iOS - Introduction to Gesture Recognizer in iOS

 

Introduction

If you need to detect gestures in your app, such as taps, pinches, pans, or rotations, it’s extremely easy with the built-in UIGestureRecognizer classes. In this post, I’ll show you how you can easily add gesture recognizers into your app, both within the Storyboard editor and programatically.

We’ll create a simple app where you can move bluebox dragging, pinching, and rotating with the help of gesture recognizers. Following are the steps that give you a brief introduction about how to recognize different gestures in your application.

Step 1 Create Xcode Project

Open up Xcode and create a new project with the iOS/ Application/ Single View Application template. For the Product Name enter GestureDemoExample, for the Device Family choose iPhone, and select the Use Storyboard and Use Automatic Reference Counting checkboxes.

Step 2 Design UI

Next, open up MainStoryboard.storyboard, and drag an View into the View Controller.

Step 3 Create IBOutlet

Create property in ViewController.h file as per following:

@property (weak, nonatomic) IBOutlet UIView *blueBox;

Step 4 Put Gesture methods

4.1 UIPanGestureRecognizer

Add the following implementations in ViewController.m

UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePanGesture:)];
[panGesture setMinimumNumberOfTouches:1];
[panGesture setMaximumNumberOfTouches:1];
[blueBox addGestureRecognizer:panGesture];
panGesture = nil;

Method to handle pan gesture:

-(void)handlePanGesture:(id)sender
{
CGPoint translatedPoint = [(UIPanGestureRecognizer*)sender translationInView:self.view];
if([(UIPanGestureRecognizer*)sender state] == UIGestureRecognizerStateBegan) {
firstX = [[sender view] center].x;
firstY = [[sender view] center].y;
}
translatedPoint = CGPointMake(firstX+translatedPoint.x, firstY+translatedPoint.y);
[[sender view] setCenter:translatedPoint];
}

4.2 UIPinchGestureRecognizer

Add the following implementations in ViewController.m

UIRotationGestureRecognizer *rotate=[[UIRotationGestureRecognizer alloc]initWithTarget:self action:@selector(rotation:)];
[blueBox addGestureRecognizer:rotate];

Method to handle pinch gesture:

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

4.3 UIRotationGestureRecognizer

Add the following implementations in ViewController.m

UIRotationGestureRecognizer *rotate=[[UIRotationGestureRecognizer alloc]initWithTarget:self action:@selector(rotation:)];
[blueBox addGestureRecognizer:rotate];

Method to handle rotation gesture:

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

4.4 UITapGestureRecognizer

Add the following implementations in ViewController.m

UITapGestureRecognizer *tapper=[[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(tapped:)]; [blueBox addGestureRecognizer:tapper];

Method to handle tap gesture:

-(void) tapped:(UIGestureRecognizer *) sender
{
CGFloat r=(CGFloat) random()/(CGFloat) RAND_MAX;
CGFloat g=(CGFloat) random()/(CGFloat) RAND_MAX;
CGFloat b=(CGFloat) random()/(CGFloat) RAND_MAX;
blueBox.backgroundColor=[UIColor colorWithRed:r green:g blue:b alpha:1];
}

4.5 UISwipeGestureRecognizer

Add the following implementations in ViewController.m

UISwipeGestureRecognizer *swipe=[[UISwipeGestureRecognizer alloc]initWithTarget:self action:@selector(swiping:)];
[blueBox addGestureRecognizer:swipe];

Method to handle swipe gesture:

-(void) swiping:(UISwipeGestureRecognizer *) sender
{
[UIView beginAnimations:nil context:nil];
[UIView setAnimationRepeatAutoreverses:YES];
[UIView setAnimationRepeatCount:5];
[UIView setAnimationDelegate:self];
[UIView setAnimationDidStopSelector:@selector(stop:)];
blueBox.backgroundColor=[UIColor whiteColor];
[UIView commitAnimations];
}
-(void) stop: sender
{
blueBox.backgroundColor=[UIColor blueColor];
}

UITapGestureRecognizer:

Add the following implementations in ViewController.m

UILongPressGestureRecognizer *longPress=[[UILongPressGestureRecognizer alloc]initWithTarget:self action:@selector(longPressed:)];
longPress.minimumPressDuration=3;

Method to handle long press gesture:

-(void) longPressed:(UIGestureRecognizer *) sender
{
CGFloat r=(CGFloat) random()/(CGFloat) RAND_MAX;
CGFloat g=(CGFloat) random()/(CGFloat) RAND_MAX;
CGFloat b=(CGFloat) random()/(CGFloat) RAND_MAX;
blueBox.backgroundColor=[UIColor colorWithRed:r green:g blue:b alpha:1];
}

I hope you found this blog helpful while working Gesture Recognizer in iOS. Let me know if you have any questions or concerns regarding iOS, please put a comment here and we will get back to you ASAP.

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