ios - Objective C Validation -

i've been watching wwdc 2014 advanced ios application architecture , patterns , found interesting , suited case. specially validation part. in example app i've check if team build way. checks be:

• more 4 players
• two female, 2 male
• etc

so i've created far:

@protocol dexvalidator <nsobject> @required - ( bool ) validate:(nserror * __autoreleasing *)error; @end  //implements procotol dexvalidator @implementation dexvalidatorhasfourplayers  - ( bool ) validate:(nserror *__autoreleasing *)error {     if( _team.length != 4 )         *error = ....      return _team.length == 4   }  @end 

so far can see how works, came part didn't understand. talks composition , creates , overall validator checks this:

//implements procotol dexvalidator @implementation dexvalidatorteam - ( instancetype ) init {     ...     _hasfourplayers = [dexvalidatorhasfourplayers new];     ...morechecks...     ... }   - ( bool ) validate:(nserror *__autoreleasing *)error {     ...  } 

but question how can return nserrors caller. can display list wrong team. since in video changes display of form elements. or should overall not implement validator protocol , else?

i didnt see video yet, might have misunderstood question. anyway, wouldn't possible use pattern return pointer nsarray containing nserrors, , not single nserror? this:

- (bool)validate:(nsarray *__autoreleasing *)errors {     nsmutablearray *temperrors = [nsmutablearray new];      if (team.length != 4) {         [temperrors addobject:[nserror errorwithdomain:@"123" code:123 userinfo:nil]];     }      if (!team.isgenderequal) {         [temperrors addobject:[nserror errorwithdomain:@"456" code:456 userinfo:nil]];     }      if (temperrors.count > 0) {         *errors = [nsarray arraywitharray:temperrors];     }      return temperrors.count == 0; } 

you call by:

nsarray *errors;  bool success = [self validate:&errors];  (nserror *error in errors) {     nslog(@"error %@", error); }