CODEWITHSUNDEEP
objective-cios
Global nomad
Global nomad

Reputation: 1022

To Implement KVC validattion method, override -(BOOL)validateIvar:error: or -validateValue:forKey:error:?

The former is described in the KVC Prog Guide, but missing from iOS API installed with Xcode 4.0.2 (with iOS 4.3 SDK) for Snow Leopard which lists the latter. This is for iOS 2.0 or newer. Thanks.

Upvotes: 3

Views: 560

Answers (2)

quellish
quellish

Reputation: 21254

You should only implement methods following the pattern validate<Key>:error: (which can be done even in a category). Don't override validateValue:forKey:error:, and do not call validateValue:forKey:error: from within a validation method. You will cause an infinite loop. This is covered in the Key-Value Coding documentation and Core Data documentation, as well as within the Foundation headers. validateValue:forKey:error: is the designated entry point into validation, both for Frameworks like CoreData and your applications.

Code that wishes to perform validation should invoke validateValue:forKey:error: rather than the custom validation method directly.

For example:

if ([[self model] validateValue:&text forKey:@"name" error:&validationError]){
    [[self model] setValue:text forKey:@"name"];
} else {
    [self didFailWithError:validationError];
}

This should not be done from within an accessor method. An action method is the perfect place to do this.

A working example can be seen here

Upvotes: 0

Yuji
Yuji

Reputation: 34185

You can use both. For key named foo, you can either implement a specific method

-(BOOL)validateFoo:(id*)ioValue error:(NSError**)error {
        ...
}

or, a non-specific method 

- (BOOL)validateValue:(id *)ioValue forKey:(NSString *)key error:(NSError **)outError {
      if([key isEqualToString:@"foo"]){
           ...
      }else{
          return [super validateValue:ioValue forKey:key error:outError];
      }
  }

It is perfectly sensible that you didn't find validateIvar:error: in the API documentation, because the part Ivar needs to be changed for each key. You don't find every method called setFoo: for keys foo you defined in the system API reference, do you?

Upvotes: 3

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