Question

I run into a very strange problem in my C# 2.0 WinForms app and I’m not even sure if its worth asking SO, because the problem occurs in a strange setup and I don’t think that you could reproduce it without my sources, but I’m totally out of ideas.

I have a Form with a TreeView on the left and an ListView on the right. The TreeView shows all available files and subfolders from a specific folder(which contains documents i need for my app). If a Folder is selected the ListView shows all files and subfolders from the selected folder. At startup I populate the TreeView form the folder and after that I select the first TreeNode by code(in my case it’s an folder). After that the Content of the TreeView looks like this:

-folder
   -file1
   -file2

Selecting the folder triggers the AfterSelecedEvent of the TreeView. Because a folder was selected I populate the ListView using the following methode:

private void fillOverview(FAFolder folder)
{
    lv_overview.Items.Clear();
    ListViewItem item;
    foreach (FAFile file in folder.sortedContent)
    {
        if (file is FAFolder)
        {
            item = new ListViewItem(file.Name, "Folder"); //exception got thrown here
        }
        else
        {
            item = new ListViewItem(file.Name, file.Name);
        }
        item.Tag = file;
        lv_overview.Items.Add(item);
    }
}

As you can see there is no subfolder, so the line item = new ListViewItem(file.Name, "Folder"); should never be touched in this setup, but every now and then a NullReferenceException got thrown. If I wrap this line with try/catch the exception got thrown inside the catch block. I tried checking everything if it’s null or not, but ther were no nullreferences. Or if I add a MessageBox right before this line the exceptions got still thrown and no MessageBoxpops up. This brings me to the conclusion that the execption stacktrace is wrong and/or this exceptions comes from an other Thread or something like that.

I’m a very optimistic person and I know how clever the SO community can be, but I don’t think that anybody can point out what the problem is. So what i’m actuallly looking for are hints and advices how i could find and debug the cause of this strange behavior.

EDIT:

internal abstract class FAFile
{
    internal string Name;
    internal readonly FAFolder Parent;
    internal FAFile(FAFolder parent)
    {
        this.Parent = parent;
    }
}

internal sealed class FAFolder : FAFile
{
    internal readonly IDictionary<string, FAFile> Content = new Dictionary<string, FAFile>();
    internal FAFolder(FAFolder parent, string name) : base(parent)
    {
        this.Name = name;
    }
}

internal sealed class FADocument : FAFile
{
    public readonly string Path;
    public FADocument(FAFolder parent, string path): base(parent)
    {
        this.Path = path;
        this.Name = System.IO.Path.GetFileNameWithoutExtension(path);
    }
}

Answer 1

A co-worker of mine just found the answer(probably). I use a Thread to load the ImageList to the ListView from the HDD and this thread sometimes freezes and if i assign a ImageKey it fails. That’s no answer why the exception is uncatchable or why it’s thrown at this (unreachable) line. But i strongly belive that this is the cause of the problem.