Jon P, you can read me like an Android Book.
Yes it's is a List<Headword> and yes you're right, RemoveAt is the way to go in
case there are multiple of the 'same' item in the list.
The problem though was that I was attaching the event handlers multiple times
because I wasn't detaching the handler when convertView parameter is passed, so
it was getting called twice with the current position, and whatever was
attached last time.
OK, last thing. When I delete the item, I want the listview to update and NOT
scroll to the top. Recreating the adapter with the now updated list updates the
view, but scrolls to the top (and is inefficient). All the SO articles and
docco say to use ArrayAdapter<T>.NotifyDataSetChanged(). I find that method
doesn't work as I expect though:
I can do along the lines of (sorry not on the coding computer):
lvHeadwords.Adapter = new MyCustomAdapterHeadwords(Headwords); //which inherits
ArrayAdapter<T>
//Then in response to a delete click....
Headwords.RemoveAt(position)
(((MyCustomAdapterHeadwords)lvHeadwords.Adapter).NotifyDataSetChanged();
Assert.AreEqual(lvHeadwords.Adapter.Count, Headwords.Count); //Boom, they're
not.... and the UI hasn't updated
That's supposed to work right? As long as the adapter and Headwords are
pointing to the same reference? What's the most efficient way to sync the list
and the adapter?
________________________________
From: Jonathan Pryor <j...@xamarin.com>
To: Steven Pack <steven_john_p...@yahoo.com.au>; Discussions related to Mono
for Android <monodroid@lists.ximian.com>
Sent: Wednesday, 8 August 2012 2:02 AM
Subject: Re: [mono-android] Detecting and responding to image clicks in a list
view item.
On Aug 7, 2012, at 2:39 AM, Steven Pack <steven_john_p...@yahoo.com.au> wrote:
> and deleting the item:
>
> void DeleteItem(int position)
> {
> _log.Debug(Tag, "Deleting from position: " + position);
>
> var item = Headwords[position];
> Headwords.Remove(item);
>
> RefreshListView();
> }
>
>
> The DeleteItem method throws IndexOutOfRangeExceptions, firstly because it
> gets called multiple times and also because the position index doesn't
> actually represent the real index in the list somehow.
What is Headwords? What is Headword?
If I assume that Headwords is a List<Headword>, List<T>.Remove() [0] uses
List<T>.IndexOf() which uses Array.IndexOf() [1] which uses
EqualityComparer<T>.Equals(). If Headword doesn't implement
IEquatable<Headword>, then EqualityComparer<Headword> will in turn use
object.Equals(), which defaults to reference equality, which may or may not be
correct.
Furthermore, if you have the same Headword instance in Headwords multiple
times, List<T>.IndexOf() will return the _first_ index, which may not be the
index you want.
In any event, you should probably be using Headwords.RemoveAt(position), _not_
Headwords.Remove(Headwords[position]). The semantics are not equivalent between
those expressions if/when the same element is present multiple times in the
list.
- Jon
[0]
https://github.com/mono/mono/blob/master/mcs/class/corlib/System.Collections.Generic/List.cs#L501
[1]
https://github.com/mono/mono/blob/master/mcs/class/corlib/System/Array.cs#L2810_______________________________________________
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