arcgis执行查询任务

 arcgis 执行查询任务（querytask）还有executeasync？需进一步了解

string.format("https://{0}/arcgis2/rest/services/baidu/mapserver/{1}", ip, layerid);
querytask querytask = new querytask(url);
querytask.executecompleted += new eventhandler(querytask_executecompleted);
querytask.failed += new eventhandler(querytask_failed);
esri.arcgis.client.tasks.query query = new esri.arcgis.client.tasks.query();
query.outfields.add("*");
query.returngeometry = true;
query.where = string.format("fid={0}", querytext);
querytask.executeasync(query);

private void querytask_failed(object sender, taskfailedeventargs e)
{
messagebox.show("query failed: " + e.error);
}

private void querytask_executecompleted(object sender, queryeventargs e)
{
featureset featureset = e.featureset;
if (featureset != null && featureset.features.count > 0)
{
graphic selectedfeature = featureset.features[0];
// 放大到选择的要素
esri.arcgis.client.geometry.envelope selectedfeatureextent = selectedfeature.geometry.extent;
double expandpercentage = 30;
double widthexpand = 2000 * (expandpercentage / 100);
double heightexpand = 2000 * (expandpercentage / 100);
esri.arcgis.client.geometry.envelope displayextent = new esri.arcgis.client.geometry.envelope(
selectedfeatureextent.xmin - (widthexpand / 2),
selectedfeatureextent.ymin - (heightexpand / 2),
selectedfeatureextent.xmax + (widthexpand / 2),
selectedfeatureextent.ymax + (heightexpand / 2));
mymap.zoomduration = new timespan(0, 0, 2);
mymap.zoomto(displayextent);
}
}