C# returning data using delegates...

Mutant_Fruit

I'm having a bit of trouble with my delegates. I'm trying to return all the items in a listview control in a winform in order to use their data to download files off the internet in a seperate "downloading" thread.

If i try:
foreach(ListViewItem item in this.MyListView.Items)
{
}

directly in my downloader thread, an illegal thread access exception thingy is thrown... How do i use delegates to return me a nice ListViewItemCollection in order to iterate through them in my foreach loop in my "download" thread?

Or is there a better way of doing this?

aidan_walsh

If you remove "this"?

Mutant_Fruit

testing that now... but i don't see how it'd help.

EDIT: Removed the "this." but it didn't help. Still getting the illegal cross-thread exception.

Chris P Duck

Try this

int itemsCount = MyListView.Items.Count;
for(int index = 0; index < itemsCount; index++)
{
    ListViewItem.ListViewSubItemCollection subCollection =
      new System.Windows.Forms.ListViewItem.ListViewSubItemCollection(MyListView.Items[index]);
    subCollection = MyListView.Items[index].SubItems;
}

Mutant_Fruit

Thing is, even running:

int itemsCount = MyListView.Items.Count;

is calling a method, which ain't allowed unless i'm running the method from the same thread the listview is on, which i'm not doing! There has to be an easy way of doing this by using a delegate with return type ListViewItemCollection, but i can only make delegates with void return work

Mutant_Fruit

Figured it out. Here's what i ended up doing (just in case anyone else ever needs to do it... its also what i tried first, but it didn't work for me then because i didn't clone the items )

// Delegate to return a listviewitem collection based on the listview passed to it
private delegate ListView.ListViewItemCollection GetItems(ListView lstview);

// Method called in order to correctly return the listview item collection
        private ListView.ListViewItemCollection getListViewItems(ListView lstview)
        {
            ListView.ListViewItemCollection temp = new ListView.ListViewItemCollection(new ListView());
            if(!lstview.InvokeRequired)
            {
                foreach(ListViewItem item in lstview.Items)
                {
                    // Clone each item and add it to my temp array.
                    // If i don't clone it, then i won't be able to use it in my second thread
                    temp.Add((ListViewItem)item.Clone());
                }
                return temp;
            }
            else
            {
                // If i need an invoke, i create a delegate variable, call it
                // and cast its return to ListViewItemCollection and return that. Problem solved.
                GetItems d = new GetItems(getListViewItems);
                return (ListView.ListViewItemCollection)this.Invoke(d, new object[] { lstview });
            }
        }