[TIMOB-20030] iOS: Repeated call of listView.addEventListener('scrollstart') should only result in 1 listener

GitHub Issue	n/a
Type	Bug
Priority	High
Status	Closed
Resolution	Fixed
Resolution Date	2015-12-10T06:02:14.000+0000
Affected Version/s	n/a
Fix Version/s	n/a
Components	iOS
Labels	Community
Reporter	Christian Waldmann
Assignee	Angel Petkov
Created	2015-07-22T13:39:29.000+0000
Updated	2017-03-22T22:44:24.000+0000

Description

Current behavior

With

listView.addEventListener('scrollstart', this.myCallback);

you can register an event listener. But there is no check if the listener is already registered. So if you do something like this:

function attach() {
    listView.addEventListener('scrollstart', this.myCallback);
}
attach();

//
// Lots of code or loop or async callback between 
//
attach();

you habe a second registered callback. You have todo something like this to unregister:

listView.removeEventListener('scrollstart', this.myCallback);
listView.removeEventListener('scrollstart', this.myCallback);

Its difficult to debug problems around that if you overlooked the second call of addEventListener.

Expected

- The second listener is not registered - (optional) Warning or notice that there is already a listener

Comments

Angel Petkov 2015-12-04

PR pending : https://github.com/appcelerator/titanium_mobile/pull/7548. The Hello message should only be displayed ones upon scrollEnd regardless of how many eventListeners are added.

 
   var win = Ti.UI.createWindow({
       backgroundColor : 'blue',
       title           : 'Main Window'
   });
   
   var listView = Ti.UI.createListView();
   
    function myFunction() {
     Ti.API.info("Hello");
    }
   
   var itemsSection = Ti.UI.createListSection({ headerTitle: 'Items'});
   var itemData = [
       {properties: { title: 'Item 1'}},
       {properties: { title: 'Item 2'}},
       {properties: { title: 'Item 3'}},
       {properties: { title: 'Item 4'}},
       {properties: { title: 'Item 5'}},
       {properties: { title: 'Item 6'}},
   ];
   
   listView.addEventListener("scrollend",myFunction);
   
   var addEventButton = Titanium.UI.createButton({
      title: 'Add Event',
      bottom: 10,
      width: 100,
      height: 50
   });
   
   addEventButton.addEventListener("click",function(e){
   listView.addEventListener("scrollend",myFunction);
   });
   
   itemsSection.setItems(itemData);
   var sections = [];
   sections.push(itemsSection);
   listView.sections = sections;
   win.add(listView);
   win.add(addEventButton);
   win.open();

Chee Kiat Ng 2015-12-10

CR and FT passed. PR Merged!
Lee Morris 2017-03-22

Closing ticket as fixed.

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