I am having an issue updating the ListView in my Android application. I have searched for the solution and read multiple answers but none solved my issue:
android-listview-repeating-old-data-after-refresh
android-requestlayout-improperly-called
android-listview-not-refreshing-after-notifydatasetchanged
android-listview-getview-being-called-multiple-times-on-unobservable-views
Issue
I have a listview with 2 items displayed like this:
Item 1 (position 0)
Item 2 (position 1)
After reloading the data from the source I get the same 2 items, but in the listview it is displayed like this:
Item 2 (position 0)
Item 2 (position 1)
However, when I click on the position 0 in new list it shows correct data of Item 1 (click on position 1 it also shows correct data of Item 2).
The problem is that it displays Item 2 on position 0 and on position 1 (twice).
Here is the code where list is updated and adapter is setup:
public class FishTankFragment extends DeviceFragment {
...
private final List<FishTankStatus.Schedule> schedulesList = new ArrayList<>();
private ScheduleAdapter scheduleAdapter;
...
#Override
public View onCreateView(#NonNull LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
...
scheduleAdapter = new ScheduleAdapter(view.getContext(), schedulesList);
screenBinding.lvSchedules.setAdapter(scheduleAdapter);
screenBinding.lvSchedules.setOnItemClickListener((parent, view1, position, id) -> {
new ScheduleItemClickListener(this.getContext(), schedulesList.get(position), position);
});
...
}
#Override
public <T> void onResponse(T responseObject) {
...
schedulesList.clear();
schedulesList.addAll(data.getSchedules());
scheduleAdapter.notifyDataSetChanged();
...
}
Here is Adapter code:
public class ScheduleAdapter extends BaseAdapter {
private ScheduleItemBinding itemBinding;
private final List<FishTankStatus.Schedule> schedules;
private final Context context;
public ScheduleAdapter(#NonNull Context context, #NonNull List<FishTankStatus.Schedule> objects) {
this.context = context;
schedules = objects;
}
#Override
public int getCount() {
return schedules.size();
}
#Override
public FishTankStatus.Schedule getItem(int position) {
return schedules.get(position);
}
#Override
public long getItemId(int position) {
return 0;
}
#Override
public View getView(int position, View view, ViewGroup parent) {
if (view == null) {
itemBinding = ScheduleItemBinding.inflate(LayoutInflater.from(context));
view = itemBinding.getRoot();
}
if (!schedules.isEmpty()) {
String start = StringUtils.printTime(schedules.get(position).getStart());
String end = StringUtils.printTime(schedules.get(position).getEnd());
itemBinding.tvScheduleStart.setText(start);
itemBinding.tvScheduleEnd.setText(end);
FishTankStatus.Schedule schedule = schedules.get(position);
for (String device : schedule.getDevices()) {
switch (device) {
case "something":
itemBinding.ivYellowlightIcon.setVisibility(View.VISIBLE);
break;
case "something 1":
itemBinding.ivBluelightIcon.setVisibility(View.VISIBLE);
break;
case "something 2":
itemBinding.ivAirIcon.setVisibility(View.VISIBLE);
}
}
if (schedules.get(position).getActive()) {
ColorStateList white = ColorStateList.valueOf(
view.getResources().getColor(R.color.white, view.getContext().getTheme()));
itemBinding.lySchedule.setBackground(ResourcesCompat.getDrawable(view.getResources(),
R.drawable.rectangle_p_light_8,
view.getContext().getTheme()));
...
}
}
return view;
}
}
ListView has width and height set to match_parent in parent ConstraintLayout where width=0dp (has parent) and height=match_parent
See the video:
screen recording
Thank you for all the help.
I debugged the app. After clearing schedulesList.clear() it contained 0 items in Fragment and also in BaseAdapter. After addAll items from the source it contained correct items in schedulesList both in Fragment and BaseAdapter.
I tried to fill the data in Adapter as separate List object using clear and addAll.
I will answer my own question for the future visitors...
Just use RecyclerView
It solved all my issues. But I still do not know why the above problem happened.
