帶你瞭解UIKit動力學

1、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框架能夠認爲是一種物理引擎，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
普遍用於遊戲開發，經典成功案例是「憤怒的小鳥」,讓開發人員能夠在遠離物理學公式的狀況下，實現炫酷的物理仿真效果提升了遊戲開發效率，產生更多優秀好玩的物理仿真遊戲

3.知名的2D物理引擎
Box2d
Chipmunk

2、使用步驟

要想使用UIDynamic來實現物理仿真效果，大體的步驟以下:

1.建立一個物理仿真器（順便設置仿真範圍）
2.建立相應的物理仿真行爲（順便添加物理仿真元素）
3.將物理仿真行爲添加到物理仿真器中開始仿真

3、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？
  　　物理仿真行爲（Dynamic Behavior）
• 讓物理仿真元素執行具體的物理仿真行爲
  　　物理仿真器（Dynamic Animator）

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

物理仿真元素要素：
任何遵照了UIDynamicItem協議的對象
UIView默認已經遵照了UIDynamicItem協議，所以任何UI控件都能作物理仿真

UICollectionViewLayoutAttributes類默認也遵照UIDynamicItem協議

3.物理仿真行爲

（1）UIDynamic提供瞭如下幾種物理仿真行爲

• UIGravityBehavior：重力行爲

• UICollisionBehavior：碰撞行爲

• UISnapBehavior：捕捉行爲

• UIPushBehavior：推進行爲

• UIAttachmentBehavior：附着行爲

• UIDynamicItemBehavior：動力元素行爲

（2）物理仿真行爲須知
上述全部物理仿真行爲都繼承自UIDynamicBehavior，全部的UIDynamicBehavior均可以獨立進行組合使用多種行爲時，能夠實現一些比較複雜的效果

4.物理仿真器

（1）物理仿真器須知
它可讓物理仿真元素執行物理仿真行爲
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，表示物理仿真的範圍

5.物理仿真器的說明

（1）UIDynamicAnimator的常見方法

//移除以前添加過的全部物理仿真行爲  
- (void)addBehavior:(UIDynamicBehavior *)behavior; 
//移除以前添加過的全部物理仿真行爲　
- (void)removeBehavior:(UIDynamicBehavior *)behavior; 
//添加1個物理仿真行爲　
- (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全部物理仿真行爲
@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，好比開始和結束）
@property (nonatomic, assign) id

4、案例介紹

先看效果吧

• UIGravityBehavior：重力行爲

• UICollisionBehavior：碰撞行爲

• UISnapBehavior：捕捉行爲

• UIPushBehavior：推進行爲

• 複合效果

最後是代碼

#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;
    
    //建立重力行爲
    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;
    //建立碰撞行爲
    UICollisionBehavior *collisionBehavior = [[UICollisionBehavior alloc]init];
    //碰撞類型爲元素和邊界
    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爲底邊界,左邊框跟右邊框做爲邊界
    [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爲,參考學習了:UIDynamic 詳細用法 中的案例.而後本身又展開了解了下UIKit動力學的知識,把捕捉行爲,推進行爲加了進去,作個完善.整理了一下.就是這樣.