openlayers研究（一） 初始化流程
下载2.13.1。解压缩。根据readme解释，openlayers.js是一个压缩库，.light是一个图像显示的简化库，mobile顾名思义应该是应对移动设备的库。build里面有py写的打包工具，可以配置生成openlayers.js。
我最开始从lib里面的openlayers.js看，对ol的初始化顺序很困惑，因为最开始就判断OpenLayers这个对象，明明没有地方创建
lib下面的openlayers.js
后来查看根目录下面的OpenLayers.js时候发现原来是先加载的singlefile.js这个文件
于是查看lib\openlayers\下面的singlefile.js文件,原来这里就是真正创建OpenLayers的地方。
OK,回到lib下面的openlayers.js，看看openLayers是如何初始化的
(function() {
/**
* Before creating the OpenLayers namespace, check to see if
* OpenLayers.singleFile is true. This occurs if the
* OpenLayers/SingleFile.js script is included before this one - as is the
* case with old single file build profiles that included both
* OpenLayers.js and OpenLayers/SingleFile.js.
*/
var singleFile = (typeof OpenLayers == "object" && OpenLayers.singleFile);
//----------------这里首先判断是否singlefile.js已经执行过了，并且通过Openlayers.singlefile来判断加载的那个openlyers.js文件（压缩和非压缩），
其实singlefile.js的逻辑已经被弃用了，因为在openlayers.js下面又创建了一遍openlayers，这段代码其实没什么实际感觉。
/**
* Relative path of this script.
*/
var scriptName = (!singleFile) ? "lib/OpenLayers.js" : "OpenLayers.js"; //--------------------------指定当前加载的js的相对路径
/*
* If window.OpenLayers isn't set when this script (OpenLayers.js) is
* evaluated (and if singleFile is false) then this script will load
* *all* OpenLayers scripts. If window.OpenLayers is set to an array
* then this script will attempt to load scripts for each string of
* the array, using the string as the src of the script.
*
* Example:
* (code)
* <script type="text/javascript">
* window.OpenLayers = [
* "OpenLayers/Util.js",
* "OpenLayers/BaseTypes.js"
* ];
* </script>
* <script type="text/javascript" src="../lib/OpenLayers.js"></script>
* (end)
* In this example OpenLayers.js will load Util.js and BaseTypes.js only.
*/
var jsFiles = window.OpenLayers;
//----------------------------------------------------根据上面解释，ol可以通过在引入openlayers.js之前，设置window.OpenLayers这个属性[]，在这个属性中来使用相对路径来显示的声明要加载那些模块。下面加载时使用。
//新初始化OpenLayers所以，先把值记录下来。
/**
* Namespace: OpenLayers
* The OpenLayers object provides a namespace for all things OpenLayers
*/
//--------------------------------------------------------下面创建一个OpenLayers对象，全局命名空间，闭包外、方法外的var变量是一个全景变量，在方法或闭包内用windows.xxx也可以声明一个全局变量，其实通过这里就可以看出来，在singlefile中创建的openlayers其实没用，在判断完加载的版本和需要加载的插件js后，在下面会重新创建一个全局域的OpenLayers，这个全局域的OpenLayers和singlefile中定义的代码是一样的。---------------
window.OpenLayers = {
/**
* Method: _getScriptLocation
* Return the path to this script. This is also implemented in
* OpenLayers/SingleFile.js
*
* Returns:
* {String} Path to this script
*/
_getScriptLocation: (function() {
var r = new RegExp("(^|(.*?\\/))(" + scriptName + ")(\\?|$)"),
s = document.getElementsByTagName('script'),
src, m, l = "";
for(var i=0, len=s.length; i<len; i++) {
src = s[i].getAttribute('src');
if(src) {
m = src.match(r);
if(m) {
l = m[1];
break;
}
}
}
return (function() { return l; });
})(),
/**
* APIProperty: ImgPath
* {String} Set this to the path where control images are stored, a path
* given here must end with a slash. If set to '' (which is the default)
* OpenLayers will use its script location + "img/".
*
* You will need to set this property when you have a singlefile build of
* OpenLayers that either is not named "OpenLayers.js" or if you move
* the file in a way such that the image directory cannot be derived from
* the script location.