I want my recycler view rows to be highlighted after a specific interval of time, say after 2 seconds.
Searched all over the internet but no luck so far.
How about, in the recycler adapter OnBindViewHolder method, put a [Handler.postDelayed](https://developer.android.com/reference/android/os/Handler.html#postDelayed(java.lang.Runnable, long)) in which you set the specific time where you want the item to change.
Inside the runner that you pass in the handler, you put in a boolean flag to check if the row will have a different colour/behaviour + a notifyDataSetChanged() in the adapter. (You will have to change your data object to accomodate this new variable)
The question is not very clear. I had two questions in mind that I mentioned in the comment of the question.
Do you want to highlight some specific rows?
Do you want to toggle the highlight after each two seconds?
So I'm going for a general solution for both.
Let us assume the object you're populating in your each row is like the following.
public class ListItem {
int value;
boolean highlight = false;
}
The list of ListItem object can be inserted in an ArrayList to be populated in the RecyclerView. Here is your adapter which may look like this.
// Declare the yourListItems globally in your Activity
List<ListItem> yourListItems = new ArrayList<ListItem>();
populateYourListItems();
public class YourAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
public class YourViewHolder extends RecyclerView.ViewHolder {
private final TextView valueTextView;
private final LinearLayout background;
public YourViewHolder(final View itemView) {
super(itemView);
valueTextView = (TextView) itemView.findViewById(R.id.value_text_view);
background = (LinearLayout) itemView.findViewById(R.id.background);
}
public void bindView(int pos) {
int value = yourListItems.get(pos).value;
boolean isHighlighted = yourListItems.get(pos).hightlight;
valueTextView.setText(value);
// Set the background colour if the highlight value is found true.
if(isHighlighted) background.setBackgroundColor(Color.GREEN);
else background.setBackgroundColor(Color.WHITE);
}
}
#Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item_activity_log, parent, false);
return new YourViewHolder(v);
}
#Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
try {
if (holder instanceof YourViewHolder) {
YourViewHolder vh = (YourViewHolder) holder;
vh.bindView(position);
}
} catch (Exception e) {
e.printStackTrace();
}
}
#Override
public int getItemCount() {
if (yourListItems == null || yourListItems.isEmpty())
return 0;
else
return yourListItems.size();
}
#Override
public int getItemViewType(int position) {
return 1;
}
}
Now when you want to highlight some specific items of your RecyclerView you need to just set the highlight value to true and then call notifyDataSetChanged() to bring into the change in effect.
So you might need a timer like the following which will highlight your rows as per your demand in every two seconds.
// Declare the timer
private Timer highlightTimer;
private TimerTask highlightTimerTask;
highlightTimer = new Timer();
highlightTimerTask = new TimerTask() {
public void run() {
highLightTheListItems();
}
};
highlightTimer.schedule(highlightTimerTask, 2000);
Now implement your highLightTheListItems function as per your need.
public void highLightTheListItems() {
// Modify your list items.
// Call notifyDataSetChanged in your adapter
yourAdapter.notifyDataSetChanged();
}
Hope that helps. Thanks.
Do you mean highlight as in colour the row's background? If so, you could do this in your listViewAdapter
#Override
public View getView(final int position, View row, ViewGroup parent){
if (row==null){
row = LayoutInflater.from(getContext()).inflate(mResource, parent, false);
}
if(foo){
row.setBackgroundColor(getResources().getColor(R.color.translucent_green));
}
else row.setBackgroundColor(Color.TRANSPARENT);
return row;
}
Then in colours.xml
<color name="translucent_green">#667cfc00</color>
The first 2 numbers(66) is the alpha value, ie opacity. The next 6 are RBG in hexadecimal.
I have an array of 30 items which i need to display in a listview. However, per my layout I'll be displaying 2 items side by side in one row of listview.
Since there are now going to be only 15 rows to display (30/2), how do i modify the position attribute of Adapter such that i see only 15 rows.
