什么是UIDynamic?

UIDynamic是從iOS 7開始引入的一種新技術，隸屬于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
重力、彈性碰撞等現象

UIDynamic使用步驟

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

物理仿真元素

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

哪些對象才能做物理仿真元素？

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

物理仿真行為

• 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

物理仿真器

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
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

UIDynamicAnimator的常見方法

//添加1個物理仿真行為

- (void)addBehavior:(UIDynamicBehavior *)behavior;

//移除1個物理仿真行為

- (void)removeBehavior:(UIDynamicBehavior *)behavior;

//移除之前添加過的所有物理仿真行為

- (void)removeAllBehaviors;

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 <UIDynamicAnimatorDelegate> delegate;

直接上代碼

#import "ViewController.h"

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

@implementation ViewController

-(void)viewDidLoad {
    [super viewDidLoad];
    self.blueView.transform =   CGAffineTransformMakeRotation(M_PI_4);
    self.segmented.transform = CGAffineTransformMakeRotation(-M_PI / 8);
 }

-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:  (UIEvent *)event {

    //創建重力行為
    UIGravityBehavior *gravityBehavior = [[UIGravityBehavior alloc]init];
    [gravityBehavior addItem:self.blueView];
    [gravityBehavior addItem:self.orangeView];
    //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];
}

- (UIDynamicAnimator *)animator{
    if (_animator == nil) {
        _animator = [[UIDynamicAnimator alloc]init];
    }
    return _animator;
}
@end

效果