Question

I have read where an event is triggered on another thread from the one that created the controls on a Windows Form.

Therefore, the event handler can’t directly update the controls (like changing a button’s color).

I read the explainations about Invoke or BeginInvoke being needed.

My question: Why can’t an event handler just be passed ‘this’ as an agrument.

‘this’ being the form whose controls have buttons that want THEIR COLORS CHANGED !! 😉

I can swear I’ve seen instances where a delegate can take a ‘this’ – but maybe not…

Answer 1

There’s nothing stopping an event handler on another thread just going in and screwing around with the internal state of the button.

However, it causes bad things to happen – as an example, what would happen if you changed a property of a control while something else was also trying to write to it?

Only one thread should be screwing around with the internal state of an object at a time – if you call methods directly on that object from another thread, you can’t guarantee that something else isn’t doing the same.

Invoke gets around this by not calling it directly – instead it says to the thread that ‘owns’ the object “Hey, could you call this method on that object when you’ve got a moment?”, thus ensuring that the method is only called when the object is in a consistent state.