I tried doing position++, in getView and also modify getCount() to return 15, but that does not work either.
Rather than do it this way, a better method may be to simply count two items as one row. The getView() method returns a View that is a representation of each item returned by getItem(). In your case, each item contains two elements. So just put the logic in that would retrieve two elements at a time. May be easier to encapsulate them in a class like for example:
ArrayList<Row> mItems = new ArrayList<Row>();
private class Row {
Object obj1;
Object obj2;
}
public void addItem(Object obj) {
Row useRow;
if(mItems.isEmpty()) {
useRow = new Row();
} else {
useRow = mItems.get(mItems.size() - 1);
if(useRow.obj2 != null) {
useRow = new Row();
}
}
if(useRow.obj1 == null) {
useRow.obj1 = obj;
} else {
useRow.obj2 = obj;
}
mItems.add(useRow);
}
In this case, your BaseAdapter is backed by a List of Row objects. Each Row object contains two of your elements. Every time you add an element, you add it to the first, then to the second, else you create a new Row object and add it.
EDIT:
In order to have clickability, you'll have to implement an OnClickListener to each item's View. Something like this may work:
public interface ItemClickListener {
public void onItemClick(Object obj);
}
private ItemClickListener mClickListener;
public void setItemClickListener(ItemClickListener listener) {
mClickListener = listener;
}
#Override
public boolean areAllItemsEnabled() {
return false;
}
#Override
public boolean isEnabled() {
return false;
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewGroup root;
if(convertView == null) {
root = buildRootView();
View item1View = buildFirstView();
View item2View = buildSecondView();
...
item1View.setOnClickListener(mItemListener);
item2View.setOnClickListener(mItemListener);
...
// Put both Views in your top level root view if they are not there already
}
Row row = getItem(position);
item1View.setTag(row.obj1);
item2View.setTag(row.obj2);
}
private View.OnClickListener mItemListener = new View.OnClickListener {
#Override
public void onClick(View v) {
Object obj = (Object) v.getTag();
if(mClickListener != null) {
mClickListener.onItemClick(obj);
}
}
}
So basically, you disable the clicking by overriding "areAllItemsEnabled()" and "isEnabled()" to return "false". Then, the click listener in the adapter will activate each time the user clicks on a row. Since you put the Object of the row in the View's tag, you can retrieve it on click. It will be swapped to a new Object even when the ListView recycles because it calls getView() each time. Then create an object that inherits from the click interface to retrieve the object and do whatever you need.
I have a custom adapter for a GridView, and I implemented my own selection handling since the custom views absorb the grid's click events. Everything worked fine, but now I want to add functionality for selecting items by code. I wrote a function for this and called it from the activity, but then when the user selects another item, the background for the code selected item (which indicates selection) does not get updated! I tried calling postInvalidate, but that didn't have any effect. Here's the adapter's code:
class PaintActionsAdapter extends BaseAdapter
{
private Context context;
private View[] listItemsViews;
private OnListItemClickListener itemClickListener;
private int[] actionsImagesResources;
private int lastSelectedPosition=-1;
private int pendingSelectedPosition=-1;
private class ActionButtonClickListener implements View.OnClickListener
{
private int position;
public ActionButtonClickListener(int position)
{ this.position=position; }
public void onClick(View view)
{
changeSelectedListItem(position);
if (itemClickListener!=null)
itemClickListener.onListItemClick(view,position);
}
}
public PaintActionsAdapter(Context context,OnListItemClickListener
itemClickListener)
{
if (context==null)
throw new IllegalArgumentException("The context must be non-null!");
this.context=context;
this.itemClickListener=itemClickListener;
TypedArray imagesResourcesNames=context.getResources().obtainTypedArray(
R.array.actions_images);
actionsImagesResources=new int[imagesResourcesNames.length()];
for (int counter=0;counter<actionsImagesResources.length;counter++)
{
actionsImagesResources[counter]=imagesResourcesNames.getResourceId(
counter,-1);
}
imagesResourcesNames.recycle();
listItemsViews=new View[actionsImagesResources.length];
}
public int getCount() { return actionsImagesResources.length; }
public long getItemId(int position)
{ return actionsImagesResources[position]; }
public Object getItem(int position)
{ return actionsImagesResources[position]; }
public View getView(int position,View convertView,ViewGroup parent)
{
ImageView actionImageView;
if (convertView==null)
{
actionImageView=new ImageView(context);
/*actionToggleButton=new ToggleButton(context);
actionToggleButton.setTextOn(null);
actionToggleButton.setTextOff(null);
actionToggleButton.setText(null);*/
AbsListView.LayoutParams layoutParams=new AbsListView.LayoutParams(
ViewGroup.LayoutParams.WRAP_CONTENT,ViewGroup.LayoutParams.
