RecyclerView使用技巧（item动画及嵌套高度适配解决方案）

原文地址 · Frank-Zhu  http://frank-zhu.github.io/android/2015/02/26/android-recyclerview-part-3/?utm_source=tuicool&utm_medium=referral

在上一篇（RecyclerView使用详解（二））文章中介绍了RecyclerView的多Item布局实现，接下来要来讲讲RecyclerView的Cursor实现，相较于之前的实现，Cursor有更多的使用场景，也更加的常用，特别是配合LoaderManager和CursorLoader进行数据的缓存及加载显示，基于此我们来重点看看RecyclerView的CursorAdapter具体要怎么实现。

一、CursorAdapter实现(配合LoaderManager和CursorLoader)

如果之前你用过ListView实现过此功能(CursorAdapter)，那么你一定对下面这两个方法并不陌生

     @Override
     public View newView(Context context, Cursor cursor, ViewGroup parent) {
         return null;
     }

     @Override
     public void bindView(View view, Context context, Cursor cursor) {

     }

其中newView方法是用来创建Item布局的，bindView 方法是用来绑定当前View数据的，就相当于之前的getView方法拆成了两个方法实现。

如果你用RecyclerView，你会发现CursorAdapter这个类没有了，既然没有了，那我们就自己仿照着ListView的CursorAdapter类来实现，具体的代码没什么大的出入，无非就是注册两个观察者去监听数据库数据的变化，但是有两个地方需要注意一下，一个就是hasStableIds() 这个方法RecyclerView.Adapter中不能复写父类的方法，需要在初始化的时候调用setHasStableIds(true); 来完成相同功能，第二个就是notifyDataSetInvalidated() 这个方法没有，统一修改成notifyDataSetChanged() 方法即可。

 void init(Context context, Cursor c, int flags) {
         boolean cursorPresent = c != null;
         mCursor = c;
         mDataValid = cursorPresent;
         mContext = context;
         mRowIDColumn = cursorPresent ? c.getColumnIndexOrThrow("_id") : -1;
         if ((flags & FLAG_REGISTER_CONTENT_OBSERVER) == FLAG_REGISTER_CONTENT_OBSERVER) {
             mChangeObserver = new ChangeObserver();
             mDataSetObserver = new MyDataSetObserver();
         } else {
             mChangeObserver = null;
             mDataSetObserver = null;
         }

         if (cursorPresent) {
             if (mChangeObserver != null) c.registerContentObserver(mChangeObserver);
             if (mDataSetObserver != null) c.registerDataSetObserver(mDataSetObserver);
         }

         setHasStableIds(true);//这个地方要注意一下，需要将表关联ID设置为true
     }

     //************//
     public Cursor swapCursor(Cursor newCursor) {
         if (newCursor == mCursor) {
             return null;
         }
         Cursor oldCursor = mCursor;
         if (oldCursor != null) {
             if (mChangeObserver != null) oldCursor.unregisterContentObserver(mChangeObserver);
             if (mDataSetObserver != null) oldCursor.unregisterDataSetObserver(mDataSetObserver);
         }
         mCursor = newCursor;
         if (newCursor != null) {
             if (mChangeObserver != null) newCursor.registerContentObserver(mChangeObserver);
             if (mDataSetObserver != null) newCursor.registerDataSetObserver(mDataSetObserver);
             mRowIDColumn = newCursor.getColumnIndexOrThrow("_id");
             mDataValid = true;
             // notify the observers about the new cursor
             notifyDataSetChanged();
         } else {
             mRowIDColumn = -1;
             mDataValid = false;
             // notify the observers about the lack of a data set
             //There is no notifyDataSetInvalidated() method in RecyclerView.Adapter
             notifyDataSetChanged();//注意此处
         }
         return oldCursor;
     }
     //************//
     private class MyDataSetObserver extends DataSetObserver {
         @Override
         public void onChanged() {
             mDataValid = true;
             notifyDataSetChanged();
         }

