ios - KVO observeValueForKeyPath method called twice -


i write demo wanted trying kvo programming,i found observevalueforkeypath method execute twice when change value once,what's wrong?please me,thanks

code

statussyncer.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= @"newtitleć¶";  }  -(statussyncer *)statussyncer{     if (_statussyncer==nil) {         _statussyncer = [statussyncer sharedinstance];     }      return _statussyncer; }

output：

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

i think method addobserver: performed twice.

you check other controllers inheritance, may extends viewcontroller


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