iPhone: How to Rotate a UIImageview Left or Right?

I want to rotate an UIImageView in the following manner: If I hold the imageview and move the finger to left, then the imageview should rotate 开发者_StackOverflow社区to the right (and vice-versa.)

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I fiddle with this last year. It proved more complex than I thought it would. IIRC, this little class did what you wanted. It's a UIButtonSubclass that displays an image and responds to clicks and drags. Note that this is just scratch code. It doesn't do any memory management, cleanup etc.

#import <UIKit/UIKit.h>
#import "BackgroundImageButton.h"
#import "WiggleImageView.h"

@interface StickerButton : UIButton {
    //ivars used to control selection animaiton
    CGAffineTransform startTransform;
    BOOL currentlyAnimating;
    BOOL shouldAnimate; 
    //ivars to handle touches and control events
    BOOL wasDrag;
    BOOL wasTouchDown;
  WiggleImageView * imgView;
}
//ivars used to control selection animaiton
@property CGAffineTransform startTransform;
@property(nonatomic, retain)  WiggleImageView *imgView;
@property BOOL currentlyAnimating;
@property BOOL shouldAnimate;
//ivars to handle touches and control events
@property BOOL wasDrag;
@property BOOL wasTouchDown;


#pragma mark Initialization
-(id) initWithImage:(UIImage *)anImage atCenterPoint:(CGPoint) centerPoint;

#pragma mark Selection Animation Methods
-(void) animateSelection;
-(void) animationDidStop:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context;

#pragma mark Self Touch Methods  //not as dirty as it sounds.
-(void) touchDragSelf:(id)sender withEvent:(UIEvent *) theEvent;
-(void) touchDownSelf:(id)sender withEvent:(UIEvent *) theEvent;
-(void) touchUpSelf:(id)sender withEvent:(UIEvent *) theEvent;

#pragma mark Graphic Edit Methods
-(void) rotateRight;
-(void) rotateLeft;
-(void) scaleUp;
-(void) scaleDown;
-(void) select;
-(void) deselect;
-(void) translateMoveByX:(CGFloat) dx andY:(CGFloat) dy; //used by self to account for translated coordinates
-(void) frameMoveByX:(CGFloat) dx andY:(CGFloat) dy; //used by external to move frame in superview    
@end

#import "StickerButton.h"

@implementation StickerButton
@synthesize startTransform;
@synthesize currentlyAnimating;
@synthesize shouldAnimate;
@synthesize wasDrag;
@synthesize wasTouchDown;
@synthesize imgView;


#pragma mark Initialization
- (id)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        startTransform=self.transform;
        currentlyAnimating=NO;
        shouldAnimate=NO;
        wasDrag=NO;
        wasTouchDown=NO;
        self.adjustsImageWhenDisabled=NO;
        self.adjustsImageWhenHighlighted=NO;
        self.showsTouchWhenHighlighted=NO;
        [self addTarget:self action:@selector(touchDownSelf:withEvent:) forControlEvents:UIControlEventTouchDown];
        [self addTarget:self action:@selector(touchDragSelf:withEvent:) forControlEvents:UIControlEventTouchDragInside];
        [self addTarget:self action:@selector(touchUpSelf:withEvent:) forControlEvents:UIControlEventTouchUpInside];
    }
    return self;
}

-(id) initWithImage:(UIImage *)anImage atCenterPoint:(CGPoint) centerPoint{
    CGFloat xOrigin,yOrigin;
    xOrigin=centerPoint.x-(anImage.size.width/2);
    yOrigin=centerPoint.y-(anImage.size.height/2);
    [self initWithFrame:CGRectMake(xOrigin, yOrigin, anImage.size.width, anImage.size.height)];
    WiggleImageView *w=[[WiggleImageView alloc] initWithFrame:self.bounds];
    imgView=w;
    imgView.image=anImage;
    [self addSubview:imgView];
    return self;
}//------------------------------------initWithImage:atCenterPoint:------------------------------------



#pragma mark Selection Animation Methods
-(void) animateSelectedThrob{
    if (!currentlyAnimating) {
        NSLog(@"animating");
        currentlyAnimating=YES;
        //startTransform=self.transform; //this has to be saved to prevent some kind of rounding error from gradually rotating the view
        [UIView beginAnimations:@"selectionAnimation" context:nil];
        [UIView setAnimationDelegate:self];
        [UIView setAnimationDuration:0.1];
        [UIView setAnimationRepeatCount:1];
        [UIView setAnimationRepeatAutoreverses:YES];
        self.transform=CGAffineTransformScale(self.transform, 1.1, 1.1);
        [UIView commitAnimations];
    } 
}//-------------------------------------(void) animateSelectedThrob------------------------------------


