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本文為您介紹帶你了解UIKit動力學的說明，具體操作請看面的內容

一、簡單介紹

1.什麼是UIDynamic UIDynamic是從IOS 7開始引入的一種新技術，隸屬於UIKit框架可以認為是一種物理引擎，能模擬和仿真現實生活中的物理現象如：重力、彈性碰撞等現象

2.物理引擎的價值 廣泛用於游戲開發，經典成功案例是“憤怒的小鳥”,讓開發人員可以在遠離物理學公式的情況下，實現炫酷的物理仿真效果提高了游戲開發效率，產生更多優秀好玩的物理仿真游戲

3.知名的2D物理引擎 Box2d Chipmunk

二、使用步驟

要想使用UIDynamic來實現物理仿真效果，大致的步驟如下:

1.創建一個物理仿真器（順便設置仿真范圍） 2.創建相應的物理仿真行為（順便添加物理仿真元素） 3.將物理仿真行為添加到物理仿真器中開始仿真

三、相關說明

1.三個概念

誰要進行物理仿真？ 　　物理仿真元素（Dynamic Item） 執行怎樣的物理仿真效果？怎樣的動畫效果？ 　　物理仿真行為（Dynamic Behavior） 讓物理仿真元素執行具體的物理仿真行為 　　物理仿真器（Dynamic Animator）

2.物理仿真元素 注意： 不是任何對象都能做物理仿真元素 不是任何對象都能進行物理仿真

物理仿真元素要素： 任何遵守了UIDynamicItem協議的對象 UIView默認已經遵守了UIDynamicItem協議，因此任何UI控件都能做物理仿真

UICollectionViewLayoutAttributes類默認也遵守UIDynamicItem協議

3.物理仿真行為

（1）UIDynamic提供了以下幾種物理仿真行為

UIGravityBehavior：重力行為

UICollisionBehavior：碰撞行為

UISnapBehavior：捕捉行為

UIPushBehavior：推動行為

UIAttachmentBehavior：附著行為

UIDynamicItemBehavior：動力元素行為

（2）物理仿真行為須知 上述所有物理仿真行為都繼承自UIDynamicBehavior，所有的UIDynamicBehavior都可以獨立進行組合使用多種行為時，可以實現一些比較復雜的效果

4.物理仿真器

（1）物理仿真器須知 它可以讓物理仿真元素執行物理仿真行為 它是UIDynamicAnimator類型的對象 （2）UIDynamicAnimator的初始化

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

view參數：是一個參照視圖，表示物理仿真的范圍

5.物理仿真器的說明

（1）UIDynamicAnimator的常見方法

//移除之前添加過的所有物理仿真行為  
- (void)addBehavior:(UIDynamicBehavior *)behavior; 
//移除之前添加過的所有物理仿真行為　
- (void)removeBehavior:(UIDynamicBehavior *)behavior; 
//添加1個物理仿真行為　
- (void)removeAllBehaviors; 

　 （2）UIDynamicAnimator的常見屬性

 //參照視圖 
@property (nonatomic, readonly) UIView* referenceView;  
//添加到物理仿真器中的所有物理仿真行為
@property (nonatomic, readonly, copy) NSArray* behaviors;
//是否正在進行物理仿真
@property (nonatomic, readonly, getter = isRunning) BOOL running;
//代理對象（能監聽物理仿真器的仿真過程，比如開始和結束）
@property (nonatomic, assign) id 

四、案例介紹

先看效果吧

UIGravityBehavior：重力行為

UISnapBehavior：捕捉行為

復合效果

#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 = CGAff.netransformMakeRotation(M_PI_4); self.segmented.transform = CGAff.netransformMakeRotation(-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; //創建重力行為 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; //創建碰撞行為 UICollisionBehavior *collisionBehavior = [[UICollisionBehavior alloc]init]; //碰撞類型為元素和邊界 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; //設置紅色的View為底邊界,左邊框跟右邊框作為邊界 [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 在執行"); }; _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動力學的部分介紹完了. 最開始項目中只是用到了重力跟碰撞行為,參考學習了:UIDynamic 詳細用法 中的案例.然後自己又展開了解了下UIKit動力學的知識,把捕捉行為,推動行為加了進去,做個完善.整理了一下.就是這樣.

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[db:作者簡介][db:原文翻譯及解析]

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