需要帮助调试CLLocation代码，找出两点

Question

我试图部署在我看来，基于应用程序下面的代码之间的距离，但我收到以下错误，当我尝试运行它：

GPSViewController.h

CLLocationManager *lm; 
CLLocation *firstLocation; 
CLLocation *secondLocation; 
CLLocationDistance *distance; 
NSString *distanceString; 

GPSViewController.m

firstLocation = [[[CLLocation alloc] initWithLatitude:lat1 longitude:lon1] autorelease]; 
secondLocation = [[[CLLocation alloc] initWithLatitude:lat2 longitude:lon2] autorelease]; 
distance = [secondLocation distanceFromLocation:firstLocation]; //CLLocation may not respond to distanceFromLocation 

double dist = distance/1000; //invalid operands to binary 

distanceString = [[NSString alloc] stringWithFormat: @"%f", dist]; 
NSLog(@"the distance between the two points is: %@", distanceString); 

在我的示例代码上面，我怎么转换变量“距离”从类型“CLLocationDistance”一类“双”？

我只是试图使用两个不同的CLLocation对象计算两点之间的距离，并将其打印到控制台。 lat1，lon1，lat2，lon2是双打。

任何人都可以看到我要去哪里错了吗？

Answer 1

CLLocationDistance是一个double，所以你不需要尝试转换为double或anysoever。

你可以计算你的数据是这样，它会工作：

CLLocationDistance distance = [secondLocation distanceFromLocation:firstLocation]; // distance is expressed in meters 

CLLocationDistance kilometers = distance/1000.0; 
NSString *distanceString = [[NSString alloc] initWithFormat: @"%f", kilometers];