C#: Why isn't my app closing its file handles?

Question

I have an app which is opening a series of DLLs on the filesystem and in the GAC, and which is holding a lock on those files. How can I release these handles explicitly so I can rebuild them in Visual Studio without closing my app?

Code follows:

private void BuildTabPage_AssemblyTree(string filename, string foldername)
{
    Assembly assembly;
    try
    {
    assembly = Assembly.LoadFrom(filename);
    }
    catch (Exception ex) 
    {
    MessageBox.Show("Error loading assembly " + filename + "\n" + ex.Message);
    return;
    }
    TreeNode tRoot = BuildNode(assembly, foldername);
    tvAssemblies.Nodes.Add(tRoot);
    tvAssemblies.ExpandAll();

    txtResults.Text =
    RefsFound.ToString() + " References Located in Filesystem\r\n" +
    RefsInFramework.ToString() + " References Located in Framework\r\n" +
    RefsInGac.ToString() + " References Located in GAC\r\n" +
    RefsNotFound.ToString() + " References Not Found: \r\n\r\n";
    foreach (string s in MissingFiles)
    txtResults.Text += s + "\r\n";
}

private TreeNode BuildNode(Assembly assembly, string foldername)
{
    TreeNode tn = new TreeNode(assembly.GetName().Name);
    tn.ToolTipText = assembly.FullName + "\n" + assembly.CodeBase;
    AssemblyName[] assemblies = assembly.GetReferencedAssemblies();

    foreach (AssemblyName a in assemblies)
    {
    string filename2 = foldername + a.Name + ".dll";
    TreeNode tn2;
    if (System.IO.File.Exists(filename2))
    { // File found in folder
        RefsFound++;
        Assembly assy = Assembly.LoadFile(filename2);
        tn2 = BuildNode(assy, foldername);
    }
    else if (a.Name.StartsWith("System"))
    { // Framework assemblies not included
        RefsInFramework++;
        tn2 = new TreeNode();
        tn2.Text = a.Name;
        tn2.ForeColor = System.Drawing.Color.Green;
        tn2.ToolTipText += "\n.NET Framework File";
    }
    else
    {
        try
        {   // Find file in GAC
        Assembly assy = Assembly.Load(a);
        tn2 = new TreeNode(a.Name);
        tn.ToolTipText = assembly.FullName + "\n" + assembly.CodeBase + "\nFile detected in GAC";
        tn2.Text = "(" + filename2.Substring(filename2.LastIndexOf("\\") + 1) + ")";
        tn2.ForeColor = System.Drawing.Color.Green;
        RefsInGac++;
        }
        catch (System.IO.FileNotFoundException)
        {   // File not Found
        RefsNotFound++;
        if (!MissingFiles.Contains(a.Name))
            MissingFiles.Add(a.Name);
        tn2 = new TreeNode();
        tn2.Text = "(" + filename2.Substring(filename2.LastIndexOf("\\") + 1) + ")";
        tn2.ToolTipText = "File Not Found";
        tn2.ForeColor = System.Drawing.Color.Red;
        }
    }
    tn.Nodes.Add(tn2);
    }

    return tn;
}

Answer 1

I think if you setup your AppDomain to use ShadowCopy it should work:

http://blogs.msdn.com/junfeng/archive/2004/02/09/69919.aspx

This link deals with your question in great detail (if I'm understanding you correctly): http://blogs.msdn.com/jasonz/archive/2004/05/31/145105.aspx

Answer 2

Once you load an assembly into your process you cannot unload it. Instead you can you create an app domain for each assembly you want to load, get the assemblies properties, then close the app domain.

Answer 3

Unfortunately, assemblies loaded into a default AppDomain will not be unloaded until the application exits. However, you can create an AppDomain and load assemblies in a created AppDomain. When the created AppDomain is unloaded, assemblies loaded in the created AppDomain will be unloaded together.