Using a Long Press Gesture only if certain conditions are met

Question

I am trying to create a long press gesture that presents a second view controller, once the press has been held for 3 seconds. However, I only want the second view controller presented if the device is in a certain accelerometer orientation for the ENTIRE 3 seconds. That is, if the gesture is not held long enough or the device is tilted too much, the gesture is dismissed and the user must try again.

// In FirstViewController.h

#import <UIKit/UIKit.h>
#import <CoreMotion/CoreMotion.h>

@interface FirstViewController : UIViewController

@property (nonatomic, strong) CMMotionManager *motionManager;

@end

// In FirstViewController.m

#import "FirstViewController"
#import "SecondViewController"

@implementation motionManager;

- (void) viewDidLoad
{
    [super viewDidLoad];
    self.motionManager = [[CMMotionManager alloc]init];
    UILongPressGestureRecognizer *longPress = [[UILongPressGestureRecognizer alloc]initWithTarget:self action:@selector(handleLongPress:)];
    longPress.minimumPressDuration = 3.0;
    [self.view addGestureRecognizer:longPress];
}

- (void) handleLongPress: (UILongPressGestureRecognizer *)sender
{
    // Not sure what to do here
}

I have previously tried chunks of code in the last method but it looks obnoxious and just is not correct. Instead, I have listed several lines of code below that I know work individually, but I need assistance in making them all work together.

// Accelerometer

if ([self.motionManager isAccelerometerAvailable])
{
    NSOperationQueue *queue = [[NSOperationQueue alloc]init];
    [self.motionManager startAccelerometerUpdatesToQueue:queue withHandler:^(CMAccelerometerData *accelerometerData,NSError *error)
    {
        if (ABS(accelerometerData.acceleration.x) < 0.3 && ABS(accelerometerData.acceleration.y) < 0.30 && ABS(accelerometerData.acceleration.z) > 0.70) // Phone is flat and screen faces up
        { 
            NSLog(@"Correct Orientation!!!");
            [self.motionManager stopAccelerometerUpdates];
        }
        else
        {
            NSLog(@"Incorrect orientation!!!");
            [self.motionManager stopAccelerometerUpdates];
        }];
}

else
{
    NSLog(@"Accelerometer is not available.");
}

// Go to second view controller

if (sender.state == UIGestureRecognizerStateBegan)
{
    SecondViewController *svc = [self.storyboard instantiateViewControllerWithIdentifier:@"SecondViewController"];
    [self presentViewController:svc animated:YES completion:nil];
}

Any ideas? Or even a more general way to cancel the gesture unless a condition is met would be very helpful.

Answer 1

You may be able to do what you want by subclassing UIGestureRecognizer to make your own gesture recognizer similar to UILongPressGestureRecognizer that listens for accelerometer data in addition to presses of at least 3 second duration.

Answer 2

I'd probably override the onTouchesBegan, and onTouchesEnded methods, rather than using a gesture recogniser.

I'd then create a NSTimer object, an NSTimeInterval var and a BOOL in your view controller; for the sake of it, I'll call them, touchTimer, initialTouchTimeStamp, and touchValid.

for the sake of complexity, it's an assumption that the viewControllers view is not multi-touch.

Assume the repeatTime = 0.25f; longPressTimeRequired = 3;

The timer selector would incorporate your accelerometer method, if the data inside your accelerometer method is invalid, I'd set a touchValid to false (and invalidate the timer), otherwise I'd set it to true After checking the accelerometer, I'd check if my initialTouchTimeStamp var is longPressTimeRequired or more seconds prior to [touchTimer fireDate] - repeatTime , if it is, and the touchValid is true, then I would go to my second controller.

onTouchesBegan, I'd invalidate touchTimer and create a new one that would repeat every repearTime seconds, and lasts for y seconds. Set touchValid to NO, and set initialTouchTimeStamp to touch.timestamp.

onTouchesEnded, I'd invalidate touchTimer, and check if my initialTouchTimeStamp var is longPressTimeRequired or more seconds prior to [touchTimer fireDate] - repeatTime , if it is, and the touchValid is true, then I would go to my second controller.

there are many common elements in here, and it's probably not the most elegant way of doing things, but it should work. Hope this helps.

Answer 3

I hope the code is verbose enough for you to read, it's pretty self explanatory - I've stuck with your accelerometer code, and used the same variable names.

