Paper-tabs Assertion Failed: You modified canPageBack twice in a single render

[betocantu93]

Im getting this error
Assertion Failed: You modified "canPageBack" twice in a single render
in mobile chrome which prevents the smoothly transition to hidden tabs.

I tracked it down to this.fixOffsetIfNeeded(); which is executed everytime the _selectedTab change which at least in my use case, it can be changed both programatically (i.e selected=someProperty) or by the end user when clicked on a tab or the next, previous arrows.

[betocantu93]

I just noticed the observer _selectedTabDidChange is getting fired, twice... I need to track why, it might be a bug in my app code.

[betocantu93]

The _selectedTab computed gets triggered N times each selected change, this leads to changing the variable twice in the single render, so changing the computed to watch selected, which in theory just changes once and finding in childs by value, will just execute the observer once.

[miguelcobain]

@betocantu93 _selectedTab is indeed triggering multiple times when clicking on a tab. Nice find.

I don't think we should remove the childComponents dependency entirely from the observer, though.
The reason is because we might want to add a tab later, and in that case the offset needs to be run to update the ink bar position.

I tried the following locally and it seems to only trigger _selectedTab once. Can you try it on your local and see if it fixes your "modified twice" errors?
If it solves, please update the PR with the changes.

-  _selectedTab: computed('childComponents.@each.isSelected', function() {
-    return this.get('childComponents').findBy('isSelected');
+  _selectedTab: computed('childComponents.@each.value', 'selected', function() {
+    return this.get('childComponents').findBy('value', this.get('selected'));
   }),
 
-  _selectedTabDidChange: observer('_selectedTab', function() {
+  _selectedTabDidChange: observer('_selectedTab', 'childComponents.[]', function() {
     let selectedTab = this.get('_selectedTab');
     let previousSelectedTab = this.get('_previousSelectedTab');

[betocantu93]

Your changes work in my app, it only gets triggered once

[miguelcobain]

Thanks a lot @betocantu93 !