How can I update a single row in a ListView

Question

I have a ListView which displays news items  They contain an image  a title and some text  The image is loaded in a separate thread  with a queue and all  and when the image is downloaded  I now call notifyDataSetChanged   on the list adapter to update the image  This works  but getView   is getting called too frequently  since notifyDataSetChanged   calls getView   for all visible items  I want to update just the single item in the list  How would I do this   Problems I have with my current approach are    Scrolling is slow I have a fade-in animation on the image which happens every time a single new image in the list is loaded

User · Answer

I used the code that provided Erik  works great  but i have a complex custom adapter for my listview and i was confronted with twice implementation of the code that updates the UI  I ve tried to get the new view from my adapters getView method the arraylist that holds the listview data has allready been updated changed    View cell   lvOptim getChildAt index - lvOptim getFirstVisiblePosition     if cell  null       cell   adapter getView index  cell  lvOptim     public View getView final int position  View convertView  ViewGroup parent      cell startAnimation animationLeftIn         It s working well  but i dont know if this is a good practice  So i don t need to implement the code that updates the list item two times

User · Answer

get the model class first as global like this  model class object   SampleModel golbalmodel new SchedulerModel      and initialise it to global   get the current row of the view by the model by initialising the it to global model  SampleModel data    SchedulerModel  sampleList get position                   golbalmodel data    set the changed value to global model object method to be set  and add the notifyDataSetChanged its works for me  golbalmodel setStartandenddate changedate    notifyDataSetChanged      Here is a related question on this with good answers

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My solution  If it is correct   update the data and viewable items without re-drawing the whole list  Else notifyDataSetChanged   Correct - oldData size    new data size  and old data IDs and their order    new data IDs and order  How          A View can only be used  visible  once  This class creates a map from int  position  to view  where the mapping    is one-to-one and on              private static class UniqueValueSparseArray extends SparseArray lt View gt        private final HashMap lt View Integer gt  m valueToKey   new HashMap lt View Integer gt           Override     public void put int key  View value            final Integer previousKey   m valueToKey put value key           if null    previousKey                remove previousKey    re-mapping                   super put key  value             Override public void setData final List lt   extends DBObject gt  data           TODO Implement  smarter  logic  for replacing just part of the data      if  data    m data  return      List lt   extends DBObject gt  oldData   m data      m data   null    data   Collections EMPTY LIST   data      if   updateExistingViews oldData  data   notifyDataSetChanged        else if  DEBUG  Log d TAG   Updated without notifyDataSetChanged               See if we can update the data within existing layout  without re-drawing the list      param oldData     param newData     return     private boolean updateExistingViews List lt   extends DBObject gt  oldData  List lt   extends DBObject gt  newData                   Iterate over new data  compare to old  If IDs out of sync  stop and return false  Else - update visible        items              final int oldDataSize   oldData size        if  oldDataSize    newData size    return false      DBObject newObj       int nVisibleViews   m visibleViews size        if nVisibleViews    0  return false       for  int position   0  nVisibleViews  gt  0  amp  amp  position  lt  oldDataSize  position              newObj   newData get position           if  oldData get position  getId      newObj getId    return false             iterate over visible objects and see if this ID is there          final View view   m visibleViews get position           if  null    view                   this position has a visible view  let s update it              bindView position  view  false               nVisibleViews--                       return true      and of course    Override public View getView final int position  final View convertView  final ViewGroup parent        final View result   createViewFromResource position  convertView  parent       m visibleViews put position  result        return result      Ignore the last param to bindView  I use it to determine whether or not I need to recycle bitmaps for ImageDrawable    As mentioned above  the total number of  visible  views is roughly the amount that fits on the screen  ignoring orientation changes etc   so no biggie memory-wise

User · Answer

I made up another solution  like RecyclyerView method void notifyItemChanged int position   create CustomBaseAdapter class just like this    public abstract class CustomBaseAdapter implements ListAdapter  SpinnerAdapter       private final CustomDataSetObservable mDataSetObservable   new CustomDataSetObservable         public boolean hasStableIds             return false             public void registerDataSetObserver DataSetObserver observer            mDataSetObservable registerObserver observer              public void unregisterDataSetObserver DataSetObserver observer            mDataSetObservable unregisterObserver observer              public void notifyDataSetChanged             mDataSetObservable notifyChanged               public void notifyItemChanged int position            mDataSetObservable notifyItemChanged position              public void notifyDataSetInvalidated             mDataSetObservable notifyInvalidated               public boolean areAllItemsEnabled             return true             public boolean isEnabled int position            return true             public View getDropDownView int position  View convertView  ViewGroup parent            return getView position  convertView  parent              public int getItemViewType int position            return 0             public int getViewTypeCount             return 1             public boolean isEmpty             return getCount      0                     Don t forget to create a CustomDataSetObservable class too for mDataSetObservable variable in CustomAdapterClass  like this    public class CustomDataSetObservable extends Observable lt DataSetObserver gt         public void notifyChanged             synchronized mObservers                   since onChanged   is implemented by the app  it could do anything  including                removing itself from   link mObservers  - and that could cause problems if                an iterator is used on the ArrayList   link mObservers                  to avoid such problems  just march thru the list in the reverse order              for  int i   mObservers size   - 1  i  gt   0  i--                    mObservers get i  onChanged                                       public void notifyInvalidated             synchronized  mObservers                for  int i   mObservers size   - 1  i  gt   0  i--                    mObservers get i  onInvalidated                                       public void notifyItemChanged int position            synchronized mObservers                   since onChanged   is implemented by the app  it could do anything  including                removing itself from   link mObservers  - and that could cause problems if                an iterator is used on the ArrayList   link mObservers                  to avoid such problems  just march thru the list in the reverse order              mObservers get position  onChanged                        on class CustomBaseAdapter there is a method notifyItemChanged int position   and you can call that method when you want update a row wherever you want  from button click or anywhere you want call that method   And voila   your single row will update instantly

