[Tip]重写PanGestureRecognizer

目标

识别当前pan方向是指定方向

需要API

重写- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event;

获取所在view上的滑动速率- (CGPoint)velocityInView:(nullable UIView *)view;

通过速率排序当前pan方向，获取方向

代码：

.h

////仿照SSWDirectionalPanGestureRecognizer，仅作为学习项目使用。

#import <UIKit/UIKit.h>

typedef NS_ENUM(NSInteger, HJPanDirection) {
    HJPanDirectionRight,
    HJPanDirectionDown,
    HJPanDirectionLeft,
    HJPanDirectionUp
};

@interface HJDirectionPanGestureRecognizer : UIPanGestureRecognizer

@property (nonatomic, assign) HJPanDirection direction;

@end

.m

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

@interface HJDirectionPanGestureRecognizer ()
@property (nonatomic, assign) BOOL dragging;
@end

@implementation HJDirectionPanGestureRecognizer

- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    [super touchesMoved:touches withEvent:event];

    if (self.state == UIGestureRecognizerStateFailed) {
        return;
    }

    CGPoint velocity = [self velocityInView:self.view];

    if (!self.dragging && !CGPointEqualToPoint(velocity, CGPointZero)) {

        NSDictionary * velocities = @{@(HJPanDirectionRight):@(velocity.x),
                                      @(HJPanDirectionDown) :@(velocity.y),
                                      @(HJPanDirectionLeft) :@(-velocity.x),
                                      @(HJPanDirectionUp)   :@(-velocity.y)};

        NSArray * keysSorted = [velocities keysSortedByValueUsingSelector:@selector(compare:)];

        if ([[keysSorted lastObject] integerValue] != self.direction) {
            self.state = UIGestureRecognizerStateFailed;
        }

        self.dragging = YES;
    }
}

////UIGestureRecognizerStateEnded after automatically called.
- (void)reset {
    [super reset];
    self.dragging = NO;//reset
}

@end