带你了解UIKit动力学

一、简单介绍

1.什么是UIDynamic
UIDynamic是从iOS 7开始引入的一种新技术，隶属于UIKit框架可以认为是一种物理引擎，能模拟和仿真现实生活中的物理现象如：重力、弹性碰撞等现象

2.物理引擎的价值
广泛用于游戏开发，经典成功案例是“愤怒的小鸟”,让开发人员可以在远离物理学公式的情况下，实现炫酷的物理仿真效果提高了游戏开发效率，产生更多优秀好玩的物理仿真游戏

3.知名的2D物理引擎
Box2d
Chipmunk

二、使用步骤

要想使用UIDynamic来实现物理仿真效果，大致的步骤如下:

1.创建一个物理仿真器（顺便设置仿真范围）
2.创建相应的物理仿真行为（顺便添加物理仿真元素）
3.将物理仿真行为添加到物理仿真器中开始仿真

三、相关说明

1.三个概念

• 谁要进行物理仿真？
  　　物理仿真元素（Dynamic Item）
• 执行怎样的物理仿真效果？怎样的动画效果？
  　　物理仿真行为（Dynamic Behavior）
• 让物理仿真元素执行具体的物理仿真行为
  　　物理仿真器（Dynamic Animator）

2.物理仿真元素
注意：
不是任何对象都能做物理仿真元素
不是任何对象都能进行物理仿真

物理仿真元素要素：
任何遵守了UIDynamicItem协议的对象
UIView默认已经遵守了UIDynamicItem协议，因此任何UI控件都能做物理仿真

UICollectionViewLayoutAttributes类默认也遵守UIDynamicItem协议

3.物理仿真行为

（1）UIDynamic提供了以下几种物理仿真行为

• UIGravityBehavior：重力行为

• UICollisionBehavior：碰撞行为

• UISnapBehavior：捕捉行为

• UIPushBehavior：推动行为

• UIAttachmentBehavior：附着行为

• UIDynamicItemBehavior：动力元素行为

（2）物理仿真行为须知
上述所有物理仿真行为都继承自UIDynamicBehavior，所有的UIDynamicBehavior都可以独立进行组合使用多种行为时，可以实现一些比较复杂的效果

4.物理仿真器

（1）物理仿真器须知
它可以让物理仿真元素执行物理仿真行为
它是UIDynamicAnimator类型的对象
（2）UIDynamicAnimator的初始化

- (instancetype)initWithReferenceView:(UIView *)view;

view参数：是一个参照视图，表示物理仿真的范围

5.物理仿真器的说明

（1）UIDynamicAnimator的常见方法

//移除之前添加过的所有物理仿真行为  
- (void)addBehavior:(UIDynamicBehavior *)behavior; 
//移除之前添加过的所有物理仿真行为　
- (void)removeBehavior:(UIDynamicBehavior *)behavior; 
//添加1个物理仿真行为　
- (void)removeAllBehaviors; 

　
（2）UIDynamicAnimator的常见属性

 //参照视图 
@property (nonatomic, readonly) UIView* referenceView;  
//添加到物理仿真器中的所有物理仿真行为
@property (nonatomic, readonly, copy) NSArray* behaviors;
//是否正在进行物理仿真
@property (nonatomic, readonly, getter = isRunning) BOOL running;
//代理对象（能监听物理仿真器的仿真过程，比如开始和结束）
@property (nonatomic, assign) id 

四、案例介绍

先看效果吧

• UIGravityBehavior：重力行为

• UICollisionBehavior：碰撞行为

• UISnapBehavior：捕捉行为

• UIPushBehavior：推动行为

• 复合效果

最后是代码

#import <UIKit/UIKit.h>

@interface SecondViewController : UIViewController
@property (weak, nonatomic) IBOutlet UIView *blueView;
@property (weak, nonatomic) IBOutlet UIView *orangeView;
@property (weak, nonatomic) IBOutlet UISegmentedControl *segmented;
@property (weak, nonatomic) IBOutlet UIView *redView;
@property (nonatomic,strong) UIDynamicAnimator *animator;

@end

#import "SecondViewController.h"

@interface SecondViewController ()
@property (nonatomic,strong)UISnapBehavior *snapBehavior;
@property (nonatomic,strong)UIPushBehavior *pushBehavior;
@property (nonatomic,strong)UIAttachmentBehavior *attachmentBehavior;

@end

@implementation SecondViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.blueView.transform =  CGAffineTransformMakeRotation(M_PI_4);
    self.segmented.transform = CGAffineTransformMakeRotation(-M_PI / 8);
    
    
    if (!_pushBehavior) {
        _pushBehavior = [[UIPushBehavior alloc]initWithItems:@[_blueView] mode:UIPushBehaviorModeContinuous];
    }
    
