I'm working on ListView. I want to know when exactly getView() is called. Is it called once the adapter is set? And does the line next to "setting adapter" get called once the getView() method completes execution?
Please help me know which line gets executed once the getView() finishes execution.
That would be a great help for me.
Thanks in advance,
Vaishnvai
getView() is called for each item in the list you pass to your adapter.
It is called when you set adapter. When getView() is finished the next line after setAdapter(myAdapter) is called.
In order to debug getView() you must toggle a breakpoint on it because you can't step into getView() from setAdapter(myAdapter).
getView() is also called after notifyDataSetChanged() and on scrolling.
To be more clear, getView() is called whenever a new item is displayed on screen, at the count of displayed items. Which means, if you have 1 million items but 15 of them fits on screen, getView is called 15 times. Whenever you scroll up/down and new items appear, getView() is called for new ones. And you should be aware of recycler mechanism, too. Which holds a template item layout for each item type, and sends in this view to getView() method as convertView parameter, so you could use it in order to prevent layout inflation.
Related
I have a grid view that show some items, in getView I need to increase the number of views on each item , what happen that getView() is called muti-times for the same item
how to make sure that my increment views method will called only one time ?
I'm using adapter.notifyDataSetChanged(). I'm just curious if I can refresh a list view item without scrolling it off screen when call that method.
adapter.notifyDataSetChanged() will automatically call getView() for every row currently at least partially visible on the screen.
You don't have to scroll anything.
From the official documentation
notifyDataSetChanged(): Notifies the attached observers that the underlying data has been changed and any View reflecting the data set should refresh itself.
So, in other words , whenever you call that method, is being called the getView() method and refresh the content of your changed slots.
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.
I have been using using listview since long but suddenly I experienced some of its random behaviour.
When I call invalidateViews() on listviews, in some cases it re-inflates the views for each row and in some cases it doesn't. This is completely random. Can you tell me exactly how does it works?
Ideally it should just refresh the data inside views(rows) and not inflate them again.
Thanks
Calling invalidateViews() on a ListView should not re-inflates the ListView item views. The only way to force the ListView to re-inflates its item views, meaning that the recycled views are cleared, is by resetting the ListView adapter ( I had to dig in the source code to discover that ).
If you take a look at the invalidateViews() method implementation (source code in AbsListView.java), you will see this (Android API 16) :
/**
* Causes all the views to be rebuilt and redrawn.
*/
public void invalidateViews() {
mDataChanged = true;
rememberSyncState();
requestLayout();
invalidate();
}
The method rememberSyncState() implemented in AdapterView.java stores the ListView's position of the selected item (if any), you can check it out.
The requestLayout() method takes care of the measuring, laying out, and drawing (as far as I know) so nothing here too.
And finally invalidate() is used to force the list view to draw (with the new measurements, ...)
So calling invalidateViews() should not force the list view to re-inflate its views.
Could you be re-setting the adapter somewhere so it re-inflates all the views ?
Actually, listview.invalidateViews() causes all the views to be rebuilt and redrawn. You can come to know this when you look on the description gets displayed in eclipse when you try to select invalidateViews().
adapter's getView() method has parameter convertView which is null first time when you populate a listview, later when you scroll/invalidate your listview convertView is not null so you can use it and dont need to inflate a new row
i have used a hashmap to store data in a custom adapter i have made by extending the BaseAdapter class in android.
in the 'getCount' method i am returning the no.of keys in the hashmap that i have populated before.
now when i come to the getView method , it has a parameter called int position.
i don't understand the funcitonality of this parameter...
everytime getView is called isn't this integer incremented by one?
thank you in advance.
The ListView class calls the getView() method every time one of its items becomes visible. So the position arguments is this item's position.
The arg0 doesn't keep on incrementing. It is nothing but the index of the item in your list.
Please set the layout_height of the ListView to fill_parent so that getView() gets called only once before you start scrolling.
The arg0 starts from 0 and goes till the size of your list. When you start scrolling, it again starts from 0 and goes on.
Hope this solves your question.