RecyclerView使用详解（三）

26 Feb 2015

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 GridLayoutManager StaggeredGridLayoutManager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

最后给出代码下载地址-->Demo Code