*
* If your custom OpenLayers build is named "my-custom-ol.js" and the images
* of OpenLayers are in a folder "/resources/external/images/ol" a correct
* way of including OpenLayers in your HTML would be:
*
* (code)
* <script src="/path/to/my-custom-ol.js" type="text/javascript"></script>
* <script type="text/javascript">
* // tell OpenLayers where the control images are
* // remember the trailing slash
* OpenLayers.ImgPath = "/resources/external/images/ol/";
* </script>
* (end code)
*
* Please remember that when your OpenLayers script is not named
* "OpenLayers.js" you will have to make sure that the default theme is
* loaded into the page by including an appropriate <link>-tag,
* e.g.:
*
* (code)
* <link rel="stylesheet" href="/path/to/default/style.css" type="text/css">
* (end code)
*/
ImgPath : ''
};
/**
* OpenLayers.singleFile is a flag indicating this file is being included
* in a Single File Library build of the OpenLayers Library.
*
* When we are *not* part of a SFL build we dynamically include the
* OpenLayers library code.
*
* When we *are* part of a SFL build we do not dynamically include the
* OpenLayers library code as it will be appended at the end of this file.
//--------------------------------------------------------如果不是压缩模式，并且没有指定加载的js文件，则默认加载如下js通过document.write
*/
if(!singleFile) {
if (!jsFiles) {
jsFiles = [
"OpenLayers/BaseTypes/Class.js",
"OpenLayers/Util.js",
"OpenLayers/Util/vendorPrefix.js",
"OpenLayers/Animation.js",
"OpenLayers/BaseTypes.js",
"OpenLayers/BaseTypes/Bounds.js",
"OpenLayers/BaseTypes/Date.js",
"OpenLayers/BaseTypes/Element.js",
"OpenLayers/BaseTypes/LonLat.js",
"OpenLayers/BaseTypes/Pixel.js",
"OpenLayers/BaseTypes/Size.js",
"OpenLayers/Console.js",
"OpenLayers/Tween.js",
"OpenLayers/Kinetic.js",
"OpenLayers/Events.js",
"OpenLayers/Events/buttonclick.js",
"OpenLayers/Events/featureclick.js",
"OpenLayers/Request.js",
"OpenLayers/Request/XMLHttpRequest.js",
"OpenLayers/Projection.js",
"OpenLayers/Map.js",
"OpenLayers/Layer.js",
"OpenLayers/Icon.js",
"OpenLayers/Marker.js",
"OpenLayers/Marker/Box.js",
"OpenLayers/Popup.js",
"OpenLayers/Tile.js",
"OpenLayers/Tile/Image.js",
"OpenLayers/Tile/Image/IFrame.js",
"OpenLayers/Tile/UTFGrid.js",
"OpenLayers/Layer/Image.js",
"OpenLayers/Layer/SphericalMercator.js",
"OpenLayers/Layer/EventPane.js",
"OpenLayers/Layer/FixedZoomLevels.js",
"OpenLayers/Layer/Google.js",
"OpenLayers/Layer/Google/v3.js",
"OpenLayers/Layer/HTTPRequest.js",
"OpenLayers/Layer/Grid.js",
"OpenLayers/Layer/MapGuide.js",
"OpenLayers/Layer/MapServer.js",
"OpenLayers/Layer/KaMap.js",
"OpenLayers/Layer/KaMapCache.js",
"OpenLayers/Layer/Markers.js",
"OpenLayers/Layer/Text.js",
"OpenLayers/Layer/WorldWind.js",
"OpenLayers/Layer/ArcGIS93Rest.js",
"OpenLayers/Layer/WMS.js",
"OpenLayers/Layer/WMTS.js",
"OpenLayers/Layer/ArcIMS.js",