WRAP_CONTENT);
actionImageView.setLayoutParams(layoutParams);
}
else actionImageView=(ImageView)convertView;
actionImageView.setImageResource(actionsImagesResources[position]);
actionImageView.setOnClickListener(new ActionButtonClickListener(position));
listItemsViews[position]=actionImageView;
if (pendingSelectedPosition==position)
{
changeSelectedListItem(position);
pendingSelectedPosition=-1;
}
return actionImageView;
}
public void setSelectedListItem(int position)
{
if ((position<0)||(position>actionsImagesResources.length))
throw new IndexOutOfBoundsException("The position of the list " +
"item to select must be between 0 and " + actionsImagesResources.
length + "! The value supplied was " + position);
if (listItemsViews[position]==null) pendingSelectedPosition=position;
else changeSelectedListItem(position);
}
private void changeSelectedListItem(int position)
{
listItemsViews[position].setBackgroundResource(R.drawable.
actions_list_selector);
if (lastSelectedPosition>-1)
{
listItemsViews[lastSelectedPosition].setBackgroundResource(0);
listItemsViews[lastSelectedPosition].postInvalidate();
}
lastSelectedPosition=position;
}
}
The function setSelectedListItem lets the activity change the selection, and calls changeSelectedListItem, which uses setBackgroundResource(0) to remove the selection indication from the last selected item. This works perfectly when the user selects the item by clicking it, but not if the selection of the last item was done through setSelectedListItem.
I hope I explained the issue clearly, and any help will be appreciated.
I have a long ListView that the user can scroll around before returning to the previous screen. When the user opens this ListView again, I want the list to be scrolled to the same point that it was previously. Any ideas on how to achieve this?
Try this:
// save index and top position
int index = mList.getFirstVisiblePosition();
View v = mList.getChildAt(0);
int top = (v == null) ? 0 : (v.getTop() - mList.getPaddingTop());
// ...
// restore index and position
mList.setSelectionFromTop(index, top);
Explanation:
ListView.getFirstVisiblePosition() returns the top visible list item. But this item may be partially scrolled out of view, and if you want to restore the exact scroll position of the list you need to get this offset. So ListView.getChildAt(0) returns the View for the top list item, and then View.getTop() - mList.getPaddingTop() returns its relative offset from the top of the ListView. Then, to restore the ListView's scroll position, we call ListView.setSelectionFromTop() with the index of the item we want and an offset to position its top edge from the top of the ListView.
Parcelable state;
#Override
public void onPause() {
// Save ListView state # onPause
Log.d(TAG, "saving listview state");
state = listView.onSaveInstanceState();
super.onPause();
}
...
#Override
public void onViewCreated(final View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
// Set new items
listView.setAdapter(adapter);
...
