openlayers4实现拖动Feature效果

拖动矢量图层feature，获取拖动后feature

官网拓展了interaction,增加了Drag的Interaction

代码说明

*handleDragEvent注册的这个事件里面是拖动后获取到的feature，
handleDownEvent这是鼠标点击feature时的事件，可以进行对拖拽的图形进行限制*

/**
 * Define a namespace for the application.
 */
var app = {};


/**
 * @constructor
 * @extends {ol.interaction.Pointer}
 */
app.Drag = function() {

    ol.interaction.Pointer.call(this, {
        handleDownEvent: app.Drag.prototype.handleDownEvent,
        handleDragEvent: app.Drag.prototype.handleDragEvent,
        handleMoveEvent: app.Drag.prototype.handleMoveEvent,
        handleUpEvent: app.Drag.prototype.handleUpEvent
    });

    /**
     * @type {ol.Pixel}
     * @private
     */
    this.coordinate_ = null;

    /**
     * @type {string|undefined}
     * @private
     */
    this.cursor_ = 'pointer';

    /**
     * @type {ol.Feature}
     * @private
     */
    this.feature_ = null;

    /**
     * @type {string|undefined}
     * @private
     */
    this.previousCursor_ = undefined;

};
ol.inherits(app.Drag, ol.interaction.Pointer);


/**
 * @param {ol.MapBrowserEvent} evt Map browser event.
 * @return {boolean} `true` to start the drag sequence.
 */
app.Drag.prototype.handleDownEvent = function(evt) {
    var map = evt.map;

    var feature = map.forEachFeatureAtPixel(evt.pixel,
        function(feature) {
            return feature;
        }, {
            layerFilter: function(l) {//限制可拖动图层，可根据实际需求进行过滤
                if (l.getProperties().name == 'locatelayer') {
                    return true;
                } else {
                    return false;
                }
            }

        });

    if (feature) {
        this.coordinate_ = evt.coordinate;
        this.feature_ = feature;
    }

    return !!feature;
};


/**
 * @param {ol.MapBrowserEvent} evt Map browser event.
 */
app.Drag.prototype.handleDragEvent = function(evt) {
    var deltaX = evt.coordinate[0] - this.coordinate_[0];
    var deltaY = evt.coordinate[1] - this.coordinate_[1];

    var geometry = this.feature_.getGeometry();
    geometry.translate(deltaX, deltaY);

  //此时的geometry就是拖动后的geometry
};


/**
 * @param {ol.MapBrowserEvent} evt Event.
 */
app.Drag.prototype.handleMoveEvent = function(evt) {
    if (this.cursor_) {
        var map = evt.map;
        var feature = map.forEachFeatureAtPixel(evt.pixel,
            function(feature) {
                return feature;
            });
        var element = evt.map.getTargetElement();
        if (feature) {

            if (element.style.cursor != this.cursor_) {
                this.previousCursor_ = element.style.cursor;
                element.style.cursor = this.cursor_;
            }
        } else if (this.previousCursor_ !== undefined) {
            element.style.cursor = this.previousCursor_;
            this.previousCursor_ = undefined;
        }
    }
};


/**
 * @return {boolean} `false` to stop the drag sequence.
 */
app.Drag.prototype.handleUpEvent = function() {
    this.coordinate_ = null;
    this.feature_ = null;
    return false;
};
//初始化地图时，初始化interaction
var map = new ol.Map({
    target: 'mapContent',
    interactions: ol.interaction.defaults().extend([new app.Drag()]), 
    controls: ol.control.defaults({
        attribution: false,
        zoom: false
    }),
    layers: [baidumap, sectionLayer, locateLayer],
    view: view
});