FileSystemWatcher.SynchronizingObject without a form

Question

I have an windows form application written in C# in which I use a FileSystemWatcher to monitor a folder for new files and then perform some processing on them. My application is designed to run in the system tray and therefore does not instantiate any forms at startup. The problem is that the Created event is firing on a separate thread and when I try to create an instance of a form in the Created event I get an ThreadStateException that states I need to be running in SingleThreadApartment. I think I need to set the FileSystemWatcher.SynchronizingObject property but don't know what to use since there is no main form in my application.

Answer 1

You will have to call Application.Run() in your Main() method to get the Windows Forms synchronziation machinery in place so that FileSystemWatcher can properly marshal the call to the main thread. The problem you'll have then is that the main form will become visible. Fix that by pasting this code into the class:

    protected override void SetVisibleCore(bool value) {
        if (!this.IsHandleCreated) {
            this.CreateHandle();
            value = false;
        }
        base.SetVisibleCore(value);
    }

There are no restrictions on what your form looks like if you do this.

Answer 2

You don’t need to pass any forms to Application.Run at all. Then you can save having to mess around with form visibility. Just do this:

var InvokerForm = new Form();
var dummy = InvokerForm.Handle; // force handle creation
Application.Run();

Just one gotcha there - the form handle creation needs to be forced by accessing it once.