CLLocationDistance:无法让"getDistanceFrom“正常工作

Question

基于视图的应用程序，

.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]);
}

怎么啦？

调试器说：

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

来自数据库的对象:长整型: 59.291114长整型: 17.816191

Answer 1

CurrentLocation是实例变量/属性吗？您正在不使用访问器的情况下直接设置它，并且不会保留它。如果在getDistance:中使用它之前就将其释放，将会导致崩溃。

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

还有建筑..。

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

..。是危险和多余的。使用...

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

..。而不是。

Answer 2

请改用distanceFromLocation: