Adding nodes dynamically ???

[serge calderara]

Dear all,

I have an application which timely create log file in XML format
I ma using the SystemFileWatcher object to monitor creation of new file in the proper path. So far no problem

When the first file is created, my SystemFile onchanged event is catch and then I add the new log file in a treview control with the following code:

Dim m_Root As New TreeNode
m_Root = Me.tLogView.Nodes.Item(0)
'For idx = 0 To sFile.Count - 1
Dim m_Node As New TreeNode(e.Name, 2, 2)
m_Root.Nodes.Add(m_Node)
m_Root.Nodes.Add(m_Node)

When the second file is created, event is cacthed again, and I am suppose to add the new file to the treeview as previous step. But at that time I have an exception which says something like I am not in the current thread and I need to call Control.Invoke before adding my new node ???

What sors it means ? how can add new nodes when Onchange event occurs?

thaks for your help
regards
serge

[Rune Bivrin]

What tis means is that every window and its controls is owned by a thread. Whenever you manipulate the window from the "wrong" thread there's a chance things might not work well, and sometimes an exception is thrown.
Control.Invoke and Control.BeginInvoke are methods that transfer execution to the owning thread.

What you need to do (and I know this is a bit cruddy) is something like this:

    private void fileSystemWatcher1_Changed(object sender, System.IO.FileSystemEventArgs e)
    {
      if (this.InvokeRequired)
      {
        this.BeginInvoke(new System.IO.FileSystemEventHandler(fileSystemWatcher1_Changed), new object[] {e});
      }
      else
      {
        MyTree.Nodes.Add(e.ToString());
      }
    }

This will result in the methood calling itself on the correct thread if needed.

Using BeginInvoke(), rather than Invoke() makes the call asyncronous. Most of the time it doesn't matter, but when you're not interested in the result anyway it can sometimes create a more responsive app.

Rune

PS. Ignore the spurious space that the forum inserts in the middle of the BeginInvoke call...