Leaflet - How to match marker and polyline on drag and drop

Question

I have a project with leafletJS. For example, I have 2 points (A, B) in map. I display it as 2 Markers I must draw a polyline from A to B. I moved marker A and I want to the head of polyline of marker A match to marker A (moved follow marker A). How can I do this? Sorry for my bad English. Thanks all very much.

Truong M.

Answer 1

Given the following L.Latlng's, L.Marker's and L.Polyline:

var a = new L.LatLng(-45, -90),
    b = new L.LatLng(45, 0),
    c = new L.LatLng(-45, 90);

var marker_a = new L.Marker(a, {draggable: true}).addTo(map),
    marker_b = new L.Marker(b, {draggable: true}).addTo(map),
    marker_c = new L.Marker(c, {draggable: true}).addTo(map);

var polyline = new L.Polyline([a, b, c]).addTo(map);

You'll need to attach eventlisteners and callbacks to your L.Marker's. You could automate this, but i'll keep it simple for now:

marker_a
    .on('dragstart', dragStartHandler)
    .on('drag', dragHandler)
    .on('dragend', dragEndHandler);

marker_b
    .on('dragstart', dragStartHandler)
    .on('drag', dragHandler)
    .on('dragend', dragEndHandler);

marker_c
    .on('dragstart', dragStartHandler)
    .on('drag', dragHandler)
    .on('dragend', dragEndHandler);

Now on dragstart you'll need to find the latlng from the polyline which corresponds with your marker's latlng and store it's key in your marker instance so you can use it later on:

function dragStartHandler (e) {

    // Get the polyline's latlngs
    var latlngs = polyline.getLatLngs(),

        // Get the marker's start latlng
        latlng = this.getLatLng();

    // Iterate the polyline's latlngs
    for (var i = 0; i < latlngs.length; i++) {

        // Compare each to the marker's latlng
        if (latlng.equals(latlngs[i])) {

            // If equals store key in marker instance
            this.polylineLatlng = i;
        }
    }
}

Now you know the key of the polyline's latlng you can change it when dragging the marker on the dragevent:

function dragHandler (e) {

    // Get the polyline's latlngs
    var latlngs = polyline.getLatLngs(),

        // Get the marker's current latlng
        latlng = this.getLatLng();

    // Replace the old latlng with the new
    latlngs.splice(this.polylineLatlng, 1, latlng);

    // Update the polyline with the new latlngs
    polyline.setLatLngs(latlngs);
}

Just to be clean and tidy remove the stored key on dragend:

function dragEndHandler (e) {

    // Delete key from marker instance
    delete this.polylineLatlng;
}

That's it. Here's a working example on Plunker: http://embed.plnkr.co/SJRec3/preview