Develop Reference

Android RecyclerView displayed item changed when I scrolled up and down everytime

I am using parse-server to develop the app which uses RecyclerView to display image items.
but the problem is that the items displayed in the view changed every time I scrolled up and down.
I want to know what is the problem on my code.
if you see below images, you can find the items are changing their position.
I tried to make holder image become null before call the holder again. but it's not working. I guess that the item's position number is changed when I call the item again.but I can't find the cause of the situation
enter image description here
enter image description here
RecyclerParseAdapter.java
public class MyTimelineAdapter extends RecyclerParseAdapter {
private interface OnQueryLoadListener<ParseObject> {
public void onLoading();
public void onLoaded(List<ParseObject> objects, Exception e);
}
private static ParseQueryAdapter.QueryFactory<ParseObject> queryFactory;
private static List<OnQueryLoadListener<ParseObject>> onQueryLoadListeners;
private static List<List<ParseObject>> objectPages;
private static ArrayList<ParseObject> items;
private static int currentPage;
private static RequestManager requestManager;
public MyTimelineAdapter(Context context, RequestManager requestManager) {
super(context);
this.requestManager = requestManager;
this.onQueryLoadListeners = new ArrayList<>();
this.currentPage = 0;
this.objectPages = new ArrayList<>();
this.items = new ArrayList<>();
this.queryFactory = new ParseQueryAdapter.QueryFactory<ParseObject>() {
#Override
public ParseQuery<ParseObject> create() {
ParseQuery<ParseObject> query = ParseQuery.getQuery("ImageClassName");
query.setCachePolicy(ParseQuery.CachePolicy.CACHE_THEN_NETWORK);
query.whereEqualTo("status", true);
query.orderByDescending("createdAt");
return query;
}
};
loadObjects(currentPage);
}
#Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View timelineView;
timelineView = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item_timeline_item2, parent, false);
TimelineItemViewHolder timelineItemViewHolder = new TimelineItemViewHolder(timelineView);
return timelineItemViewHolder;
}
#Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
final ParseObject timelineOb = getItem(position);
FunctionPost functionPost = new FunctionPost(context);
functionPost.TimelineArtistPostAdapterBuilder( timelineOb, holder, requestManager);
//기능 추가
}
#Override
public int getItemCount() {
return items.size();
}
#Override
public ParseObject getItem(int position) {
return items.get(position);
}
#Override
public void loadObjects(final int page) {
final ParseQuery<ParseObject> query = this.queryFactory.create();
if (this.objectsPerPage > 0 && this.paginationEnabled) {
this.setPageOnQuery(page, query);
}
this.notifyOnLoadingListeners();
if (page >= objectPages.size()) {
objectPages.add(page, new ArrayList<ParseObject>());
}
query.findInBackground(new FindCallback<ParseObject>() {
#Override
public void done(List<ParseObject> foundObjects, ParseException e) {
if ((e != null) && ((e.getCode() == ParseException.CONNECTION_FAILED) || (e.getCode() != ParseException.CACHE_MISS))) {
hasNextPage = true;
} else if (foundObjects != null) {
// Only advance the page, this prevents second call back from CACHE_THEN_NETWORK to
// reset the page.
if (page >= currentPage) {
currentPage = page;
// since we set limit == objectsPerPage + 1
hasNextPage = (foundObjects.size() > objectsPerPage);
}
if (paginationEnabled && foundObjects.size() > objectsPerPage) {
// Remove the last object, fetched in order to tell us whether there was a "next page"
foundObjects.remove(objectsPerPage);
}
List<ParseObject> currentPage = objectPages.get(page);
currentPage.clear();
currentPage.addAll(foundObjects);
syncObjectsWithPages(items, objectPages);
// executes on the UI thread
notifyDataSetChanged();
}
notifyOnLoadedListeners(foundObjects, e);
}
});
}
public void loadNextPage() {
if (items.size() == 0) {
loadObjects(0);
} else {
loadObjects(currentPage + 1);
}
}
public void syncObjectsWithPages(ArrayList<ParseObject> items, List<List<ParseObject>> objectPages) {
items.clear();
for (List<ParseObject> pageOfObjects : objectPages) {
items.addAll(pageOfObjects);
}
}
protected void setPageOnQuery(int page, ParseQuery<ParseObject> query) {
query.setLimit(this.objectsPerPage + 1);
query.setSkip(page * this.objectsPerPage);
}
public void addOnQueryLoadListener(OnQueryLoadListener<ParseObject> listener) {
this.onQueryLoadListeners.add(listener);
}
public void removeOnQueryLoadListener(OnQueryLoadListener<ParseObject> listener) {
this.onQueryLoadListeners.remove(listener);
}
public void notifyOnLoadingListeners() {
for (OnQueryLoadListener<ParseObject> listener : this.onQueryLoadListeners) {
listener.onLoading();
}
}
public void notifyOnLoadedListeners(List<ParseObject> objects, Exception e) {
for (OnQueryLoadListener<ParseObject> listener : this.onQueryLoadListeners) {
listener.onLoaded(objects, e);
}
}
}

