接着上一个动画继续学习UIDynamic Animation 相关，通过 UIGravityBehavior 重力行为、UICollisionBehavior 碰撞行为、UIAttachmentBehavior吸附行为实现橡皮筋的功能。
将其创建为 View，通过子 View 逐一设置来特征
- RubberBaseView -- 初始化 View
- RubberAttachView -- 增加吸附行为
- RubberView -- 增加弹性行为
#import <UIKit/UIKit.h>
@interface RubberBaseView : UIView
@property (nonatomic, strong) UIImageView *box;
@property (nonatomic, strong) UIDynamicAnimator *animator;
@end
#import "RubberBaseView.h"
@implementation RubberBaseView
- (instancetype)initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
if (self) {
// 设置背景颜色（通过图片）
self.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"back"]];
// 设置方块 橡皮
_box = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"rubber"]];
_box.center = self.center;
[self addSubview: _box];
// 创建UIDynamicAnimator
_animator = [[UIDynamicAnimator alloc] initWithReferenceView:self];
}
return self;
}
#import "RubberBaseView.h"
@interface RubberAttachView : RubberBaseView
@property (strong, nonatomic) UIAttachmentBehavior *attachment;
@end
#import "RubberAttachView.h"
@implementation RubberAttachView {
UIImageView *_imageView;
}
- (instancetype)initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
if (self) {
// 添加拖动手势
UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(pan:)];
[self addGestureRecognizer:pan];
// 添加附着行为
UIOffset offset = UIOffsetMake(-25, -25);
_attachment = [[UIAttachmentBehavior alloc] initWithItem:self.box offsetFromCenter:offset attachedToAnchor:CGPointMake(self.box.center.x, self.box.center.y - 100)];
[self.animator addBehavior:_attachment];
// 添加box内部锚点图像
_imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"lineCircle"]];
_imageView.center = CGPointMake(self.box.bounds.size.width / 2 + offset.horizontal, self.box.bounds.size.height / 2 + offset.vertical);
[self.box addSubview:_imageView];
}
return self;
}
- (void)pan:(UIPanGestureRecognizer *)gesture {
if (UIGestureRecognizerStateChanged == gesture.state) {
self.attachment.anchorPoint = [gesture locationInView:self];
// 重新绘制
[self setNeedsDisplay];
}
}
- (void)drawRect:(CGRect)rect
{
// 上下文
CGContextRef context = UIGraphicsGetCurrentContext();
// 位置
CGPoint position = [self convertPoint:_imageView.center fromView:self.box];
// 设置开始点
CGContextMoveToPoint(context, position.x, position.y);
CGContextAddLineToPoint(context, self.attachment.anchorPoint.x, self.attachment.anchorPoint.y);
// 设置线宽
CGContextSetLineWidth(context, 5.0f);
CGFloat length[] = {5.0, 5.0};
CGContextSetLineDash(context, 0.0, length, 2);
[[UIColor blackColor] set];
// 设置路径
CGContextDrawPath(context, kCGPathStroke);
}
@end
#import "RubberAttachView.h"
@interface RubberView : RubberAttachView
@end
#import "RubberView.h"
static NSString *const RubberViewCenterKVOName = @"center";
@implementation RubberView
- (instancetype)initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
if (self) {
// 设置物理属性
self.attachment.damping = 1; // 震荡
self.attachment.frequency = 1; // 阻力
// 设置观察者，在手指离开以后继续画线
[self.box addObserver:self forKeyPath:RubberViewCenterKVOName options:NSKeyValueObservingOptionNew context:nil];
//创建并添加重力
UIGravityBehavior *gravity = [[UIGravityBehavior alloc] initWithItems:@[self.box]];
[self.attachment addChildBehavior:gravity];
//创建并添加碰撞行为对象
UICollisionBehavior *collision = [[UICollisionBehavior alloc] initWithItems:@[self.box]];
collision.translatesReferenceBoundsIntoBoundary = YES;
[self.attachment addChildBehavior:collision];
}
return self;
}
- (void)dealloc {
[self.box removeObserver:self forKeyPath:RubberViewCenterKVOName];
}
//画线
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
if ([keyPath isEqualToString:RubberViewCenterKVOName]) {
[self setNeedsDisplay];
}
}
@end
最后实现
#import "ViewController.h"
#import "RubberView.h"
#define SCREEN_WIDTH [UIScreen mainScreen].bounds.size.width
#define SCREEN_HEIGHT [UIScreen mainScreen].bounds.size.height
@interface ViewController ()
@property (nonatomic, strong) RubberView *rubberView;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
[self.view addSubview:self.rubberView];
}
- (RubberView *)rubberView {
if (!_rubberView) {
_rubberView = [[RubberView alloc] initWithFrame:CGRectMake(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT)];
}
return _rubberView;
}
@end
注意点1： 此处为什么要通过 子类的 View（继承） 逐一去设置呢？
- 方便理解，一目了解
- 不改变原来的基础上，拓充方法，扩充功能性强。
当然此处也可以不这样写咯。
注意点2： UIAttachmentBehavior
附着行为，让物体附着在某个点或另外一个物体上。可以设置附着点的到物体的距离，阻尼系数和振动频率等。
_attachment = [[UIAttachmentBehavior alloc] initWithItem:self.box offsetFromCenter:offset attachedToAnchor:CGPointMake(self.box.center.x, self.box.center.y - 100)];
注意这个初始化中方法的offset 和 point 的设置（就是决定线和 box 位置和距离的），当然UIAttachmentBehavior 还有其他的初始化方法，可以根据不同场景相应使用。
- (instancetype)initWithItem:(id <UIDynamicItem>)item attachedToAnchor:(CGPoint)point;
- (instancetype)initWithItem:(id <UIDynamicItem>)item offsetFromCenter:(UIOffset)offset attachedToAnchor:(CGPoint)point NS_DESIGNATED_INITIALIZER;
- (instancetype)initWithItem:(id <UIDynamicItem>)item1 attachedToItem:(id <UIDynamicItem>)item2;
- (instancetype)initWithItem:(id <UIDynamicItem>)item1 offsetFromCenter:(UIOffset)offset1 attachedToItem:(id <UIDynamicItem>)item2 offsetFromCenter:(UIOffset)offset2 NS_DESIGNATED_INITIALIZER;
PS：场景来自：【iOS开发范例实战宝典.进阶篇】。
