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
@interface QueryDemoViewController: UIViewController {
AGSMapView       *mapview;
AGSQueryTask      *queryTask;
AGSQuery                *query;
AGSGraphicsLayer    *graphicsLayer;
}
@property(nonatomic, retain) IBOutlet AGSMapView   *mapView;
@property(nonatomic, retain) IBOutlet AGSQueryTask     *queryTask;
@property(nonatomic, retain) IBOutlet AGSQuery   *query;
@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
@implementation QueryDemoView
b90f
Controller
@synthesize mapView;
@synthesize queryTask;
@synthesize query;
@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
-(void)viewDidLoad{
[super viewDidLoad];
self.mapView.mapViewDelegate = self;
AGSTitledMapServiceLayer *tiledLayer = [[AGSTiledMapServiceLayer alloc]initWithURL:[NSURL URLWithString:kTiledMapServiceURL]];
[self.mapView addMapLayer:tiledLayer withName:@"Tiled Layer"];
[tiledLayer release];
self.graphicsLayer = [AGSGraphicsLayer graphicsLayer];
[self.mapView addMapLayer: self.graphicsLayer withName:@"graphicsLayer"];
NSString *countiesLayerURL = kMapServiceLayerURL;
//set up query task against layer, specify the delegate
self.queryTask = [AGSQueryTask queryTaskWithURL:[NSURL URLWithString:countiesLayerURL];
self.queryTask.delegate = self;
//return all fields in query
self.query = [AGSQuery query];
self.query.outFields = [NSArray arrayWithObjects:@"*",nil];
self.query.returnGeometry = YES;
self.query.text = @”California”;
[self.queryTask executeWithQuery:self.query];
}
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
-(void)queryTask: (AGSQueryTask*) queryTask operation:(NSOperation*) opdidExecuteWithFeatureSetResult:(AGSFeatureSet*) featureSet{
//get feature, and load in to table
Int i = 0;
for(i=0; i<[featureSet.featurescount]; i++)
{
AGSSimpleFillSymbol *fillSym = [AGSSimpleFillSymbol simpleFillSymbol];
fillSym.style = AGSSimpleFillSymbolStyleSolid;
fillSym.color = [UIColororangeColor];
AGSGraphic *gra = [featureSet.features objectAtIndex:i];
gra.symbol = fillSym;
[self.graphicsLayer addGraphic:gra];
}
[self.graphicsLayer dataChanged];
}

//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
-(void)queryTask: (AGSQueryTask*)queryTask operation:(NSOperation*)opdidFailWithError:(NSError*)error{
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
UIAlertView *alertView = [UIAlertView alloc]initWithTitle:@”Error”
message:[error localizedDescription]
delegate:nil
cancelButtonTitle:@”OK”
otherButtonTitles:nil];
[alertView show];
[alertView release];
}

7、编译、执行。结果如下图所示：