I did find the problem
I add overide method in the adapter then It works find.
#Override
public int getItemViewType(int position) {
return position;
}
I am not sure why it happens now. any one help me to know the cause of problem?

I has a similar problem the other day see this post. onBindViewHolder needs to know how to display the row when it's called. I returned two different view types depending on the need in getItemViewType, inflated the view type conditionally in onCreateViewHolder, then I was able to set the data on the ViewHolder as needed.

Assert proper number of items in list with espresso

What is the best way to inspect and assert that a listview is the expected size with android espresso?
I wrote this matcher, but don't quite know how to integrate it into the test.
public static Matcher<View> withListSize (final int size) {
return new TypeSafeMatcher<View> () {
#Override public boolean matchesSafely (final View view) {
return ((ListView) view).getChildCount () == size;
}
#Override public void describeTo (final Description description) {
description.appendText ("ListView should have " + size + " items");
}
};
}

Figured this out.
class Matchers {
public static Matcher<View> withListSize (final int size) {
return new TypeSafeMatcher<View> () {
#Override public boolean matchesSafely (final View view) {
return ((ListView) view).getCount () == size;
}
#Override public void describeTo (final Description description) {
description.appendText ("ListView should have " + size + " items");
}
};
}
}
If expecting one item in the list, put this in the actual test script.
onView (withId (android.R.id.list)).check (ViewAssertions.matches (Matchers.withListSize (1)));

There are two different approaches of getting items count in a list with espresso:
First one is as #CoryRoy mentioned above - using TypeSafeMatcher, the other one is to use BoundedMatcher.
And because #CoryRoy already showed how to assert it, here I'd like to tell how to get(return) the number using different matchers.
public class CountHelper {
private static int count;
public static int getCountFromListUsingTypeSafeMatcher(#IdRes int listViewId) {
count = 0;
Matcher matcher = new TypeSafeMatcher<View>() {
#Override
protected boolean matchesSafely(View item) {
count = ((ListView) item).getCount();
return true;
}
#Override
public void describeTo(Description description) {
}
};
onView(withId(listViewId)).check(matches(matcher));
int result = count;
count = 0;
return result;
}
public static int getCountFromListUsingBoundedMatcher(#IdRes int listViewId) {
count = 0;
Matcher<Object> matcher = new BoundedMatcher<Object, String>(String.class) {
#Override
protected boolean matchesSafely(String item) {
count += 1;
return true;
}
#Override
public void describeTo(Description description) {
}
};
try {
// do a nonsense operation with no impact
// because ViewMatchers would only start matching when action is performed on DataInteraction
onData(matcher).inAdapterView(withId(listViewId)).perform(typeText(""));
} catch (Exception e) {
}
int result = count;
count = 0;
return result;
}
}
Also want to mention that you should use ListView#getCount() instead of ListView#getChildCount():
getCount() - number of data items owned by the Adapter, which may be larger than the number of visible views.
getChildCount() - number of children in the ViewGroup, which may be reused by the ViewGroup.