// Restore previous state (including selected item index and scroll position)
if(state != null) {
Log.d(TAG, "trying to restore listview state");
listView.onRestoreInstanceState(state);
}
}
I adopted the solution suggested by #(Kirk Woll), and it works for me. I have also seen in the Android source code for the "Contacts" app, that they use a similar technique. I would like to add some more details:
On top on my ListActivity-derived class:
private static final String LIST_STATE = "listState";
private Parcelable mListState = null;
Then, some method overrides:
#Override
protected void onRestoreInstanceState(Bundle state) {
super.onRestoreInstanceState(state);
mListState = state.getParcelable(LIST_STATE);
}
#Override
protected void onResume() {
super.onResume();
loadData();
if (mListState != null)
getListView().onRestoreInstanceState(mListState);
mListState = null;
}
#Override
protected void onSaveInstanceState(Bundle state) {
super.onSaveInstanceState(state);
mListState = getListView().onSaveInstanceState();
state.putParcelable(LIST_STATE, mListState);
}
Of course "loadData" is my function to retrieve data from the DB and put it onto the list.
On my Froyo device, this works both when you change the phone orientation, and when you edit an item and go back to the list.
A very simple way:
/** Save the position **/
int currentPosition = listView.getFirstVisiblePosition();
//Here u should save the currentPosition anywhere
/** Restore the previus saved position **/
listView.setSelection(savedPosition);
The method setSelection will reset the list to the supplied item. If not in touch mode the item will actually be selected if in touch mode the item will only be positioned on screen.
A more complicated approach:
listView.setOnScrollListener(this);
//Implements the interface:
#Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
mCurrentX = view.getScrollX();
mCurrentY = view.getScrollY();
}
#Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
}
//Save anywere the x and the y
/** Restore: **/
listView.scrollTo(savedX, savedY);
I found something interesting about this.
I tried setSelection and scrolltoXY but it did not work at all, the list remained in the same position, after some trial and error I got the following code that does work
final ListView list = (ListView) findViewById(R.id.list);
list.post(new Runnable() {
#Override
public void run() {
list.setSelection(0);
}
});
If instead of posting the Runnable you try runOnUiThread it does not work either (at least on some devices)
This is a very strange workaround for something that should be straight forward.
CAUTION!! There is a bug in AbsListView that doesn't allow the onSaveState() to work correctly if the ListView.getFirstVisiblePosition() is 0.
So If you have large images that take up most of the screen, and you scroll to the second image, but a little of the first is showing, the scroll position Won't be saved...
from AbsListView.java:1650 (comments mine)
// this will be false when the firstPosition IS 0
if (haveChildren && mFirstPosition > 0) {
...
} else {
ss.viewTop = 0;
ss.firstId = INVALID_POSITION;
ss.position = 0;
}
But in this situation, the 'top' in the code below will be a negative number which causes other issues that prevent the state to be restored correctly. So when the 'top' is negative, get the next child
// save index and top position
int index = getFirstVisiblePosition();
View v = getChildAt(0);
int top = (v == null) ? 0 : v.getTop();
if (top < 0 && getChildAt(1) != null) {
index++;
v = getChildAt(1);
top = v.getTop();
}
// parcel the index and top
// when restoring, unparcel index and top
listView.setSelectionFromTop(index, top);
For some looking for a solution to this problem, the root of the issue may be where you are setting your list views adapter. After you set the adapter on the listview, it resets the scroll position. Just something to consider. I moved setting the adapter into my onCreateView after we grab the reference to the listview, and it solved the problem for me. =)
private Parcelable state;
#Override
public void onPause() {
state = mAlbumListView.onSaveInstanceState();
super.onPause();
}
#Override
public void onResume() {
super.onResume();
if (getAdapter() != null) {
mAlbumListView.setAdapter(getAdapter());
if (state != null){
mAlbumListView.requestFocus();
mAlbumListView.onRestoreInstanceState(state);
}
}
}
That's enough
Am posting this because I am surprised nobody had mentioned this.
After user clicks the back button he will return to the listview in the same state as he went out of it.
This code will override the "up" button to behave the same way as the back button so in the case of Listview -> Details -> Back to Listview (and no other options) this is the simplest code to maintain the scrollposition and the content in the listview.
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
onBackPressed();
return(true);
}
return(super.onOptionsItemSelected(item)); }
Caution: If you can go to another activity from the details activity the up button will return you back to that activity so you will have to manipulate the backbutton history in order for this to work.
