OpenLayers 3 - 几何集合为空

Question

我对使用 Ol_3 编写几何有疑问。

当我使用 ol.interaction.Draw 时，我注意到在编写功能时有一些奇怪的行为。使用提到的交互我想添加矢量（点、线串、多边形等）但是在第一次尝试（或单击）时我得到 GEOMETRYCOLLECTION EMPTY 但是当我第二次使用相同的命令时我得到了想要的结果有人可以解释这种行为吗？如何避免这种行为？

是否可以先获取几何体 try/click？

下面的示例片段：

var vector = new ol.layer.Vector({
    source: new ol.source.Vector(),
    style: new ol.style.Style({
            image: new ol.style.Circle({
                radius: 12,
                fill: new ol.style.Fill()
            })
        })
});

var map = new ol.Map({
    layers: [
        new ol.layer.Tile({
            source: new ol.source.OSM()
        }),
        vector
    ],
    target: 'map',
    view: new ol.View({
        center: [-11000000, 4600000],
        zoom: 4
    })
});

map.on('pointermove', function(e) {
    if (e.dragging) return;
    var
        pixel = map.getEventPixel(e.originalEvent),
        hit = map.hasFeatureAtPixel(pixel);
    map.getTargetElement().style.cursor = hit ? 'pointer' : '';
});

var button = $('#pan').button('toggle');
var interaction;
var features = undefined;;
$('div.btn-group button').on('click', function(event) {
    var id = event.target.id;
    var features;
    var selectedFeatures = undefined;
    button.button('toggle');
    button = $('#' + id).button('toggle');
    map.removeInteraction(interaction);

    switch (id) {
        case "select":
            document.getElementById("export").innerHTML="";
            interaction = new ol.interaction.Select();
            map.addInteraction(interaction);
            features = interaction.getFeatures();

            dragBoxInteraction = new ol.interaction.DragBox({
                condition: ol.events.condition.platformModifierKeyOnly,
                style: new ol.style.Style({
                    stroke: new ol.style.Stroke({
                        color: [12, 25, 25, 4]
                    })
                })
            });
            dragBoxInteraction.on('boxend', function(event) {
                selectedFeatures = interaction.getFeatures();
                selectedFeatures.clear();
                var extent = dragBoxInteraction.getGeometry().getExtent();
                vector.getSource().forEachFeatureIntersectingExtent(extent, function(feature) {
                    selectedFeatures.push(feature);
                });
            });
            map.addInteraction(dragBoxInteraction);

            break;
        case "point":
            interaction = new ol.interaction.Draw({
                type: 'Point',
                source: vector.getSource()
            });
            vector.getSource().on('addfeature', function(e) {
                var source = e.target;
                var writer = new ol.format.WKT();

                if (vector.getSource().getState() === 'ready') {
                    //https://gis.stackexchange.com/questions/179907/openlayers-3-geojson-save-and-load
                    var wkt = writer.writeFeatures(vector.getSource().getFeatures());
                    document.getElementById("export").innerHTML = wkt;
                }
            });
            map.addInteraction(interaction);
            break;


        default:
            break;
    }
    var snap = new ol.interaction.Snap({
        source: vector.getSource()
    });
    map.addInteraction(snap);
});

<!DOCTYPE html>
<html lang="en">

<head>
    <!-- Required meta tags -->
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
    <!-- Bootstrap CSS -->
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/css/bootstrap.min.css" integrity="sha384-/Y6pD6FV/Vv2HJnA6t+vslU6fwYXjCFtcEpHbNJ0lyAFsXTsjBbfaDjzALeQsN6M" crossorigin="anonymous">
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/openlayers/4.3.2/ol.css" type="text/css">
</head>

<body>
    <div class="container">
        <div id="map" class="map"></div>
        <br>
 
            <pre>
            <div id="export"></div>
            </pre>
        <!-- <button type="button" class="btn btn-outline-danger" id="js-remove">Izbriši</button> -->
        <div class="btn-group btn-group-sm" id="bar" role="group" aria-label="Draw">
            <button id="pan" type="button" class="btn btn-primary">Pan</button>
            <button id="select" type="button" class="btn btn-default active">Select</button>
            <button id="point" value="pointless" type="button" class="btn btn-success">Point</button>
        </div>
        <!-- Optional JavaScript -->
        <!-- jQuery first, then Popper.js, then Bootstrap JS -->
        <script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
        <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.11.0/umd/popper.min.js" integrity="sha384-b/U6ypiBEHpOf/4+1nzFpr53nxSS+GLCkfwBdFNTxtclqqenISfwAzpKaMNFNmj4" crossorigin="anonymous"></script>
        <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/js/bootstrap.min.js" integrity="sha384-h0AbiXch4ZDo7tp9hKZ4TsHbi047NrKGLO3SEJAg45jXxnGIfYzk4Si90RDIqNm1" crossorigin="anonymous"></script>
        <script src="https://cdnjs.cloudflare.com/ajax/libs/openlayers/4.3.2/ol.js" type="text/javascript"></script>
        <script src="script.js" type="text/javascript"></script>
        <!-- <script src="functions_draw.js" type="text/javascript"></script> -->
</body>

</html>

更新

我根据 JGH 的回答编辑了代码片段，希望对您有所帮助:)

Answer 1

drawend 事件在功能实际添加到其源之前触发。它在 finishDrawing() 定义下（不明显）记录在案 here。

因此，为了让您的代码正常工作，您可以在图层源而不是交互上侦听事件。

尝试替换行

interaction.on('drawend', function(e) {

来自

vector.getSource().on('addfeature', function(e){

OpenLayers 3 - 几何集合为空

OpenLayers 3 - Geometry Collection Empty

javascript

gis

openlayers

openlayers-3