OpenLayers 2具有这些层事件“ loadstart和loadend”。
在OpenLayers 3中它们等效于什么?
当矢量层加载并渲染时,我需要显示一个加载图标。
您使用哪种类型的矢量源?您能否提供更多背景信息?
—
erilem
OpenLayers 2具有这些层事件“ loadstart和loadend”。
在OpenLayers 3中它们等效于什么?
当矢量层加载并渲染时,我需要显示一个加载图标。
Answers:
假设您将an ol.layer.Vector
与an 搭配使用ol.source.GeoJSON
,则可以使用以下代码:
var vectorSource = new ol.source.GeoJSON({
projection : 'EPSG:3857',
url: 'http://examples.org/fearures.json'
});
var vectorLayer = new ol.layer.Vector({
source: vectorSource
});
map.addLayer(vectorLayer);
// show loading icon
// ...
var listenerKey = vectorSource.on('change', function(e) {
if (vectorSource.getState() == 'ready') {
// hide loading icon
// ...
// and unregister the "change" listener
ol.Observable.unByKey(listenerKey);
// or vectorSource.unByKey(listenerKey) if
// you don't use the current master branch
// of ol3
}
});
这显示了在加载矢量源时如何获取通知。它仅适用于从继承的源ol.source.StaticVector
。示例包括ol.source.GeoJSON
和ol.source.KML
。
另外,请注意,当ol3提供一种一致的方式来了解是否/何时加载源代码时,此代码将来可能不再起作用。
vectorSource.once('change', function(e){...}
呢?
在ol3版本3.10.0中,情况已更改。因此比旧版本更清晰,但仍比ol2复杂。
因此,对于TILE(ol.layer.Tile)层,您的代码片段应如下所示:
//declare the layer
var osmLayer = new ol.layer.Tile({
source: new ol.source.OSM()
});
//asign the listeners on the source of tile layer
osmLayer.getSource().on('tileloadstart', function(event) {
//replace with your custom action
document.getElementById('tilesloaderindicatorimg').src = 'css/images/tree_loading.gif';
});
osmLayer.getSource().on('tileloadend', function(event) {
//replace with your custom action
document.getElementById('tilesloaderindicatorimg').src = 'css/images/ok.png';
});
osmLayer.getSource().on('tileloaderror', function(event) {
//replace with your custom action
document.getElementById('tilesloaderindicatorimg').src = 'css/images/no.png';
});
对于WMS层,方法有些不同:
//declare the layer
var wmsLayer = new ol.layer.Image({
source: new ol.source.ImageWMS({
attributions: [new ol.Attribution({
html: '© ' +
'<a href="http://www.geo.admin.ch/internet/geoportal/' +
'en/home.html">' +
'National parks / geo.admin.ch</a>'
})],
crossOrigin: 'anonymous',
params: {'LAYERS': 'ch.bafu.schutzgebiete-paerke_nationaler_bedeutung'},
serverType: 'mapserver',
url: 'http://wms.geo.admin.ch/'
})
});
//and now asign the listeners on the source of it
var lyrSource = wmsLayer.getSource();
lyrSource.on('imageloadstart', function(event) {
console.log('imageloadstart event',event);
//replace with your custom action
var elemId = event.target.params_.ELEMENTID;
document.getElementById(elemId).src = 'css/images/tree_loading.gif';
});
lyrSource.on('imageloadend', function(event) {
console.log('imageloadend event',event);
//replace with your custom action
var elemId = event.target.params_.ELEMENTID;
document.getElementById(elemId).src = 'css/images/ok.png';
});
lyrSource.on('imageloaderror', function(event) {
console.log('imageloaderror event',event);
//replace with your custom action
var elemId = event.target.params_.ELEMENTID;
document.getElementById(elemId).src = 'css/images/no.png';
});
对于WFS Vector图层,情况更加复杂:
//declare the vector source
sourceVector = new ol.source.Vector({
loader: function (extent) {
//START LOADING
//place here any actions on start loading layer
document.getElementById('laodingcont').innerHTML = "<font color='orange'>start loading.....</font>";
$.ajax('http://demo.opengeo.org/geoserver/wfs', {
type: 'GET',
data: {
service: 'WFS',
version: '1.1.0',
request: 'GetFeature',
typename: 'water_areas',
srsname: 'EPSG:3857',
bbox: extent.join(',') + ',EPSG:3857'
}
}).done(loadFeatures)
.fail(function () {
//FAIL LOADING
//place here any actions on fail loading layer
document.getElementById('laodingcont').innerHTML = "<font color='red'>error loading vector layer.</font>";
});
},
strategy: ol.loadingstrategy.bbox
});
//once we have a success responce, we need to parse it and add fetaures on map
function loadFeatures(response) {
formatWFS = new ol.format.WFS(),
sourceVector.addFeatures(formatWFS.readFeatures(response));
//FINISH LOADING
document.getElementById('laodingcont').innerHTML = "<font color='green'>finish loading vector layer.</font>";
}
我还没有找到课程ol.source.GeoJSON
,也没有找到案例vectorSource.getState() != 'ready'
。所以我最终做了这样的事情:
function spin(active) {
if (active) {
// start spinning the spinner
} else {
// stop spinning the spinner
}
}
// Toggle spinner on layer loading
layer.on('change', function() {
spin();
});
layer.getSource().on('change', function() {
spin(false);
});
您还可以使用getState()函数
if (source instanceof ol.source.Vector) {
source.on("change", function () {
//console.log("Vector change, state: " + source.getState());
switch (source.getState()) {
case "loading":
$("#ajaxSpinnerImage").show();
break;
default:
$("#ajaxSpinnerImage").hide();
}
});
}
source.getState()
总是返回“就绪”