RecyclerView使用详解（三）
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：
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 {
}
} 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
