OpenLayers – Understanding Polygon Handler Function in OpenLayers

javascriptopenlayers-2polygon

Using openlayers, I want to be able to draw one polygon on a map. After one polygon is drawn, I want an event to fire that stops any more from being drawn until a button is pressed. My current code allows the user to draw more than one polygon and I'm trying to figure out how to limit it. This is my current code:

// Add drawing layer 
analysisLayer = new OpenLayers.Layer.Vector("analysisLayer");   
map.addLayer(analysisLayer);

// add polygon drawing control
polygon = new OpenLayers.Control.DrawFeature(analysisLayer, OpenLayers.Handler.Polygon);
map.addControl(polygon);

What I tried doing was adding a callback to the Control.DrawFeature function as follows:

// add polygon drawing control
polygon = new OpenLayers.Control.DrawFeature(
    analysisLayer, 
    OpenLayers.Handler.Polygon, {callbacks: { "finalize" : function(){alert('poly made')} } } );
    map.addControl(polygon);

This does not work, but it does not give me an error. I'm not sure how exactly to structure this function. I did find the function finalize in the documentation which is what I thought I needed, but I'm also not sure how to structure the callback.

EDIT:
I'm starting to understand how these callbacks work. For example this detects that a feature has been added (using @Vadim's advice):

// detect polygon events 
function newPolygonAdded (evt) {
        alert('Polygon completed');
        polygon.deactivate(); //stops the drawing
    }   

// add polygon drawing control
polygon = new OpenLayers.Control.DrawFeature(analysisLayer, OpenLayers.Handler.Polygon, 
                            {eventListeners:{"featureadded": newPolygonAdded}});                                            
map.addControl(polygon);

What I still don't understand is how to limit the drawing layer from allowing more polygons to be drawn.

Best Answer

yourControl.events.register("featureadded", ' ' , controlFeatureHandler); 
...

function controlFeatureHandler(data)
{
    // do regular stuff


    // DISABLE control to draw
    yourControl.deactivate();
}
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