How to listen for user generated zoom in Google Maps?

Question

I want to know when a Google Maps zoom_changed event is fired specifically by a user interaction with the +/- zoom buttons. If I use a general event listener for zoom_changed,

Answer 1

I solved this issue by creating Custom Zoom buttons for my Map.

Here is the code from my project:
Edit: Removed unnecessary and self explanatory common code

your zoomControl function:

function zoomControl(map, div) {

  var controlDiv = div,
      control = this;

  // Set styles to your own pa DIV
  controlDiv.style.padding = '5px';

  // Set CSS for the zoom in div.
  var zoomIncrease = document.createElement('div');
  zoomIncrease.title = 'Click to zoom in';
  // etc.

  // Set CSS for the zoom in interior.
  var zoomIncreaseText = document.createElement('div');
  // Use custom image
  zoomIncreaseText.innerHTML = '<strong><img src="./images/plusBut.png" width="30px" height="30px"/></strong>';
  zoomIncrease.appendChild(zoomIncreaseText);

  // Set CSS for the zoom out div, in asimilar way
  var zoomDecreaseText = document.createElement('div');
  // .. Code .. Similar to above

  // Set CSS for the zoom out interior.
  // .. Code ..

  // Setup the click event listener for Zoom Increase:
  google.maps.event.addDomListener(zoomIncrease, 'click', function() {
      zoom = MainMap.getZoom();
      MainMap.setZoom(zoom+1);
      // Other Code parts
  });

  // Setup the click event listener for Zoom decrease:
  google.maps.event.addDomListener(zoomDecrease, 'click', function() {
      zoom = MainMap.getZoom();
      MainMap.setZoom(zoom-1);
  });
}

your initialize function:

function initializeMap() {

    var latlng = new google.maps.LatLng(38.6, -98);
    var options = {
        zoom : 5,
        center : latlng,
        mapTypeId : google.maps.MapTypeId.ROADMAP,  
        // Other Options
    };
    MainMap = new google.maps.Map(document.getElementById("google-map-canvas"),
            options);

    // The main part - Create your own Custom Zoom Buttons
    // Create the DIV to hold the control and call the zoomControl()
    var zoomControlDiv = document.createElement('div'), 
        zoomLevelControl = new zoomControl(MainMap, zoomControlDiv);

    zoomControlDiv.index = 1;
    MainMap.controls[google.maps.ControlPosition.RIGHT_TOP].push(zoomControlDiv);
}

Hope it helps

Answer 2

var zoomFlag = "user"; // always assume it's user unless otherwise

// some method changing the zoom through API
zoomFlag = "api";
map.setZoom(map.getZoom() - 1);
zoomFlag = "user";

// google maps event handler
zoom_changed: function() {
  if (zoomFlag === "user") {
    // user zoom
  }
}

Answer 3

I wouldn't just hook in to the +/- buttons (or buttons on your own custom control for that matter). The user can change the zoom on the map with the mouse wheel, or by double-clicking on the map. Plus, you'd be relying on implementation detail rather than documented API, which is a major no-no.

This really means the only reliable, documented way to detect a change in zoom is to listen to the zoom_changed event of the Map.

If your event handler can't determine whether the event came from user action or an API call, there's two approaches:

• Set a flag before calling an API function so that you know you can ignore this change.
• Can you re-architect your app such that it does not matter whether a zoom change came from code or the user?

Answer 4

I would suggest using a custom control for zoom in/out and then using event listeners on the custom congrol:

http://goo.gl/u8gKC

You can easily hide the default zoom control:

http://goo.gl/N5HIE

(zoomControl to be specific)

Answer 5

I was looking to do the same thing. I was hoping to find that there was a way built into the Google Maps API, but at a minimum, you should be able to store the starting zoom level as a variable when you initialize the map. Then, compare the result of getZoom() to it to know whether it was a zoom in or a zoom out.

For example:

map = new google.maps.Map(document.getElementById('map_canvas'), { zoom: 11 });
var previous_zoom = 11;

google.maps.event.addListener(map,'zoom_changed',function(){
  if(map.getZoom() > previous_zoom) {
    alert('You just zoomed in.');
  }
  previous_zoom = map.getZoom();
}