Add 'movestart' event on map.

[shaunakv1]

Just like there is a 'moveend' event available on map, it would be very convenient to have a movestart event.

Use Case
In case when triggering a ol.animation.pan I may want to toggle once before the animation starts and toggle it back once after animation ends.
We have to remember here that animation might not actually happen based on where we are panning to. So just doing something before triggering pan is not enough, because toggle back might not happen if it doesn't actually pan (`moveend') doesn't get called in this event.

fix 1
This can be fixed , if moveend is called even if the actual move doesn't happen, if pan was triggered.

fix2
movestart event should be provided which just like moveend doesnt get called if there is no movement happening in the map.

Currently it is possible to achieve this using map.beforeRender but, it just seems too much ugly coding to achieve something very simple.

* current solution*

           var pan = ol.animation.pan({
                duration: 700,
                source: map.getView().getCenter()
            });

            map.beforeRender(function(map, frameState) {
              var stillPanning = pan(map, frameState); // returns false panning is done

              if (stillPanning){
                 // do movestart stuff here
                 if(!everDone){
                       doSomething();
                       everDone = true;
                  }
              }
              else{
                 // do move end stuff here
                 undoSomething();
                 everDone = false; 
              }              
              return stillPanning;
            });

            map.getView().setCenter(geom);    

This could all have been done in two simple map.on("movestart") and map.on("moveend") callbacks like it was supported in OpenLayers2.

Here's a jsFiddle that demonstrates what I need to do with the non-ideal solution I posted. Try pressing the pan-map second time and see how moveend does not fire, but animation end does.

update

I have updated my original question and answer on stackoverflow to summarize the discussion here:

http://stackoverflow.com/questions/31896300/openlayers-3-movestart-event-on-map/31897512.
Thanks!

[elmuSSo]

I would also like to see movestart event.

[shaunakv1]

@elmuSSo I have working example of a solution in my stack-overflow question. Its not ideal but works just fine. Still agree it would be good to have that event generated by the OL3

[milovanderlinden]

+1, this is really a great miss when upgrading an ol2 application that uses navhistory to ol3. And please, don't tell me to look at the permalink example ;-)

[ahocevar]

@milovanderlinden I'm failing to understand how a movestart event would help you with navigation history. Are you sure you commented on the correct ticket?

[milovanderlinden]

Yes, I am. Sorry if I got you confused.

I have an application using ol2 that has had http://dev.openlayers.org/releases/OpenLayers-2.6/doc/apidocs/files/OpenLayers/Control/NavigationHistory-js.html implemented on custom buttons since day 1. So when I cherry-picking upgraded it, I discovered that the navigation control was missing in ol3. Then I tried to recreate it "ol3-style", but I noticed that there is no setCenter(center, zoom); so I tried to call the actions individually, to find out they fired seperate moveend events and when I added rotation, even 3.

Then I got stuck in un('moveend') not un-ing the way I wanted, duplicating moveend events. And finally, using moveend complicated array manipulation for the back and forward arrays. So I stopped trying.

It would be nice if I could rewrite https://github.com/cscott530/leaflet-history for ol3. It uses movestart.

Perhaps this is the wrong discussion. But I am strongly in favour of having a movestart event.

[joaorodr84]

Hi. It seems the 'movestart' event is still not available in OpenLayers 3.17.1. Are you planning to add that event? It is really useful. Thanks

[ahocevar]

You can give your map a movestart event with the following code:

function onpropertychange() {
  map.dispatchEvent('movestart');
  var view = map.getView();
  view.un('propertychange', onpropertychange);
  map.on('moveend', function() {
    view.on('propertychange', onpropertychange);
  });
};
map.getView().on('propertychange', onpropertychange);

[shaunakv1]

Great Suggestion! Listening to map.getView().on('propertychange', onpropertychange); will also get triggered when the user zooms and not just on pan though.

[fredj]

@shaunakv1 try to use 'change:center' instead of 'propertychange'

[shaunakv1]

Center too updates when the map zooms (with scroll wheel, and on subsequent zoom button use), so it still gets triggered:

Example:
http://jsfiddle.net/5mwpq7g1/2/

[joaorodr84]

@ahocevar Thank you for your precious suggestion. It seems to work exactly like I wanted. :)

@fredj Thanks. I use 'change:center' and it it triggers only on pans. ;)

@shaunakv1 In your fiddle, the 'movestart' event gets triggered on each mouse move. I use 'change:center' everywhere. And so, it only gets triggered once ant the start of a pan. See my fiddle.

Thank you to all of you. :D

[cs09g]

but this solution creates a lot of moveend event. maybe the side effect is when you add two listeners on movestart event, it runs 4 times(2 x 2).

[ischas]

@joaorodr84 If you zoom with mousewheel or doubleclick, 'change:center' will be triggered as well.

[cs09g]

@ischas that's expected behavior. it's the same when you use 'moveend' event. zoom event triggers moveend event as well.