Develop Reference

ObjectListView add images to items/objects

I'm using the ObjectListViewand am trying to add images to my items. I got it to work by looping through all the items and then manually editing the image index per item. I would like to know if this is possible when adding the items. This is the code I have at the moment:
Adding the items
for (int i = 0; i < listName.Count; i++)
{
games newObject = new games(listName[i], "?");
lstvwGames.AddObject(newObject);
}
Adding the images
foreach (string icon in listIcon)
{
imglstGames.Images.Add(LoadImage(icon)); // Download, then convert to bitmap
}
for (int i = 0; i < lstvwGames.Items.Count; i++)
{
ListViewItem item = lstvwGames.Items[i];
item.ImageIndex = i;
}

It is not entirely clear to me what exactly you try to achieve, but there are several ways to "assign" an image to a row. Note that you probably have to set
myOlv.OwnerDraw = true;
which can also be set from the designer.
If you have a specific image for each of your model objects, its probably best to assign that image directly to your object and make it accessible through a property (myObject.Image for example). Then you can use the ImageAspectName property of any row to specify that property name and the OLV should fetch the image from there.
myColumn.ImageAspectName = "Image";
Another way to do it is using the ImageGetter of a row. This is more efficient if several of your objects use the same image, because you can fetch the image from anywhere you want or even use the assigned ImageList from the OLV by just returning an index.
indexColumn.ImageGetter += delegate(object rowObject) {
// this would essentially be the same as using the ImageAspectName
return ((Item)rowObject).Image;
};
As pointed out, the ImageGetter can also return an index with respect to the ObjectListView's assigned ImageList:
indexColumn.ImageGetter += delegate(object rowObject) {
int imageListIndex = 0;
// some logic here
// decide which image to use based on rowObject properties or any other criteria
return imageListIndex;
};
This would be the way to reuse images for multiple objects.

Both your approach and the one I show below will have problems if the list is ever sorted as sorting will change the order of the objects in the list. But really all you have to do is keep track of your object count in your foreach loop.
int Count = 0;
foreach (string icon in listIcon)
{
var LoadedImage = LoadImage(icon);
LoadedImage.ImageIndex = Count;
imglstGames.Images.Add(LoadedImage); // Download, then convert to bitmap
Count++;
}

Removing an item from a list c#

I am having trouble with removing an item from a list in c#. My current code is below:
for (int i = current.Count - 1; i >= 0; i--)
{
foreach (ListItem li in sp_list.Items)
{
if (li.Text == current[i].uname)
{
current.RemoveAt(i);
}
}
}
The aim of the code is to compare the existing items in a list box with newly added items so I know which items have just been added. So currently I am getting the current list box items from the database (they are stored here, it is a databound list box), entering these into a list and for each of the list items, comparing them with the items in a list box and if they match, remove the item from the list.
Therefore, in the end, if I add two new entries, the list should only be storing the two newly added values.
The code does not work as the first item is removed fine, but then, the value of i is greater than current.count - and therefore I get an out of range exception!
Could someone help me with this issue? Apologies about the confusing question, it's hard to explain! Thanks

You can do it with Linq. Not sure if casting to ListItem needed (you can remove it)
current.RemoveAll(x => sp_list.Items.Cast<ListItem>()
.Any(li => li.Text == x.uname));

Once you've found the matching value, and removed it from the list, you want to break out of the inner loop to check the next item.
if (li.Text == current[i].uname)
{
current.RemoveAt(i);
break;
}

Your nesting is wrong, I think you wanted,
foreach (ListItem li in sp_list.Items)
{
for (int i = current.Count - 1; i >= 0; i--)
{
if (li.Text == current[i].uname)
{
current.RemoveAt(i);
}
}
}
alternatively, use linq,
// For lookup performance.
var items = new HashSet(sp_list.Items.Select(i => i.text));
current = current.Where(c => !items.Contains(c.uname)).ToList();

How about this:
foreach (ListItem li in sp_list.Items) {
if (current.Contains(li.Text)) {
current.Remove(li.Text);
}
}

Put a break statement after the RemoveAt so you don't remove that item again.

you can travel the list in reverse order and remove items using RemoveAt(i).
also for efficiency purposes you may want to put the ListItem texts in a Set so you can don't have to loop though the sp_list.Items for each of your current items.

Check all item in listview with huge list item?

I want to check about 3000 item in listview. This is a bit of code :
foreach (ListViewItem item in this.lvItem.Items)
{
item.Checked = !item.Checked;
}
But listview is very slow when item is checked. Please give me some ideas to solve this problem? Thanks.

I had the same problem but I found why.
I had an "ItemChecked" event handler attached to my listView that was doing some heavy stuff.
I removed the eventHandler and it solved my problem.
Try removing any "ItemChecked" eventhandler and see if the speed is better.

You need to call BeginUpdate before the loop and EndUpdate after the loop:
listView1.BeginUpdate();
foreach (ListViewItem item in listView1.Items)
item.Checked = true;
listView1.EndUpdate();
Calling BeginUpdate prevents the control from drawing until the EndUpdate method is called.

