Images Pinch Zoom using UIPinchGestureRecognizer Tutorial

After seeing many pinch zoom samples I am unhappy, most of samples show only how to use UIPinchGestureRecognizer but none of sample tell how to continue apply pinch zoom from where it left. In this sample I tried to support pinch zoom from where it left.

Before Zoom

After Zoom

Creating UIPinchGestureRecognizer  And adding To Pich View.

UIPinchGestureRecognizer *pinchGesture = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(handlePinch:)];

[mGestureView addGestureRecognizer:pinchGesture];

    [pinchGesture release];

Heare mGestureView is UIView on which we adding UIPinchGestureRecognizer instance

Handling Pinch Zoom

-(void)handlePinch:(UIPinchGestureRecognizer*)sender {

        

    /*

     There are different actions to take for the different states of the gesture recognizer.

     * In the Began state, use the pinch location to find the index path of the row with which the pinch is associated, and keep a reference to that in pinchedIndexPath. Then get the current height of that row, and store as the initial pinch height. Finally, update the scale for the pinched row.

     * In the Changed state, update the scale for the pinched row (identified by pinchedIndexPath).

     * In the Ended or Canceled state, set the pinchedIndexPath property to nil.

     */

         NSLog(@"latscale = %f",mLastScale);

         mCurrentScale += [sender scale] - mLastScale;

         mLastScale = [sender scale];

        

         if (sender.state == UIGestureRecognizerStateEnded)

         {

                  mLastScale = 1.0;

         }

        

         CGAffineTransform currentTransform = CGAffineTransformIdentity;

         CGAffineTransform newTransform = CGAffineTransformScale(currentTransform, mCurrentScale, mCurrentScale);

         mGestureView.transform = newTransform;

        

}

The logic here is simple first we getting current  scale value.

mCurrentScale += [sender scale] - mLastScale;

we are minusing it with previos pinch only to get current zoom. And once user lifts finger we are reseting lastscale value to 0.0 (i.e UIPinchGestureRecognizer values start from 1.0 actual zoom ) in UIGestureRecognizerStateEnded.

Lastly we applying CGAffineTransformScale to view to zoom.

CGAffineTransform currentTransform = CGAffineTransformIdentity;

         CGAffineTransform newTransform = CGAffineTransformScale(currentTransform, mCurrentScale, mCurrentScale);

    mGestureView.transform = newTransform;


Note:
One more nice and full coverage tutorial about UIGestureRecognize is return by Raywanderlich
click here to Read Tutorial.

Download Sample