UIPanGestureRecognizer上下左右滑动方向推断算法

CGFloat
const gestureMinimumTranslation = 20.0;

typedef enum :NSInteger {

kCameraMoveDirectionNone,

kCameraMoveDirectionUp,

kCameraMoveDirectionDown,

kCameraMoveDirectionRight,

kCameraMoveDirectionLeft

} CameraMoveDirection;

@interfaceViewController ()

{

CameraMoveDirection direction;

}

@end

@implementation
ViewController

- (void)viewDidLoad

{

[super viewDidLoad];

UIPanGestureRecognizer *recognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handleSwipe:)];

[self.viewWithGestureRecognizer addGestureRecognizer:recognizer];

}

// This is my gesture recognizer handler, which detects movement in a particular

// direction, conceptually tells a camera to start moving in that direction

// and when the user lifts their finger off the screen, tells the camera to stop.

- (void)handleSwipe:(UIPanGestureRecognizer *)gesture

{

CGPoint translation = [gesture translationInView:self.view];

if (gesture.state ==UIGestureRecognizerStateBegan)

{

direction = kCameraMoveDirectionNone;

}

else
if (gesture.state == UIGestureRecognizerStateChanged && direction == kCameraMoveDirectionNone)

{

direction = [self determineCameraDirectionIfNeeded:translation];

// ok, now initiate movement in the direction indicated by the user's gesture

switch (direction) {

case kCameraMoveDirectionDown:

NSLog(@"Start moving down");

break;

case kCameraMoveDirectionUp:

NSLog(@"Start moving up");

break;

case kCameraMoveDirectionRight:

NSLog(@"Start moving right");

break;

case kCameraMoveDirectionLeft:

NSLog(@"Start moving left");

break;

default:

break;

}

}

elseif (gesture.state ==
UIGestureRecognizerStateEnded)

{

// now tell the camera to stop

NSLog(@"Stop");

}

}

// This method will determine whether the direction of the user's swipe

- (CameraMoveDirection)determineCameraDirectionIfNeeded:(CGPoint)translation

{

if (direction != kCameraMoveDirectionNone)

return direction;

// determine if horizontal swipe only if you meet some minimum velocity

if (fabs(translation.x) > gestureMinimumTranslation)

{

BOOL gestureHorizontal = NO;

if (translation.y ==0.0)

gestureHorizontal = YES;

else

gestureHorizontal = (fabs(translation.x / translation.y) >5.0);

if (gestureHorizontal)

{

if (translation.x >0.0)

return kCameraMoveDirectionRight;

else

return kCameraMoveDirectionLeft;

}

}

// determine if vertical swipe only if you meet some minimum velocity

else
if (fabs(translation.y) > gestureMinimumTranslation)

{

BOOL gestureVertical = NO;

if (translation.x ==0.0)

gestureVertical = YES;

else

gestureVertical = (fabs(translation.y / translation.x) >5.0);

if (gestureVertical)

{

if (translation.y >0.0)

return kCameraMoveDirectionDown;

else

return kCameraMoveDirectionUp;

}

}

return direction;

}

@end