDecorations.get(i).onDraw(c, this, mState);
    8.         }
    9.     }
  3. 那必然在measureChild()方法中,会调用分割线的其他方法
    1. public void measureChild(View child, int widthUsed, int heightUsed) {
    2.             final LayoutParams lp = (LayoutParams) child.getLayoutParams();
    4.             final Rect insets = mRecyclerView.getItemDecorInsetsForChild(child);
    5.             widthUsed += insets.left + insets.right;
    6.             heightUsed += insets.top + insets.bottom;
    7.             final int widthSpec = getChildMeasureSpec(getWidth(), getWidthMode(),
    8.                     getPaddingLeft() + getPaddingRight() + widthUsed, lp.width,
    9.                     canScrollHorizontally());
    10.             final int heightSpec = getChildMeasureSpec(getHeight(), getHeightMode(),
    11.                     getPaddingTop() + getPaddingBottom() + heightUsed, lp.height,
    12.                     canScrollVertically());
    13.             if (shouldMeasureChild(child, widthSpec, heightSpec, lp)) {
    14.                 child.measure(widthSpec, heightSpec);
    15.             }
    16.         }
  4. 发现调用了方法getItemDecorInsetsForChild();意思是获取每个childView插入的分割线大小.然后再测量childView
    1.   Rect getItemDecorInsetsForChild(View child) {
    2.         final LayoutParams lp = (LayoutParams) child.getLayoutParams();
    3.         if (!lp.mInsetsDirty) {
    4.             return lp.mDecorInsets;
    5.         }
    7.         final Rect insets = lp.mDecorInsets;
    8.         insets.set(0, 0, 0, 0);
    9.         final int decorCount = mItemDecorations.size();
    10.         for (int i = 0; i < decorCount; i++) {
    11.             mTempRect.set(0, 0, 0, 0);
    12.             mItemDecorations.get(i).getItemOffsets(mTempRect, child, this, mState);
    13.             insets.left += mTempRect.left;
    14.             insets.top += mTempRect.top;
    15.             insets.right += mTempRect.right;
    16.             insets.bottom += mTempRect.bottom;
    17.         }
    18.         lp.mInsetsDirty = false;
    19.         return insets;
    20.     }
  5. 分割线偏移量方法getItemOffsets()方法也找到了最终调用的位置
  • 了解了RecyclerView的分割线源码实现过程,要实现就不难了
  1. 列表分割线的代码实现
    1. public class DividerItemDecoration extends RecyclerView.ItemDecoration {
    3.     private static final int[] ATTRS = new int[]{
    4.             android.R.attr.listDivider
    5.     };
    7.     public static final int HORIZONTAL_LIST = LinearLayoutManager.HORIZONTAL;
    9.     public static final int VERTICAL_LIST = LinearLayoutManager.VERTICAL;
    11.     private Drawable mDivider;
    13.     private int mOrientation;
    15.     public DividerItemDecoration(Context context, int orientation) {
    16.         final TypedArray a = context.obtainStyledAttributes(ATTRS);
    17.         mDivider = a.getDrawable(0);
    18.         a.recycle();
    19.         setOrientation(orientation);
    20.     }
    22.     public void setOrientation(int orientation) {
    23.         if (orientation != HORIZONTAL_LIST && orientation != VERTICAL_LIST) {
    24.             throw new IllegalArgumentException("invalid orientation");
    25.         }
    26.         mOrientation = orientation;
    27.     }
    29.     @Override
    30.     public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
    31.         if (mOrientation == VERTICAL_LIST) {
    32.             drawVertical(c, parent);
    33.         } else {
    34.             drawHorizontal(c, parent);
    35.         }
    36.     }
    38.     /**
    39.      * 垂直方向分割线
    40.      * @param c
    41.      * @param parent
    42.      */
    43.     public void drawVertical(Canvas c, RecyclerView parent) {
    44.         final int left = parent.getPaddingLeft();
    45.         final int right = parent.getWidth() - parent.getPaddingRight();
    47.         final int childCount = parent.getChildCount();
    48.         for (int i = 0; i < childCount; i++) {
    49.             final View child = parent.getChildAt(i);
    50.             final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
    51.                     .getLayoutParams();
    52.             final int top = child.getBottom() + params.bottomMargin;
    53.             final int bottom = top + mDivider.getIntrinsicHeight();
    54.             mDivider.setBounds(left, top, right, bottom);
    55.             mDivider.draw(c);
    56.         }
    57.     }
    59.     public void drawHorizontal(Canvas c, RecyclerView parent) {
    60.         final int top = parent.getPaddingTop();
    61.         final int bottom = parent.getHeight() - parent.getPaddingBottom();
