我正在尝试实现一个简单的类别SKPhysicsBody这将使我能够将“完美弹跳”应用于物理体。
这将简单地做的是当perfectBouncing = YES将会发生以下情况：
restitution = 1.0
linearDamping = 0.0
friction = 0.0
但是，当我尝试使用我的实现（如下所示）时，我收到一个奇怪的崩溃，告诉我无法发送perfectBouncing消息发送至PKPhysicsBody，这是一个我从未引用过的类，并且在我的项目中也不存在，也不存在于 SpriteKit SDK 中。
是的，该类别正在被导入。
崩溃消息
-[PKPhysicsBody setPerfectBouncing:]: unrecognized selector sent to instance 0x7fa828f84610
*** First throw call stack:
(
0 CoreFoundation 0x000000010882b3f5 __exceptionPreprocess + 165
1 libobjc.A.dylib 0x0000000107dbfbb7 objc_exception_throw + 45
2 CoreFoundation 0x000000010883250d -[NSObject(NSObject) doesNotRecognizeSelector:] + 205
3 CoreFoundation 0x000000010878a7fc ___forwarding___ + 988
4 CoreFoundation 0x000000010878a398 _CF_forwarding_prep_0 + 120
5 Squash The Dot 0x000000010785662c -[gameNode viewDidAnimateIn] + 1116
6 Squash The Dot 0x000000010783e709 -[lzyViewHandler initViewChild:] + 3305
7 Squash The Dot 0x000000010783d93d -[lzyViewHandler initViewChildren:] + 573
8 Squash The Dot 0x000000010785d3e0 __28-[splashVC viewDidAnimateIn]_block_invoke + 256
9 SpriteKit 0x000000010933837e _ZN9SKCAction25didFinishWithTargetAtTimeEP9SKCSprited + 44
10 SpriteKit 0x0000000109399638 _ZN9SKCSprite6updateEd + 170
11 SpriteKit 0x0000000109352dd4 -[SKScene _update:] + 119
12 SpriteKit 0x000000010936d299 -[SKView(Private) _update:] + 563
13 SpriteKit 0x000000010936ac2f -[SKView renderCallback:] + 829
14 SpriteKit 0x0000000109367cec __29-[SKView setUpRenderCallback]_block_invoke + 54
15 SpriteKit 0x0000000109394744 -[SKDisplayLink _callbackForNextFrame:] + 256
16 QuartzCore 0x00000001091f88f7 _ZN2CA7Display15DisplayLinkItem8dispatchEv + 37
17 QuartzCore 0x00000001091f87bf _ZN2CA7Display11DisplayLink14dispatch_itemsEyyy + 315
18 CoreFoundation 0x00000001087934e4 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 20
19 CoreFoundation 0x00000001087930a5 __CFRunLoopDoTimer + 1045
20 CoreFoundation 0x00000001087563dd __CFRunLoopRun + 1901
21 CoreFoundation 0x0000000108755a06 CFRunLoopRunSpecific + 470
22 GraphicsServices 0x000000010be319f0 GSEventRunModal + 161
23 UIKit 0x000000010953f550 UIApplicationMain + 1282
24 Squash The Dot 0x00000001078550a3 main + 115
25 libdyld.dylib 0x000000010b6cb145 start + 1
)
类别实施
#import <SpriteKit/SpriteKit.h>
@interface SKPhysicsBody (lzySKPhysics)
// Enables perfect boucing by setting friction = 0, linearDamping = 0 and restitution = 1.
@property (nonatomic) BOOL perfectBouncing;
@end
@implementation SKPhysicsBody (lzySKPhysics)
-(BOOL) perfectBouncing {
return (self.restitution == 1 && self.linearDamping == 0 && self.friction == 0);
}
-(void) setPerfectBouncing:(BOOL)perfectBouncing {
self.restitution = perfectBouncing;
self.linearDamping = !perfectBouncing;
self.friction = !perfectBouncing;
}
@end
使用示例
hero = [[SKSpriteNode alloc] initWithColor:[SKColor blueColor] size:CGSizeMake(heroRadius*2, heroRadius*2)];
hero.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:heroRadius];
hero.physicsBody.perfectBouncing = YES;
任何想法这难以捉摸PKPhysicsBody是以及为什么我会发生这次崩溃？
在内部，Sprite Kit 为许多公共类提供了自定义类。在这种情况下，SKPhysicsBody 实际上创建了内部类 PKPhysicsBody 的实例。据推测，PK 代表“物理套件”。
这就是为什么你的类别不起作用，如果我记得正确的话，铸造也不会成功，因为 SKPhysicsBody 不是从 PKPhysicsBody 继承的，但如果我错了，你可以这样尝试：
((SKPhysicsBody)hero.physicsBody).perfectBouncing = YES;
无论如何，这里不需要类别。相反，您可以使用辅助类和类方法实现相同的效果，例如：
@implementation SKPhysicsHelper
+(BOOL) perfectBouncingWithBody:(SKPhysicsBody*)body {
return (body.restitution == 1 && body.linearDamping == 0 && body.friction == 0);
}
+(void) setPerfectBouncing:(BOOL)perfectBouncing body:(SKPhysicsBody*)body {
body.restitution = perfectBouncing;
body.linearDamping = !perfectBouncing;
body.friction = !perfectBouncing;
}
@end
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