Adding a row to a growing database pre-release.

I have the database already finished and I would like to add a few rows that are present on the first time opening the app. The main issue, not knowing where in the application to implement this. For example, when the user opens the app for the first time, there is an example item. The item can be deleted. After the row is deleted it will never show up again. I am using Androrm (object relational mapper) androrm home page. My main question: How do I add a single row to the database (where & how) before release. Within the onCreate, will add a row each time, the class is opened.
Took out most code to make it simple.
Implementation
public class LogFirst extends Model {
protected CharField db_oneName;
public LogFirst() {
super(true);
db_oneName = new CharField(80);
}
public void setDB_oneName(String name1) {
db_oneName.set(name1);
}
public String getDB_oneName() {
return db_oneName.get();
}
#Override
public String toString() {
return db_oneName.get();
}
public static List<LogFirst> all() {
return LogFirst.objects().all().toList();
}
public static QuerySet<LogFirst> objects() {
return LogFirst.objects(context(), LogFirst.class);
}
public boolean save() {
Format formatter = new SimpleDateFormat("ddmmhhss");
String id = formatter.format(Calendar.getInstance().getTime()) + "";
return this.save(context(), Integer.valueOf(id));
}
public boolean delete() {
return this.delete(context());
}
private static Context context() {
return ExtendsActivity.context();
}
}
Saving
LogFirst lf = new LogFirst();
lf.setDB_oneName(name.getText().toString());
lf.save();
Adapter
public class LogFirstAdapter extends ArrayAdapter<LogFirst> {
Context mContext;
List<LogFirst> mLogs;
public LogFirstAdapter(Context context, int textViewResourceId, List<LogFirst> logs) {
super(context, textViewResourceId);
mContext = context;
mLogs = logs;
}
public void setLogs(List<LogFirst> logs) {
mLogs = logs;
}
public List<LogFirst> getLogs() {
return mLogs;
}
public void add(LogFirst log) {
mLogs.add(log);
}
public void remove(LogFirst log) {
mLogs.remove(log);
}
public int getCount() {
return mLogs.size();
}
public LogFirst getItem(int position) {
return mLogs.get(position);
}
public View getView(int position, View convertView, ViewGroup parent) {
LogFirstRow view = (LogFirstRow) convertView;
if (view == null) {
view = new LogFirstRow(mContext);
}
LogFirst log = getItem(position);
view.setLog(log);
return view;
}
}

Ideally you'd do something like that in a migration. I'm not familiar with Androrm but it looks like they have some support for migration: http://www.androrm.com/documentation/models/migrations/
Try putting in the code to create the new records in the overriden migrate function. The docs say migrations will be kept track of but I'm not sure how it will play out so test to see what happens.

Listview Empty View is always shown

I use a custom ParseQueryAdapter to load data in listview. I want to show a message when there is no data but the message is shown even when data are not empty. I think it is due to the fact that data are not yet loaded. I tried with setEmptyView and also with a test on the adapter if mAdapter.isEmpty().
I tried waiting a few seconds before testing if adapter is empty but although it works, I think it's not a good practice.
My custom adapter where I make the query:
public class CategoryEventsAdapter extends ParseQueryAdapter<Event> {
public CategoryEventsAdapter(Context context, final String c) {
super(context, new ParseQueryAdapter.QueryFactory<Event>() {
public ParseQuery<Event> create() {
ParseQuery<Event> query = new ParseQuery<Event>("Event");
query.whereEqualTo("published", true);
query.whereEqualTo("category", c);
return query;
}
});
}
#Override
public View getItemView(Event event, View v, ViewGroup parent) {
...
}
}
And I simply call it in a Fragment:
mAdapter = new CategoryEventsAdapter(getActivity(), category);
listview.setAdapter(mAdapter);
if (mAdapter.isEmpty()) {
// show message
}