#import "ViewController.h"
#import <CoreMotion/CoreMotion.h>

@interface ViewController () {

    NSOperationQueue    *motionQueue;
    NSTimer             *touchTimer;
    NSTimeInterval      initialTimeStamp;
    BOOL                touchValid;

    float                timerPollInSeconds;
    float                longPressTimeRequired;
}

@property (strong, nonatomic)            NSTimer             *touchTimer;
@property (assign, nonatomic)            NSTimeInterval      initialTimeStamp;
@property (assign, nonatomic)            BOOL                touchValid;
@property (assign, nonatomic)            float               timerPollInSeconds;
@property (assign, nonatomic)            float               longPressTimeRequired;
@property (strong, nonatomic)            CMMotionManager     *motionManager;
@property (strong, nonatomic)            NSOperationQueue    *motionQueue;


@end

@implementation ViewController

@synthesize touchTimer = _touchTimer, initialTimeStamp, touchValid, motionQueue = _motionQueue;
@synthesize timerPollInSeconds, longPressTimeRequired, motionManager = _motionManager;

- (void)viewDidLoad
{
    self.timerPollInSeconds = 0.25f;
    self.longPressTimeRequired = 3.0f;
    self.touchTimer = nil;
    self.touchValid = NO;
    self.initialTimeStamp = NSTimeIntervalSince1970;
    self.motionManager = [[CMMotionManager alloc] init];
    self.motionQueue = [[NSOperationQueue alloc] init];
    [_motionQueue setName:@"MotionQueue"];
    [_motionQueue setMaxConcurrentOperationCount:NSOperationQueueDefaultMaxConcurrentOperationCount];

    [super viewDidLoad];

    self.view.multipleTouchEnabled = NO;
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Operations

-(void) startLongPressMonitorWithTimeStamp:(NSTimeInterval) timeStamp {
    NSLog(@"Starting monitoring - %g", timeStamp);
    if( self.touchTimer ) {
        if( [_touchTimer isValid] ) {
            [_touchTimer invalidate];
        }
    }

    self.touchTimer = [NSTimer timerWithTimeInterval:self.timerPollInSeconds target:self selector:@selector(timerPolled:) userInfo:nil repeats:YES];

    if( [_motionManager isAccelerometerAvailable] ) {
        NSLog(@"Accelerometer Available");
        if( ![_motionManager isAccelerometerActive] ) {
            NSLog(@"Starting Accelerometer");
            [_motionManager startAccelerometerUpdatesToQueue:self.motionQueue withHandler:^(CMAccelerometerData *accelerometerData, NSError *error) {

                if (ABS(accelerometerData.acceleration.x) < 0.3 && ABS(accelerometerData.acceleration.y) < 0.30 && ABS(accelerometerData.acceleration.z) > 0.70) // Phone is flat and screen faces up
                {
                    dispatch_sync(dispatch_get_main_queue(), ^{
                        self.touchValid = YES;
                    });
                }
                else
                {
                    dispatch_sync(dispatch_get_main_queue(), ^{
                        self.touchValid = NO;
                        [self stopLongPressMonitoring:YES];
                    });
                };
            }];
        }
        else {
            NSLog(@"Accelerometer already active");
        }
    }
    else {
        NSLog(@"Accelerometer not available");
    }

    self.initialTimeStamp = timeStamp;

    self.touchValid = YES;
    [_touchTimer fire];

    [[NSRunLoop mainRunLoop] addTimer:self.touchTimer forMode:NSRunLoopCommonModes];
}



-(void) stopLongPressMonitoring:(BOOL) touchSuccessful {
    [_motionManager stopAccelerometerUpdates];
    [_touchTimer invalidate];
    self.touchValid = NO;

    if( touchSuccessful ) {
        NSLog(@"Yes");
    }
    else {
         NSLog(@"No");
    }
}

#pragma mark - User Interaction
-(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    //We're using the current times, interval since the touches timestamp refers to system boot up
    // it is more than feasible to use this boot up time, but for simplicity, I'm just using this
    NSTimeInterval timestamp = [NSDate timeIntervalSinceReferenceDate];
    [self startLongPressMonitorWithTimeStamp:timestamp];
}

-(void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    if( self.touchValid && [NSDate timeIntervalSinceReferenceDate] - self.initialTimeStamp == self.longPressTimeRequired ) {
        [self stopLongPressMonitoring:YES];
    }
    else {
        [self stopLongPressMonitoring:NO];
    }
}



#pragma mark - Timer Call back
-(void) timerPolled:(NSTimer *) timer {
    NSTimeInterval firedTimeStamp = [NSDate timeIntervalSinceReferenceDate];
    NSLog(@"Timer polled - %g", firedTimeStamp);
    if( self.touchValid ) {
        NSLog(@"Time elapsed: %d", (int)(firedTimeStamp - self.initialTimeStamp));

        if( firedTimeStamp - self.initialTimeStamp >= self.longPressTimeRequired ) {
            NSLog(@"Required time has elapsed");
            [self stopLongPressMonitoring:YES];
        }
    }
    else {
        NSLog(@"Touch invalidated");
        [self stopLongPressMonitoring:NO];
    }
}


@end