         @Override
         public void onInvalidated() {
             mDataValid = false;
             //There is no notifyDataSetInvalidated() method in RecyclerView.Adapter
             notifyDataSetChanged();//注意此处
         }
     }

怎么样，是不是很简单，没错，就是这么简单，这里是完整的BaseAbstractRecycleCursorAdapter代码,用法和ListView的CursorAdapter用法一致，具体的可以看看我的Recyclerview LoaderManager Provider

二、Item的动画实现 RecyclerView本身就已经实现了ITEM的动画，只需要调用以下几个函数来增删Item即可出现默认动画。

 notifyItemChanged(int)
 notifyItemInserted(int)
 notifyItemRemoved(int)
 notifyItemRangeChanged(int, int)
 notifyItemRangeInserted(int, int)
 notifyItemRangeRemoved(int, int)

怎么样，是不是很轻松，如果你不满足系统默认动画，那么你可以自定义实现RecyclerView.ItemAnimator的接口方法，实现代码可以参考DefaultItemAnimator.当然，如果你不想自己实现，那么也没关系，这里有人已经写了开源库，你可以去看看recyclerview-animators,这里给出默认动画实现方式代码AnimFragment

三、嵌套RecycleView

一般是不推荐使用嵌套RecycleView的，和ListView是类似的，遇到这种需要嵌套的View一般都是想别的办法来规避，比如动态AddView，或者通过RecycleView的MultipleItemAdapter来实现，通过设置不同的ItemType布局不同的View，但是有时候会闲麻烦，想直接就用嵌套的方式来做，那么和ListView实现方式不同的是，ListView的实现一般都是继承ListView然后复写onMeasure方法，如下所示：

     @Override
     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
         int expandSpec = MeasureSpec.makeMeasureSpec(Integer.MAX_VALUE >> 2, MeasureSpec.AT_MOST);
         super.onMeasure(widthMeasureSpec, expandSpec);
     }

　　但是需要特别注意的一点，RecycleView的实现方式不再是继承RecycleView来做，而是通过修改LayoutManager的方式，即通过继承LinearLayoutManager GridLayoutManagerStaggeredGridLayoutManager来修改子控件的测量，下面给出主要代码：

FullyLinearLayoutManager

 private int[] mMeasuredDimension = new int[2];

     @Override
     public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state,
                           int widthSpec, int heightSpec) {

         final int widthMode = View.MeasureSpec.getMode(widthSpec);
         final int heightMode = View.MeasureSpec.getMode(heightSpec);
         final int widthSize = View.MeasureSpec.getSize(widthSpec);
         final int heightSize = View.MeasureSpec.getSize(heightSpec);

         Log.i(TAG, "onMeasure called. \nwidthMode " + widthMode
                 + " \nheightMode " + heightSpec
                 + " \nwidthSize " + widthSize
                 + " \nheightSize " + heightSize
                 + " \ngetItemCount() " + getItemCount());

         int width = 0;
         int height = 0;
         for (int i = 0; i < getItemCount(); i++) {
             measureScrapChild(recycler, i,
                     View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
                     View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
                     mMeasuredDimension);

             if (getOrientation() == HORIZONTAL) {
                 width = width + mMeasuredDimension[0];
                 if (i == 0) {
                     height = mMeasuredDimension[1];
                 }
             } else {
                 height = height + mMeasuredDimension[1];
                 if (i == 0) {
                     width = mMeasuredDimension[0];
                 }
             }
         }
         switch (widthMode) {
             case View.MeasureSpec.EXACTLY:
                 width = widthSize;
             case View.MeasureSpec.AT_MOST:
             case View.MeasureSpec.UNSPECIFIED:
         }

         switch (heightMode) {
             case View.MeasureSpec.EXACTLY:
                 height = heightSize;
             case View.MeasureSpec.AT_MOST:
             case View.MeasureSpec.UNSPECIFIED:
         }

