objective c - NSNotification sent once, but is received multiple times -

i communicating between 2 classes nsnotificationcenter. problem although tap button once (and button fires off once) unintentionally producing increasing numbers of notifications 1 call nsnotificationcenter.

here better explanation of problem, code:

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my 2 classes mainview class , menu class.

when view in mainview class tapped, launches view created , governed menu class. code called when mainview initialized:

menu=[[mymenu alloc] init]; uitapgesturerecognizer * tap=[[uitapgesturerecognizer alloc] initwithtarget:self action:@selector(ontapped:)]; [tap setnumberoftapsrequired:1]; [container addgesturerecognizer:tap]; [[nsnotificationcenter defaultcenter] addobserver:self selector:@selector(onchangeitem:) name:@"itemchange" object:nil]; 

this gesture recognizer fires off method, in mainview class:

- (void) ontapped: (uigesturerecognizer*) recognizer {     nslog(@"tap");     [menu displaymenu]; } 

this how menu class initializes:

- (mymenu*) init {     self=[super init];     uicollectionviewflowlayout * layout=[[uicollectionviewflowlayout alloc] init];     menuview=[[uicollectionview alloc] initwithframe:cgrectmake(0, 0, 200, 200) collectionviewlayout:layout];     [menuview setdatasource:self];     [menuview setdelegate:self];     [menuview registerclass:[uicollectionviewcell class] forcellwithreuseidentifier:@"cell"];     [menuview setautoresizessubviews:yes];     [menuview setautoresizingmask:uiviewautoresizingflexibleheight | uiviewautoresizingflexiblewidth];     [menuview setbackgroundcolor:[uicolor clearcolor]];     [menuview setindicatorstyle:uiscrollviewindicatorstylewhite];     return self; } 

and displaymenu method inside menu class:

- (void) displaymenu {     [viewformenu addsubview:menuview]; } 

the menu class has clearmenu method:

- (void) clearmenu {     [menuview removefromsuperview]; } 

this code each cell in uicollectionview, contained within menu class:

- (uicollectionviewcell*) collectionview:(uicollectionview *)collectionview cellforitematindexpath:(nsindexpath *)indexpath {     uicollectionviewcell * cell=[collectionview dequeuereusablecellwithreuseidentifier:@"cell" forindexpath:indexpath];     [cell settag:indexpath.row];     uitapgesturerecognizer * tap=[[uitapgesturerecognizer alloc] initwithtarget:self action:@selector(onbuttontapped:)];     [tap setnumberoftapsrequired:1];     [cell addgesturerecognizer:tap];     nslog(@"button tapped : %d",indexpath.row);     return cell; } 

this calls onbuttontapped: method, within menu class:

- (void) onbuttontapped:(uigesturerecognizer*) recognizer {     nsinteger buttontapped=[[recognizer view] tag];     [[nsnotificationcenter defaultcenter] postnotificationname:@"itemchange" object:nil userinfo:@{@"selected":@(buttontapped)}]; [self clearmenu]; } 

this notification picked mainview class code:

[[nsnotificationcenter defaultcenter] addobserver:self selector:@selector(onchangeitem:) name:@"itemchange" object:nil]; 

this calls onchangeitem: method, inside mainview class:

- (void) onchangeitem: (nsnotification*) notification {     nslog(@"change item %d",[[[notification userinfo] objectforkey:@"clock"] intvalue]); } 

so that's code.

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ok, here's problem: first time menu displays in log:

...[43023:11f03] tap ...[43023:11f03] button tapped : 1 ...[43023:11f03] change item 1 

and fine, expect. second time around this:

...[43023:11f03] tap ...[43023:11f03] button tapped : 1 ...[43023:11f03] change item 1 ...[43023:11f03] change item 1 

third time around this:

...[43023:11f03] tap ...[43023:11f03] button tapped : 1 ...[43023:11f03] change item 1 ...[43023:11f03] change item 1 ...[43023:11f03] change item 1 ...[43023:11f03] change item 1 

and on. each successive tap on menu item doubles amount of notification calls.

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to begin thought adding multiple views, , resulting in multiple button taps, , therefore multiple notifications calls.

however can see logs, not case. the buttons receiving 1 tap event - firing off 1 notification - receiving class gets sent multiple notifications.

can explain me?

sorry lengthy post!

well, assuming [[nsnotificationcenter defaultcenter] addobserver:self selector:@selector(onchangeitem:) name:@"itemchange" object:nil]; being added more once.

i remove potential observer before adding observer, so:

[[nsnotificationcenter defaultcenter] removeobserver:self name:@"itemchange" object:nil]; [[nsnotificationcenter defaultcenter] addobserver:self selector:@selector(onchangeitem:) name:@"itemchange" object:nil]; 

that way there ever 1 observer callback.