RecyclerView使用详解（三）

时间  2019-11-29
标签 recyclerview 使用 详解 繁體版
原文   原文链接

在上一篇（RecyclerView使用详解（二））文章中介绍了RecyclerView的多Item布局实现，接下来要来说讲RecyclerView的Cursor实现，相较于以前的实现，Cursor有更多的使用场景，也更加的经常使用，特别是配合LoaderManager和CursorLoader进行数据的缓存及加载显示，基于此咱们来重点看看RecyclerView的CursorAdapter具体要怎么实现。java

1、CursorAdapter实现(配合LoaderManager和CursorLoader)

若是以前你用过ListView实现过此功能(CursorAdapter)，那么你必定对下面这两个方法并不陌生android

@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方法是用来建立Item布局的，bindView 方法是用来绑定当前View数据的，就至关于以前的getView方法拆成了两个方法实现。git

若是你用RecyclerView，你会发现CursorAdapter这个类没有了，既然没有了，那咱们就本身仿照着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，可是有两个地方须要注意一下，一个就是hasStableIds() 这个方法RecyclerView.Adapter中不能复写父类的方法，须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，统一修改为notifyDataSetChanged() 方法便可。github

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，须要将表关联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，是否是很简单，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，具体的能够看看个人Recyclerview LoaderManager Provider数据库

2、Item的动画实现

RecyclerView自己就已经实现了ITEM的动画，只须要调用如下几个函数来增删Item便可出现默认动画。缓存

notifyItemChanged(int)
     notifyItemInserted(int)
     notifyItemRemoved(int)
     notifyItemRangeChanged(int, int)
     notifyItemRangeInserted(int, int)
     notifyItemRangeRemoved(int, int)

怎么样，是否是很轻松，若是你不知足系统默认动画，那么你能够自定义实现RecyclerView.ItemAnimator的接口方法，实现代码能够参考DefaultItemAnimator.固然，若是你不想本身实现，那么也不要紧，这里有人已经写了开源库，你能够去看看recyclerview-animators,这里给出默认动画实现方式代码AnimFragmentruby

3、嵌套RecycleView

通常是不推荐使用嵌套RecycleView的，和ListView是相似的，遇到这种须要嵌套的View通常都是想别的办法来规避，好比动态AddView，或者经过RecycleView的MultipleItemAdapter来实现，经过设置不一样的ItemType布局不一样的View，可是有时候会闲麻烦，想直接就用嵌套的方式来作，那么和ListView实现方式不一样的是，ListView的实现通常都是继承ListView而后复写onMeasure方法，以下所示：app

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

可是RecycleView的实现方式再也不是继承RecycleView来作，而是经过修改LayoutManager的方式，即经过继承LinearLayoutManager GridLayoutManager StaggeredGridLayoutManager来修改子控件的测量，下面给出主要代码：ide

FullyLinearLayoutManager函数

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();
            }
        }
    }

4、效果图以下：

Item默认动画效果

嵌套ScrollView效果

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