Android 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

[代码]java代码：

@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：

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：

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：

@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：

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),

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：

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),

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