UITapGestureRecognizer - make it work on touch down, not touch up?

What I'm using the tap event for is very time-sensitive, so I'm curious if it's possible to make UITapGestureRecognizer activate when the user simply touches down, rather than requiring them to touch up as well?

Use a UILongPressGestureRecognizer and set its minimumPressDuration to 0. It will act like a touch down during the UIGestureRecognizerStateBegan state.

#For Swift 4+

func setupTap() {
    let touchDown = UILongPressGestureRecognizer(target:self, action: #selector(didTouchDown))
    touchDown.minimumPressDuration = 0
    view.addGestureRecognizer(touchDown)
}

@objc func didTouchDown(gesture: UILongPressGestureRecognizer) {
    if gesture.state == .began {
        doSomething()
    }
}

#For Objective-C

-(void)setupLongPress
{
   self.longPress = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(didLongPress:)];
   self.longPress.minimumPressDuration = 0;
   [self.view addGestureRecognizer:self.longPress];
}

-(void)didLongPress:(UILongPressGestureRecognizer *)gesture
{
   if (gesture.state == UIGestureRecognizerStateBegan){
      [self doSomething];
   }
}

Create your custom TouchDownGestureRecognizer subclass and implement gesture in touchesBegan:

TouchDownGestureRecognizer.h

#import <UIKit/UIKit.h>

@interface TouchDownGestureRecognizer : UIGestureRecognizer

@end

TouchDownGestureRecognizer.m

#import "TouchDownGestureRecognizer.h"
#import <UIKit/UIGestureRecognizerSubclass.h>

@implementation TouchDownGestureRecognizer
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    if (self.state == UIGestureRecognizerStatePossible) {
        self.state = UIGestureRecognizerStateRecognized;
    }
}

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
    self.state = UIGestureRecognizerStateFailed;
}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{
    self.state = UIGestureRecognizerStateFailed;
}


@end

implementation:

#import "TouchDownGestureRecognizer.h"
    TouchDownGestureRecognizer *touchDown = [[TouchDownGestureRecognizer alloc] initWithTarget:self action:@selector(handleTouchDown:)];
    [yourView addGestureRecognizer:touchDown];

-(void)handleTouchDown:(TouchDownGestureRecognizer *)touchDown{
    NSLog(@"Down");
}

---

Swift implementation:

import UIKit
import UIKit.UIGestureRecognizerSubclass

class TouchDownGestureRecognizer: UIGestureRecognizer
{
    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent)
    {
        if self.state == .Possible
        {
            self.state = .Recognized
        }
    }
    
    override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent)
    {
        self.state = .Failed
    }
    
    override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent)
    {
        self.state = .Failed
    }
}

---

Here is the Swift syntax for 2017 to paste:

import UIKit.UIGestureRecognizerSubclass

class SingleTouchDownGestureRecognizer: UIGestureRecognizer {
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) {
        if self.state == .possible {
            self.state = .recognized
        }
    }
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) {
        self.state = .failed
    }
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent) {
        self.state = .failed
    }
}

Note that this is a drop-in replacement for UITap. So in code like...

func add(tap v:UIView, _ action:Selector) {
	let t = UITapGestureRecognizer(target: self, action: action)
	v.addGestureRecognizer(t)
}

you can safely swap to....

func add(hairtriggerTap v:UIView, _ action:Selector) {
	let t = SingleTouchDownGestureRecognizer(target: self, action: action)
	v.addGestureRecognizer(t)
}

Testing shows it will not be called more than once. It works as a drop-in replacement; you can just swap between the two calls.

Swift (without subclassing)

Here is a Swift version similar to Rob Caraway's Objective-C answer.

The idea is to use a long press gesture recognizer with the minimumPressDuration set to zero rather than using a tap gesture recognizer. This is because the long press gesture recognizer reports touch began events while the tap gesture does not.

import UIKit
class ViewController: UIViewController {

    @IBOutlet weak var myView: UIView!

    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Add "long" press gesture recognizer
        let tap = UILongPressGestureRecognizer(target: self, action: #selector(tapHandler))
        tap.minimumPressDuration = 0
        myView.addGestureRecognizer(tap)
    }

    // called by gesture recognizer
    @objc func tapHandler(gesture: UITapGestureRecognizer) {
        
        // handle touch down and touch up events separately
        if gesture.state == .began {
            // do something...
            print("tap down")
        } else if gesture.state == .ended { // optional for touch up event catching
            // do something else...
            print("tap up")
        }
    }
}

This is another solution. Create subclass of UIControl. You can use it like UIView even in Storyboard because UIControl is subclass of UIView.

class TouchHandlingView: UIControl {
}

And addTarget to it:

@IBOutlet weak var mainView: TouchHandlingView!
...

mainView.addTarget(self, action: "startAction:", forControlEvents: .TouchDown)
...

Then the designated action will be called like UIButton:

func startAction(sender: AnyObject) {
    print("start")
}

I needed the ability for my view to have a hair trigger so as soon as it's tapped it responds. Using both @LESANG answer worked and so did using @RobCaraway answer. The problem I ran into with both answers was I lost the ability to recognize swipes. I needed my view to rotate when swiped but as soon as my finger touched the view only the tap was recognized. The tapRecognizer was too sensitive and couldn't differentiate between a tap and a swipe.

This is what I came up with based off of @LESANG answer combined with this answer and this answer.

I put 6 comments in each event.

import UIKit.UIGestureRecognizerSubclass

class SingleTouchDownGestureRecognizer: UIGestureRecognizer {
    
    
    var wasSwiped = false
    
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) {
        
        guard let view = self.view else { return }
        guard let touches = event.touches(for: view) else { return } // 1. compare that event in touchesBegan has touches for the view that is the same as the view to which your gesture recognizer was assigned

        if touches.first != nil {
            print("Finger touched!") // 2. this is when the user's finger first touches the view and is at locationA
            wasSwiped = false // 3. it would seem that I didn't have to set this to false because the property was already set to false but for some reason when I didn't add this it wasn't responding correctly. Basically set this to false
        }
    }
    
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) {
        
        guard let touch = touches.first else { return }
        
        let newLocation = touch.location(in: self.view)
        let previousLocation = touch.previousLocation(in: self.view)
        
        if (newLocation.x > previousLocation.x) || (newLocation.x < previousLocation.x) {
            print("finger touch went right or left") // 4. when the user's finger first touches it's at locationA. If the the user moves their finger to either the left or the right then the finger is no longer at locationA. That means it moved which means a swipe occurred so set the "wasSwiped" property to true
            
            wasSwiped = true // 5. set the property to true because the user moved their finger
        }
    }
    
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent) {
        print("finger is no longer touching.") // 6. the user has lifted their finger off of the view. If "wasSwiped" is true then ".fail" but if it wasn't swiped then ".recognize"
        
        if wasSwiped {
            self.state = .failed
        } else {
            self.state = .recognized
        }
    }
}

And to use it so that view that uses it gets the hair trigger response and left and right swipe gestures.:

let tapGesture = SingleTouchDownGestureRecognizer(target: self, action: #selector(viewWasTapped(_:)))
myView.addGestureRecognizer(tapGesture)

let rightGesture = UISwipeGestureRecognizer(target: self, action: #selector(respondToSwipeGesture(recognizer:)))
rightGesture.direction = .right
myView.addGestureRecognizer(rightGesture)
        
let leftGesture = UISwipeGestureRecognizer(target: self, action: #selector(respondToSwipeGesture(recognizer:)))
leftGesture.direction = .left
myView.addGestureRecognizer(leftGesture)