    63.         final int childCount = parent.getChildCount();
    64.         for (int i = 0; i < childCount; i++) {
    65.             final View child = parent.getChildAt(i);
    66.             final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
    67.                     .getLayoutParams();
    68.             final int left = child.getRight() + params.rightMargin;
    69.             final int right = left + mDivider.getIntrinsicHeight();
    70.             mDivider.setBounds(left, top, right, bottom);
    71.             mDivider.draw(c);
    72.         }
    73.     }
    75.     @Override
    76.     public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
    77.         if (mOrientation == VERTICAL_LIST) {
    78.             outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
    79.         } else {
    80.             outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
    81.         }
    82.     }
    83. }
  2. 网格分割线的代码实现-注意最后一行和最后一列不添加分割线
  1. public class DividerGridItemDecoration extends RecyclerView.ItemDecoration {
  3.     private String TAG = this.getClass().getSimpleName();
  4.     private static final int[] ATTRS = new int[]{
  5.             android.R.attr.listDivider
  6.     };
  8.     private Drawable mDivider;
  10.     public DividerGridItemDecoration(Context context) {
  11.         final TypedArray a = context.obtainStyledAttributes(ATTRS);
  12.         mDivider = a.getDrawable(0);
  13.         a.recycle();
  14.     }
  16.     @Override
  17.     public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
  18.         drawVertical(c, parent);
  19.         drawHorizontal(c, parent);
  20.     }
  22.     /**
  23.      * 水平方向分割线
  24.      * @param c
  25.      * @param parent
  26.      */
  27.     public void drawHorizontal(Canvas c, RecyclerView parent) {
  28.         final int childCount = parent.getChildCount();
  29.         for (int i = 0; i < childCount; i++) {
  30.             if (isLastRow(parent, i, getSpanCount(parent), childCount))//最后一行不绘制
  31.                 continue;
  33.             final View child = parent.getChildAt(i);
  34.             final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
  35.                     .getLayoutParams();
  36.             final int left = child.getLeft() - params.leftMargin;
  37.             final int right = child.getRight() + params.rightMargin;
  38.             final int top = child.getBottom() + params.bottomMargin;
  39.             final int bottom = top + mDivider.getIntrinsicHeight();
  40.             mDivider.setBounds(left, top, right, bottom);
  41.             mDivider.draw(c);
  42.         }
  43.     }
  45.     public void drawVertical(Canvas c, RecyclerView parent) {
  46.         final int childCount = parent.getChildCount();
  47.         for (int i = 0; i < childCount; i++) {
  48.             final View child = parent.getChildAt(i);
  49.             if (isLastColumn(parent, i, getSpanCount(parent), childCount))//最后一列不绘制
  50.                 continue;
  52.             final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
  53.                     .getLayoutParams();
  55.             final int top = child.getTop() - params.topMargin;
  56.             final int bottom = child.getBottom() + params.bottomMargin;
  57.             final int left = child.getRight() + params.rightMargin;
  58.             final int right = left + mDivider.getIntrinsicWidth();
  59.             mDivider.setBounds(left, top, right, bottom);
  60.             mDivider.draw(c);
  61.         }
  62.     }
  64.     @Override
  65.     public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
  66.         int right = mDivider.getIntrinsicWidth();
  67.         int bottom = mDivider.getIntrinsicHeight();
  68.         outRect.set(0, 0, right, bottom);
  69.     }
  71.     /**
  72.      * 是否是最后一列
  73.      *
  74.      * @param parent
  75.      * @param currChildPos
  76.      * @param spanCount
  77.      * @param itemCount
  78.      * @return
  79.      */
  80.     private boolean isLastColumn(RecyclerView parent, int currChildPos, int spanCount, int itemCount) {
  81.         RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
  82.         if (layoutManager != null && layoutManager instanceof GridLayoutManager) {
  83.             if ((currChildPos + 1) % spanCount == 0) {
  84.                 return true;
  85.             }
  86.         } else if (layoutManager != null && layoutManager instanceof StaggeredGridLayoutManager) {
