Question

When you subscribe to an event on an object from within a form, you are essentially handing over control of your callback method to the event source. You have no idea whether that event source will choose to trigger the event on a different thread.

The problem is that when the callback is invoked, you cannot assume that you can make update controls on your form because sometimes those controls will throw an exception if the event callback was called on a thread different than the thread the form was run on.

Answer 1

To simplify Simon’s code a bit, you could use the built in generic Action delegate. It saves peppering your code with a bunch of delegate types you don’t really need. Also, in .NET 3.5 they added a params parameter to the Invoke method so you don’t have to define a temporary array.

void SomethingHappened(object sender, EventArgs ea) {    if (InvokeRequired)    {       Invoke(new Action<object, EventArgs>(SomethingHappened), sender, ea);       return;    }     textBox1.Text = 'Something happened'; }