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 {@Overridepublic 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 {@Overridepublic 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() {@Overridepublic 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。