一、背景说明
通过调用GP服务，Android客户端也能实现专业的、复杂的GIS分析处理功能，从而增加应用的实用价值。
ArcGIS Server发布的GP服务，分为同步和异步两种类型，一般执行步骤较多，耗时较长的GP服务都采用异步方式，执行速度较快的服务则采用同步方式。如果不确定GP服务是同步还是异步方式，则可以通过服务目录查看，如下图：
本文将介绍如何通过异步的方式来调用GP服务（同步方式在SDK的示例程序中有，较为简单），本例调用的GP服务来自ArcGIS Online，服务地址为：http://sampleserver4.arcgisonline.com/ArcGIS/rest/services/HomelandSecurity/Incident_Data_Extraction/GPServer/Extract%20Data%20Task。该服务相关的业务数据服务为：http://sampleserver4.arcgisonline.com/ArcGIS/rest/services/HomelandSecurity/Incident_Data_Extraction/MapServer。该GP服务提供数据提取的功能，就是根据用户选择的待提取图层、提取范围、输出格式，将数据提取，并打包返回客户端，由客户下载zip压缩包。先来看一下GP服务的参数要求：
可见该服务提供了三个输入参数，分别是：待提取的图层、提取范围和输出格式，此外还有一个输出参数，用于获取提取结果。
二、示例效果
本例的执行效果如下：
1.底图与待提取的业务数据：
2.绘制用于提取的多边形范围：
3.提交提取任务，开始执行提取操作：
4.提取任务执行完成，获得了提取结果的URL（图片上方），点击可下载：
5.完成下载提取结果：
6.到下载目录中查看下载结果，output-1.zip：
三、关键代码
1.设置参数
public void startAsynchronous(Polygon aoiGeometry){
//被裁切的目标图层
GPString pointLayer = new GPString();
pointLayer.setValue("Incident Points");
GPString lineLayer = new GPString();
pointLayer.setValue("Incident Lines");
GPString polygonLayer = new GPString();
pointLayer.setValue("Incident Areas");
GPMultiValue<GPString> clipLayers = new GPMultiValue<GPString>("Layers_to_Clip");
clipLayers.addValue(pointLayer);
clipLayers.addValue(lineLayer);
clipLayers.addValue(polygonLayer);
//用于裁切的范围
Graphic g = new Graphic(aoiGeometry, fillSymbol);
GPFeatureRecordSetLayer aoi = new GPFeatureRecordSetLayer("Area_of_Interest");
aoi.setGeometryType(Geometry.Type.POLYGON);
aoi.addGraphic(g);
//返回的数据格式
GPString format = new GPString("Feature_Format");
format.setValue("Shapefile - SHP - .shp");
params2 = new ArrayList<GPParameter>();
params2.add(clipLayers);
params2.add(aoi);
params2.add(format);
try {
dialog = ProgressDialog.show(Viewshed.this, "", "Extacting. Please wait...", true, true);
gpExtract = new Geoprocessor("http://sampleserver4.arcgisonline.com/ArcGIS/rest/services/HomelandSecurity/Incident_Data_Extraction/GPServer/Extract%20Data%20Task");
gpExtract.setOutSR(map.getSpatialReference());
gpExtract.setProcessSR(map.getSpatialReference());
ExtractRunable queryRunable = new ExtractRunable();
Thread thread = new Thread(queryRunable);
thread.start();
}
catch (Exception e) {
e.printStackTrace();
}
}
2.提交任务，开始异步执行
class ExtractRunable implements Runnable {
@Override
public void run() {
GPJobResource jobResource = null;
try {
jobResource = gpExtract.submitJob(params2);
}
catch (Exception e1) {
e1.printStackTrace();
}
jobID = jobResource.getJobID();
}
}
3.通过Timer定时查询任务状态并处理结果
class ExtractRunable implements Runnable {
@Override
public void run() {
GPJobResource jobResource = null;
try {
jobResource = gpExtract.submitJob(params2);
}
catch (Exception e1) {
e1.printStackTrace();
}
jobID = jobResource.getJobID();
//通过定时器每隔2秒查询Job状态
checkJobStatusTimer = new Timer();
checkJobStatusTimer.schedule(new TimerTask() {
@Override
public void run() {
GPJobResource jobRes = null;
try {
jobRes = gpExtract.checkJobStatus(jobID);
}
catch (Exception e) {
e.printStackTrace();
}
if(jobRes == null) return;
JobStatus status = jobRes.getJobStatus();
switch(status){
case CANCELLED:
Toast.makeText(Viewshed.this, "CANCELLED", Toast.LENGTH_LONG).show();
break;
case DELETED:
Toast.makeText(Viewshed.this, "DELETED", Toast.LENGTH_LONG).show();
break;
case FAILED:
GPMessage[] message = jobRes.getMessages();
Toast.makeText(Viewshed.this, "FAILED:"+message[0].toString(), Toast.LENGTH_LONG).show();
break;
case SUCCEEDED:
try {
GPDataFile result = (GPDataFile)gpExtract.getResultData(jobID, "Output_Zip_File");
url = result.getUrl();
uiHandler.sendEmptyMessage(CLOSE_LOADING_WINDOW);
}
catch (Exception e) {
e.printStackTrace();
}
break;
case TIMED_OUT:
Toast.makeText(Viewshed.this, "TIMED_OUT", Toast.LENGTH_LONG).show();
break;
default:
break;
}
}
}, 1000, 2000);
}
}
以上是本例的关键代码，如需完整代码，请在评论中留下邮箱。