Rotate image on center using one finger touch

Question

I want to rotate the below image on a center point using one finger touch...

And i want to display the value of the image with the label when I rotate the image usin

Answer 1

Wasn't totally sure what you were after; but try out this code.

If you create a new View-based Application project called 'Rotation' and replace the code in RotationViewController.h and .m for the following you'll get a green block that you can rotate using your calculations. You can replace the green block UIView with your UIImageView, or anything else you want to spin.

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RotationViewController.h

#import <UIKit/UIKit.h>

@interface RotationViewController : UIViewController
{
    UIView* m_block;
    UILabel* m_label;
    CGPoint m_locationBegan;
    float m_currentAngle;
}

- (float) updateRotation:(CGPoint)_location;

@end

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RotationViewController.m

#import "RotationViewController.h"

double wrapd(double _val, double _min, double _max)
{
    if(_val < _min) return _max - (_min - _val);
    if(_val > _max) return _min - (_max - _val);
    return _val;
}

@implementation RotationViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    CGRect blockFrame = CGRectMake(0, 0, 200, 200);
    m_block = [[UIView alloc] initWithFrame:blockFrame];
    m_block.backgroundColor = [UIColor greenColor];
    m_block.center = self.view.center;
    [self.view addSubview:m_block];
    [m_block release];
    
    CGRect labelFrame = CGRectMake(0, 0, 320, 30);
    m_label = [[UILabel alloc] initWithFrame:labelFrame];
    m_label.text = @"Loaded";
    [self.view addSubview:m_label];
}

- (void) touchesBegan:(NSSet *)_touches withEvent:(UIEvent *)_event
{
    UITouch* touch = [_touches anyObject];
    CGPoint location = [touch locationInView:self.view];
    m_locationBegan = location;
}

- (void) touchesMoved:(NSSet *)_touches withEvent:(UIEvent *)_event
{
    UITouch* touch = [_touches anyObject];
    CGPoint location = [touch locationInView:self.view];
    [self updateRotation:location];
}

- (void) touchesEnded:(NSSet *)_touches withEvent:(UIEvent *)_event
{
    UITouch* touch = [_touches anyObject];
    CGPoint location = [touch locationInView:self.view];
    m_currentAngle = [self updateRotation:location];
}

- (float) updateRotation:(CGPoint)_location
{
    float fromAngle = atan2(m_locationBegan.y-m_block.center.y, m_locationBegan.x-m_block.center.x);
    float toAngle = atan2(_location.y-m_block.center.y, _location.x-m_block.center.x);
    float newAngle = wrapd(m_currentAngle + (toAngle - fromAngle), 0, 2*3.14);

    CGAffineTransform cgaRotate = CGAffineTransformMakeRotation(newAngle);
    m_block.transform = cgaRotate;
    
    int oneInFifty = (newAngle*50)/(2*3.14);
    
    m_label.text = [NSString stringWithFormat:@"Angle: %f 1in50: %i", newAngle, oneInFifty];

    return newAngle;
}

@end

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