获取当前位置（Core Location）

Core Location框架提供了三种用于追踪设备当前位置的服务，Core Location框架从内置的蜂窝，Wi-Fi或者GPS来获取位置

The significant-change location

service 提供了低耗电的方法来获取当前位置，当前位置改变时会发出通知

The standard location service 提供了一种可设置的方法来获取当前位置

Region monitoring 监视特定地区的跨越

如果程序必须使用位置服务
在程序的info.plist中添加UIRequiredDeviceCapabilities键，它是一个包含多个字符串的数组，然后添加location-services，gps字符串

１.The Standard Location Service　

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Listing 1-1 Starting the standard location service

- (void)startStandardUpdates

{

// 创建location manager

if (nil == locationManager)

locationManager = [[CLLocationManager alloc] init];

locationManager.delegate = self;

[plain]

<span style="font-size:16px;">　　// 设置获取位置的精确度，越精确越耗电</span>

[plain]

<span style="font-size:16px;"> locationManager.desiredAccuracy = kCLLocationAccuracyKilometer;

// 设置距离过滤器，超过次距离就更新一次位置

locationManager.distanceFilter = 500;

[locationManager startUpdatingLocation];

}</span>

使用location manager之前一般要检查位置服务是否可用，

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<span style="font-size:16px;">+ (BOOL)locationServicesEnabled</span>

当位置信息更新时，会给location manager发送消息

２.Significant-Change Location Service

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<span style="font-size:16px;">- (void)startSignificantChangeUpdates

{

// Create the location manager if this object does not

// already have one.

if (nil == locationManager)

locationManager = [[CLLocationManager alloc] init];

locationManager.delegate = self;

[locationManager startMonitoringSignificantLocationChanges];

}</span>

可以叫醒在后台的程序

３.Region monitoring Service
使用之前调用CLLocationManager的regionMonitoringAvailable and regionMonitoringEnabled

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<span style="font-size:16px;">- (BOOL)registerRegionWithCircularOverlay:(MyCircle*)overlay andIdentifier:(NSString*)identifier

{

// Do not create regions if support is unavailable or disabled.

if ( ![CLLocationManager regionMonitoringAvailable] ||

![CLLocationManager regionMonitoringEnabled] )

return NO;

// If the radius is too large, registration fails automatically,

// so clamp the radius to the max value.

CLLocationDegrees radius = overlay.radius;

if (radius > self.locationManager.maximumRegionMonitoringDistance)

radius = self.locationManager.maximumRegionMonitoringDistance;

// Create the region and start monitoring it.

CLRegion* region = [[CLRegion alloc] initCircularRegionWithCenter:overlay.coordinate

radius:radius identifier:identifier];

[self.locationManager startMonitoringForRegion:region

desiredAccuracy:kCLLocationAccuracyHundredMeters];

[region release];

return YES;

}</span>

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