I've never used this particular part of Parse but looking at the docs, the query seems to be async. Instead you can try this maybe:
mAdapter = new CategoryEventsAdapter(getActivity(), category);
// add a listener for when the query is done.
mAdapter.addOnQueryLoadListener(new OnQueryLoadListener<ParseObject>() {
public void onLoaded(List<ParseObject> objects, ParseException e) {
// Check if empty here and show message.
if (objects.size == 0){
// show message
}
}
});
listview.setAdapter(mAdapter);
So once the query is done, it should call onLoaded so then you can determine if it is empty or not. In onLoaded you can check the count of the objects parameter. Not sure if it's already set in the adapter if you do mAdapter.isEmpty at that point.

This is my ParseQueryAdapter implementation that lets you choose an "empty" placeholder. You just call adapter.setEmptyLayoutId(R.layout.empty) from outside.
public class ParseAdapter extends ParseQueryAdapter {
private final static int EMPTY_VIEW = 2;
private int emptyViewLayoutId;
private boolean isEmpty;
public ParseAdapter(Context c, QueryFactory<? extends ParseObject> q) {
super(c, q);
addOnQueryLoadListener(new OnQueryLoadListener() {
#Override
public void onLoading() {
isEmpty = false;
}
#Override
public void onLoaded(List list, Exception e) {
if (list == null || list.size() == 0) {
isEmpty = true;
}
}
});
}
#Override
public void notifyDataSetChanged() {
isEmpty = false;
super.notifyDataSetChanged();
}
public void setEmptyLayoutId(int emptyViewLayoutId) {
this.emptyViewLayoutId = emptyViewLayoutId;
}
#Override
public View getItemView(ParseObject object, View v, ViewGroup parent) {
if (isEmpty) {
v = View.inflate(getContext(), emptyViewLayoutId, null);
return v;
}
v = v != null ? v : View.inflate(getContext(), rowLayoutId, null);
//do whatever you want on v
return v;
}
#Override
public int getViewTypeCount() {
return super.getViewTypeCount() + 1; //3
}
#Override
public int getItemViewType(int position) {
return isEmpty ? EMPTY_VIEW : super.getItemViewType(position);
}
#Override
public int getCount() {
return isEmpty ? 1 : super.getCount();
}
}
You need to add an item view type because otherwise, if empty, getItemView() won't be called in some cases. Overriding getCount() to return 1 is not enough, because ParseQueryAdapter performs some checks over the view type inside getView(), and won't pass the call to getItemView().

how to create a circular list view or populate values in a circular view? [duplicate]

I want to create a customized ListView (or similar) which will behave like a closed (circular) one:
scrolling down - after the last item was reached the first begins (.., n-1, n, 1, 2, ..)
scrolling upward - after the first item was reached the last begins (.., 2, 1, n, n-1, ..)
It sounds simple conceptually but, apparently, there is no straightforward approach to do this.
Can anyone point me to the right solution ?
Thank you !
I have already received an answer (from Streets Of Boston on Android-Developers google groups), but it sounds somehow ugly :) -
I did this by creating my own
list-adapter (subclassed from
BaseAdapter).
I coded my own list-adapter in such a
way that its getCount() method returns
a HUUUUGE number.
And if item 'x' is selected, then this
item corresponds to adapter
position='adapter.getCount()/2+x'
And for my adapter's method
getItem(int position), i look in my
array that backs up the adapter and
fetch the item on index:
(position-getCount()/2) % myDataItems.length
You need to do some more 'special'
stuff to make it all work correctly,
but you get the idea.
In principle, it is still possible to
reach the end or the beginning of the
list, but if you set getCount() to
around a million or so, this is hard
to do :-)