I heard a rumor that for large list items a for loop will work faster than a foreach loop
try
for(int i = 0; i = < this.1vItem.Items.Count; i++)
{
//Stuff
}

I also don't think it's wise to expect a user to click 3000 items. But something I did recently, when adding the items, knowing that there would never be many and by default they should be checked, is check the items before adding them to the list.
Something like this:
foreach (Recipient recipient in recipients)
{
var item = new ListViewItem(recipient.FirstName + " " + recipient.LastName);
item.Tag = recipient;
item.Checked = true;
lvRicipients.Items.Add(item);
}

Will something like this work for you? ...when checked, add the items to a Dictionary ...when unchecked, remove from the Dictionary. Not tested code but wondering if you could do something like this:
Dictionary<String, ListViewItem> Dic = listView.Items
.Cast<ListViewItem>()
.ToDictionary(x => x.Text, x => x.SubItems[0].Checked);
You asked how to better go about it. What I am saying is on your Check Event you will want to add items to your list view. I doubt that a user will actually check all 3000, so change your code to decide how you would want to handle checked items, the example that I have given you uses Lambda expression. If not familiar, then please alter your question to reflect what it is that you actually need and/or want...

for (int i = 0; i <= listView1.Items.Count - 1; i++)
{
if (!listView1.Items[i].Checked)
listView1.Items[i].Checked = true;
}

Select the specific column of ListView and print it in a new messagebox in C#.net

I've just started to use ListView in C#.net.
I got to know how to add items and subitems. Going through the listview I wanted to fetch all the data from a whole column with multiple rows.
I want to know how to do this.
I found this code to list a specific selected data from a row:
ListView.SelectedIndexCollection sel = listView1.SelectedIndices;
if (sel.Count == 1)
{
ListViewItem selItem = listView1.Items[sel[0]];
MessageBox.Show(selItem.SubItems[2].Text);
}
That was helpful but i want to list all the items in a row, may be i want to add all the column items in array?

private string[] GetListViewItemColumns(ListViewItem item) {
var columns = new string[item.SubItems.Count];
for (int column = 0; column < columns.Length; column++) {
columns[column] = item.SubItems[column].Text;
}
return columns;
}
I would recommend some caution against doing this. A ListView is really meant to display information, it is not a great collection class. Getting the data out of it is slow and crummy, it can only store strings. Keep the data in your program in its original form, maybe a List<Foo>. Now it is simple and fast.

foreach (ListViewItem item in listView1.Items) {
// Do something with item
}

you could do this by
foreach(ListViewItem item in listView1.Items)
{
foreach(var subtem in item.SubItems)
{
// Do what ever you want to do with the items.
}
}

Foreach doesn't go through all items?

I have this code:
foreach (var item in ListView1.Items)
{
ListView1.Items.Remove(item);
ListView21.Items.Add(item);
}
the loop stops at half of the items?
Any idea?
EDIT
Well, maybe it's my mistake, I need to clarify that this is UltraListView control from Infrajistics, where I can't add item to another list unless I remove it or clone it from the original list.
But thanks, most of the comments regarding do not modify the list within the loop were correct, so this code works:
foreach (var item in listView1.Items)
{
var i = item.Clone(true);
listView2.Items.Add(i);
}
listView1.Items.Clear();
Thanks,

You cannot modify iterated collection, it should die with exception (or in undefined behavior).
Try making a copy of the array:
foreach (var item in ListView1.Items.ToArray())
{
ListView1.Items.Remove(item);
ListView21.Items.Add(item);
}
EDIT:
in fact, your example code can be achieved by writing:
ListView21.Items.AddRange(ListView1.Items);
ListView1.Items.Clear();
(which in fact isn't EXACTLY what you are doing, but gives the same result and I think it won't bother you having the same content in both listviews for a moment). The latter is supported since .NET2.0, first solution requires linq, and therefore .NET3.5.

You are modifying the collection you are looping through. Try using a for statement from top to bottom (from the item with the highest index to 0).
for (int i = ListView1.Items.Count - 1; i >= 0; i--)
{
var item = ListView1.Items[i];
ListView1.Items.Remove(item);
ListView21.Items.Insert(0, item);
}

It will cause a runtime exception, complaining that you cannot modify the collection while iterating through it. You have to use for loop instead.
for(int index = Items.Count; index > 0; index--)
{
.......
// use Add and RemoveAt
}
EDIT : As mentioned by others. If you just need to move items from one collection to the other. AddRange and Clear will be better.

Do you get any exception or error message? Looping in a collection and remove items from the same collection is always a bad idea.

This looks like the WinForms list view control, so:
ListViewItem[] items = ListView1.Items.ToArray();
ListView1.Items.Clear();
ListView21.Items.AddRange(items);

Why just not CopyTo() to new list and then Clear() items?

You are looping through all items, removing all of them, then adding them to another list. As others have commented, you cannot remove items from a list in a for-each. Why not looping through all items to add them to your other list, and then remove them all in one go?
foreach (var item in ListView1.Items)
{
ListView21.Items.Add(item);
}
ListView1.Items.Clear(); // remove all
PS: is this an ASP.NET listview or a WinForms listview?

That's because you're changing the collection inside the loop.
Use a normal for loop as follows:
for(int i=0; i < ListView1.Items.Count-1; i++)
{
ListView21.Items.Add(ListView1.Items[i]);
ListView1.Items.RemoveAt(i);
}