• 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

    1     @Override
2     public View newView(Context context, Cursor cursor, ViewGroup parent) {
3         return null;
4     }
5 
6     @Override
7     public void bindView(View view, Context context, Cursor cursor) {
8 
9     }

    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。

     1 void init(Context context, Cursor c, int flags) {
 2         boolean cursorPresent = c != null;
 3         mCursor = c;
 4         mDataValid = cursorPresent;
 5         mContext = context;
 6         mRowIDColumn = cursorPresent ? c.getColumnIndexOrThrow("_id") : -1;
 7         if ((flags & FLAG_REGISTER_CONTENT_OBSERVER) == FLAG_REGISTER_CONTENT_OBSERVER) {
 8             mChangeObserver = new ChangeObserver();
 9             mDataSetObserver = new MyDataSetObserver();
10         } else {
11             mChangeObserver = null;
12             mDataSetObserver = null;
13         }
14 
15         if (cursorPresent) {
16             if (mChangeObserver != null) c.registerContentObserver(mChangeObserver);
17             if (mDataSetObserver != null) c.registerDataSetObserver(mDataSetObserver);
18         }
19 
20         setHasStableIds(true);//这个地方要注意一下，需要将表关联ID设置为true
21     }
22 
23     //************//
24     public Cursor swapCursor(Cursor newCursor) {
25         if (newCursor == mCursor) {
26             return null;
27         }
28         Cursor oldCursor = mCursor;
29         if (oldCursor != null) {
30             if (mChangeObserver != null) oldCursor.unregisterContentObserver(mChangeObserver);
31             if (mDataSetObserver != null) oldCursor.unregisterDataSetObserver(mDataSetObserver);
32         }
33         mCursor = newCursor;
34         if (newCursor != null) {
35             if (mChangeObserver != null) newCursor.registerContentObserver(mChangeObserver);
36             if (mDataSetObserver != null) newCursor.registerDataSetObserver(mDataSetObserver);
37             mRowIDColumn = newCursor.getColumnIndexOrThrow("_id");
38             mDataValid = true;
39             // notify the observers about the new cursor
40             notifyDataSetChanged();
41         } else {
42             mRowIDColumn = -1;
43             mDataValid = false;
44             // notify the observers about the lack of a data set
45             //There is no notifyDataSetInvalidated() method in RecyclerView.Adapter
46             notifyDataSetChanged();//注意此处
47         }
48         return oldCursor;
49     }
50     //************//
51     private class MyDataSetObserver extends DataSetObserver {
52         @Override
53         public void onChanged() {
54             mDataValid = true;
55             notifyDataSetChanged();
56         }
57 
58         @Override
59         public void onInvalidated() {
60             mDataValid = false;
61             //There is no notifyDataSetInvalidated() method in RecyclerView.Adapter
62             notifyDataSetChanged();//注意此处
63         }
64     }

    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。

    1 notifyItemChanged(int)
2 notifyItemInserted(int)
3 notifyItemRemoved(int)
4 notifyItemRangeChanged(int, int)
5 notifyItemRangeInserted(int, int)
6 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：

    1     @Override
2     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
3         int expandSpec = MeasureSpec.makeMeasureSpec(Integer.MAX_VALUE >> 2, MeasureSpec.AT_MOST);
4         super.onMeasure(widthMeasureSpec, expandSpec);
5     }

