iOS框架学习之UIKit Dynamics

UIKit Dynamics 用来模拟物理动作，有重力、碰撞、弹跳、附着、瞬间位移、推力、元素行为。下面分别是各个行为的效果图。

所有动画行为都要添加到一个UIDynamicAnimator中，需要绑定一个引用视图，动态行为的视图必须是引用视图的子视图。

UIKit Dynamics框架.gif

分别来讲解

• 重力行为

- (void)startAnimation {
    //animator必须是全局的，要不然没有动画效果
//    UIDynamicAnimator *animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
    animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
    
    UIGravityBehavior *gravityBehavior = [[UIGravityBehavior alloc] initWithItems:@[self.ballView]];
    [gravityBehavior setGravityDirection:CGVectorMake(0.0f, 0.1f)];//重力方向向下，0.1表示以地球重力十分之一的力下落。
    [animator addBehavior:gravityBehavior];
}

这里只设置了重力行为，没有设置碰撞行为，所以小球会一直下落至不见。

• 碰撞行为

- (void)startCollidesion {
    self.animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
    
    //重力行为
    UIGravityBehavior *gravityBehavior = [[UIGravityBehavior alloc] initWithItems:@[self.frogIV, self.dragonIV]];
    gravityBehavior.gravityDirection = CGVectorMake(0.0, 0.1);
    
    //碰撞行为
    UICollisionBehavior *collisionBehavior = [[UICollisionBehavior alloc] initWithItems:@[self.frogIV, self.dragonIV]];
    collisionBehavior.collisionMode = UICollisionBehaviorModeEverything;
    collisionBehavior.translatesReferenceBoundsIntoBoundary = YES;
    collisionBehavior.collisionDelegate = self;
    
    [self.animator addBehavior:gravityBehavior];
    [self.animator addBehavior:collisionBehavior];
}

#pragma mark - UICollisionBehaviorDelegate

- (void)collisionBehavior:(UICollisionBehavior *)behavior beganContactForItem:(nonnull id)item withBoundaryIdentifier:(nullable id)identifier atPoint:(CGPoint)p {
    
    if ([item isEqual:self.dragonIV]) {
        self.dragonL.text = @"龙撞击到了地面";
    }
    if ([item isEqual:self.frogIV]) {
        self.frogL.text = @"青蛙撞击到了地面";
    }
}

- (void)collisionBehavior:(UICollisionBehavior *)behavior endedContactForItem:(id)item withBoundaryIdentifier:(id)identifier {
    NSLog(@"撞击结束");
}

碰撞行为可以设置代理，可以在碰撞开始和结束时做想要的操作。

• 附着行为

- (void)startAnimator {
    //添加碰撞行为
    self.animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
    
    UICollisionBehavior *collisionBehavior = [[UICollisionBehavior alloc] initWithItems:@[self.frogIV, self.dragonIV]];
    collisionBehavior.collisionMode = UICollisionBehaviorModeBoundaries;
    collisionBehavior.translatesReferenceBoundsIntoBoundary = YES;
    
    [self.animator addBehavior:collisionBehavior];
    
    //添加附着行为
    CGPoint frogCenter = CGPointMake(self.frogIV.center.x, self.frogIV.center.y);
    
    //让龙的图片随着青蛙的中心点运动
    UIAttachmentBehavior *attachmentBehavior = [[UIAttachmentBehavior alloc] initWithItem:self.dragonIV attachedToAnchor:frogCenter];
    self.attachmentBehavior = attachmentBehavior;
    
    [self.animator addBehavior:attachmentBehavior];
}

//让青蛙图片可以移动
- (IBAction)handleAttachmentGesture:(UIPanGestureRecognizer *)sender {
    //将拖动的点设置为青蛙图片的中心点
    CGPoint panPoint = [sender locationInView:self.view];
    self.frogIV.center = panPoint;
    
    self.attachmentBehavior.anchorPoint = panPoint;
}

让某个元素根据另一个元素的变化而变化。

• 弹跳行为

- (void)startAnimator {
    
    UIDynamicAnimator *animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
    self.animator = animator;
    
    UICollisionBehavior *collisionBehavior = [[UICollisionBehavior alloc] initWithItems:@[self.frogIV, self.dragonIV]];
    collisionBehavior.collisionMode = UICollisionBehaviorModeBoundaries;
    collisionBehavior.translatesReferenceBoundsIntoBoundary = YES;
    
