Rotate the image corresponding to the touch drag in iPhone

Question

I want to rotate the image in clockwise or anticlockwise direction corresponding to the user touch drag with its speed. I think this can be done with some math and logic. What would a code sample for this look like?

Answer 1

If you're targeting iOS 3.2 or greater, you can use UIRotationGestureRecognizer. The code would look something like this:

In your setup method (viewDidLoad or init, etc,):

UIRotationGestureRecognizer *rotationGesture = 
  [[UIRotationGestureRecognizer alloc] initWithTarget:self
                                               action:@selector(handleRotate:)];
rotationGesture.delegate = self;
[myImageView addGestureRecognizer:rotationGesture];
[rotationGesture release];

The event handler:

- (void)handleRotate:(UIRotationGestureRecognizer *)recognizer {
  if(recognizer.state == UIGestureRecognizerStateBegan || 
     recognizer.state == UIGestureRecognizerStateChanged)
  {
    recognizer.view.transform = CGAffineTransformRotate(recognizer.view.transform, 
                                                        recognizer.rotation);
    [recognizer setRotation:0];
  }
}

I have some more examples of gesture recognizers (including the one above) on github.

Answer 2

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    for (UITouch *touch in touches)
    {
        currentTouch=touch;
        if (CGRectContainsPoint([self.view frame], [touch locationInView:self.ViewRotationArrow]))
        {
            [self transformSpinnerwithTouches:touch];
        }
        else if (!CGRectContainsPoint([ViewRotationArrow frame], [touch locationInView:self.ViewRotationArrow])) {
            [self dispatchTouchEvent:[touch view]WithTouch:touch];
        }
    }
}

-(void)transformSpinnerwithTouches:(UITouch *)touchLocation
{
    CGPoint touchLocationpoint = [touchLocation locationInView:self.view];
    CGPoint PrevioustouchLocationpoint = [touchLocation previousLocationInView:self.view];

    //Origin is the respective point. From that I am going to measure the
    //angle of the current position with respect to the previous position ....
    CGPoint origin;
    origin.x=240;
    origin.y=160;
    //NSLog(@"currentTouch Touch In Location In View:%F %F\n",touchLocationpoint.x,touchLocationpoint.y);
    //NSLog(@"currentTouch Touch previous Location In View:%F %F\n",PrevioustouchLocationpoint.x,PrevioustouchLocationpoint.y);
    CGPoint previousDifference = [self vectorFromPoint:origin toPoint:PrevioustouchLocationpoint];
    CGAffineTransform newTransform =CGAffineTransformScale(ViewRotationArrow.transform, 1, 1);
    CGFloat previousRotation = atan2(previousDifference.y, previousDifference.x);
    CGPoint currentDifference = [self vectorFromPoint:origin toPoint:touchLocationpoint];
    CGFloat currentRotation = atan2(currentDifference.y, currentDifference.x);
    CGFloat newAngle = currentRotation- previousRotation;
    NSLog(@"currentRotation of x %F  previousRotation %F\n",currentRotation,previousRotation);
    NSLog(@"Angle:%F\n",(temp1*180)/M_PI);
    temp1=temp1+newAngle;
    //NSLog(@"Angle:%F\n",(temp1*180)/M_PI);
    newTransform = CGAffineTransformRotate(newTransform, newAngle);
    [self animateView:ViewRotationArrow toPosition:newTransform];
}

 -(CGPoint)vectorFromPoint:(CGPoint)firstPoint toPoint:(CGPoint)secondPoint
{
        CGPoint result;
        CGFloat x = secondPoint.x-firstPoint.x;
        CGFloat y = secondPoint.y-firstPoint.y;
        result = CGPointMake(x, y);
        return result;
}



-(void)animateView:(UIView *)theView toPosition:(CGAffineTransform) newTransform
{
    //animating the rotator arrow...
    [UIView setAnimationsEnabled:YES];
    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationCurve:UIViewAnimationCurveLinear];
    [UIView setAnimationBeginsFromCurrentState:YES];
    [UIView setAnimationDuration:0.0750];
    ViewRotationArrow.transform = newTransform;
    [UIView commitAnimations];
}