UIView锚点->拖动->旋转变换导致闪烁

Question

目标

我正在尝试复制 UI Dynamics 拉动动画/行为。我在UIView 上设置了一个UIPanGestureRecognizer 用于拖动它。发生拖动时，我将触摸点设置为UIView.layer.anchorPoint 以允许围绕触摸点旋转。在拖动过程中，我检查触摸速度方向并顺时针或逆时针应用CGAffineTransformRotate。这就是我所说的。

问题

动画不流畅，UIView 在拖动和应用旋转时闪烁（在短实例中出现多条视图痕迹）。视频录制为 30fps，因此看不到闪烁。我希望我的解释清楚。

我的视图控制器中的源代码如下。我正在 iOS5.0+ 上尝试这个

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    UIView *animationView = [[UIView alloc] initWithFrame:CGRectMake(50, 50, 100, 100)];
    animationView.layer.backgroundColor = [UIColor redColor].CGColor;
    animationView.layer.shouldRasterize = YES; // Does not help :(
    animationView.autoresizingMask = UIViewAutoresizingNone; // Does not help :(

    [self.view addSubview:animationView];

    UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(pan:)];
    [animationView addGestureRecognizer:pan];
    [animationView release];
    [pan release];
}

- (void) pan:(UIPanGestureRecognizer*) gesture {

    if(gesture.state==UIGestureRecognizerStateBegan) {
        CGPoint anchor = [gesture locationInView:gesture.view];

        gesture.view.layer.anchorPoint = CGPointMake(anchor.x/gesture.view.bounds.size.width,
                                                     anchor.y/gesture.view.bounds.size.height);

        gesture.view.center = CGPointMake(anchor.x/gesture.view.bounds.size.width,
                                          anchor.y/gesture.view.bounds.size.height);
    }
    else if(gesture.state==UIGestureRecognizerStateChanged) {
        CGPoint point1 = [gesture locationInView:self.view];
        gesture.view.center=point1;

        CGPoint velocity = [gesture velocityInView:gesture.view];
        if(velocity.x > 0)
        {
            // Dragged right
            if(velocity.y > 0) {
                // Dragged down
                // counter clock
                CGFloat angle = -0.2;
                gesture.view.transform = CGAffineTransformRotate(gesture.view.transform, angle);
            }
            else {
                // Dragged up
                // clock
                CGFloat angle = 0.2;
                gesture.view.transform = CGAffineTransformRotate(gesture.view.transform, angle);
            }
        }
        else
        {
            // Dragged left
            if(velocity.y > 0) {
                // Dragged down
                // clock
                CGFloat angle = 0.2;
                gesture.view.transform = CGAffineTransformRotate(gesture.view.transform, angle);
            }
            else {
                // Dragged up
                // counter clock
                CGFloat angle = -0.2;
                gesture.view.transform = CGAffineTransformRotate(gesture.view.transform, angle);
            }
        }
    }
}

我尝试将CATransform3DMakeRotation (angle, 0.0f, 0.0f, 1.0f) 应用于图层而不是视图CGAffineTransformRotate。但是闪烁仍然发生。有什么想法为什么会出现这个问题？我欢迎任何其他方法的建议，以达到相同的结果。

Answer 1

在解决这个问题经过认真思考后，我意识到这是一个微不足道的错误。闪烁是因为我正在旋转以使拖动方向发生最轻微的变化。为了解决这个问题，我在进行旋转之前假设了像素变化的任意余量。

解决问题的修改代码如下

- (void) pan:(UIPanGestureRecognizer*) gesture {

    if(gesture.state==UIGestureRecognizerStateBegan) {
        CGPoint anchor = [gesture locationInView:gesture.view];
        gesture.view.layer.anchorPoint = CGPointMake(anchor.x/gesture.view.bounds.size.width,
                                                     anchor.y/gesture.view.bounds.size.height);
    }
    else if(gesture.state==UIGestureRecognizerStateChanged) {
        CGPoint point1 = [gesture locationInView:self.view];
        gesture.view.layer.position=point1;

        CGPoint velocity = [gesture velocityInView:gesture.view];
        CGFloat angle = 0.0;
        if(velocity.x > self.view.bounds.size.width*0.15)
        {
            // Dragged right
            if(velocity.y > self.view.bounds.size.height*0.02) {
                // Dragged down
                // counter clock
                angle = -0.05;
            }
            else if (velocity.y < -self.view.bounds.size.height*0.02) {
                // Dragged up
                // clock
                angle = 0.05;
            }
        }
        else if (velocity.x < -self.view.bounds.size.width*0.15)
        {
            // Dragged left
            if(velocity.y > self.view.bounds.size.height*0.02) {
                // Dragged down
                // clock
                angle = 0.05;
            }
            else if (velocity.y < -self.view.bounds.size.height*0.02) {
                // Dragged up
                // counter clock
                angle = -0.05;
            }
        }
        [self applyRotationToView:gesture.view byAngle:angle];
    }
}

- (void) applyRotationToView:(UIView*)rotationView byAngle:(CGFloat)angle {
    rotationView.transform = CGAffineTransformRotate(rotationView.transform, angle);
}

动画仍然没有人们想象的那么流畅，但是我已经设法减少了烦人的闪烁。