C# When explicit delegate declaration is required when working with events -

this question has answer here:

• creating delegates manually vs using action/func delegates 8 answers

all know delegate function pointer. when work event declare delegate know in kind of situation have declare delegate when working events public delegate void onbuttonclickdelegate();

here refering code sample show can use in built delegate eventhandler instead of declare delegate explicitly.

public class argsspecial : eventargs {     public argsspecial (string val)     {         operation=val;     }      public string operation {get; set;} }   public class animal {     // empty delegate. in way sure value != null      // because no 1 outside of class can change it.     public event eventhandler<argsspecial> run = delegate{}       public void raiseevent()     {            run(this, new argsspecial("run faster"));     } }  animale animal= new animal(); animal.run += (sender, e) => console.writeline("i'm running. value {0}", e.operation); animal.raiseevent(); 

so when eventhandler in built delegate solve purpose no need declare delegate explicitly when working events. tell me have declare delegate explicitly , eventhandler may not solve our purpose. thanks

eventhandler has limited signature, 2 parameters first type object, , second has class type inheriting system.eventargs. considering system.action<t, ...> , system.func<t, ..., treturn>, rare need declare another. in fact of original bcl delegate types methodinvoker, converter<t, u>, predicate<t>, , eventhandler<t> wouldn't have been defined if action , func families had existed @ time.

where still need declare own delegate when need by-reference parameters. ref , out keyword cannot passed through generic type parameter, if want delegate matching tryparse family, you'd unable func<string, out t, bool> , need custom declaration

/* return true if parsing successful */ delegate bool tryparser<t>(string from, out t into); 

it's uncommon use by-reference parameters events, you'll never have declare delegate use event type.