Isn't simply android:saveEnabled="true" in the ListView xml declaration enough?
BEST SOLUTION IS:
// save index and top position
int index = mList.getFirstVisiblePosition();
View v = mList.getChildAt(0);
int top = (v == null) ? 0 : (v.getTop() - mList.getPaddingTop());
// ...
// restore index and position
mList.post(new Runnable() {
#Override
public void run() {
mList.setSelectionFromTop(index, top);
}
});
YOU MUST CALL IN POST AND IN THREAD!
You can maintain the scroll state after a reload if you save the state before you reload and restore it after. In my case I made a asynchronous network request and reloaded the list in a callback after it completed. This is where I restore state. Code sample is Kotlin.
val state = myList.layoutManager.onSaveInstanceState()
getNewThings() { newThings: List<Thing> ->
myList.adapter.things = newThings
myList.layoutManager.onRestoreInstanceState(state)
}
If you're using fragments hosted on an activity you can do something like this:
public abstract class BaseFragment extends Fragment {
private boolean mSaveView = false;
private SoftReference<View> mViewReference;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
if (mSaveView) {
if (mViewReference != null) {
final View savedView = mViewReference.get();
if (savedView != null) {
if (savedView.getParent() != null) {
((ViewGroup) savedView.getParent()).removeView(savedView);
return savedView;
}
}
}
}
final View view = inflater.inflate(getFragmentResource(), container, false);
mViewReference = new SoftReference<View>(view);
return view;
}
protected void setSaveView(boolean value) {
mSaveView = value;
}
}
public class MyFragment extends BaseFragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
setSaveView(true);
final View view = super.onCreateView(inflater, container, savedInstanceState);
ListView placesList = (ListView) view.findViewById(R.id.places_list);
if (placesList.getAdapter() == null) {
placesList.setAdapter(createAdapter());
}
}
}
If you are saving/restoring scroll position of ListView yourself you are essentially duplicating the functionality already implemented in android framework. The ListView restores fine scroll position just well on its own except one caveat: as #aaronvargas mentioned there is a bug in AbsListView that won't let to restore fine scroll position for the first list item. Nevertheless the best way to restore scroll position is not to restore it. Android framework will do it better for you. Just make sure you have met the following conditions:
make sure you have not called setSaveEnabled(false) method and not set android:saveEnabled="false" attribute for the list in the xml layout file
for ExpandableListView override long getCombinedChildId(long groupId, long childId) method so that it returns positive long number (default implementation in class BaseExpandableListAdapter returns negative number). Here are examples:
.
#Override
public long getChildId(int groupPosition, int childPosition) {
return 0L | groupPosition << 12 | childPosition;
}
#Override
public long getCombinedChildId(long groupId, long childId) {
return groupId << 32 | childId << 1 | 1;
}
#Override
public long getGroupId(int groupPosition) {
return groupPosition;
}
#Override
public long getCombinedGroupId(long groupId) {
return (groupId & 0x7FFFFFFF) << 32;
}
if ListView or ExpandableListView is used in a fragment do not recreate the fragment on activity recreation (after screen rotation for example). Obtain the fragment with findFragmentByTag(String tag) method.
make sure the ListView has an android:id and it is unique.
To avoid aforementioned caveat with first list item you can craft your adapter the way it returns special dummy zero pixels height view for the ListView at position 0.
Here is the simple example project shows ListView and ExpandableListView restore their fine scroll positions whereas their scroll positions are not explicitly saved/restored. Fine scroll position is restored perfectly even for the complex scenarios with temporary switching to some other application, double screen rotation and switching back to the test application. Please note, if you are explicitly exiting the application (by pressing the Back button) the scroll position won't be saved (as well as all other Views won't save their state).
