本文主要是介绍Extent Interaction——Extent交互控件，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
This example shows how to use an Extent interaction to draw a modifiable extent.
这个例子展示了如何使用Extent交互控件来绘制一个可以修改的范围。
Use Shift+Drag to draw an extent. Shift+Drag on the corners or edges of the extent to resize it. Shift+Click off the extent to remove it.
按下shift键并拖动来绘制范围，在范围的角落或者边界按住shift键并拖动来调整范围的大小。在范围之外的地方按住shift键并单击来移除绘制的范围。
代码：
<!DOCTYPE html>
<html><head><title>Extent Interaction</title><link rel="stylesheet" href="https://openlayers.org/en/v4.2.0/css/ol.css" type="text/css"><!-- The line below is only needed for old environments like Internet Explorer and Android 4.x --><script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script><script src="https://openlayers.org/en/v4.2.0/build/ol.js"></script></head><body><div id="map" class="map"></div><script>var vectorSource = new ol.source.Vector({url: 'https://openlayers.org/en/v4.2.0/examples/data/geojson/countries.geojson',format: new ol.format.GeoJSON()});var map = new ol.Map({layers: [new ol.layer.Tile({source: new ol.source.OSM()}),new ol.layer.Vector({source: vectorSource})],target: 'map',view: new ol.View({center: [0, 0],zoom: 2})});// 创建Extent交互控件var extent = new ol.interaction.Extent({condition: ol.events.condition.platformModifierKeyOnly});map.addInteraction(extent);// 不激活Extent交互控件
extent.setActive(false);// Enable interaction by holding shift// 通过按住shift键来激活Extent交互控件
this.addEventListener('keydown', function(event) {if (event.keyCode == 16) {extent.setActive(true);}});// 当shift键释放的时候，不激活Extent控件
this.addEventListener('keyup', function(event) {if (event.keyCode == 16) {extent.setActive(false);}});</script></body>
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