RecyclerView使用技巧（item動畫及嵌套高度適配解決方案）

時間 2019-11-20

標籤 recyclerview 使用技巧 item 動畫嵌套高度適配解決方案简体版

原文原文鏈接

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

在上一篇（RecyclerView使用詳解（二））文章中介紹了RecyclerView的多Item佈局實現，接下來要來說講RecyclerView的Cursor實現，相較於以前的實現，Cursor有更多的使用場景，也更加的經常使用，特別是配合LoaderManager和CursorLoader進行數據的緩存及加載顯示，基於此咱們來重點看看RecyclerView的CursorAdapter具體要怎麼實現。android

1、CursorAdapter實現(配合LoaderManager和CursorLoader)git

若是以前你用過ListView實現過此功能(CursorAdapter)，那麼你必定對下面這兩個方法並不陌生github

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方法是用來建立Item佈局的，bindView 方法是用來綁定當前View數據的，就至關於以前的getView方法拆成了兩個方法實現。數據庫

若是你用RecyclerView，你會發現CursorAdapter這個類沒有了，既然沒有了，那咱們就本身仿照着ListView的CursorAdapter類來實現，具體的代碼沒什麼大的出入，無非就是註冊兩個觀察者去監聽數據庫數據的變化，可是有兩個地方須要注意一下，一個就是hasStableIds() 這個方法RecyclerView.Adapter中不能複寫父類的方法，須要在初始化的時候調用setHasStableIds(true); 來完成相同功能，第二個就是notifyDataSetInvalidated() 這個方法沒有，統一修改爲notifyDataSetChanged() 方法便可。緩存

 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);//這個地方要注意一下，須要將表關聯ID設置爲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();//注意此處
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();//注意此處
63         }
64     }

怎麼樣，是否是很簡單，沒錯，就是這麼簡單，這裏是完整的BaseAbstractRecycleCursorAdapter代碼,用法和ListView的CursorAdapter用法一致，具體的能夠看看個人Recyclerview LoaderManager Providerapp

2、Item的動畫實現 RecyclerView自己就已經實現了ITEM的動畫，只須要調用如下幾個函數來增刪Item便可出現默認動畫。ide

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

怎麼樣，是否是很輕鬆，若是你不知足系統默認動畫，那麼你能夠自定義實現RecyclerView.ItemAnimator的接口方法，實現代碼能夠參考DefaultItemAnimator.固然，若是你不想本身實現，那麼也不要緊，這裏有人已經寫了開源庫，你能夠去看看recyclerview-animators,這裏給出默認動畫實現方式代碼AnimFragment函數

3、嵌套RecycleView佈局

通常是不推薦使用嵌套RecycleView的，和ListView是相似的，遇到這種須要嵌套的View通常都是想別的辦法來規避，好比動態AddView，或者經過RecycleView的MultipleItemAdapter來實現，經過設置不一樣的ItemType佈局不一樣的View，可是有時候會閒麻煩，想直接就用嵌套的方式來作，那麼和ListView實現方式不一樣的是，ListView的實現通常都是繼承ListView而後複寫onMeasure方法，以下所示：

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     }

　　可是須要特別注意的一點，RecycleView的實現方式再也不是繼承RecycleView來作，而是經過修改LayoutManager的方式，即經過繼承LinearLayoutManager GridLayoutManagerStaggeredGridLayoutManager來修改子控件的測量，下面給出主要代碼：

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. \nwidthMode " + widthMode
13                 + " \nheightMode " + heightSpec
14                 + " \nwidthSize " + widthSize
15                 + " \nheightSize " + heightSize
16                 + " \ngetItemCount() " + 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 動態添加時報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 動態添加時報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     }