Я создал простое какао-приложение. В MainMenu.xib я добавил NSDatePicker и NSTextField. У обоих этих объектов есть привязки Value к свойствам App Delegate. Я ожидаю, что когда пользователь изменит дату в NSDatePicker, NSTextField будет обновлен. Этого не происходит. Вот делегат приложения:
// AppDelegate.h
#import <Cocoa/Cocoa.h>
@interface AppDelegate : NSObject <NSApplicationDelegate>
@property (assign) IBOutlet NSWindow *window;
@property (nonatomic, strong) NSDate *dateFromPicker;
@property (nonatomic, readonly) NSString *dateString;
@end
// AppDelegate.m
#import "AppDelegate.h"
@implementation AppDelegate
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
}
- (NSString *)dateString
{
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
return [formatter stringFromDate:self.dateFromPicker];
}
+ (NSSet *)keyPathsForValuesAffectingDateString
{
return [NSSet setWithObject:@"dateFromPicker"];
}
@end
Обновленный код с наблюдателем для dateFromPicker и некоторыми операторами NSLog:
@implementation AppDelegate
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
[self addObserver:self forKeyPath:@"dateFromPicker" options:0 context:NULL];
self.dateFromPicker = [NSDate dateWithNaturalLanguageString:@"12/12/12"];
}
- (NSString *)dateString
{
NSLog(@"dateString was called.");
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
return [formatter stringFromDate:self.dateFromPicker];
}
+ (NSSet *)keyPathsForValuesAffectingDateString
{
NSLog(@"keyPathsForValuesAffectingDateString was called.");
return [NSSet setWithObject:@"dateFromPicker"];
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change: (NSDictionary *)change context:(void *)context
{
NSLog(@"dateFromPicker changed.");
}
@end
Вот журнал:
2012-08-10 15:37:15.086 ... keyPathsForValuesAffectingDateString was called.
2012-08-10 15:37:15.087 ... dateString was called.
2012-08-10 15:37:15.116 ... dateFromPicker changed.
2012-08-10 15:37:15.117 ... dateString was called.
2012-08-10 15:37:19.831 ... dateFromPicker changed.
2012-08-10 15:37:19.831 ... dateString was called.