"OpenLayers/Layer/GeoRSS.js",
"OpenLayers/Layer/Boxes.js",
"OpenLayers/Layer/XYZ.js",
"OpenLayers/Layer/UTFGrid.js",
"OpenLayers/Layer/OSM.js",
"OpenLayers/Layer/Bing.js",
"OpenLayers/Layer/TMS.js",
"OpenLayers/Layer/TileCache.js",
"OpenLayers/Layer/Zoomify.js",
"OpenLayers/Layer/ArcGISCache.js",
"OpenLayers/Popup/Anchored.js",
"OpenLayers/Popup/Framed.js",
"OpenLayers/Popup/FramedCloud.js",
"OpenLayers/Feature.js",
"OpenLayers/Feature/Vector.js",
"OpenLayers/Handler.js",
"OpenLayers/Handler/Click.js",
"OpenLayers/Handler/Hover.js",
"OpenLayers/Handler/Point.js",
"OpenLayers/Handler/Path.js",
"OpenLayers/Handler/Polygon.js",
"OpenLayers/Handler/Feature.js",
"OpenLayers/Handler/Drag.js",
"OpenLayers/Handler/Pinch.js",
"OpenLayers/Handler/RegularPolygon.js",
"OpenLayers/Handler/Box.js",
"OpenLayers/Handler/MouseWheel.js",
"OpenLayers/Handler/Keyboard.js",
"OpenLayers/Control.js",
"OpenLayers/Control/Attribution.js",
"OpenLayers/Control/Button.js",
"OpenLayers/Control/CacheRead.js",
"OpenLayers/Control/CacheWrite.js",
"OpenLayers/Control/ZoomBox.js",
"OpenLayers/Control/ZoomToMaxExtent.js",
"OpenLayers/Control/DragPan.js",
"OpenLayers/Control/Navigation.js",
"OpenLayers/Control/PinchZoom.js",
"OpenLayers/Control/TouchNavigation.js",
"OpenLayers/Control/MousePosition.js",
"OpenLayers/Control/OverviewMap.js",
"OpenLayers/Control/KeyboardDefaults.js",
"OpenLayers/Control/PanZoom.js",
"OpenLayers/Control/PanZoomBar.js",
"OpenLayers/Control/ArgParser.js",
"OpenLayers/Control/Permalink.js",
"OpenLayers/Control/Scale.js",
"OpenLayers/Control/ScaleLine.js",
"OpenLayers/Control/Snapping.js",
"OpenLayers/Control/Split.js",
"OpenLayers/Control/LayerSwitcher.js",
"OpenLayers/Control/DrawFeature.js",
"OpenLayers/Control/DragFeature.js",
"OpenLayers/Control/ModifyFeature.js",
"OpenLayers/Control/Panel.js",
"OpenLayers/Control/SelectFeature.js",
"OpenLayers/Control/NavigationHistory.js",
"OpenLayers/Control/Measure.js",
"OpenLayers/Control/WMSGetFeatureInfo.js",
"OpenLayers/Control/WMTSGetFeatureInfo.js",
"OpenLayers/Control/Graticule.js",
"OpenLayers/Control/TransformFeature.js",
"OpenLayers/Control/UTFGrid.js",
"OpenLayers/Control/SLDSelect.js",
"OpenLayers/Control/Zoom.js",
"OpenLayers/Geometry.js",
"OpenLayers/Geometry/Collection.js",
"OpenLayers/Geometry/Point.js",
"OpenLayers/Geometry/MultiPoint.js",
"OpenLayers/Geometry/Curve.js",
"OpenLayers/Geometry/LineString.js",
"OpenLayers/Geometry/LinearRing.js",
"OpenLayers/Geometry/Polygon.js",
"OpenLayers/Geometry/MultiLineString.js",
"OpenLayers/Geometry/MultiPolygon.js",
"OpenLayers/Renderer.js",
"OpenLayers/Renderer/Elements.js",
"OpenLayers/Renderer/SVG.js",
"OpenLayers/Renderer/Canvas.js",
"OpenLayers/Renderer/VML.js",
"OpenLayers/Layer/Vector.js",
"OpenLayers/Layer/PointGrid.js",
"OpenLayers/Layer/Vector/RootContainer.js",