  87.             //瀑布流也有两种方向
  88.             StaggeredGridLayoutManager staggeredGridLayoutManager = (StaggeredGridLayoutManager) layoutManager;
  89.             int orientation = staggeredGridLayoutManager.getOrientation();
  90.             if (orientation == StaggeredGridLayoutManager.VERTICAL) {//垂直
  91.                 if ((currChildPos + 1) % spanCount == 0) {
  92.                     return true;
  93.                 }
  94.             } else {
  95.                 if (itemCount % spanCount != 0) {
  96.                     itemCount = itemCount - itemCount % spanCount;
  97.                     if (currChildPos >= itemCount) {//这种判断方式在item最后一行未填满的情况下可行
  98.                         return true;
  99.                     }
  100.                 } else {//最后一行填满的情况处理
  101.                     itemCount = itemCount - spanCount;
  102.                     if (currChildPos >= itemCount) {
  103.                         return true;
  104.                     }
  105.                 }
  106.             }
  107.         }
  108.         return false;
  109.     }
  112.     /**
  113.      * 是否是最后一行
  114.      *
  115.      * @param parent
  116.      * @param currChildPos
  117.      * @param spanCount
  118.      * @param itemCount
  119.      * @return
  120.      */
  121.     private boolean isLastRow(RecyclerView parent, int currChildPos, int spanCount, int itemCount) {
  122.         boolean result = false;
  123.         RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
  124.         if (layoutManager != null && layoutManager instanceof GridLayoutManager) {
  125.             if (itemCount % spanCount != 0) {
  126.                 itemCount = itemCount - itemCount % spanCount;
  127.                 if (currChildPos >= itemCount) {//这种判断方式在item最后一行未填满的情况下可行
  128.                     return true;
  129.                 }
  130.             } else {//最后一行填满的情况处理
  131.                 itemCount = itemCount - spanCount;
  132.                 if (currChildPos >= itemCount) {
  133.                     return true;
  134.                 }
  135.             }
  136.         } else if (layoutManager != null && layoutManager instanceof StaggeredGridLayoutManager) {
  137.             //瀑布流也有两种方向
  138.             StaggeredGridLayoutManager staggeredGridLayoutManager = (StaggeredGridLayoutManager) layoutManager;
  139.             int orientation = staggeredGridLayoutManager.getOrientation();
  140.             if (orientation == StaggeredGridLayoutManager.VERTICAL) {//垂直
  142.                 if (itemCount % spanCount != 0) {
  143.                     itemCount = itemCount - itemCount % spanCount;
  144.                     if (currChildPos >= itemCount) {//这种判断方式在item最后一行未填满的情况下可行
  145.                         return true;
  146.                     }
  147.                 } else {//最后一行填满的情况处理
  148.                     itemCount = itemCount - spanCount;
  149.                     if (currChildPos >= itemCount) {
  150.                         return true;
  151.                     }
  152.                 }
  153.             } else {
  154.                 if (currChildPos % spanCount == 0) {
  155.                     return true;
  156.                 }
  157.             }
  158.         }
  159.         return false;
  160.     }
  162.     /**
  163.      * 获取当前item在recycler的adapter的位置
  164.      *
  165.      * @param parent
  166.      * @param view
  167.      * @return
  168.      */
  169.     private int getCurrentChildPosition(RecyclerView parent, View view) {
  170.         return parent.getChildAdapterPosition(view);
  171.     }
  173.     private int getSpanCount(RecyclerView parent) {
  174.         int spanCount = -1;
  175.         RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
  176.         if (layoutManager instanceof GridLayoutManager) {
  177.             GridLayoutManager gridLayoutManager = (GridLayoutManager) layoutManager;
  178.             spanCount = gridLayoutManager.getSpanCount();
  179.         } else if (layoutManager instanceof StaggeredGridLayoutManager) {
  180.             StaggeredGridLayoutManager staggeredGridLayoutManager = (StaggeredGridLayoutManager) layoutManager;
  181.             spanCount = staggeredGridLayoutManager.getSpanCount();
  182.         }
  183.         return spanCount;
  184.     }
  185. }
  • 总结:在处理最后一行分割线不绘制的时候发现,在偏移量方法getItemOffset()方法中处理并不起效果,为了准确我将判断最后一行和最后一列的childView的分割线放到绘制方法中调用,是最后一行就不绘制.
  • 网上的判断最后一行的方法有缺陷,未考虑最后一行是否填满,在未填满时,绘制没有问题,这也反映了很多人的博客都是复制粘贴过来,而没有自己真正考虑过.


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