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.
Related
I thought I understood the recycler mechanism of Listview... but it seems I didn't.
I have a ListView of 20 items, only 10 items is visible initially. Why Android calls getView() of positions like 15 or 17 (non visible rows)?
Why convertView parameter of visible rows passed to getView() are the same? I thought if convertView is not null, it refers to a row that isn't visible anymore.
After adding some logging in getView(), I couldn't explain what really happens.
convertView is a View instance that was previously returned by the getView method and is not visible anymore, its purpose is TO BE converted to a NEW ITEM assigned by the new position in the method. The adapter do it to reuse views and avoid inflating new ones. If it is calling the same visible row twice it can only be at listview inflation time (it happens).
To the first question, it inflates non-visible views so it will be available to be scrolled when you reach it.
YOU MUST: re-set all values in a convertView to a new item.
I've got a strange situation here.
There's a list view with a custom adapter. The view has a few different item types which are correctly used in getViewItemType. On just about every device and supported OS the getView method in the adapter is called without any weird behavior.
I know getView can be called many times and that isn't the issue. On a Nexus 5 and Nexus 6, however, getView is called twice for the same item type and passes a convertView of null.
The result is we end up creating two views for the same row in the list. It seems that one will actually get attached or added to the listview while the other isn't.
Any suggestions, or tips that might be causing this?
How do you know called twice for same item?
I ran the app with a debugger. It stopped on my breakpoint in getView multiple times (as expected) but two of the stops for the item passed null convertViews. It is a very small list, only four rows, each a different item type. They all show on the screen easily
You should check the position in getView() to make sure if called twice.
I suppose not because that the first time of each item view(convertView) always null, then you need inflate the view with item view layout and return it. While next time show the same view(even though for different item), the convertView will be not null, but you still need set views with value that according to the item position.
Hope you got!
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.
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
I have a ListView with custom_row , every row has a textView1 and a textView2 , the list has now 2 records , and i have a button that is not on the list.
When i click the button i want to get the text from textView2 of the 2 records.
Is it possible?
I would take a shortcut, you ListView is being populated by an Adapter that uses a dataset. This dataset can be almost any datastructure such as Array, ArrayList, etc.
The layout you define, such as custom_row in you case only defines the structure of your view i.e. "where" items will show within on item on the list.
On the other hand, it is still your responsibility to tell the ListView "what" to show within the textView1 and textView2. You do this using the Adapter which connects the ListView to the dataset. More often than not, the ListView is a one-to-one mapping of the dataset i.e. the first item on the list is the first item in you dataset (I don't know what you are using for only two items, might be an array).
The ListView calls getCount() on the Adapter to find out how many total views there will be. It then call getView() for each view to be shown on the screen. It is in this method that you define what will actually show in a single view on the list (your custom_row).
Now you would know which entry of the dataset is supposed to populate which view in the ListView so you can just read it off there. For example, if your getView() does:
textView2.setText(getItem(position).getSomeTextField());
And the original dataset is an ArrayList named listDataSet
You could just do listDataSet.get(2).getSomeTextField()
NOTE: You will have to manage the scope of the dataset so that it's visible from wherever you are calling.
Get back your ListView (maybe already stored in an object thanks to findViewById, or by calling getListView() on your ListActivity).
Then call getItemAtPosition() on your list view, with the position you want.