javascript - How to start mouseover event while dragging

Question

When I drag an element over another div on which I have a mouseover event, the event doesn't trigger. However, it works if I hover over it without dragging.

Is there a way to detect hover events on an element if I drag another one over it?

Answer 1

Here is an example using the X-Y coordinate solution.

Working example on jsfiddle

The example can be improved, but is a good starting point.

Simply keeps track of the mouse location and checks if it appears to be inside any bounding boxes of the droppable objects. Hence, if the mouseup event fires on any one of them, dragged object is dropped.

You can also use the coordinates of the object you are dragging for detecting if its on a droppable box, but it requires a little more code for finding the bounding box coords and using the mouse is enough for me.

The code uses jQuery but no jQueryUI. I tested in Chrome, Firefox and Opera, but not IE :)

I'm also adding the code to here if jsfiddle is not accessible.

HTML

<p>Drag orange boxes to grey ones</p>
<div class="droppable"></div>
<div class="droppable"></div>
<div class="droppable"></div>
<div class="droppable"></div>

<div class="draggable"></div>
<div class="draggable"></div>
<div class="draggable"></div>

CSS

.droppable {
    width:50px;
    height:50px;
    float: left;
    background-color: #DDD;
    margin: 5px;
}

.draggable {
    width:40px;
    height:40px;
    float: right;
    background-color: #FC0;
    margin: 5px;
    cursor: pointer;
}

.dropped {
    background-color: #FC0;
}

.somethingover {
    background-color: #FCD;
}

JS

var dragged, mousex, mousey, coordinates = [];

var continueDragging = function(e) {
    // Change the location of the draggable object
    dragged.css({
        "left": e.pageX - (dragged.width() / 2),
        "top": e.pageY - (dragged.height() / 2)
    });

    // Check if we hit any boxes
    for (var i in coordinates) {
        if (mousex >= coordinates[i].left && mousex <= coordinates[i].right) {
            if (mousey >= coordinates[i].top && mousey <= coordinates[i].bottom) {
                // Yes, the mouse is on a droppable area
                // Lets change the background color
                coordinates[i].dom.addClass("somethingover");
            }
        } else {
            // Nope, we did not hit any objects yet
            coordinates[i].dom.removeClass("somethingover");
        }
    }

    // Keep the last positions of the mouse coord.s
    mousex = e.pageX;
    mousey = e.pageY;
}

var endDragging = function(e) {
    // Remove document event listeners
    $(document).unbind("mousemove", continueDragging);
    $(document).unbind("mouseup", endDragging);

    // Check if we hit any boxes
    for (var i in coordinates) {
        if (mousex >= coordinates[i].left && mousex <= coordinates[i].right) {
            if (mousey >= coordinates[i].top && mousey <= coordinates[i].bottom) {
                // Yes, the mouse is on a droppable area
                droptarget = coordinates[i].dom;
                droptarget.removeClass("somethingover").addClass("dropped");
                dragged.hide("fast", function() {
                    $(this).remove();
                });
            }
        }
    }

    // Reset variables
    mousex = 0;
    mousey = 0;
    dragged = null;
    coordinates = [];
}

var startDragging = function(e) {
    // Find coordinates of the droppable bounding boxes
    $(".droppable").each(function() {
        var lefttop = $(this).offset();
        // and save them in a container for later access
        coordinates.push({
            dom: $(this),
            left: lefttop.left,
            top: lefttop.top,
            right: lefttop.left + $(this).width(),
            bottom: lefttop.top + $(this).height()
        });
    });

    // When the mouse down event is received
    if (e.type == "mousedown") {
        dragged = $(this);
        // Change the position of the draggable
        dragged.css({
            "left": e.pageX - (dragged.width() / 2),
            "top": e.pageY - (dragged.height() / 2),
            "position": "absolute"
        });
        // Bind the events for dragging and stopping
        $(document).bind("mousemove", continueDragging);
        $(document).bind("mouseup", endDragging);
    }
}

// Start the dragging
$(".draggable").bind("mousedown", startDragging);