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首页 手记 Android RecyclerView使用详解（三）

Android RecyclerView使用详解（三）

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Android

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

[代码]java代码：

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@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。

[代码]java代码：

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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。

[代码]java代码：

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   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：

[代码]java代码：

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@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

[代码]java代码：

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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

[代码]java代码：

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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();

            }

        }

    }

原文链接：http://www.apkbus.com/blog-705730-61152.html


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发表于 2018.10.11 10:44， 共 2384 人浏览

本文原创发布于慕课网 ，转载请注明出处，谢谢合作

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