2d barcode generator c# free An example using location and distance in Objective-C

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17.4.2 An example using location and distance
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Listing 17.9 shows an example of using Core Location to record a starting location, monitor the current location, and calculate the distance between them. It s the first of two longer examples in this chapter.
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Positioning: accelerometers and location
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Listing 17.9 An application of Core Location for distances
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- (void)viewDidLoad { [super viewDidLoad]; myLM = [[CLLocationManager alloc] init]; myLM.delegate = self; myLM.desiredAccuracy = kCLLocationAccuracyNearestTenMeters; myLM.distanceFilter = 100; [myLM startUpdatingLocation]; } - (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {
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Starts location manager Sets standard properties
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Starts location updates
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Waits for updates
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if (startLoc == nil) { Sets starting location startLoc = newLocation; [self updateLocationFor:startLabel toLocation:newLocation]; [startLoc retain]; }
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[self updateLocationFor:endLabel toLocation:newLocation]; [self updateDistanceLabel:newLocation]; } - (IBAction)setEnd:(id)sender { [myLM stopUpdatingLocation]; [myLM startUpdatingLocation]; } - (IBAction)controlChange:(id)sender { if (myLM.location) { [self updateDistanceLabel:myLM.location]; } }
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Calls label updates
Forces location update
Forces label update
- (void)updateDistanceLabel:(CLLocation *)newLocation { if (startLoc != nil) { CLLocationDistance traveled = [startLoc getDistanceFrom:newLocation] / 1000;
Updates distance label
if (segmentControl.selectedSegmentIndex == 1) { traveled *= .62; } distanceLabel.text = [NSString stringWithFormat:@"%5.1f",traveled]; } } - (void)updateLocationFor:(UILabel *)thisLabel toLocation:(CLLocation *)newLocation {
Updates location label
CLLocationCoordinate2D curCoords = newLocation.coordinate; thisLabel.text = [NSString stringWithFormat: @"Lat: %2.4f; Long: %2.4f",curCoords.latitude,curCoords.longitude]; }
All about Core Location
As usual, the foundation of this program is built in Interface Builder. Figure 17.3 displays the general setup that s used. There are three labels: startLabel (at the top) and endLabel (at the bottom) each display information about a location; distanceLabel shows the distance between the two. There are two controls: a button control instantly updates the current location, and a segmented control chooses between miles and kilometers. They re each linked to an IBAction, which executes a method that we ll meet in the code. This program generally follows the broad outline of steps that we ve already discussed, but we ll go through each step in turn. You start off initializing a CLLocationManager object B and then set some standard properties C here a delegate, the desiredAccuracy, and the distanceFilter. The desired accuracy of tens of meters and the update interval of every 100 meters Figure 17.3 This simple utility might be more than this particular application shows off locations and distance. requires, but you can tune these in your projects as seems appropriate. Remember that demanding more accuracy and updating more frequently will decrease the battery life of your user s iPhone. Finally, you have to start the CLLocationManager running D. The locationManager:didUpdateToLocation:fromLocation: method is the workhorse of this program E. It should get called shortly after the LocationManager starts updating and every time your user walks 100 meters or so. First, it saves the current location as the starting location the first time it s called, updating the startLabel at the same time F. Then, every time it gets run, it updates the endLabel and the distanceLabel G. Note that you don t have to use the LocationManager s location property here (or at almost any other time in the program), because this method always provides you with the current location of the device, and seems to do so well before the location property is updated, based on our own tests. Caveat programmer. The next few methods have to do with I/O. setEnd: gets run whenever the button control is pushed, to update the current location H. Unfortunately, there s no particularly clean way to ask for an update, so you must stop and start the location updates, as shown here. Letting the user force a location update is particularly important if you re using a high distanceFilter or if you re trying to measure altitude changes. In our altitude example, in the next section, we ll see an alternative way to do this, where the location manager usually isn t running at all. The controlChange: method gets run whenever the segmented control is updated I. It just updates the distanceLabel. Note that this is the one time that you depend on the location property, because there isn t a location event when you change the button.
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