RecyclerView使用详解

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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ListViewCursorAdapter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

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