ArcGIS API for iOS开发教程（五）数据查询

http://www.giser.net/?p=23

在大量数据及信息面前，如何获得符合自己所需的数据及信息是非常必要且重要的。同其他WebAPIs 一样，ArcGIS API for iOS中同样可以使用queryTask来进行数据查询，并且使用方式也一致。下面我们以一实例来进行详细介绍。
1、按照前几章介绍的步骤来创建一个基本的地图应用程序，这里我们将其命名为QueryDemo。
2、按照【ArcGIS API for iOS开发之旅】Graphic Layer中的步骤，定义一个GraphicsLayer并添加到地图视图中。
3、打开QueryDemoViewController.h文件。在QueryDemoViewController类中定义AGSQueryTask 对象和AGSQuery对象，并声明为QueryDemoViewController类的属性。此外，在声明中添加 AGSQueryTaskDelegate。代码如下

1. @interface QueryDemoViewController: UIViewController {
2. AGSMapView       *mapview;
3. AGSQueryTask      *queryTask;
4. AGSQuery                *query;
5. AGSGraphicsLayer    *graphicsLayer;
6. }
7. @property(nonatomic, retain) IBOutlet AGSMapView   *mapView;
8. @property(nonatomic, retain) IBOutlet AGSQueryTask     *queryTask;
9. @property(nonatomic, retain) IBOutlet AGSQuery   *query;
10. @property(nonatomic, retain) IBOutlet AGSGraphicsLayer   *graphicsLayer;

4、打开QueryDemoViewController.m文件，完成queryTask和query的属性定义。代码如下

1. @implementation QueryDemoViewController
2. @synthesize mapView;
3. @synthesize queryTask;
4. @synthesize query;
5. @synthesize graphicsLayer;

5、在viewDidLoad函数中，初始化queryTask和query，并执行查询操作。代码如下

1. -(void)viewDidLoad{
2. [super viewDidLoad];
3. self.mapView.mapViewDelegate = self;
4. AGSTitledMapServiceLayer *tiledLayer = [[AGSTiledMapServiceLayer alloc]initWithURL:[NSURL URLWithString:kTiledMapServiceURL]];
5. [self.mapView addMapLayer:tiledLayer withName:@"Tiled Layer"];
6. [tiledLayer release];
7. self.graphicsLayer = [AGSGraphicsLayer graphicsLayer];
8. [self.mapView addMapLayer: self.graphicsLayer withName:@"graphicsLayer"];
9. NSString *countiesLayerURL = kMapServiceLayerURL;
10. //set up query task against layer, specify the delegate
11. self.queryTask = [AGSQueryTask queryTaskWithURL:[NSURL URLWithString:countiesLayerURL];
12. self.queryTask.delegate = self;
13. //return all fields in query
14. self.query = [AGSQuery query];
15. self.query.outFields = [NSArray arrayWithObjects:@"*",nil];
16. self.query.returnGeometry = YES;
17. self.query.text = @”California”;
18. [self.queryTask executeWithQuery:self.query];
19. }

6、添加AGSQueryTaskDelegate中的查询响应函数。代码如下
// 在Query成功后响应，将查询结果显示到graphicsLayer上

1. -(void)queryTask: (AGSQueryTask*) queryTask operation:(NSOperation*) opdidExecuteWithFeatureSetResult:(AGSFeatureSet*) featureSet{
2. //get feature, and load in to table
3. Int i = 0;
4. for(i=0; i<[featureSet.featurescount]; i++)
5. {
6. AGSSimpleFillSymbol *fillSym = [AGSSimpleFillSymbol simpleFillSymbol];
7. fillSym.style = AGSSimpleFillSymbolStyleSolid;
8. fillSym.color = [UIColororangeColor];
9. AGSGraphic *gra = [featureSet.features objectAtIndex:i];
10. gra.symbol = fillSym;
11. [self.graphicsLayer addGraphic:gra];
12. }
13. [self.graphicsLayer dataChanged];
14. }
16. //if there’s an error with the query display it to the uesr 在Query失败后响应，弹出错误提示框
17. -(void)queryTask: (AGSQueryTask*)queryTask operation:(NSOperation*)opdidFailWithError:(NSError*)error{
18. [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
19. UIAlertView *alertView = [UIAlertView alloc]initWithTitle:@”Error”
20. message:[error localizedDescription]
21. delegate:nil
22. cancelButtonTitle:@”OK”
23. otherButtonTitles:nil];
24. [alertView show];
25. [alertView release];
26. }

7、编译、执行。结果如下图所示：