UIDynamicAnimator
可以通过该类添加不同的行为，来实现一些动态效果。
初始化方法
// the behaviors (and their dynamic items) that you add to the animator employ the reference view’s coordinate system.
- (instancetype)initWithReferenceView:(UIView *)view
添加到animator上的行为使用reference view的坐标系统。
添加和移除行为
- (void)addBehavior:(UIDynamicBehavior *)behavior;//添加指定的行为动画
- (void)removeBehavior:(UIDynamicBehavior *)behavior;//移除指定的行为动画
- (void)removeAllBehaviors;//移除所有的行为
其他属性
- (NSTimeInterval)elapsedTime;
行为执行的时间，需要注意的是如果我们对同一个行为进行添加和移除操作时，时间会累积。
@property (nonatomic, readonly, getter = isRunning) BOOL running;
判定animator中是否还有行为正在执行
@property (nullable, nonatomic, weak) id <UIDynamicAnimatorDelegate> delegate;
代理协议的实现
- (void)dynamicAnimatorWillResume:(UIDynamicAnimator *)animator;//add行为时调用
- (void)dynamicAnimatorDidPause:(UIDynamicAnimator *)animator;//remove行为时调用
UIDynamicItem
说明一下，在很多方法里注意到有很多UIDynamicItem参数的存在。如
- (void)updateItemUsingCurrentState:(id <UIDynamicItem>)item;
其实是说item是实现了UIDynamicItem协议的类，我们发现 UIView(所有视图控件的父类)实现了该协议。一般情况下，在遇到UIDynamicItem时，直接传我们的视图就行了。
UISnapBehavior
将物体通过动画吸附到一个点上
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.imageView1 snapToPoint:tapPoint];
_snapBehavior.action = ^(){
NSLog(@"UISnapBehavior 在执行");
};
_snapBehavior.damping = 0.9;
[self.animator addBehavior:_snapBehavior];
}
通过观察action和协议方法的实现，发现物体到达指定点之后会停止行为。
UIGravityBehavior
给物体添加一个类似于自由落体的运动
_gravityBehavior = [[UIGravityBehavior alloc]initWithItems:@[_imageView1]];
_gravityBehavior.gravityDirection = CGVectorMake(0.0f, 1.0f);
[self.animator addBehavior:_gravityBehavior];
gravityDirection
运动的方向，默认是(0.0f, 1.0f)。dx为-1.0f时向左运动，dy为-1.0时向上运动，所以根据0.0~1.0可以定位所有的方向。
angle
也是设置运动的方向，是根据角度来计算的。坐标系为左侧为x的正方向，下侧为y的正方向。可使用0~M_PI*2之间的值来定位所有方向。
magnitude
可以理解为重力加速度，默认值为1.0。可取负值。
UICollisionBehavior
碰撞检测，和上面的重力配合查看效果
if (!_gravityBehavior) {
_gravityBehavior = [[UIGravityBehavior alloc]initWithItems:@[_imageView1]];
}
_gravityBehavior = [[UIGravityBehavior alloc]initWithItems:@[_imageView1]];
_gravityBehavior.angle = M_PI_2;
_gravityBehavior.magnitude = 2.0f;
// _gravityBehavior.gravityDirection = CGVectorMake(1.0f, 0.0f);
NSLog(@"magni = %f",_gravityBehavior.magnitude);
if(!_collisionBehavior){
_collisionBehavior = [[UICollisionBehavior alloc]initWithItems:@[_imageView1,_imageView2]];
}
// _collisionBehavior.collisionMode = UICollisionBehaviorModeBoundaries;
_collisionBehavior.translatesReferenceBoundsIntoBoundary = YES;
[self.animator addBehavior:_gravityBehavior];
[self.animator addBehavior:_collisionBehavior];
translatesReferenceBoundsIntoBoundary默认是NO。
另外，UICollisionBehavior有它自己的代理
- (void)collisionBehavior:(UICollisionBehavior *)behavior beganContactForItem:(id <UIDynamicItem>)item1 withItem:(id <UIDynamicItem>)item2 atPoint:(CGPoint)p;
- (void)collisionBehavior:(UICollisionBehavior *)behavior endedContactForItem:(id <UIDynamicItem>)item1 withItem:(id <UIDynamicItem>)item2;
// The identifier of a boundary created with translatesReferenceBoundsIntoBoundary or setTranslatesReferenceBoundsIntoBoundaryWithInsets is nil
- (void)collisionBehavior:(UICollisionBehavior*)behavior beganContactForItem:(id <UIDynamicItem>)item withBoundaryIdentifier:(nullable id <NSCopying>)identifier atPoint:(CGPoint)p;
- (void)collisionBehavior:(UICollisionBehavior*)behavior endedContactForItem:(id <UIDynamicItem>)item withBoundaryIdentifier:(nullable id <NSCopying>)identifier;
UIPushBehavior
给物体一个力的作用
typedef NS_ENUM(NSInteger, UIPushBehaviorMode) {
UIPushBehaviorModeContinuous,//持续的力
UIPushBehaviorModeInstantaneous//一次性的力
}
使用代码：
if (!_pushBehavior) {
_pushBehavior = [[UIPushBehavior alloc]initWithItems:@[_imageView1] mode:UIPushBehaviorModeContinuous];
}
_pushBehavior.active = YES;
_pushBehavior.pushDirection = CGVectorMake(10.0f, 10.0f);
_pushBehavior.magnitude = 1.0f;
[self.animator addBehavior:_pushBehavior];
pushDirection
给了物体一个运动的方向和初速度
magnitude
给物体一个加速度，默认值为0.0f
active
默认值是YES，将其设置为NO，可以将行为停止。
UIAttachmentBehavior
实现一个效果让物体跟随手指移动
- (void)panGestureRecognizer:(UIPanGestureRecognizer *)gesture
{
CGPoint location = [gesture locationInView:self.view];
CGPoint imageLocation = [gesture locationInView:self.imageView1];
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.imageView1.bounds), imageLocation.y - CGRectGetMidY(self.imageView1.bounds));
_attachmentBehavior = [[UIAttachmentBehavior alloc]initWithItem:self.imageView1 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;
}
}
