问题
I have a pager adapter that suppose to inflate a complex view representing a calendar.
It takes around ~350 ms to inflate each year of the calendar.
To improve performance I would like to implement the same mechanism that exists in the ListView array adapter of recycling views (convertView parameter in getView()).
Here is my current getView() from the adapter.
@Override
protected View getView(VerticalViewPager pager, final DateTileGrid currentDataItem, int position)
{
mInflater = LayoutInflater.from(pager.getContext());
// This is were i would like to understand weather is should use a recycled view or create a new one.
View datesGridView = mInflater.inflate(R.layout.fragment_dates_grid_page, pager, false);
DateTileGridView datesGrid = (DateTileGridView) datesGridView.findViewById(R.id.datesGridMainGrid);
TextView yearTitle = (TextView) datesGridView.findViewById(R.id.datesGridYearTextView);
yearTitle.setText(currentDataItem.getCurrentYear() + "");
DateTileView[] tiles = datesGrid.getTiles();
for (int i = 0; i < 12; i++)
{
String pictureCount = currentDataItem.getTile(i).getPictureCount().toString();
tiles[i].setCenterLabel(pictureCount);
final int finalI = i;
tiles[i].setOnCheckedChangeListener(new DateTileView.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(DateTileView tileChecked, boolean isChecked)
{
DateTile tile = currentDataItem.getTile(finalI);
tile.isSelected(isChecked);
}
});
}
return datesGridView;
}
Any pointers or direction for implementing such a behavior?
In particular how can I know in the adapter that one of the DateTileGridViews is being swiped of the screen so I could save it in memory to reuse it next time.
回答1:
So I have figured it out.
- overwrite
destroyItem(ViewGroup container, int position, Object view)ans save you cached view - create a separate method to see if there is any chance to use a recycled view or should you inflate a new one.
- remember to remove the recycled view from cache once its been used to avoid having same view attaching same view to the pager.
here is the code.. I used a Stack of view to cache all removed views from my pager
private View inflateOrRecycleView(Context context)
{
View viewToReturn;
mInflater = LayoutInflater.from(context);
if (mRecycledViewsList.isEmpty())
{
viewToReturn = mInflater.inflate(R.layout.fragment_dates_grid_page, null, false);
}
else
{
viewToReturn = mRecycledViewsList.pop();
Log.i(TAG,"Restored recycled view from cache "+ viewToReturn.hashCode());
}
return viewToReturn;
}
@Override
public void destroyItem(ViewGroup container, int position, Object view)
{
VerticalViewPager pager = (VerticalViewPager) container;
View recycledView = (View) view;
pager.removeView(recycledView);
mRecycledViewsList.push(recycledView);
Log.i(TAG,"Stored view in cache "+ recycledView.hashCode());
}
do not forget to instantiate the stack in the adapter constructor.
回答2:
i did it like this ..first create abstract softCache class:
public abstract class SoftCache<T> {
private Stack<Reference<T>> mRecyclingStack;
final Class<T> classType;
public SoftCache(Class<T> typeParameterClass) {
this.classType = typeParameterClass;
mRecyclingStack = new Stack<Reference<T>>();
}
/* implement this to create new object of type T if cache is empty */
public abstract T runWhenCacheEmpty();
/*
* retrieves last item from cache or creates a new T object if cache is
* empty
*/
public T get() {
T itemCached = null;
if (mRecyclingStack.isEmpty()) {
itemCached = runWhenCacheEmpty();
} else {
SoftReference<T> softRef = (SoftReference<T>) mRecyclingStack
.pop();
Object obj = softRef.get();
/*
* if referent object is empty(due to GC) then create a new
* object
*/
if (obj == null) {
itemCached = runWhenCacheEmpty();
}
/*
* otherwise restore from cache by casting the referent as the
* class Type that was passed to constructor
*/
else {
itemCached = (classType.cast(softRef.get()));
}
}
return itemCached;
}
now inherit from SoftCache so we can implement the runWhenCacheEmpty method:
public class ViewCache extends SoftCache<View>{
public ViewCache(Class<View> typeParameterClass) {
super(typeParameterClass);
}
@Override
public View runWhenCacheEmpty() {
return mFragment.getActivity().getLayoutInflater()
.inflate(R.layout.mypagelayout, null);
}
}
then in your constructor instantiate it like this if you want it to be for a View class for example (but it can work for any type of class):
SoftCache<View> myViewCache = new ViewCache(View.class);
now in destroyItem save the view to the cache:
@Override
public void destroyItem(final ViewGroup container, final int position, final Object object) {
final View v = (View) object;
if(v.getId() == R.id.mypagelayout)
myViewCache.put(v); //this saves it
}
now method instantiateItem make use of it simply like this:
@Override
public Object instantiateItem(final ViewGroup container, final int position) {
View MyPageView=myViewCache.get();
}
update: if you want to use the cache for different layouts or dont like to extend it i came up with a solution where you can use the same cache for multiple layouts where you would retrieve the layout you put in using the layouts ID:
public class SoftViewCache {
private HashMap<Integer,ArrayList<SoftReference<View>>> multiMap;
public SoftViewCache() {
multiMap= new HashMap<Integer, ArrayList<SoftReference<View>>>();
}
/*
* retrieves cached item or return null if cache is
* empty
*/
public View get(int id) {
View itemCached = null;
if (!multiMap.containsKey(id)) {
return null;
}
else {
/*get the referent object and check if its already been GC if not we re-use*/
SoftReference<View> softRef =multiMap.get(id).get(0);
Object obj = softRef.get();
/*
* if referent object is empty(due to GC) then caller must create a new
* object
*/
if (null == obj) {
return null;
}
/*
* otherwise restore from cache
*/
else {
itemCached = (softRef.get());
}
}
return itemCached;
}
/* saves a view object to the cache by reference, we use a multiMap to allow
* duplicate IDs*/
public void put(View item) {
SoftReference<View> ref = new SoftReference<View>(item);
int key = item.getId();
/*check if we already have a reuseable layouts saved if so just add to the list
* of reusable layouts*/
if (multiMap.containsKey(key)) {
multiMap.get(key).add(ref);
} else {
/*otherwise we have no reusable layouts lets create a list of reusable layouts
* and add it to the multiMap*/
ArrayList<SoftReference<View>> list = new ArrayList<SoftReference<View>>();
list.add(ref);
multiMap.put(key, list);
}
}
}
回答3:
I solved this by defining a RecycleCache, like this
protected static class RecycleCache {
private final RecyclerPagerAdapter mAdapter;
private final ViewGroup mParent;
private final int mViewType;
private List<ViewHolder> mCaches;
public RecycleCache(RecyclerPagerAdapter adapter, ViewGroup parent, int viewType) {
mAdapter = adapter;
mParent = parent;
mViewType = viewType;
mCaches = new ArrayList<>();
}
public ViewHolder getFreeViewHolder() {
int i = 0;
ViewHolder viewHolder;
for (int n = mCaches.size(); i < n; i++) {
viewHolder = mCaches.get(i);
if (!viewHolder.mIsAttached) {
return viewHolder;
}
}
viewHolder = mAdapter.onCreateViewHolder(mParent, mViewType);
mCaches.add(viewHolder);
return viewHolder;
}
}
Check out my sample code here RecyclerPagerAdapter
来源：https://stackoverflow.com/questions/19020114/how-do-i-implement-view-recycling-mechanism-for-pageradapter