仅使用CGAffineTransform旋转而不移动？

Question

i have an app contains a needle that points toward a specific location wherever you're in the world, but when i use the code below it works but the needle both rotates and moves, so how to stop it from moving while rotating ?

CLLocationCoordinate2D  currentLocation;
CLLocationDirection     currentHeading;
CLLocationDirection     cityHeading;
#define toRad(X) (X*M_PI/180.0)
#define toDeg(X) (X*180.0/M_PI)
#define FONT_SIZE 14.0f
#define CELL_CONTENT_WIDTH 320.0f
#define CELL_CONTENT_MARGIN 10.0f

- (void)viewDidLoad
{
    [super viewDidLoad];
    currentHeading=0.0;




    //  isArabic=[starter isArabic];


    locationManager = [[CLLocationManager alloc] init];
    locationManager.delegate = self;
    locationManager.distanceFilter = kCLDistanceFilterNone;
    locationManager.desiredAccuracy = kCLLocationAccuracyBest;



    if([CLLocationManager locationServicesEnabled]){
        [locationManager startUpdatingLocation];
    }
    [locationManager startUpdatingHeading];
}
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {

    currentLocation = newLocation.coordinate;

    [self updateHeadingDisplays];
}
- (void)locationManager:(CLLocationManager *)manager
       didUpdateHeading:(CLHeading *)newHeading{


    float oldRad =  -manager.heading.trueHeading * M_PI / 180.0f;
    float newRad =  -newHeading.trueHeading * M_PI / 180.0f;
    CABasicAnimation *theAnimation;
    theAnimation=[CABasicAnimation animationWithKeyPath:@"transform.rotation"];
    theAnimation.fromValue = [NSNumber numberWithFloat:oldRad];
    theAnimation.toValue=[NSNumber numberWithFloat:newRad];
    theAnimation.duration = 0.5f;
    [compass.layer addAnimation:theAnimation forKey:@"animateMyRotation"];
    compass.transform = CGAffineTransformMakeRotation(newRad);

    NSLog(@"%f (%f) => %f (%f)", manager.heading.trueHeading, oldRad, newHeading.trueHeading, newRad);
    // if (newHeading.headingAccuracy < 0)
    //    return;

    // Use the true heading if it is valid.
    CLLocationDirection  theHeading = ((newHeading.trueHeading > 0) ?
                                       newHeading.trueHeading : newHeading.magneticHeading);


    cityHeading = [self directionFrom:currentLocation ];


    currentHeading = theHeading;

    [self updateHeadingDisplays];



}
- (void)updateHeadingDisplays {
    // Animate Compass


    [UIView     animateWithDuration:0.6
                              delay:0.0
                            options:UIViewAnimationOptionBeginFromCurrentState | UIViewAnimationOptionCurveEaseOut | UIViewAnimationOptionAllowUserInteraction
                         animations:^{
                             CGAffineTransform headingRotation = CGAffineTransformRotate(CGAffineTransformMakeTranslation(0, 0), (CGFloat)toRad(cityHeading)-toRad(currentHeading));

                             needle.transform = headingRotation;
                         }
                         completion:^(BOOL finished) {

                         }];



}

-(CLLocationDirection) directionFrom: (CLLocationCoordinate2D) startPt  {

    double lat1 = toRad(startPt.latitude);
    double lat2 = toRad(21.4266700 );
    double lon1 = toRad(startPt.longitude);
    double lon2 = toRad(39.8261100);
    double dLon = (lon2-lon1);

    double y = sin(dLon) * cos(lat2);
    double x = cos(lat1) * sin(lat2) - sin(lat1) * cos(lat2) * cos(dLon);
    double brng = toDeg(atan2(y, x));

    brng = (brng+360);
    brng = (brng>360)? (brng-360) : brng;

    return brng;

}

Answer 1

In your screenshot from your comment it looks like you're using Auto Layout (as you should be). But with Auto Layout comes certain behavior. You can see the warning from interface builder in the size inspector:

The selected views have no constraints. At build time explicit left, top, width and height constraints will be generated for the view.

Who knows what constraints are being applied to your view by default! If you constrain the center of your image view to be in a specific spot, the compass image should rotate around its center.

For example, you could control drag from the image view to the parent and choose Center in Container for both vertical and horizontal directions.