iOS判断捏合手势方向（UIPanGestureRecogniz

如题，捏合手势并没有提供判断横向还是竖向的判定方式。

但是手势中有提供这个方法：

• (CGPoint)locationOfTouch:(NSUInteger)touchIndex inView:(nullable UIView*)view;
  「返回一个给定视图发生手势的点（为了在多个手势中捕获位置）」

可以根据捏合手势手指起止点做差比较判定捏合手势方向：
方式一：
如果两个捏合点X的差值大于Y的差值变化，那么就是横向捏合；反之，为竖向捏合。搭配手势提供的scale，可判断为捏合放大还是捏合缩小。
方式二：
只根据两个捏合点之间的角度，估算捏合方向；

简单实现代码如下：

#import "ViewController.h"

#define UI_SCREEN_HEIGHT ([[UIScreen mainScreen] bounds].size.height)
#define UI_SCREEN_WIDTH [[UIScreen mainScreen] bounds].size.width

@interface ViewController ()

@property (nonatomic, assign) CGPoint pointOne;
@property (nonatomic, assign) CGPoint pointTwo;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    UIView *panView = [[UIView alloc]initWithFrame:CGRectMake((UI_SCREEN_WIDTH - 300) / 2.0, (UI_SCREEN_HEIGHT - 300) / 2.0, 300, 300)];
    panView.backgroundColor = [UIColor redColor];
    [self.view addSubview:panView];
    panView.userInteractionEnabled = YES;

    UIPinchGestureRecognizer *pin = [[UIPinchGestureRecognizer alloc]initWithTarget:self action:@selector(pinAction:)];
    [panView addGestureRecognizer:pin];
}

- (void)pinAction:(UIPinchGestureRecognizer *)recognizer {
    if (recognizer.numberOfTouches == 2) {
        CGPoint locationOne = [recognizer locationOfTouch:0 inView: recognizer.view];
        CGPoint locationTwo = [recognizer locationOfTouch:1 inView: recognizer.view];
        
        //方式一：比较X-Y差值变化
        CGFloat difference_X = fabs((locationOne.x - locationTwo.x) - (self.pointOne.x - self.pointTwo.x));
        CGFloat difference_Y = fabs((locationOne.y - locationTwo.y) - (self.pointOne.y - self.pointTwo.y));
        CGFloat scale = recognizer.scale;
        if (difference_X > difference_Y){
            NSLog(@"横向捏合");
            //简单边界处理
            if (recognizer.view.frame.size.width * scale  > UI_SCREEN_WIDTH - 40 || recognizer.view.frame.size.width * scale < 100) {
                return;
            }
            recognizer.view.transform = CGAffineTransformScale(recognizer.view.transform, scale, 1);
        } else {
            NSLog(@"竖向捏合");
            //简单边界处理
            if (recognizer.view.frame.size.height * scale > UI_SCREEN_HEIGHT - 40 || recognizer.view.frame.size.height * scale < 100) {
                return;
            }
            recognizer.view.transform = CGAffineTransformScale(recognizer.view.transform, 1, scale);
        }
        recognizer.scale = 1.0;
        self.pointOne = [recognizer locationOfTouch:0 inView:recognizer.view];
        self.pointTwo = [recognizer locationOfTouch:1 inView:recognizer.view];
        
        //方式二：计算角度，估算捏合方向
//        CGFloat abSlope = ABS((locationTwo.y - locationOne.y) / (locationTwo.x - locationOne.x));
//        CGFloat scale = recognizer.scale;
//        if (abSlope < 1.0) {
//            //简单边界处理
//            if (recognizer.view.frame.size.width * scale  > UI_SCREEN_WIDTH - 40 || recognizer.view.frame.size.width * scale < 100) {
//                return;
//            }
//            recognizer.view.transform = CGAffineTransformScale(recognizer.view.transform, scale, 1);
//        }else {
//            //简单边界处理
//            if (recognizer.view.frame.size.height * scale > UI_SCREEN_HEIGHT - 40 || recognizer.view.frame.size.height * scale < 100) {
//                return;
//            }
//            recognizer.view.transform = CGAffineTransformScale(recognizer.view.transform, 1, scale);
//        }
//        recognizer.scale = 1.0;
    }
}

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

@end