Titanium Infinite Scroll : Not working - titanium

Question

I am trying to add views to my scroll view when it reaches 40% scroll. This is the way I am doing it :
scrollView.add(//add first 10 initial containerView's);
var triggerScroll = true;
var scrollPercentage = 0;
scrollView.addEventListener('scroll', function(e) {
var devHeight = Ti.Platform.displayCaps.platformHeight;
var currPos = scrollView.contentOffset.y;
if(currPos > devHeight){
currPos = currPos - devHeight;
}
scrollPercentage = (currPos)/devHeight * 100;
if(scrollPercentage > 40 && triggerScroll){
triggerScroll = false;
var containerView = myapp.createMyView();
scrollView.add(containerView);
}
//reset scroll to true after the offset reaches end of the screen, so that the
//'scroll' event listener only gets called ONCE every time it crosses 40%
if(scrollPercentage > 101){
triggerScroll = true;
}
});
But its just not working. I am trying to support infinite scroll in my vertical scroll view. Any idea whats going wrong ?

Answer 1

I use the module below when working with infinite scrolling. It use a TableView, but I would think you can apply it to a ScrollView as well. You need to pass in a function that will be called when the TableView register that more content should be loaded.
When you have finished loading you must call the loadingDone-function in order to enable the TableView to initiate another loading sequence.
The value m_bNoDataFound ensure that the loading sequence is not initiated, when there is no more data to fill into the list.
You can alter the offsets (currently 0.75 for Android and 0.90 for iOS) if want the loading sequence to be initiated sooner or later during scroll.
function TableView( onLoad ) {
var isAndroid = Ti.Platform.osname === 'android' ? true : false;
var m_bNoDataFound = false;
var m_nLastDistance = 0;
var m_bPulling = false;
var m_bLoading = false;
var table = Ti.UI.createTableView( {
height : Ti.UI.FILL
} );
table.addEventListener( 'scroll', function( evt ) {
//Scroll to load more data
if( !m_bNoDataFound ) {
if( isAndroid ) {
if( !m_bLoading && ( evt.firstVisibleItem + evt.visibleItemCount ) >= ( evt.totalItemCount * 0.75 ) ) {
onLoad( true );
m_bLoading = true;
}
}
else {
var nTotal = evt.contentOffset.y + evt.size.height;
var nEnd = evt.contentSize.height;
var nDistance = nEnd - nTotal;
if( nDistance < m_nLastDistance ) {
var nNearEnd = nEnd * 0.90;
if( !m_bLoading && ( nTotal >= nNearEnd ) ) {
onLoad( true );
m_bLoading = true;
}
}
m_nLastDistance = nDistance;
}
}
} );
function m_fLoadingDone( a_bNoDataFound ) {
m_bNoDataFound = a_bNoDataFound;
if( m_bLoading )
setTimeout( function( ) {
m_bLoading = false;
}, 250 );
}
return {
table : table,
loadingDone : m_fLoadingDone
};
};
module.exports = TableView;

Answer 2

When integrating an infinite scroll within a scrollview, there are some important things you have to consider:
1. scroll event is triggered a lot: try to throttle your scroll event callback using underscoreJS.
Throttle creates and returns a new, throttled version of the passed function, that, when invoked repeatedly, will only actually call the original function at most once per every wait milliseconds. Useful for rate-limiting events that occur faster than you can keep up with. See the underscorejs documentation for more.
2. Default and system units on Android vs iOS: The size of a view on Android uses a different display unit than coordinates of a view. This mismatch in units will cause incorrect calculation of your trigger for the infinite scroll. To solve this, you have to get and set the default unit yourself. The solution can be found in this widget (see getDefaultUnit()): https://github.com/FokkeZB/nl.fokkezb.color/blob/master/controllers/widget.js
3. The ti-infini-scroll can help you with this: this library creates a wrapper around the default Titanium ScrollView. This wrapper contains the calculation of the end of scroll (your trigger for updating/getting new data). When using this library, don't forget to implement bullet number 2.
https://github.com/goodybag/ti-infini-scroll