[RESOLVED] Add an Item to a ListView in VitualMode ?

[M-Dayyan]

Hi,
I'm gonna add an item to a ListView in VirtualMode.
Below is my C# code to do that :

listView1.VirtualMode = true;
listView1.VirtualListSize = query.Count();
foreach (var item in query)
{
    i++;
    string tableNumber = item.TableNumber.HasValue ? item.TableNumber.Value.ToString() : "";
    ListViewItem newItem = new ListViewItem(new string[] { i.ToString(), 
                           item.FactorType.ToString(), 
                           item.FactorNumber.ToString(),
                           tableNumber.ToString(),
                           item.Price.ToString(), 
                           DateTime.Now.ToString() });
    newItem.Font = new Font("Tahoma", 12);
    newItem.Name = "Item" + i.ToString();

    listView1.Items.Add(newItem);//Exception
}

void listView1_RetrieveVirtualItem(object sender, RetrieveVirtualItemEventArgs e)
{
    e.Item = new ListViewItem(e.ItemIndex.ToString());
}

The Exception :

When the ListView is in virtual mode, you cannot add items to the ListView items collection. Use  the VirtualListSize property instead to change the size of the ListView items collection.

Would you please guide me ?
Thanks.

[memeloo]

the ListView.VirtualMode documentation clearly states that

In order to use virtual mode, you must handle the RetrieveVirtualItem event, which is raised every time the ListView requires an item. This event handler should create the ListViewItem object that belongs at the specified index.

ListView.RetrieveVirtualItem

you don't follow the examples

[M-Dayyan]

I've done it, I forgot to post :

void listView1_RetrieveVirtualItem(object sender, RetrieveVirtualItemEventArgs e)
{
    e.Item = new ListViewItem(e.ItemIndex.ToString());
}

[memeloo]

so why are trying to add new items like that

listView1.Items.Add(newItem);//Exception

if this is not allowed in virtual mode?

[M-Dayyan]

My question is exactly it,
How can I add a new item to a listview in VirtualMode ?

[memeloo]

read my first response here, this is the second post (#2) you're even doing the same. I don't understand where is the problem? have you not subscribed to the event?

listView1.RetrieveVirtualItem += new RetrieveVirtualItemEventHandler(this.listView1_RetrieveVirtualItem)

[M-Dayyan]

Thanks memeloo.
I have done it too !!!
I think you couldn't understand me well ! let's explain more :

I'm working with SQL to LINQ,
before I use ListView in VirtulMode, whenever I was getting a query with LINQ , I added them to the ListView with a loop :

foreach (var item in query)
{
    i++;
    string tableNumber = item.TableNumber.HasValue ? item.TableNumber.Value.ToString() : "";
    ListViewItem newItem = new ListViewItem(new string[] { i.ToString(), 
                           item.FactorType.ToString(), 
                           item.FactorNumber.ToString(),
                           tableNumber.ToString(),
                           item.Price.ToString(), 
                           DateTime.Now.ToString() });
    newItem.Font = new Font("Tahoma", 12);
    newItem.Name = "Item" + i.ToString();

    listView1.Items.Add(newItem);//Exception
} 

The mount of data was too large, so I decided to use VirtualMode.
Next, I implemented listView1_RetrieveVirtualItem as I read it on MSDN.

listView1.VirtualMode = true;
listView1.VirtualListSize = query.Count();

listView1.RetrieveVirtualItem += new RetrieveVirtualItemEventHandler(this.listView1_RetrieveVirtualItem)
void listView1_RetrieveVirtualItem(object sender, RetrieveVirtualItemEventArgs e)
{
    e.Item = new ListViewItem(e.ItemIndex.ToString());
} 

But now I receive an exception on the line that I marked it in above foreach loop.

My Problem :
I don't now, how I can add new item in VitualMode ?

Do you understand what I mean ?

[memeloo]

I do understand. you do not populate the entire list in a loop like before. it is automatically populated as needed in the listView1_RetrieveVirtualItem event handler. there you must put the code that retrieves the right items.

you can cache the result from the query so that you don't have to run the query every time.

[M-Dayyan]

You mean I have to put foreach contents in listView1_RetrieveVirtualItem method ?

[memeloo]

no. you get the e.ItemIndex which corresponds to the listView's item that will be displayed next.

I don't know what your query result looks like, but you have to do something like this:

void listView1_RetrieveVirtualItem(object sender, RetrieveVirtualItemEventArgs e) 
{ 
    // var query = from ... // run the query here or cache it somewhere else and just use the cache    
    e.Item = new ListViewItem(query[e.ItemIndex]);
}

but probably this won't work. your query result has to be some array or a list and you must get the item at the e.ItemIndex position.

[M-Dayyan]

Excellent ,
I got it my friend.
Thanks a lot