CLLocationDistance：无法让“getDistanceFrom”工作答案

【问题标题】：CLLocationDistance: Cant get "getDistanceFrom" to workCLLocationDistance：无法让“getDistanceFrom”工作
【发布时间】：2010-02-09 18:48:06
【问题描述】：

基于视图的应用，

.m
- (void)viewDidLoad {
    [super viewDidLoad];
    self.locationManager = [[[CLLocationManager alloc] init] autorelease];
    self.locationManager.delegate = self;
    [[self locationManager] startUpdatingLocation];

}


- (void)locationManager:(CLLocationManager *)manager
    didUpdateToLocation:(CLLocation *)newLocation
           fromLocation:(CLLocation *)oldLocation {

    CurrentLocation = newLocation;
    [locationManager stopUpdatingLocation];
    myActivity.hidden=YES;
    [self reStart];
}


-(void)reStart{

        [self checkAndCreateDatabase];  //Sucess
    [self readFromDatabase]; //Success if I comment the get distance part
    [self sort]; //Success
}


-(void) readFromDatabase {
...

    CLLocationCoordinate2D cord;
    cord.latitude = [[NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 2)] doubleValue];
    cord.longitude =[[NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 3)] doubleValue];
    NSDate *today = [NSDate date];
    CLLocation *objectLocation = [[CLLocation alloc] initWithCoordinate:cord altitude:1 horizontalAccuracy:1 verticalAccuracy:-1 timestamp:today];
    CLLocationDistance distance = [objectLocation getDistanceFrom:CurrentLocation]/1000;
    NSLog([NSString stringWithFormat:@"%.0f", distance]);
}

怎么了？

调试器说：

obj_msgSend
0x912e8688  <+0024>  mov    0x20(%edx),%edi

来自数据库的对象：长：59.291114 纬度：17.816191

【问题讨论】：

标签： iphone objective-c cllocationmanager cllocation

【解决方案1】：

改用 distanceFromLocation:

【讨论】：

【解决方案2】：

CurrentLocation 是实例变量/属性吗？您在没有访问器的情况下直接设置它，并且您没有保留它。如果在getDistance: 中使用它之前释放它会导致崩溃。

如果它是一个属性，请使用self.CurrentLocation 来确保它被保留。

还有，建筑...

NSLog([NSString stringWithFormat:@"%.0f", distance]);

... 是有风险和多余的。使用...

NSLog(@"%.0f", distance);

... 相反。

【讨论】：