UILongPressGestureRecognizer的工作方式

Question

I am trying to understand how the gesture recognizer works and trying to get a gesture recognizer to tell me when a long touch BEGINS and when it ENDS even if the touch does not move.

In viewDidLoad , I add a subview called game. In game, I have implemented two ways to recognize touches. One works but does not do what I want. The other does not work.

Method1 I just added two methods:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    NSLog(@"Began");
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *) event {
    NSLog(@"Ended");
}

This worked, without instantiating a gesture recognizer. Can someone tell me why?

The issue with this is that - (void)touchedEnded: only gets called if the touch moved and not if the touch ended at the same location it started. So if I touched and moved and let go, both functions get called. If I touch and hold and let go (without moving), only the - (void)touchesBegan gets called.

METHOD 2 I instantiated a gesture recognizer:

@property (nonatomic, strong) UILongPressGestureRecognizer *lprg;

then in my setup:

self.lprg = [UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(handleLongPress:)];

then:

- (void)handleLongPress:(UILongPressGestureRecognizer *)recognizer {
    NSLog(@"Handling");
    switch (recognizer.state) {
     case UIGestureRecognizerStateBegan:
         // ...
    }
}

But this one, where I programmatically instantiated the recognizer, did not work. I never got any NSLog output in the console.

Answer 1

All subclasses of UIResponder (which UIView is) respond to touchesBegan, that's why you don't have to do anything and you get it for free. However it is far from a gesture recognizer. At a high level gesture recognizers track a lot of things, fore example state. Sure you can use touches began, but imagine extending that to pick up something like a three finger long press, swipe or pinch. Things get ugly quick. Installing a gesture recognizer simplifies things.

For example a long press:

UILongPressGestureRecognizer *longPress = [[UILongPressGestureRecognizer alloc] init];
longPress.numberOfTouchesRequired = 3;
[longPress addTarget:self action:@selector(longPressDetected:)];
[self.view addGestureRecognizer:longPress];

Edit

To implement the delegate:

In your implementation file (.m) add the line at the end of your @implemation line. It should look something like

 @implementation ViewController <UIGestureRecognizerDelegate>

Then after you alloc and init your gesture recognizer set the delegate as follows

 longPress.delegate = self;

Then implement as many methods as you need from https://developer.apple.com/library/ios/documentation/uikit/reference/UILongPressGestureRecognizer_Class/Reference/Reference.html . For example you might consider these two

- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer {
    return YES;
}

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldReceiveTouch:(UITouch *)touch {
    return YES;
}

Answer 2

you have to use this code to intialized gesture

  UILongPressGestureRecognizer *gesture1 = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(celllongpressed:)];
    [gesture1 setDelegate:self];
    [gesture1 setMinimumPressDuration:1];
    [self addGestureRecognizer:gesture1];

and to target method use this

-(void)celllongpressed:(UIGestureRecognizer *)longPress
{
}