My colleague Joe, and I believe we have found a simpler way to solve the same problem. In our solution though instead of extending BaseAdapter we extend ArrayAdapter.
The code is as follows :
public class CircularArrayAdapter< T > extends ArrayAdapter< T >
{
public static final int HALF_MAX_VALUE = Integer.MAX_VALUE/2;
public final int MIDDLE;
private T[] objects;
public CircularArrayAdapter(Context context, int textViewResourceId, T[] objects)
{
super(context, textViewResourceId, objects);
this.objects = objects;
MIDDLE = HALF_MAX_VALUE - HALF_MAX_VALUE % objects.length;
}
#Override
public int getCount()
{
return Integer.MAX_VALUE;
}
#Override
public T getItem(int position)
{
return objects[position % objects.length];
}
}
So this creates a class called CircularArrayAdapter which take an object type T (which may be anything) and uses it to create an array list. T is commonly a string though may be anything.
The constructor is the same as is for ArrayAdapter though initializes a constant called middle. This is the middle of the list. No matter what the length of the array MIDDLE can be used to center the ListView in the mid of the list.
getCount() is overrides to return a huge value as is done above creating a huge list.
getItem() is overrides to return the fake position on the array. Thus when filling the list the list is filled with objects in a looping manner.
At this point CircularArrayAdapter simply replaces ArrayAdapter in the file creating the ListView.
To centre the ListView the fallowing line must be inserted in your file creating the ListView after the ListView object has been initialised:
listViewObject.setSelectionFromTop(nameOfAdapterObject.MIDDLE, 0);
and using the MIDDLE constant previously initialized for the list the view is centered with the top item of the list at the top of the screen.
: ) ~ Cheers, I hope this solution is useful.

The solution you mention is the one I told other developers to use in the past. In getCount(), simply return Integer.MAX_VALUE, it will give you about 2 billion items, which should be enough.

I have, or I think I have done it right, based on the answers above.
Hope this will help you.
private static class RecipeListAdapter extends BaseAdapter {
private static LayoutInflater mInflater;
private Integer[] mCouponImages;
private static ImageView viewHolder;
public RecipeListAdapter(Context c, Integer[] coupomImages) {
RecipeListAdapter.mInflater = LayoutInflater.from(c);
this.mCouponImages = coupomImages;
}
#Override
public int getCount() {
return Integer.MAX_VALUE;
}
#Override
public Object getItem(int position) {
// you can do your own tricks here. to let it display the right item in your array.
return position % mCouponImages.length;
}
#Override
public long getItemId(int position) {
return position;
// return position % mCouponImages.length;
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = mInflater.inflate(R.layout.coupon_list_item, null);
viewHolder = (ImageView) convertView.findViewById(R.id.item_coupon);
convertView.setTag(viewHolder);
} else {
viewHolder = (ImageView) convertView.getTag();
}
viewHolder.setImageResource(this.mCouponImages[position % mCouponImages.length]);
return convertView;
}
}
And you would like to do this if you want to scroll down the list.
Commonly we can just scroll up and list then scroll down.
// see how many items we would like to sroll. in this case, Integer.MAX_VALUE
int listViewLength = adapter.getCount();
// see how many items a screen can dispaly, I use variable "span"
final int span = recipeListView.getLastVisiblePosition() - recipeListView.getFirstVisiblePosition();
// see how many pages we have
int howManySpans = listViewLength / span;
// see where do you want to be when start the listview. you dont have to do the "-3" stuff.
it is for my app to work right.
recipeListView.setSelection((span * (howManySpans / 2)) - 3);

I could see some good answers for this, One of my friend has tried to achieve this via a simple solution. Check the github project.