https://github.com/voromto/RestoreScrollPosition/releases
For an activity derived from ListActivity that implements LoaderManager.LoaderCallbacks using a SimpleCursorAdapter it did not work to restore the position in onReset(), because the activity was almost always restarted and the adapter was reloaded when the details view was closed. The trick was to restore the position in onLoadFinished():
in onListItemClick():
// save the selected item position when an item was clicked
// to open the details
index = getListView().getFirstVisiblePosition();
View v = getListView().getChildAt(0);
top = (v == null) ? 0 : (v.getTop() - getListView().getPaddingTop());
in onLoadFinished():
// restore the selected item which was saved on item click
// when details are closed and list is shown again
getListView().setSelectionFromTop(index, top);
in onBackPressed():
// Show the top item at next start of the app
index = 0;
top = 0;
Neither of the solutions offered here seemed to work for me. In my case, I have a ListView in a Fragment which I'm replacing in a FragmentTransaction, so a new Fragment instance is created each time the fragment is shown, which means that the ListView state can not be stored as a member of the Fragment.
Instead, I ended up storing the state in my custom Application class. The code below should give you an idea how this works:
public class MyApplication extends Application {
public static HashMap<String, Parcelable> parcelableCache = new HashMap<>();
/* ... code omitted for brevity ... */
}
public class MyFragment extends Fragment{
private ListView mListView = null;
private MyAdapter mAdapter = null;
#Override
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
mAdapter = new MyAdapter(getActivity(), null, 0);
mListView = ((ListView) view.findViewById(R.id.myListView));
Parcelable listViewState = MyApplication.parcelableCache.get("my_listview_state");
if( listViewState != null )
mListView.onRestoreInstanceState(listViewState);
}
#Override
public void onPause() {
MyApplication.parcelableCache.put("my_listview_state", mListView.onSaveInstanceState());
super.onPause();
}
/* ... code omitted for brevity ... */
}
The basic idea is that you store the state outside the fragment instance. If you don't like the idea of having a static field in your application class, I guess you could do it by implementing a fragment interface and storing the state in your activity.
Another solution would be to store it in SharedPreferences, but it gets a bit more complicated, and you would need to make sure you clear it on application launch unless you want the state to be persisted across app launches.
Also, to avoid the "scroll position not saved when first item is visible", you can display a dummy first item with 0px height. This can be achieved by overriding getView() in your adapter, like this:
#Override
public View getView(int position, View convertView, ViewGroup parent) {
if( position == 0 ) {
View zeroHeightView = new View(parent.getContext());
zeroHeightView.setLayoutParams(new ViewGroup.LayoutParams(0, 0));
return zeroHeightView;
}
else
return super.getView(position, convertView, parent);
}
My answer is for Firebase and position 0 is a workaround
Parcelable state;
DatabaseReference everybody = db.getReference("Everybody Room List");
everybody.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
state = listView.onSaveInstanceState(); // Save
progressBar.setVisibility(View.GONE);
arrayList.clear();
for (DataSnapshot messageSnapshot : dataSnapshot.getChildren()) {
Messages messagesSpacecraft = messageSnapshot.getValue(Messages.class);
arrayList.add(messagesSpacecraft);
}
listView.setAdapter(convertView);
listView.onRestoreInstanceState(state); // Restore
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
and convertView
position 0 a add a blank item that you are not using
public class Chat_ConvertView_List_Room extends BaseAdapter {
private ArrayList<Messages> spacecrafts;
private Context context;
#SuppressLint("CommitPrefEdits")
Chat_ConvertView_List_Room(Context context, ArrayList<Messages> spacecrafts) {
this.context = context;
this.spacecrafts = spacecrafts;
}
#Override
public int getCount() {
return spacecrafts.size();
}
#Override
public Object getItem(int position) {
return spacecrafts.get(position);
}
#Override
public long getItemId(int position) {
return position;
}
#SuppressLint({"SetTextI18n", "SimpleDateFormat"})
#Override
public View getView(final int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = LayoutInflater.from(context).inflate(R.layout.message_model_list_room, parent, false);
}
final Messages s = (Messages) this.getItem(position);
if (position == 0) {
convertView.getLayoutParams().height = 1; // 0 does not work
} else {
convertView.getLayoutParams().height = RelativeLayout.LayoutParams.WRAP_CONTENT;
}
return convertView;
}
}
I have seen this work temporarily without disturbing the user, I hope it works for you
use this below code :
int index,top;
#Override
protected void onPause() {
super.onPause();
index = mList.getFirstVisiblePosition();
View v = challengeList.getChildAt(0);
top = (v == null) ? 0 : (v.getTop() - mList.getPaddingTop());
}
and whenever your refresh your data use this below code :
adapter.notifyDataSetChanged();
mList.setSelectionFromTop(index, top);
I'm using FirebaseListAdapter and couldn't get any of the solutions to work. I ended up doing this. I'm guessing there are more elegant ways but this is a complete and working solution.
