I try to understand why a BeginInvoke method won't accept an anonymous method.
void bgWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
if (InvokeRequired)
{
//Won't compile
BeginInvoke(delegate(object sender, ProgressChangedEventArgs e)
{ bgWorker_ProgressChanged(sender, e); });
}
progressBar1.Increment(e.ProgressPercentage);
}
It tells me 'cannot convert from 'anonymous method' to 'System.Delegate' while when I cast the anonymous method to a delegate it does work ?
BeginInvoke((progressDelegate)delegate { bgWorker_ProgressChanged(sender, e); });
Most of the time you're dealing with either a parameterless delegate or a predicate in these cases. The easiest way of sorting this is by casting your anonymous method directly to either
Action
orPredicate
respectively; you just don't need to create a custom delegate type for simple things like that.So you'll have something like
or
HTH
You need to tell the compiler what type of delegate to create, since
Invoke
(etc) just takeDelegate
(rather than something more specific).To apply to the largest audience,
MethodInvoker
is a handy delegate typeHowever...
BackgroundWorker.ProgressChanged
fires on the UI thread automatically - so you don't even need this.The Delegate class is the base class for delegate types. However, only the system and compilers can derive explicitly from the Delegate class or from the MulticastDelegate class. It is also not permissible to derive a new type from a delegate type. The Delegate class is not considered a delegate type; it is a class used to derive delegate types. Source -- MSDN
Hence the need for the explicit cast to a derived-from-Delegate type. You'd encounter this particular compiler error when you pass an anonymous method for a parameter of System.Delegate type - fortunately this is a rare scenario. That's just too much flexibility.
More on this at this page by Ian Griffith. (See the paras after the Notes header)