If using LoadersCallbacks I have created MyCircularCursor class which wraps the typical cursor like this:
#Override
public void onLoadFinished(Loader<Cursor> pCursorLoader, Cursor pCursor) {
mItemListAdapter.swapCursor(new MyCircularCursor(pCursor));
}
the decorator class code is here:
public class MyCircularCursor implements Cursor {
private Cursor mCursor;
public MyCircularCursor(Cursor pCursor) {
mCursor = pCursor;
}
#Override
public int getCount() {
return mCursor.getCount() == 0 ? 0 : Integer.MAX_VALUE;
}
#Override
public int getPosition() {
return mCursor.getPosition();
}
#Override
public boolean move(int pOffset) {
return mCursor.move(pOffset);
}
#Override
public boolean moveToPosition(int pPosition) {
int position = MathUtils.mod(pPosition, mCursor.getCount());
return mCursor.moveToPosition(position);
}
#Override
public boolean moveToFirst() {
return mCursor.moveToFirst();
}
#Override
public boolean moveToLast() {
return mCursor.moveToLast();
}
#Override
public boolean moveToNext() {
if (mCursor.isLast()) {
mCursor.moveToFirst();
return true;
} else {
return mCursor.moveToNext();
}
}
#Override
public boolean moveToPrevious() {
if (mCursor.isFirst()) {
mCursor.moveToLast();
return true;
} else {
return mCursor.moveToPrevious();
}
}
#Override
public boolean isFirst() {
return false;
}
#Override
public boolean isLast() {
return false;
}
#Override
public boolean isBeforeFirst() {
return false;
}
#Override
public boolean isAfterLast() {
return false;
}
#Override
public int getColumnIndex(String pColumnName) {
return mCursor.getColumnIndex(pColumnName);
}
#Override
public int getColumnIndexOrThrow(String pColumnName) throws IllegalArgumentException {
return mCursor.getColumnIndexOrThrow(pColumnName);
}
#Override
public String getColumnName(int pColumnIndex) {
return mCursor.getColumnName(pColumnIndex);
}
#Override
public String[] getColumnNames() {
return mCursor.getColumnNames();
}
#Override
public int getColumnCount() {
return mCursor.getColumnCount();
}
#Override
public byte[] getBlob(int pColumnIndex) {
return mCursor.getBlob(pColumnIndex);
}
#Override
public String getString(int pColumnIndex) {
return mCursor.getString(pColumnIndex);
}
#Override
public short getShort(int pColumnIndex) {
return mCursor.getShort(pColumnIndex);
}
#Override
public int getInt(int pColumnIndex) {
return mCursor.getInt(pColumnIndex);
}
#Override
public long getLong(int pColumnIndex) {
return mCursor.getLong(pColumnIndex);
}
#Override
public float getFloat(int pColumnIndex) {
return mCursor.getFloat(pColumnIndex);
}
#Override
public double getDouble(int pColumnIndex) {
return mCursor.getDouble(pColumnIndex);
}
#Override
public int getType(int pColumnIndex) {
return 0;
}
#Override
public boolean isNull(int pColumnIndex) {
return mCursor.isNull(pColumnIndex);
}
#Override
public void deactivate() {
mCursor.deactivate();
}
#Override
#Deprecated
public boolean requery() {
return mCursor.requery();
}
#Override
public void close() {
mCursor.close();
}
#Override
public boolean isClosed() {
return mCursor.isClosed();
}
#Override
public void registerContentObserver(ContentObserver pObserver) {
mCursor.registerContentObserver(pObserver);
}
#Override
public void unregisterContentObserver(ContentObserver pObserver) {
mCursor.unregisterContentObserver(pObserver);
}
#Override
public void registerDataSetObserver(DataSetObserver pObserver) {
mCursor.registerDataSetObserver(pObserver);
}
#Override
public void unregisterDataSetObserver(DataSetObserver pObserver) {
mCursor.unregisterDataSetObserver(pObserver);
}
#Override
public void setNotificationUri(ContentResolver pCr, Uri pUri) {
mCursor.setNotificationUri(pCr, pUri);
}
#Override
public boolean getWantsAllOnMoveCalls() {
return mCursor.getWantsAllOnMoveCalls();
}
#Override
public Bundle getExtras() {
return mCursor.getExtras();
}
#Override
public Bundle respond(Bundle pExtras) {
return mCursor.respond(pExtras);
}
#Override
public void copyStringToBuffer(int pColumnIndex, CharArrayBuffer pBuffer) {
mCursor.copyStringToBuffer(pColumnIndex, pBuffer);
}
}