User · Answer

int wantedPosition   25     Whatever position you re looking for int firstPosition   linearLayoutManager findFirstVisibleItemPosition       This is the same as child  0 int wantedChild   wantedPosition - firstPosition   if  wantedChild  lt  0    wantedChild  gt   linearLayoutManager getChildCount          Log w TAG   Unable to get view for desired position  because it s not being displayed on screen         return     View wantedView   linearLayoutManager getChildAt wantedChild   mlayoutOver   LinearLayout wantedView findViewById R id layout over   mlayoutPopup    LinearLayout wantedView findViewById R id layout popup    mlayoutOver setVisibility View INVISIBLE   mlayoutPopup setVisibility View VISIBLE     For RecycleView please use  this code

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This is how I did it   Your items  rows  must have unique ids so you can update them later  Set the tag of every view when the list is getting the view from adapter   You can also use key tag if the default tag is used somewhere else    Override public View getView int position  View convertView  ViewGroup parent        View view   super getView position  convertView  parent       view setTag getItemId position        return view      For the update check every element of list  if a view with given id is there it s visible so we perform the update   private void update long id         int c   list getChildCount        for  int i   0  i  lt  c  i                  View view   list getChildAt i           if   Long view getTag      id                           update view                     It s actually easier than other methods and better when you dealing with ids not positions  Also you must call update for items which get visible

User · Answer

In addition to this solution  https   stackoverflow com a 3727813 5218712  just want to add that it should work only if listView getChildCount      yourDataList size    There could be additional view inside ListView   Example of how the child elements are populated

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I found the answer  thanks to your information Michelle  You can indeed get the right view using View getChildAt int index   The catch is that it starts counting from the first visible item  In fact  you can only get the visible items  You solve this with ListView getFirstVisiblePosition     Example   private void updateView int index       View v   yourListView getChildAt index -          yourListView getFirstVisiblePosition          if v    null         return       TextView someText    TextView  v findViewById R id sometextview       someText setText  Hi  I updated you manually

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exactly I used this  private void updateSetTopState int index            View v   listview getChildAt index -                 listview getFirstVisiblePosition   listview getHeaderViewsCount              if v    null              return           TextView aa    TextView  v findViewById R id aa           aa setVisibility View VISIBLE

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This question has been asked at the Google I O 2010  you can watch it here   The world of ListView  time 52 30  Basically what Romain Guy explains is to call getChildAt int  on the ListView to get the view and  I think  call getFirstVisiblePosition   to find out the correlation between position and index   Romain also points to the project called Shelves as an example  I think he might mean the method ShelvesActivity updateBookCovers    but I can t find the call of getFirstVisiblePosition     AWESOME UPDATES COMING   The RecyclerView will fix this in the near future  As pointed out on http   www grokkingandroid com first-glance-androids-recyclerview   you will be able to call methods to exactly specify the change  such as   void notifyItemInserted int position  void notifyItemRemoved int position  void notifyItemChanged int position    Also  everyone will want to use the new views based on RecyclerView because they will be rewarded with nicely-looking animations  The future looks awesome   -

User · Answer

The answers are clear and correct  I ll add an idea for CursorAdapter case here   If youre subclassing CursorAdapter  or ResourceCursorAdapter  or SimpleCursorAdapter   then you get to either implement ViewBinder or override bindView   and newView   methods  these don t receive current list item index in arguments  Therefore  when some data arrives and you want to update relevant visible list items  how do you know their indices    My workaround was to     keep a list of all created list item views  add items to this list from newView   when data arrives  iterate them and see which one needs updating--better than doing notifyDatasetChanged   and refreshing all of them   Due to view recycling the number of view references I ll need to store and iterate will be roughly equal the number of list items visible on screen

[android] How can I update a single row in a ListView?

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