CODEWITHSUNDEEP
iphoneiosxcodeipad
Sam B
Sam B

Reputation: 27608

CGAffineTransformMakeRotation counter clockwise always

I an trying to animate a UIImageView to rotate counter clockwise when a user touches it and moves its finger on it in clockwise direction.
Basically I want the UIImageView to go back to its original position once the touch ends and it should move in counter clockwise direction.

The problem I have is that every time angle (in degrees) is greater than 180 then the image rotates clockwise back to its original position. Its apparently taking the shortest path back. As for angles 179 degrees or less the image rotate counter clockwise (what i need).

I tried both these pieces of code and they behave the same way. Any suggestions?

NOTE: here angle variable is a double and its initialized to be zero and it remains 0 throughout my code

-(void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event 
{
    [self handleObject:touches withEvent:event isLast:YES];

    /* this doesn't make rotation counter clockwise for rotations greater than 180 */
    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationCurve: UIViewAnimationCurveLinear];
    [UIView setAnimationDuration:1.0];
    [UIView setAnimationRepeatCount:1]; 
    CGAffineTransform transform = CGAffineTransformMakeRotation(angle);
    circle1ImgVw.transform = CGAffineTransformRotate(transform, angle);
    // ends animation
    [UIView commitAnimations];


    /* this doesn't make rotation counter clockwise for rotations greater than 180 */
    [UIView animateWithDuration:1.0 animations:^{
            circle1ImgVw.transform = CGAffineTransformMakeRotation(angle);
        }];
}

I tried looking into this post and there are couple of problems with it

Upvotes: 8

Views: 7523

Answers (2)

Hot Licks
Hot Licks

Reputation: 47729

The technique I've used is to divide the rotation angle by 2 and separate the rotate into two separate animations, linked by the completion: parameter of animateWithDuration:delay:options:animations:completion:. But, since the view has been rotated to its current position, you need to start with that position and "unrotate" back to zero, vs attempting to rotate CCW from zero.

Upvotes: 0

Darren
Darren

Reputation: 10129

I had a similar issue, check the accepted answer out, it might help you:

Rotate a UIView clockwise for an angle greater than 180 degrees

In response to comments, maybe this will help:

In my code I actually use 

rotationAnimation.fromValue
rotationAnimation.toValue

instead of 

rotationAnimation.byValue.

The rotation is always going to be counter clockwise if the toValue is less than the fromValue. It doesn't matter if your values are positive or negative, only the relation between them.

Figure out what your starting angle is, figure out which direction you want to rotate and figure out what your ending angle is. Make sure that it's less than your starting angle if you want to go counter clockwise. Here is the code I use for animating a clock hand clockwise from 12:00 to the current time.

-(void) viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];

    [self updateClockArmAngle];
}

- (void)updateClockArmAngle
{
    // Get the time
    NSDate *date = [NSDate date];
    NSCalendar* calendar = [[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar] autorelease];
    [calendar setTimeZone:[NSTimeZone timeZoneWithName:@"America/Toronto"]];
    NSDateComponents* components = [calendar components:(NSHourCalendarUnit | NSMinuteCalendarUnit) fromDate:date];

    CGFloat hour = [components hour];
    CGFloat angle = (hour/24.0)*(2*M_PI);

    CGFloat minute = [components minute];
    angle += (minute/(24*60))*(2*M_PI);

    [self rotateViewAnimated:self.clockArm withDuration:1.5 byAngle:angle];
}


- (void) rotateViewAnimated:(UIView*)view
               withDuration:(CFTimeInterval)duration
                    byAngle:(CGFloat)angle
{    
    CABasicAnimation *rotationAnimation;
    rotationAnimation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
    rotationAnimation.fromValue = 0;
    rotationAnimation.toValue = [NSNumber numberWithFloat:angle];
    rotationAnimation.duration = duration;
    rotationAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
    [rotationAnimation setRemovedOnCompletion:NO];
    [rotationAnimation setFillMode:kCAFillModeForwards];
    [view.layer addAnimation:rotationAnimation forKey:@"rotationAnimation"];
}

Upvotes: 3

Related Questions