"OpenLayers/Strategy.js",
"OpenLayers/Strategy/Filter.js",
"OpenLayers/Strategy/Fixed.js",
"OpenLayers/Strategy/Cluster.js",
"OpenLayers/Strategy/Paging.js",
"OpenLayers/Strategy/BBOX.js",
"OpenLayers/Strategy/Save.js",
"OpenLayers/Strategy/Refresh.js",
"OpenLayers/Filter.js",
"OpenLayers/Filter/FeatureId.js",
"OpenLayers/Filter/Logical.js",
"OpenLayers/Filter/Comparison.js",
"OpenLayers/Filter/Spatial.js",
"OpenLayers/Filter/Function.js",
"OpenLayers/Protocol.js",
"OpenLayers/Protocol/HTTP.js",
"OpenLayers/Protocol/WFS.js",
"OpenLayers/Protocol/WFS/v1.js",
"OpenLayers/Protocol/WFS/v1_0_0.js",
"OpenLayers/Protocol/WFS/v1_1_0.js",
"OpenLayers/Protocol/CSW.js",
"OpenLayers/Protocol/CSW/v2_0_2.js",
"OpenLayers/Protocol/Script.js",
"OpenLayers/Protocol/SOS.js",
"OpenLayers/Protocol/SOS/v1_0_0.js",
"OpenLayers/Layer/PointTrack.js",
"OpenLayers/Style.js",
"OpenLayers/Style2.js",
"OpenLayers/StyleMap.js",
"OpenLayers/Rule.js",
"OpenLayers/Format.js",
"OpenLayers/Format/QueryStringFilter.js",
"OpenLayers/Format/XML.js",
"OpenLayers/Format/XML/VersionedOGC.js",
"OpenLayers/Format/Context.js",
"OpenLayers/Format/ArcXML.js",
"OpenLayers/Format/ArcXML/Features.js",
"OpenLayers/Format/GML.js",
"OpenLayers/Format/GML/Base.js",
"OpenLayers/Format/GML/v2.js",
"OpenLayers/Format/GML/v3.js",
"OpenLayers/Format/Atom.js",
"OpenLayers/Format/EncodedPolyline.js",
"OpenLayers/Format/KML.js",
"OpenLayers/Format/GeoRSS.js",
"OpenLayers/Format/WFS.js",
"OpenLayers/Format/OWSCommon.js",
"OpenLayers/Format/OWSCommon/v1.js",
"OpenLayers/Format/OWSCommon/v1_0_0.js",
"OpenLayers/Format/OWSCommon/v1_1_0.js",
"OpenLayers/Format/WCSCapabilities.js",
"OpenLayers/Format/WCSCapabilities/v1.js",
"OpenLayers/Format/WCSCapabilities/v1_0_0.js",
"OpenLayers/Format/WCSCapabilities/v1_1_0.js",
"OpenLayers/Format/WFSCapabilities.js",
"OpenLayers/Format/WFSCapabilities/v1.js",
"OpenLayers/Format/WFSCapabilities/v1_0_0.js",
"OpenLayers/Format/WFSCapabilities/v1_1_0.js",
"OpenLayers/Format/WFSDescribeFeatureType.js",
"OpenLayers/Format/WMSDescribeLayer.js",
"OpenLayers/Format/WMSDescribeLayer/v1_1.js",
"OpenLayers/Format/WKT.js",
"OpenLayers/Format/CQL.js",
"OpenLayers/Format/OSM.js",
"OpenLayers/Format/GPX.js",
"OpenLayers/Format/Filter.js",
"OpenLayers/Format/Filter/v1.js",
"OpenLayers/Format/Filter/v1_0_0.js",
"OpenLayers/Format/Filter/v1_1_0.js",
"OpenLayers/Format/SLD.js",
"OpenLayers/Format/SLD/v1.js",
"OpenLayers/Format/SLD/v1_0_0.js",
"OpenLayers/Format/SLD/v1_0_0_GeoServer.js",
"OpenLayers/Format/OWSCommon.js",
"OpenLayers/Format/OWSCommon/v1.js",
"OpenLayers/Format/OWSCommon/v1_0_0.js",
"OpenLayers/Format/OWSCommon/v1_1_0.js",
"OpenLayers/Format/CSWGetDomain.js",
"OpenLayers/Format/CSWGetDomain/v2_0_2.js",
"OpenLayers/Format/CSWGetRecords.js",
"OpenLayers/Format/CSWGetRecords/v2_0_2.js",
"OpenLayers/Format/WFST.js",