    _pushBehavior.active = YES;
    _pushBehavior.pushDirection = CGVectorMake(10.0f, 10.0f);
    _pushBehavior.magnitude = 1.0f;
    [self.animator addBehavior:_pushBehavior];
    
}
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:    (UIEvent *)event {
    _pushBehavior.active = NO;
    
    //创建重力行为
    UIGravityBehavior *gravityBehavior = [[UIGravityBehavior alloc]init];
    [gravityBehavior addItem:self.blueView];
    [gravityBehavior addItem:self.orangeView];
    [gravityBehavior addItem:self.segmented];
    gravityBehavior.gravityDirection = CGVectorMake(-0.3f, 1.0f);
    //加速度
    gravityBehavior.magnitude = 3;
    //创建碰撞行为
    UICollisionBehavior *collisionBehavior = [[UICollisionBehavior alloc]init];
    //碰撞类型为元素和边界
    collisionBehavior.collisionMode = UICollisionBehaviorModeEverything;
    
    CGFloat Y = self.view.frame.size.height - CGRectGetHeight(self.redView.frame);
    CGFloat X = self.view.frame.size.width;
    CGFloat height = self.view.frame.size.height;
    
    //设置红色的View为底边界,左边框跟右边框作为边界
    [collisionBehavior addBoundaryWithIdentifier:@"collision1" fromPoint:CGPointMake(0,Y) toPoint:CGPointMake(X, Y)];
    [collisionBehavior addBoundaryWithIdentifier:@"collision2" fromPoint:CGPointMake(0, 0) toPoint:CGPointMake(0, height)];
    [collisionBehavior addBoundaryWithIdentifier:@"collision3" fromPoint:CGPointMake(X,0) toPoint:CGPointMake(X, height)];
    
    [collisionBehavior addItem:self.blueView];
    [collisionBehavior addItem:self.segmented];
    [collisionBehavior addItem:self.orangeView];
    [self.animator addBehavior:collisionBehavior];
    [self.animator addBehavior:gravityBehavior];
    
    UIDynamicItemBehavior *itemBehavior = [[UIDynamicItemBehavior alloc] initWithItems:@[self.blueView]];
    [itemBehavior setElasticity:0.5];
    [self.animator addBehavior:itemBehavior];
    
    UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(tapGesture:)];
    [self.view addGestureRecognizer:tap];
}
- (void)tapGesture:(UITapGestureRecognizer *)gesture
{
    CGPoint tapPoint = [gesture locationInView:self.view];
    if (_snapBehavior) {
        [self.animator removeBehavior:_snapBehavior];
        _snapBehavior = nil;
    }
    _snapBehavior = [[UISnapBehavior alloc]initWithItem:self.blueView snapToPoint:tapPoint];
    _snapBehavior.action = ^(){
        NSLog(@"UISnapBehavior 在执行");
    };
    _snapBehavior.damping = 0.9;
    [self.animator addBehavior:_snapBehavior];
}
- (UIDynamicAnimator *)animator{
    if (_animator == nil) {
        _animator = [[UIDynamicAnimator alloc]init];
    }
    return _animator;
}

- (void)panGestureRecognizer:(UIPanGestureRecognizer *)gesture
{
    CGPoint location = [gesture locationInView:self.view];
    CGPoint imageLocation = [gesture locationInView:self.orangeView];
    switch (gesture.state) {
        case UIGestureRecognizerStateBegan:
        {
            NSLog(@"touch position %@",NSStringFromCGPoint(location));
            NSLog(@"loction in image %@",NSStringFromCGPoint(imageLocation));
            [self.animator removeAllBehaviors];
            
            UIOffset centerOffset = UIOffsetMake(imageLocation.x - CGRectGetMidX(self.orangeView.bounds), imageLocation.y - CGRectGetMidY(self.orangeView.bounds));
            _attachmentBehavior = [[UIAttachmentBehavior alloc]initWithItem:self.orangeView offsetFromCenter:centerOffset attachedToAnchor:location];
            _attachmentBehavior.damping = 0.5;
            _attachmentBehavior.frequency = 0.8;
            [self.animator addBehavior:_attachmentBehavior];
            
        }
            break;
        case UIGestureRecognizerStateEnded:
        {
            [self.animator removeBehavior:_attachmentBehavior];
        }
            break;
        default:
        {
            [_attachmentBehavior setAnchorPoint:[gesture locationInView:self.view]];
        }
            break;
    }
}

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

/*
 #pragma mark - Navigation
 
 // In a storyboard-based application, you will often want to do a little preparation before navigation
 - (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
 // Get the new view controller using [segue destinationViewController].
 // Pass the selected object to the new view controller.
 }
 */

@end
 

UIKit动力学的部分介绍完了.
最开始项目中只是用到了重力跟碰撞行为,参考学习了:UIDynamic 详细用法 中的案例.然后自己又展开了解了下UIKit动力学的知识,把捕捉行为,推动行为加了进去,做个完善.整理了一下.就是这样.