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最近，当我在玩 Stuart Hall 的 UIKit Dynamics 教程 ( http://stuartkhall.com/posts/flipcase-bounce-in-uikit-dynamics ) 时，我发现存在性能问题。

在我向动画师添加了大约 50 个项目（弹跳球）后，应用程序变得非常缓慢——几乎冻结了。分析显示 [UIDynamicAnimator _animatorStep] 占用了 96% 的 CPU。

有人知道如何提高具有大量 UIDynamicItems 的 UIKit Dynamics 应用程序的性能吗？

您可以下载我的代码并自己查看性能问题：

https://www.dropbox.com/s/zy7ajj6molxm9up/Flipper-UIKit-Dynamics-Poor-Performance.zip

以下是一切发生的代码：

#import "ViewController.h"
#import <CoreMotion/CoreMotion.h>

@interface ViewController () {
    CMMotionManager *_motionManager;
    NSOperationQueue *_queue;

    int _count;
}

@property(nonatomic, strong) UIDynamicAnimator *animator;
@property(nonatomic, strong) UIGravityBehavior *gravityBehavior;
@property(nonatomic, strong) UICollisionBehavior *collisionBehavior;
@property(nonatomic, strong) UIDynamicItemBehavior *bounceBehaviour;

@end

@implementation ViewController

static NSInteger const kBallSize = 25;

- (void)startMotion {
    if (_motionManager == nil) {
        _queue = [[NSOperationQueue alloc] init];
        _motionManager = [[CMMotionManager alloc] init];
        _motionManager.deviceMotionUpdateInterval = 0.1;
    }
    [_motionManager startDeviceMotionUpdatesToQueue:_queue withHandler:^(CMDeviceMotion *motion, NSError *error) {
//        angleLabel.text = [NSString stringWithFormat:@"%g", motion.attitude.pitch];
        self.gravityBehavior.angle = atan2(motion.gravity.x + motion.userAcceleration.x, motion.gravity.y + motion.userAcceleration.y); // motion.attitude.pitch + M_PI / 2.0;
    }];
}

- (void)stopMotion {
    if (_motionManager) {
        [_motionManager stopDeviceMotionUpdates];
    }

    _motionManager = nil;
}

- (void)viewDidLoad {
    [super viewDidLoad];

    [self startMotion];

    // Simple tap gesture
    UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(onTap:)];
    [self.view addGestureRecognizer:tapGesture];

    // Create our animator, we retain this ourselves
    self.animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];

    // Gravity
    self.gravityBehavior = [[UIGravityBehavior alloc] initWithItems:@[]];
    self.gravityBehavior.magnitude = 10;
    [self.animator addBehavior:self.gravityBehavior];

    // Collision - make a fake platform
    self.collisionBehavior = [[UICollisionBehavior alloc] initWithItems:@[]];

    UIBezierPath *aPath = [UIBezierPath bezierPathWithArcCenter:CGPointMake(284, 160)
                                                         radius:160
                                                     startAngle:(CGFloat) (M_PI * 0.0)
                                                       endAngle:(CGFloat) (M_PI * 2)
                                                      clockwise:YES];

    [self.collisionBehavior addBoundaryWithIdentifier:@"bottom" forPath:aPath];
    self.collisionBehavior.translatesReferenceBoundsIntoBoundary = YES;
    [self.animator addBehavior:self.collisionBehavior];

    CAShapeLayer *layer = [CAShapeLayer layer];
    layer.path = aPath.CGPath;
    layer.fillColor = [UIColor lightGrayColor].CGColor;

    [self.view.layer addSublayer:layer];

    // Bounce!
    self.bounceBehaviour = [[UIDynamicItemBehavior alloc] initWithItems:@[]];
    self.bounceBehaviour.elasticity = 0.75;
    self.bounceBehaviour.resistance = 0.1;
    self.bounceBehaviour.friction = 0.01;
    [self.animator addBehavior:self.bounceBehaviour];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}

- (BOOL)prefersStatusBarHidden {
    return YES;
}

#pragma mark - Gesture Recognizer

- (void)onTap:(UITapGestureRecognizer *)gesture {
    if (gesture.state == UIGestureRecognizerStateEnded) {
        // Grab the x of the touch for the center of our ball
        // Ignore the y, we'll drop from the top
        CGPoint pt = [gesture locationInView:self.view];
        [self dropBallAtX:pt];
    }
}

#pragma mark - Helpers

- (void)dropBallAtX:(CGPoint)p {
    _count++;
    self.label.text = [NSString stringWithFormat:@"Balls: %d", _count];

    // Create a ball and add it to our view
    UIView *ball = [[UIView alloc] initWithFrame:CGRectMake(p.x - (kBallSize / 2), p.y - (kBallSize / 2), kBallSize, kBallSize)];
    CGFloat hue = (arc4random() % 256 / 256.0);               //  0.0 to 1.0
    CGFloat saturation = (arc4random() % 64 / 256.0) + 0.75;  //  0.5 to 1.0, away from white
    CGFloat brightness = (arc4random() % 64 / 256.0) + 0.75;
    ball.backgroundColor = [UIColor colorWithHue:hue saturation:saturation brightness:brightness alpha:1.0];
    ball.layer.cornerRadius = kBallSize / 2;
    ball.layer.masksToBounds = YES;
    [self.view addSubview:ball];

    // Add some gravity
    [self.gravityBehavior addItem:ball];

    // Add the collision
    [self.collisionBehavior addItem:ball];

    // Add the bounce
    [self.bounceBehaviour addItem:ball];
}

@end
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1 回答 1

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这让我觉得这是一个非常棘手的问题，每个球都会影响它的邻居，这反过来又会递归地影响他们的邻居等等。我并不惊讶这个非线性复杂性问题会随着你添加更多而遭受相当严重的性能下降球。我发现当你接近 30-40 个球（在 iPhone 5 上）时，fps 开始明显下降，就像你说的，当你接近 50 个球时，它很快接近 1-2 fps。如果你让它达到静止状态（如果你继续CMMotionManager混音，这不太可能），几秒钟后 fps 会恢复，但是一旦你丢下另一个球或CMMotionManager再次改变重力，问题的复杂性很快就会带来 fps再次跪下。

简单的修复（如增加摩擦、减少弹跳、引入角阻力、移动到矩形形状、通过添加附件行为将项目停止移动后固定在一个位置（如果使用CMMotionManager，无论如何）等）似乎影响不大。让我感到震惊的是，解决这个问题的唯一方法是放弃 UIKit Dynamics 以采用其​​他方法，这些方法可以根据您的特定问题做出一些简化假设（例如，因为您正在处理角对称的圆形对象，您可以消除旋转复杂性，您可以使用更简单的碰撞逻辑，调整一些上述变量以更快地抑制行为；等等）。我不熟悉任何可以为您做到这一点的框架，因此这可能需要大量的代码。即使你这样做了，你仍然在处理非线性复杂性的问题，并且性能在某些时候可能仍然会下降。

于 2014-06-25T04:18:46.083 回答