    　　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

     1 private int[] mMeasuredDimension = new int[2];
 2 
 3     @Override
 4     public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state,
 5                           int widthSpec, int heightSpec) {
 6 
 7         final int widthMode = View.MeasureSpec.getMode(widthSpec);
 8         final int heightMode = View.MeasureSpec.getMode(heightSpec);
 9         final int widthSize = View.MeasureSpec.getSize(widthSpec);
10         final int heightSize = View.MeasureSpec.getSize(heightSpec);
11 
12         Log.i(TAG, "onMeasure called. 
widthMode " + widthMode
13                 + " 
heightMode " + heightSpec
14                 + " 
widthSize " + widthSize
15                 + " 
heightSize " + heightSize
16                 + " 
getItemCount() " + getItemCount());
17 
18         int width = 0;
19         int height = 0;
20         for (int i = 0; i < getItemCount(); i++) {
21             measureScrapChild(recycler, i,
22                     View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
23                     View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
24                     mMeasuredDimension);
25 
26             if (getOrientation() == HORIZONTAL) {
27                 width = width + mMeasuredDimension[0];
28                 if (i == 0) {
29                     height = mMeasuredDimension[1];
30                 }
31             } else {
32                 height = height + mMeasuredDimension[1];
33                 if (i == 0) {
34                     width = mMeasuredDimension[0];
35                 }
36             }
37         }
38         switch (widthMode) {
39             case View.MeasureSpec.EXACTLY:
40                 width = widthSize;
41             case View.MeasureSpec.AT_MOST:
42             case View.MeasureSpec.UNSPECIFIED:
43         }
44 
45         switch (heightMode) {
46             case View.MeasureSpec.EXACTLY:
47                 height = heightSize;
48             case View.MeasureSpec.AT_MOST:
49             case View.MeasureSpec.UNSPECIFIED:
50         }
51 
52         setMeasuredDimension(width, height);
53     }
54 
55     private void measureScrapChild(RecyclerView.Recycler recycler, int position, int widthSpec,
56                                    int heightSpec, int[] measuredDimension) {
57         try {
58             View view = recycler.getViewForPosition(0);//fix 动态添加时报IndexOutOfBoundsException
59 
60             if (view != null) {
61                 RecyclerView.LayoutParams p = (RecyclerView.LayoutParams) view.getLayoutParams();
62 
63                 int childWidthSpec = ViewGroup.getChildMeasureSpec(widthSpec,
64                         getPaddingLeft() + getPaddingRight(), p.width);
65 
66                 int childHeightSpec = ViewGroup.getChildMeasureSpec(heightSpec,
67                         getPaddingTop() + getPaddingBottom(), p.height);
68 
69                 view.measure(childWidthSpec, childHeightSpec);
70                 measuredDimension[0] = view.getMeasuredWidth() + p.leftMargin + p.rightMargin;
71                 measuredDimension[1] = view.getMeasuredHeight() + p.bottomMargin + p.topMargin;
72                 recycler.recycleView(view);
73             }
74         } catch (Exception e) {
75             e.printStackTrace();
76         } finally {
77         }
78     }

    FullyGridLayoutManager

     1 private int[] mMeasuredDimension = new int[2];
 2 
 3     @Override
 4     public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state, int widthSpec, int heightSpec) {
 5         final int widthMode = View.MeasureSpec.getMode(widthSpec);
 6         final int heightMode = View.MeasureSpec.getMode(heightSpec);
 7         final int widthSize = View.MeasureSpec.getSize(widthSpec);
 8         final int heightSize = View.MeasureSpec.getSize(heightSpec);
 9 
10         int width = 0;
11         int height = 0;
12         int count = getItemCount();
13         int span = getSpanCount();
14         for (int i = 0; i < count; i++) {
15             measureScrapChild(recycler, i,
16                     View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
17                     View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
18                     mMeasuredDimension);
19 
20             if (getOrientation() == HORIZONTAL) {
21                 if (i % span == 0) {
22                     width = width + mMeasuredDimension[0];
23                 }
24                 if (i == 0) {
25                     height = mMeasuredDimension[1];
26                 }
27             } else {
28                 if (i % span == 0) {
29                     height = height + mMeasuredDimension[1];
30                 }
31                 if (i == 0) {
32                     width = mMeasuredDimension[0];
33                 }
34             }
35         }
36 
37         switch (widthMode) {
38             case View.MeasureSpec.EXACTLY:
39                 width = widthSize;
40             case View.MeasureSpec.AT_MOST:
41             case View.MeasureSpec.UNSPECIFIED:
42         }
43 
44         switch (heightMode) {
45             case View.MeasureSpec.EXACTLY:
46                 height = heightSize;
47             case View.MeasureSpec.AT_MOST:
48             case View.MeasureSpec.UNSPECIFIED:
49         }
50 
51         setMeasuredDimension(width, height);
52     }
53 
54     private void measureScrapChild(RecyclerView.Recycler recycler, int position, int widthSpec,
55                                    int heightSpec, int[] measuredDimension) {
56         if (position < getItemCount()) {
57             try {
58                 View view = recycler.getViewForPosition(0);//fix 动态添加时报IndexOutOfBoundsException
59                 if (view != null) {
60                     RecyclerView.LayoutParams p = (RecyclerView.LayoutParams) view.getLayoutParams();
61                     int childWidthSpec = ViewGroup.getChildMeasureSpec(widthSpec,
62                             getPaddingLeft() + getPaddingRight(), p.width);
63                     int childHeightSpec = ViewGroup.getChildMeasureSpec(heightSpec,
64                             getPaddingTop() + getPaddingBottom(), p.height);
65                     view.measure(childWidthSpec, childHeightSpec);
66                     measuredDimension[0] = view.getMeasuredWidth() + p.leftMargin + p.rightMargin;
67                     measuredDimension[1] = view.getMeasuredHeight() + p.bottomMargin + p.topMargin;
68                     recycler.recycleView(view);
69                 }
70             } catch (Exception e) {
71                 e.printStackTrace();
72             }
73         }
74     }

    ##四、效果图如下：

    Item默认动画效果

    嵌套ScrollView效果
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  • 原文地址：https://www.cnblogs.com/BobGo/p/5626691.html
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