public void Delegates()
{
// delegates - objects that point to methods
// with the help of delegates we can call these methods
Oper oper; // create variable of delegate
var random = new Random();
int i = random.Next(3);
switch (i)
{
case 0:
oper = Add; // assign adress ofa method to the delegte
break;
case 1:
oper = Substract;
break;
case 2:
oper = Mult;
break;
default:
oper = Math.Min; // delegtes can point to methods outside the class
break;
}
int r = oper(10, 4); // call method
Console.WriteLine(r);
Oper oper1 = new Oper(Mult); // can also create method with constructor, that receives the method of signature
// ref and out also to be taken into account
//oper = MultRef; - ERROR
// delegate can point to multiple methods - invocation list
Message mes;
mes = Hello;
mes += HelloNext; // in reality new delegte is created, that receives copy of the old one
mes += Hello; // this method will be called two times
mes();
mes -= Hello; // deleting from incok list
// if no method while deleting - no error;
Message mes1 = Hello;
Message mes2 = HelloNext;
Message mes3 = mes1 + mes2; // unification of delegates - incok. lists added
mes3.Invoke(); // also calling the delegate;
oper1.Invoke(3, 5);
// if no methods in list of delegate - Invoke will throw error;
oper1?.Invoke(10, 10); // this way no exception will be thrown
// if delegate returns value and a couple a celled, the last one will return the final value;
// delegates can be parameters in methods:
ShowMessage(mes3);
// delegates can be generic
OperGen <int> operGen = Mult;
int k = Mult(2, 2);
}
