状態 (つまり、暗号化キー) を持つサブクラスのカスタム インスタンスを作成し、キーを使用してオプション ディクショナリにNSValueTransformer
渡すことができます。-bind:toObject:withKeyPath:options:
NSValueTransformerBindingOption
IB は値トランスフォーマーをクラス名で参照するため、IB でこれを直接設定することはできませんが、コードで行うことができます。非常に野心的である場合は、IB でバインディングをセットアップし、後でコード内の別のオプションに置き換えることができます。
次のようになります。
@interface EncryptingValueTransformer : NSValueTransformer
@property (nonatomic,readwrite,copy) NSData* encryptionKey;
@end
@implementation EncryptingValueTransformer
- (void)dealloc
{
_encryptionKey = nil;
}
- (id)transformedValue:(id)value
{
if (!self.encryptionKey)
return nil;
// do the transformation
return value;
}
- (id)reverseTransformedValue:(id)value
{
if (!self.encryptionKey)
return nil;
// Do the reverse transformation
return value;
}
@end
@interface MyViewController : NSViewController
@property (nonatomic, readwrite, assign) IBOutlet NSControl* controlBoundToEncryptedValue;
@end
@implementation MyViewController
// Other stuff...
- (void)loadView
{
[super loadView];
// Replace IB's value tansformer binding settings (which will be by class and not instance) with specific,
// stateful instances.
for (NSString* binding in [self.controlBoundToEncryptedValue exposedBindings])
{
NSDictionary* bindingInfo = [self.controlBoundToEncryptedValue infoForBinding: binding];
NSDictionary* options = bindingInfo[NSOptionsKey];
if ([options[NSValueTransformerNameBindingOption] isEqual: NSStringFromClass([EncryptingValueTransformer class])])
{
// Out with the old
[self.controlBoundToEncryptedValue unbind: binding];
// In with the new
NSMutableDictionary* mutableOptions = [options mutableCopy];
mutableOptions[NSValueTransformerNameBindingOption] = nil;
mutableOptions[NSValueTransformerBindingOption] = [[EncryptingValueTransformer alloc] init];
[self.controlBoundToEncryptedValue bind: binding
toObject: bindingInfo[NSObservedObjectKey]
withKeyPath: bindingInfo[NSObservedKeyPathKey]
options: mutableOptions];
}
}
}
// Assuming you're using the standard representedObject pattern, this will get set every time you want
// your view to expose new model data. This is a good place to update the encryption key in the transformers'
// state...
- (void)setRepresentedObject:(id)representedObject
{
for (NSString* binding in [self.controlBoundToEncryptedValue exposedBindings])
{
id transformer = [self.controlBoundToEncryptedValue infoForBinding: NSValueBinding][NSOptionsKey][NSValueTransformerBindingOption];
EncryptingValueTransformer* encryptingTransformer = [transformer isKindOfClass: [EncryptingValueTransformer class]] ? (EncryptingValueTransformer*)transformer : nil;
encryptingTransformer.encryptionKey = nil;
}
[super setRepresentedObject:representedObject];
// Get key from model however...
NSData* encryptionKeySpecificToThisUser = /* Whatever it is... */ nil;
for (NSString* binding in [self.controlBoundToEncryptedValue exposedBindings])
{
id transformer = [self.controlBoundToEncryptedValue infoForBinding: NSValueBinding][NSOptionsKey][NSValueTransformerBindingOption];
EncryptingValueTransformer* encryptingTransformer = [transformer isKindOfClass: [EncryptingValueTransformer class]] ? (EncryptingValueTransformer*)transformer : nil;
encryptingTransformer.encryptionKey = encryptionKeySpecificToThisUser;
}
}
// ...Other stuff
@end