ios - KVO observeValueForKeyPath 方法被调用了两次

Question

我写了一个演示想尝试 KVO 编程，我找到了 observeValueForKeyPath当我只更改一次值时，方法总是执行两次，怎么了？请帮助我，谢谢

代码

状态同步器.h

#import <Foundation/Foundation.h>

 @interface StatusSyncer : NSObject
 @property NSString *title;
 +(instancetype)sharedInstance;
@end

StatusSyncer.m

#import "StatusSyncer.h"
@implementation StatusSyncer
+ (instancetype)sharedInstance {
   static id _sharedInstance = nil;
   static dispatch_once_t oncePredicate;
   dispatch_once(&oncePredicate, ^{
      _sharedInstance = [[self alloc] init];
   });
   return _sharedInstance;
}
@end

ViewController.m

- (void)viewDidLoad {
   [super viewDidLoad];
   [self.statusSyncer addObserver:self forKeyPath:@"title"    options:NSKeyValueObservingOptionNew context:nil];

 }

 -(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{
    if ([keyPath isEqualToString:@"title"]) {
        NSLog(@"chane");
    }
}

-(StatusSyncer *)statusSyncer{
    if (_statusSyncer==nil) {
        _statusSyncer = [StatusSyncer sharedInstance];
    }

    return _statusSyncer;
}

DetailViewController.m

- (IBAction)changeAction:(id)sender {
    self.statusSyncer.title= @"newTitle叶";

}

-(StatusSyncer *)statusSyncer{
    if (_statusSyncer==nil) {
        _statusSyncer = [StatusSyncer sharedInstance];
    }

    return _statusSyncer;
}

输出:

2015-06-15 12:58:49.849 KVOAdvence[2433:74541] chane
2015-06-15 12:58:49.850 KVOAdvence[2433:74541] chane

Answer 1

我认为 addObserver: 方法执行了两次。

你会检查其他 Controller 继承，它可能会扩展 ViewController