         setMeasuredDimension(width, height);
     }

     private void measureScrapChild(RecyclerView.Recycler recycler, int position, int widthSpec,
                                    int heightSpec, int[] measuredDimension) {
         try {
             View view = recycler.getViewForPosition(0);//fix 动态添加时报IndexOutOfBoundsException

             if (view != null) {
                 RecyclerView.LayoutParams p = (RecyclerView.LayoutParams) view.getLayoutParams();

                 int childWidthSpec = ViewGroup.getChildMeasureSpec(widthSpec,
                         getPaddingLeft() + getPaddingRight(), p.width);

                 int childHeightSpec = ViewGroup.getChildMeasureSpec(heightSpec,
                         getPaddingTop() + getPaddingBottom(), p.height);

                 view.measure(childWidthSpec, childHeightSpec);
                 measuredDimension[0] = view.getMeasuredWidth() + p.leftMargin + p.rightMargin;
                 measuredDimension[1] = view.getMeasuredHeight() + p.bottomMargin + p.topMargin;
                 recycler.recycleView(view);
             }
         } catch (Exception e) {
             e.printStackTrace();
         } finally {
         }
     }

FullyGridLayoutManager

 private int[] mMeasuredDimension = new int[2];

     @Override
     public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state, int widthSpec, int heightSpec) {
         final int widthMode = View.MeasureSpec.getMode(widthSpec);
         final int heightMode = View.MeasureSpec.getMode(heightSpec);
         final int widthSize = View.MeasureSpec.getSize(widthSpec);
         final int heightSize = View.MeasureSpec.getSize(heightSpec);

         int width = 0;
         int height = 0;
         int count = getItemCount();
         int span = getSpanCount();
         for (int i = 0; i < count; i++) {
             measureScrapChild(recycler, i,
                     View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
                     View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
                     mMeasuredDimension);

             if (getOrientation() == HORIZONTAL) {
                 if (i % span == 0) {
                     width = width + mMeasuredDimension[0];
                 }
                 if (i == 0) {
                     height = mMeasuredDimension[1];
                 }
             } else {
                 if (i % span == 0) {
                     height = height + mMeasuredDimension[1];
                 }
                 if (i == 0) {
                     width = mMeasuredDimension[0];
                 }
             }
         }

         switch (widthMode) {
             case View.MeasureSpec.EXACTLY:
                 width = widthSize;
             case View.MeasureSpec.AT_MOST:
             case View.MeasureSpec.UNSPECIFIED:
         }

         switch (heightMode) {
             case View.MeasureSpec.EXACTLY:
                 height = heightSize;
             case View.MeasureSpec.AT_MOST:
             case View.MeasureSpec.UNSPECIFIED:
         }

         setMeasuredDimension(width, height);
     }

     private void measureScrapChild(RecyclerView.Recycler recycler, int position, int widthSpec,
                                    int heightSpec, int[] measuredDimension) {
         if (position < getItemCount()) {
             try {
                 View view = recycler.getViewForPosition(0);//fix 动态添加时报IndexOutOfBoundsException
                 if (view != null) {
                     RecyclerView.LayoutParams p = (RecyclerView.LayoutParams) view.getLayoutParams();
                     int childWidthSpec = ViewGroup.getChildMeasureSpec(widthSpec,
                             getPaddingLeft() + getPaddingRight(), p.width);
                     int childHeightSpec = ViewGroup.getChildMeasureSpec(heightSpec,
                             getPaddingTop() + getPaddingBottom(), p.height);
                     view.measure(childWidthSpec, childHeightSpec);
                     measuredDimension[0] = view.getMeasuredWidth() + p.leftMargin + p.rightMargin;
                     measuredDimension[1] = view.getMeasuredHeight() + p.bottomMargin + p.topMargin;
                     recycler.recycleView(view);
                 }
             } catch (Exception e) {
                 e.printStackTrace();
             }
         }
     }

##四、效果图如下：

Item默认动画效果

嵌套ScrollView效果