javascript - Set extent of view in OpenLayers 3

Question

I've just started having a look at OpenLayers 3 and am attempting to zoom to a single feature whose extent is to be a geoJSON object sent by the server (which will change at each refresh, so I can't hard code the zoom/central point). I would like this to happen preferably as soon as the page loads, but I'm struggling to get it to work.

在我尝试从 geoJSON 对象读取几何图形的行中，我不断收到一条错误消息，提示“未捕获的 TypeError：未定义不是函数”，但我不确定如何修复它。geoJSON 字符串看起来不错（我也尝试在将其传递给 readGeometry 之前对其进行解析，但结果相同）。

如果有比我现在更容易/更快的方法来做到这一点，我也很想听听！任何帮助是极大的赞赏。

var feature = new ol.Feature({
});

var view = new ol.View({
  center: [0, 0],
  zoom: 1
});


var client = new XMLHttpRequest();
client.open('GET', 'http://localhost:3000/extent');
client.send();
client.onreadystatechange=function(){
    if (client.readyState==4 && client.status==200){
        var geomstring = client.responseText;
        console.log(geomstring)
        var geojson = new ol.format.GeoJSON();
        var geom = geojson.readGeometry(geomstring);
        var size = (map.getSize());
        feature.setGeometry(geom);
        view.fitGeometry(
        geom,
        size,
        {
            padding: [170, 50, 30, 150],
            constrainResolution: false
        });
    }
}

var map = new ol.Map({
  layers: [raster, vector, feature],
  target: 'map',
  });    

Answer 1

读取几何应该是这样的：

var geojson = new ol.format.GeoJSON();    
var json = {"st_asgeojson":"{\"type\":\"Polygon\",\"coordinates\":[[[-2416.91312435933,6700304.87650272],[-2416.91312435933,6700339.02584392],[-2255.97853651961,6700339.02584392],[-2255.97853651961,6700304.87650272],[-2416.91312435933,6700304.87650272]]]}"};
var geom = geojson.readGeometry(json['st_asgeojson']);
console.log(geom.getArea());