Difference between ‘ += new EventHandler’ and ‘ -= new EventHandler(anEvent)’

Question

I saw some code using -= new EventHandler(anEvent) , can you one tell me what is the different to ‘ += new EventHandler’ ?

Thanks

Answer 1

One adds a delegate to the collection of subscribers, the other removes it.

For example, if you had previously subscribed to an event, but you wanted the reference removed when you, say, closed a form, you would use the -= version and you would no longer be notified.

Answer 2

The -= operator removes an even handler from an event, while += adds an event handler to an event.

For example:

if (checkSomething())
{
//handle clicks on myControl
myControl.Click += MyEventHanderMethod;
}
else
{
//stop handling clicks on myControl
myControl.Click -= MyEventHanderMethod;
}