Develop Reference

RecyclerView item view updates after scrolling up or down

I have a recyclerView and list of items. Items are observed in viewModel, adapter gets a changed list whenever list in viewModel changes.
However, I have a problem when updating certain item views in existing list item - these changes happen, but to see them I have to scroll up or down a bit. In view holder I have all necessary if/else cases what to update according to item values. Is there a way to update item view instantly, without having to scroll?

You can call adapter.notifyDataSetChanged() function to force the adapter to redraw all items again.

you should use adapter.notifyItemChanged(int indexOfChangedItem) or adapter.notifyDataSetChanged() after you changing any item of the list.
the first one will update 'all' item viewes but the second one will update only the view that you passed it's index.

newview not invoke in ResourceCursorAdapter

I use ResourceCursorAdapter , first screen show 4 item， I scroll to bottom ,the 5 and next repeat ,in fact the fifth item is show the first item, I found is directly invoke bindview not newview,I don't know why?

It is because the fifth item is actually a recycled first item. Android recycles its list items for better performance. newView only called when the adapter want to inflate new view from XML file. So there is no guarantee that for every list item the newView will be called.

does ListView re-draws itself every time the adapter changed?

I want to make a list of SMSs in my own application..
my question is about the steps makes by the adapter (automatic)
-when new message arrived I adds it to list object (not the ListView).
-then I passes the list to the adapter of the listView.
the adapter GetView() method run for every Item in the list
-I notify the listview about the change.
- the listview re-draws all its existing rows and then draw the new row.
My question: this behavior (re-draw and redraw, it mean every row will be drown times equal to the total rows) affect the performance?
*if the question is not clear I say: does the ListView Draw all the Raws just to add new row? *

The ListView doesn't redraw every single item in order to add one. It will only be drawn when you scroll to it. And yes you have to notify ListView that the change had happened.

I guess you want to add the item at the top position. So all other item's position and index will change . Adapter will redraw the whole list(only elements which are visible on the screen) .
For performance you can use viewHolder pattern.
see this link
[Making ListView Scrolling Smooth][1]http://developer.android.com/training/improving-layouts/smooth-scrolling.html

Custom List View items

I am writing code for a listview which has fixed number of rows and when the user scrolls the listview, instead of moving the list elements (views), I want to change the content of the views where as the list elements (views) stay at the there position.
For this I am returning a number Eg. 5 in getCount(), however I am no clue on how can I change contents of list items while keeping the list items in a fixed position.
Any help is welcomed.
Regards

with getItemAtPosition()
you get the item at position, there you can change its content and then call notifyDataSetChanged() to signal the adapter that the data has changed.

List view duplicate data

I am using list view to populate data in the custom dialog. I am passing a List to adapter. The list has 250 different items.
The problem I have is getView method of adapter is being called only 7 times and then the data is displayed in dialog. The dialog has first 7 items repeated to fill all the 250 rows in the dialog.
I couldn't understand why the getView is called only 7 times (and also in my dialog I can see 7 items at a time.. and i need to scroll to view other items. Is there any relation between the number of elements I see and number of times the getView will be called).
Any idea why it happens. Thanks in advance.

Yes, I think getView is called when the item is actually displayed on the screen. When you scroll, more items become visible and getView will be called more times.

i am creating new row only if convertView is null otherwise I return the same row. I couldn't understand why the data is duplicated in my dialog"
You can try to set the data of each item every time you return from getView method. convertView is reused, you need to update the data of the convertView bind of. You can use ViewHolder to save widgets in each item.