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I am trying to implement an undo/redo functionality during drawing a fetaure using the draw interaction. For the modify interaction I was able to to do it using the 'modifyend' event. like so:

modifyInteraction.on('modifyend',function(e){ 
}

while for the draw interaction no such events exist. 'drawend' event fires when finishing my drawing. But I need to trace all the vertices drawn in the meantime. For the time being I came up with this:

myapp.Editor.editDraw = new ol.interaction.Draw({
    source: myapp.Editor.PseudoEditLyr.getSource(),
    type: type,/** @type {ol.geom.GeometryType} */ 
    style: drawStyle,
    condition : function(e){
        //fires the mousedown event while drawing
        console.log("e.browserEvent.type",e.browserEvent.type);
        if (myapp.Editor.editSketch ){
        myapp.Editor.checkAndPushUndo(myapp.Editor.editSketch);
        }
        return true;//always return true but need to listen for the mousedown event
    }
    });

Which does the job but this is not elegant, as it trace the 'mousedown' event and not the 'vertexadd'.

Do any of you have any idea?

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Using some code out of Openlayers drawing interaction geometryFunction and with a little bit of imagination I ended up with the following, which is not perfect but it is more elegant than the one I allready have.

var coords_length = 0;
myapp.Editor.editDraw = new ol.interaction.Draw({
    source: myapp.Editor.PseudoEditLyr.getSource(),
    type: type,/** @type {ol.geom.GeometryType} */ 
    style: drawStyle,
    geometryFunction: function(coords, geom) {
    if (type === "Polygon"){
        if (!geom) {
            geom = new ol.geom.Polygon(null);
        }        
        geom.setCoordinates(coords);
        //if coords is changing
        if(coords[0].length !== coords_length){
            //set the new length
            coords_length = coords[0].length;
            console.log("polyogn geom changing. You may fire the undo action here!!!!   "+coords_length);
            if (myapp.Editor.editSketch ){
            myapp.Editor.checkAndPushUndo(myapp.Editor.editSketch);
            }
        }
    }
    if (type === "LineString"){
        if (!geom) {
            geom = new ol.geom.LineString(null);
        }        
        geom.setCoordinates(coords);
        if(coords.length !== coords_length){
            //set the new length
            coords_length = coords.length;
            console.log("line geom changing. You may fire the undo action here!!!!   "+coords_length);
            if (myapp.Editor.editSketch ){
            myapp.Editor.checkAndPushUndo(myapp.Editor.editSketch);
            }
        }
    }
    return geom;
    }

    });

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