    UIGravityBehavior *gravityBehavior = [[UIGravityBehavior alloc] initWithItems:@[self.dragonIV]];
    
    CGPoint frogCenter = CGPointMake(self.frogIV.center.x, self.frogIV.center.y);
    UIAttachmentBehavior *attachmentBehavior = [[UIAttachmentBehavior alloc] initWithItem:self.dragonIV attachedToAnchor:frogCenter];
    attachmentBehavior.frequency = 1.0f;  //越大晃动越快
    attachmentBehavior.damping = 0.1f; //越小晃动幅度越大
    attachmentBehavior.length = 100.0f; //越大距离附着的点越远
    
    [animator addBehavior:collisionBehavior];
    [animator addBehavior:gravityBehavior];
    [animator addBehavior:attachmentBehavior];
}

其实就是附着行为的几个属性设置，frequency、damping、length。

• 瞬间位移

- (IBAction)handleTapGesture:(UITapGestureRecognizer *)sender {
    // 手指点到哪儿，就让图片瞬间移动哪儿
    CGPoint panPoint = [sender locationInView:self.view];
    
    UIDynamicAnimator *animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
    self.animator = animator;
    
    UISnapBehavior *snapBehavior = [[UISnapBehavior alloc] initWithItem:self.frogIV snapToPoint:panPoint];
    snapBehavior.damping = 0.5;
    
    [self.animator addBehavior:snapBehavior];
}

让某个元素瞬间移动到某个点

• 推力行为

- (void)startAnimator {
    UIDynamicAnimator *animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
    self.animator = animator;
    
    UICollisionBehavior *collisionBehavior = [[UICollisionBehavior alloc] initWithItems:@[self.dragonIV]];
    collisionBehavior.collisionMode = UICollisionBehaviorModeBoundaries;
    collisionBehavior.translatesReferenceBoundsIntoBoundary = YES;
    
    UIPushBehavior *pushBehavior = [[UIPushBehavior alloc] initWithItems:@[self.dragonIV] mode:UIPushBehaviorModeContinuous];
    self.pushBehavior = pushBehavior;
    pushBehavior.magnitude = 0.0;
    pushBehavior.angle = 0.0;
    
    [self.animator addBehavior:collisionBehavior];
    [self.animator addBehavior:pushBehavior];
    
    
}


- (IBAction)handlePanGesture:(UIPanGestureRecognizer *)sender {
    //根据移动的点计算推力的角度和距离、
    if (sender.state == UIGestureRecognizerStateEnded) {
        CGPoint panPoint = [sender locationInView:self.view];
        
        CGPoint originPoint = CGPointMake(CGRectGetMidX(self.dragonIV.bounds), CGRectGetMidY(self.dragonIV.bounds));
        
        CGFloat angle = atan2(panPoint.y - originPoint.y, panPoint.x - originPoint.x);
        CGFloat distance = sqrtf(powf(panPoint.x - originPoint.x, 2) + powf(panPoint.y - originPoint.y, 2));
        distance = MIN(distance, 100);
     
        self.pushBehavior.magnitude = distance/100;
        self.pushBehavior.angle = angle;
        self.pushBehavior.active = YES;

    }
}

• 元素行为

- (void)startAnimator {
    UIDynamicAnimator *animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
    self.animator = animator;
    
    UIGravityBehavior *gravityBehavior = [[UIGravityBehavior alloc] initWithItems:@[self.dragonIV, self.frogIV]];
    
    UICollisionBehavior *collisionBehavior = [[UICollisionBehavior alloc] initWithItems:@[self.dragonIV, self.frogIV]];
    collisionBehavior.collisionMode = UICollisionBehaviorModeBoundaries;
    collisionBehavior.translatesReferenceBoundsIntoBoundary = YES;
    
    //只对青蛙图片设置元素属性，用龙图片进行对比
    UIDynamicItemBehavior *propertiesBehavior = [[UIDynamicItemBehavior alloc] initWithItems:@[self.frogIV]];
    propertiesBehavior.elasticity = 1.0f;
    propertiesBehavior.allowsRotation = NO;
    propertiesBehavior.angularResistance = 0.0f;
    propertiesBehavior.density = 3.0f;
    propertiesBehavior.friction = 0.5f;
    propertiesBehavior.resistance = 1.0f;
    
    [self.animator addBehavior:gravityBehavior];
    [self.animator addBehavior:collisionBehavior];
    [self.animator addBehavior:propertiesBehavior];
    
}