Before onCreate:
private int reset;
private int top;
private int index;
Inside of the FirebaseListAdapter:
#Override
public void onDataChanged() {
super.onDataChanged();
// Only do this on first change, when starting
// activity or coming back to it.
if(reset == 0) {
mListView.setSelectionFromTop(index, top);
reset++;
}
}
onStart:
#Override
protected void onStart() {
super.onStart();
if(adapter != null) {
adapter.startListening();
index = 0;
top = 0;
// Get position from SharedPrefs
SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);
top = sharedPref.getInt("TOP_POSITION", 0);
index = sharedPref.getInt("INDEX_POSITION", 0);
// Set reset to 0 to allow change to last position
reset = 0;
}
}
onStop:
#Override
protected void onStop() {
super.onStop();
if(adapter != null) {
adapter.stopListening();
// Set position
index = mListView.getFirstVisiblePosition();
View v = mListView.getChildAt(0);
top = (v == null) ? 0 : (v.getTop() - mListView.getPaddingTop());
// Save position to SharedPrefs
SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);
sharedPref.edit().putInt("TOP_POSITION" + "", top).apply();
sharedPref.edit().putInt("INDEX_POSITION" + "", index).apply();
}
}
Since I also had to solve this for FirebaseRecyclerAdapter I'm posting the solution here for that too:
Before onCreate:
private int reset;
private int top;
private int index;
Inside of the FirebaseRecyclerAdapter:
#Override
public void onDataChanged() {
// Only do this on first change, when starting
// activity or coming back to it.
if(reset == 0) {
linearLayoutManager.scrollToPositionWithOffset(index, top);
reset++;
}
}
onStart:
#Override
protected void onStart() {
super.onStart();
if(adapter != null) {
adapter.startListening();
index = 0;
top = 0;
// Get position from SharedPrefs
SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);
top = sharedPref.getInt("TOP_POSITION", 0);
index = sharedPref.getInt("INDEX_POSITION", 0);
// Set reset to 0 to allow change to last position
reset = 0;
}
}
onStop:
#Override
protected void onStop() {
super.onStop();
if(adapter != null) {
adapter.stopListening();
// Set position
index = linearLayoutManager.findFirstVisibleItemPosition();
View v = linearLayoutManager.getChildAt(0);
top = (v == null) ? 0 : (v.getTop() - linearLayoutManager.getPaddingTop());
// Save position to SharedPrefs
SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);
sharedPref.edit().putInt("TOP_POSITION" + "", top).apply();
sharedPref.edit().putInt("INDEX_POSITION" + "", index).apply();
}
}
To clarify the excellent answer of Ryan Newsom and to adjust it for fragments and for the usual case that we want to navigate from a "master" ListView fragment to a "details" fragment and then back to the "master"
private View root;
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
if(root == null){
root = inflater.inflate(R.layout.myfragmentid,container,false);
InitializeView();
}
return root;
}
public void InitializeView()
{
ListView listView = (ListView)root.findViewById(R.id.listviewid);
BaseAdapter adapter = CreateAdapter();//Create your adapter here
listView.setAdpater(adapter);
//other initialization code
}
The "magic" here is that when we navigate back from the details fragment to the ListView fragment, the view is not recreated, we don't set the ListView's adapter, so everything stays as we left it!