计算Pan手势到指定点的角度

效果图:

源码:

////  RootViewController.m//  Circle////  Copyright (c) 2014年 Y.X. All rights reserved.//#import "RootViewController.h"#import "Radian.h"#import "FrameAccessor.h"@interface RootViewController ()@property (nonatomic, strong) CALayer *layer;@end@implementation RootViewController- (void)viewDidLoad{    [super viewDidLoad];    // 显示参考用的view    UIView *showView = [[UIView alloc] initWithFrame:CGRectMake(0, 20, 300, 300)];    showView.layer.borderWidth = 1.f;    showView.layer.cornerRadius = 150.f;    showView.layer.borderColor = [UIColor redColor].CGColor;    showView.center = self.view.center;    [self.view addSubview:showView];        // 新建layer    _layer = [CALayer layer];    _layer.backgroundColor = [UIColor blackColor].CGColor;        // 重置锚点    _layer.anchorPoint = CGPointMake(0.f, 0.f);        // 设置layer的frame值(在showView正中间摆放)    _layer.frame = CGRectMake(showView.middleX, showView.middleY, 150, 1);        // 添加进showView中    [showView.layer addSublayer:_layer];        // 给showView添加手势    UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];    [panGesture setMaximumNumberOfTouches:1];    [showView addGestureRecognizer:panGesture];}- (void)handlePan:(UIPanGestureRecognizer *)recognizer{    // 获取触摸点点    CGPoint translation = [recognizer locationInView:self.view];        // 计算触摸点到中心点的弧度    CGFloat angleInRadians = [Radian tanA:translation.y - self.view.center.y                                        B:translation.x - self.view.center.x];        // layer的动画    [CATransaction setDisableActions:YES];    _layer.transform = CATransform3DMakeRotation(angleInRadians, 0.0, 0.0, 1.0);}@end

以下3步非常关键:

引入POP库设计阻尼动画

效果如下:

////  RootViewController.m//  Circle////  Copyright (c) 2014年 Y.X. All rights reserved.//#import "RootViewController.h"#import "Radian.h"#import "FrameAccessor.h"#import "POP.h"@interface RootViewController ()@property (nonatomic, strong) CALayer *layer;@end@implementation RootViewController- (void)viewDidLoad{    [super viewDidLoad];    // 显示参考用的view    UIView *showView = [[UIView alloc] initWithFrame:CGRectMake(0, 20, 300, 300)];    showView.layer.borderWidth = 1.f;    showView.layer.cornerRadius = 150.f;    showView.layer.borderColor = [UIColor redColor].CGColor;    showView.center = self.view.center;    [self.view addSubview:showView];        // 新建layer    _layer = [CALayer layer];    _layer.backgroundColor = [UIColor blackColor].CGColor;        // 重置锚点    _layer.anchorPoint = CGPointMake(0.f, 0.f);        // 设置layer的frame值(在showView正中间摆放)    _layer.frame = CGRectMake(showView.middleX, showView.middleY, 150, 1);        // 添加进showView中    [showView.layer addSublayer:_layer];        // 给showView添加手势    UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];    [panGesture setMaximumNumberOfTouches:1];    [showView addGestureRecognizer:panGesture];}- (void)handlePan:(UIPanGestureRecognizer *)recognizer{    // 获取触摸点点    CGPoint translation = [recognizer locationInView:self.view];    // 将度数转换为弧度#define   RADIAN(degrees)  ((M_PI * (degrees))/ 180.f)        // 将弧度转换为度数#define   DEGREES(radian)  ((radian) * 180.f / M_PI)        if(recognizer.state == UIGestureRecognizerStateChanged)    {        // 计算触摸点到中心点的弧度        CGFloat angleInRadians = [Radian tanA:translation.y - self.view.center.y                                            B:translation.x - self.view.center.x];                POPBasicAnimation *positionAnimation = \        [POPBasicAnimation animationWithPropertyNamed:kPOPLayerRotation];        // 设置速度动画        positionAnimation.toValue = @(angleInRadians);        positionAnimation.duration = 0.01f;                // 添加动画        [_layer pop_removeAnimationForKey:@"kPOPLayerRotation"];        [_layer pop_addAnimation:positionAnimation                          forKey:@"kPOPLayerRotation"];    }        // 拖拽动作结束    if(recognizer.state == UIGestureRecognizerStateEnded)    {        // 计算触摸点到中心点的弧度        CGFloat angleInRadians = [Radian tanA:translation.y - self.view.center.y                                            B:translation.x - self.view.center.x];                // 计算出移动的速度        CGPoint velocity = [recognizer velocityInView:self.view];        CGFloat x = velocity.x;        CGFloat y = velocity.y;                // 衰退减速动画        POPDecayAnimation *positionAnimation = \        [POPDecayAnimation animationWithPropertyNamed:kPOPLayerRotation];        positionAnimation.velocity = @(+(x*ABS(cosf(angleInRadians)/100.f) +                                         y*ABS(sinf(angleInRadians)/100.f)));                // 添加动画        [_layer pop_removeAnimationForKey:@"kPOPLayerRotation"];        [_layer pop_addAnimation:positionAnimation                          forKey:@"layerPositionAnimation"];    }}@end

重点地方:

其实,实现这个效果真心挺难的......