"OpenLayers/Format/WFST/v1.js",
"OpenLayers/Format/WFST/v1_0_0.js",
"OpenLayers/Format/WFST/v1_1_0.js",
"OpenLayers/Format/Text.js",
"OpenLayers/Format/JSON.js",
"OpenLayers/Format/GeoJSON.js",
"OpenLayers/Format/WMC.js",
"OpenLayers/Format/WMC/v1.js",
"OpenLayers/Format/WMC/v1_0_0.js",
"OpenLayers/Format/WMC/v1_1_0.js",
"OpenLayers/Format/WCSGetCoverage.js",
"OpenLayers/Format/WMSCapabilities.js",
"OpenLayers/Format/WMSCapabilities/v1.js",
"OpenLayers/Format/WMSCapabilities/v1_1.js",
"OpenLayers/Format/WMSCapabilities/v1_1_0.js",
"OpenLayers/Format/WMSCapabilities/v1_1_1.js",
"OpenLayers/Format/WMSCapabilities/v1_3.js",
"OpenLayers/Format/WMSCapabilities/v1_3_0.js",
"OpenLayers/Format/WMSCapabilities/v1_1_1_WMSC.js",
"OpenLayers/Format/WMSGetFeatureInfo.js",
"OpenLayers/Format/SOSCapabilities.js",
"OpenLayers/Format/SOSCapabilities/v1_0_0.js",
"OpenLayers/Format/SOSGetFeatureOfInterest.js",
"OpenLayers/Format/SOSGetObservation.js",
"OpenLayers/Format/OWSContext.js",
"OpenLayers/Format/OWSContext/v0_3_1.js",
"OpenLayers/Format/WMTSCapabilities.js",
"OpenLayers/Format/WMTSCapabilities/v1_0_0.js",
"OpenLayers/Format/WPSCapabilities.js",
"OpenLayers/Format/WPSCapabilities/v1_0_0.js",
"OpenLayers/Format/WPSDescribeProcess.js",
"OpenLayers/Format/WPSExecute.js",
"OpenLayers/Format/XLS.js",
"OpenLayers/Format/XLS/v1.js",
"OpenLayers/Format/XLS/v1_1_0.js",
"OpenLayers/Format/OGCExceptionReport.js",
"OpenLayers/Control/GetFeature.js",
"OpenLayers/Control/NavToolbar.js",
"OpenLayers/Control/PanPanel.js",
"OpenLayers/Control/Pan.js",
"OpenLayers/Control/ZoomIn.js",
"OpenLayers/Control/ZoomOut.js",
"OpenLayers/Control/ZoomPanel.js",
"OpenLayers/Control/EditingToolbar.js",
"OpenLayers/Control/Geolocate.js",
"OpenLayers/Symbolizer.js",
"OpenLayers/Symbolizer/Point.js",
"OpenLayers/Symbolizer/Line.js",
"OpenLayers/Symbolizer/Polygon.js",
"OpenLayers/Symbolizer/Text.js",
"OpenLayers/Symbolizer/Raster.js",
"OpenLayers/Lang.js",
"OpenLayers/Lang/en.js",
"OpenLayers/Spherical.js",
"OpenLayers/TileManager.js",
"OpenLayers/WPSClient.js",
"OpenLayers/WPSProcess.js"
]; // etc.
}
// use "parser-inserted scripts" for guaranteed execution order
// http://hsivonen.iki.fi/script-execution/
var scriptTags = new Array(jsFiles.length);
var host = OpenLayers._getScriptLocation() + "lib/";
for (var i=0, len=jsFiles.length; i<len; i++) {
scriptTags[i] = "<script src='" + host + jsFiles[i] +
"'></script>";
}
if (scriptTags.length > 0) {
document.write(scriptTags.join(""));
}
}
})();
/**
* Constant: VERSION_NUMBER
*
* This constant identifies the version of OpenLayers.
*
* When asking questions or reporting issues, make sure to include the output of
* OpenLayers.VERSION_NUMBER in the question or issue-description.
*/
OpenLayers.VERSION_NUMBER="Release 2.13.1";
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