我需要从for循环中得到倒数第二个结果

Question

我存储了一个具有纬度和经度值的路点数组。我创建了一个for循环来循环数组，并比较我当前的CLLocation位置纬度和经度，以找到我最接近的路点。我还需要获得第二个最近的航路点，并将此ac存储为CLLocation对象，但无法使其工作。

逻辑应该是这样的

am I closest
     yes
move closest location to second closest
     set as second closest
loop again to get the closest point

我代码:

-(void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations{
    //set latestlocation as the last object from the locations array
    CLLocation *currentLocation = [locations lastObject];
    //declare a closestpoint object
    CLLocation *closestWayPointToCurrentLocation;
    //declare a second closest point object
    CLLocation *secondClosestWayPointToCurrentLocation;
    //set the distance to a high number
    float distance = 10000000;
    float secondClosestWaypointDistance = 10000000;
    //load in plist
    NSString *plistName = [self.mapsInfo objectForKey:@"plistName"];
    NSString *path = [[NSBundle mainBundle] pathForResource:@"Chester" ofType:@"plist"];
    NSString *path = [[NSBundle mainBundle] pathForResource:plistName ofType:@"plist"];
    //store in array called waypoints
    NSArray *waypoints= [NSArray arrayWithContentsOfFile:path];
    //declare a variable for locationNum (the waypoints)
    int locationNum = 0;
    for (NSDictionary *point in waypoints) {
        CLLocation *waypointLocation = [[CLLocation alloc]initWithLatitude:[(NSNumber *)[point  objectForKey:@"Lat"]floatValue] longitude:[(NSNumber *)[point objectForKey:@"Long"]floatValue]];
        float waypointDistanceFromCurrentLocation = [currentLocation distanceFromLocation:waypointLocation];
        //secondClosestWayPointToCurrentLocation = waypointLocation;
        if(waypointDistanceFromCurrentLocation < distance) {
            //todo: move the current closestWayPointToCurrentLocation into second postion
            //update the second closest waypoint distance variable also with distance
            distance = waypointDistanceFromCurrentLocation;
            closestWayPointToCurrentLocation = waypointLocation;

            if(closestWayPointToCurrentLocation == waypointLocation) {
            }
        }
        else
        {
            //check against the second position
        //if closer than second position, replace it with new waypoint with code similar to above
        }

Answer 1

如果你确定你总是倒数第二个点，那么你可以像这样检索它

int totalNumberOfWaypoints = [waypoints count];
//Get penultimate waypoints
NSDictionary *penultimateWaypoint = [waypoints objectAtIndex:(totalNumberOfWaypoints - 2)];  

Answer 2

为什么不做一个点的排序数组，按距离升序排序?

NSMutableArray *waypoints= [NSArray arrayWithContentsOfFile:path];
    for (NSDictionary *point in waypoints) {

[waypoints sortUsingComparator: (NSComparisonResult) ^ (id obj1, id obj2) {
        CLLocation *waypointLocation1 = [[CLLocation alloc]initWithLatitude:[(NSNumber *)[obj1 objectForKey:@"Lat"]floatValue] longitude:[(NSNumber *)[obj1 objectForKey:@"Long"]floatValue]];
        CLLocation *waypointLocation2 = [[CLLocation alloc]initWithLatitude:[(NSNumber *)[obj2 objectForKey:@"Lat"]floatValue] longitude:[(NSNumber *)[obj2 objectForKey:@"Long"]floatValue]];
        float distance1 = [currentLocation distanceFromLocation:waypointLocation1];
        float distance2 = [currentLocation distanceFromLocation:waypointLocation2];
        if (distance1 < distance2) {
            return NSOrderedAscending;
        }
        else if (distance1 > distance2) {
            return NSOrderedDescending
        }
        else
            return NSOrderedSame;
}];

这样你总是可以在[waypoints objectAtIndex:0]上有最近的点，在[waypoints objectAtIndex:1]上有第二个最近的点，以此类推。

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