-(void) animateSelection{
    if (!currentlyAnimating) {
        //NSLog(@"animating");
        currentlyAnimating=YES;
        startTransform=self.transform; //this has to be saved to prevent some kind of rounding error from gradually rotating the view
        [UIView beginAnimations:@"selectionAnimation" context:nil];
        [UIView setAnimationDelegate:self];
        [UIView setAnimationDuration:0.1];
        [UIView setAnimationRepeatCount:2];
        [UIView setAnimationRepeatAutoreverses:YES];
        self.transform=CGAffineTransformRotate(self.transform, (2 * M_PI / 180) );
        [UIView commitAnimations];
    } 

}//-------------------------------------(void) animateSelection------------------------------------

-(void) animationDidStop:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context{
    self.transform=startTransform;
    currentlyAnimating=NO;
    if (shouldAnimate) {

        [self animateSelection];
    }   
}//------------------------------------animationDidStop:finished:context:------------------------------------

#pragma mark Self Touch Methods

-(void) touchDownSelf:(id)sender withEvent:(UIEvent *) theEvent{
    NSLog(@"touchDownSelf");
    wasTouchDown=YES;
    shouldAnimate=NO;
}//------------------------------------touchDownSelf:withEvent:------------------------------------

-(void) touchDragSelf:(id)sender withEvent:(UIEvent *) theEvent{
    NSLog(@"touchDragSelf");
    if ([[theEvent touchesForView:self] count]==1) {
        UITouch *t=[[theEvent touchesForView:self] anyObject];
        CGPoint l,p;
        l=[t locationInView:self];
        p=[t previousLocationInView:self];
        [self translateMoveByX:(l.x-p.x) andY:(l.y-p.y)];
        wasDrag=YES;        
    }

}//------------------------------------touchDragSelf:withEvent:------------------------------------

-(void) touchUpSelf:(id)sender withEvent:(UIEvent *) theEvent{
    NSLog(@"touchUpSelf");
//  if (!wasDrag && wasTouchDown) {
//      [self select];
//  }
    if (wasTouchDown) {
        [self select];
    }
    wasDrag=NO;
    wasTouchDown=NO;
}//------------------------------------touchUpSelf:withEvent:------------------------------------

#pragma mark Graphic Edit Methods 
-(void) rotateRight{
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:0.1];
    [UIView setAnimationBeginsFromCurrentState:YES];
    self.transform=CGAffineTransformRotate(self.transform, (M_PI / 180) );
    [UIView commitAnimations];  
}//-------------------------------------(void) rotateRight------------------------------------

-(void) rotateLeft{
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:0.1];
    [UIView setAnimationBeginsFromCurrentState:YES];
    self.transform=CGAffineTransformRotate(self.transform, (-1*M_PI / 180) );
    [UIView commitAnimations];
}//-------------------------------------(void) rotateLeft------------------------------------

-(void) scaleUp{
    //todo add variable to track total scale so it doesn't get to big and cause problems
    shouldAnimate=NO;
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:0.1];
    [UIView setAnimationBeginsFromCurrentState:YES];
    self.transform=CGAffineTransformScale(self.transform, 1.1, 1.1);
    [UIView commitAnimations];
    startTransform=self.transform;
}//-------------------------------------(void) scaleUp------------------------------------

-(void) scaleDown{
    //todo add variable to track total scale so it doesn't get to small and cause problems
    shouldAnimate=NO;
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:0.1];
    [UIView setAnimationBeginsFromCurrentState:YES];
    self.transform=CGAffineTransformScale(self.transform, 0.9, 0.9);
    [UIView commitAnimations];
    startTransform=self.transform;
}//-------------------------------------(void) scaleDown------------------------------------

-(void) select{ 
    [self animateSelectedThrob];
    imgView.shouldWiggle=YES;
}
//-------------------------------------(void) select------------------------------------

-(void) deselect{
    imgView.shouldWiggle=NO;
}

-(void) translateMoveByX:(CGFloat) dx andY:(CGFloat) dy{ //necessary for all points that orignate within the transformed view
    NSLog(@"dx=%f,dy=%f",dx,dy);
    shouldAnimate=NO;
    self.transform=CGAffineTransformTranslate(self.transform, dx,dy);
    startTransform=self.transform;
}//------------------------------------translateMoveByX:andY:------------------------------------

-(void) frameMoveByX:(CGFloat) dx andY:(CGFloat) dy{ //necessary for all points that originate outside the transformed view

    self.frame=CGRectMake(self.frame.origin.x+dx, self.frame.origin.y+dy, self.frame.size.width, self.frame.size.height);
}//------------------------------------frameMoveByX:andY:------------------------------------
- (void)drawRect:(CGRect)rect {
    // Drawing code
}

- (void)dealloc {
    [super dealloc];
}

@end

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You could have an ivar in your controller for tracking the start of the drag. When you get a 'touch down' event, save the starting point. As you get 'touch moved' events, calculate the distance from the current point to the saved point. The Euclidean distance between the two can give you the rotation (the sign telling you which direction to rotate). Scale the rotation appropriately (ie. perhaps half the view width is equivalent to 180deg), and set the rotation of the image's transform.