iPhone 核心动画 - 画一个圆

Question

我想制作一个动画。我能解释这一点的最好方法是，如果你能想象画一个圆圈。它从顶部或 12 点开始，一直沿顺时针方向绘制，直到在 10 秒左右的空间内变成一个完整的圆圈。

我来到这里的壁橱是使用Core Animation（使用示例代码here）绘制一个围绕中心点旋转的点。但是我不知道如何画圆圈？非常欢迎任何建议。

非常感谢:)

Answer 1

您真正应该做的是为 CAShapeLayer 的笔划设置动画，其中路径是一个圆。这将使用 Core Animation 加速，并且比在 -drawRect: 中绘制圆的一部分更容易。

下面的代码将在屏幕中心创建一个圆形图层，并按顺时针方向对其笔划进行动画处理，使其看起来好像正在绘制。你当然可以使用任何你喜欢的形状。 （您可以阅读 Ole Begemanns 博客上的 this article 了解更多关于如何为形状图层的笔划设置动画的信息。）

注意： stoke 属性与图层上的边框属性不同。要更改笔画的宽度，您应该使用“lineWidth”而不是“borderWitdh”等。

// Set up the shape of the circle
int radius = 100;
CAShapeLayer *circle = [CAShapeLayer layer];
// Make a circular shape
circle.path = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(0, 0, 2.0*radius, 2.0*radius) 
                                         cornerRadius:radius].CGPath;
// Center the shape in self.view
circle.position = CGPointMake(CGRectGetMidX(self.view.frame)-radius, 
                              CGRectGetMidY(self.view.frame)-radius);

// Configure the apperence of the circle
circle.fillColor = [UIColor clearColor].CGColor;
circle.strokeColor = [UIColor blackColor].CGColor;
circle.lineWidth = 5;

// Add to parent layer
[self.view.layer addSublayer:circle];

// Configure animation
CABasicAnimation *drawAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
drawAnimation.duration            = 10.0; // "animate over 10 seconds or so.."
drawAnimation.repeatCount         = 1.0;  // Animate only once..

// Animate from no part of the stroke being drawn to the entire stroke being drawn
drawAnimation.fromValue = [NSNumber numberWithFloat:0.0f];
drawAnimation.toValue   = [NSNumber numberWithFloat:1.0f];

// Experiment with timing to get the appearence to look the way you want
drawAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseIn];

// Add the animation to the circle
[circle addAnimation:drawAnimation forKey:@"drawCircleAnimation"];

Answer 2

根据@David 的回答，这是该问题的另一种解决方案。这种方法可以让您设置圆圈动画的方向，并提供更多控制。 编辑：我已经在how to draw a circle with Swift 上写了一篇博文，我会尽量跟上测试版的最新情况。如果下面的代码不适合您，请检查那里。

let radius = 100.0

// Create the circle layer
var circle = CAShapeLayer()

// Set the center of the circle to be the center of the view
let center = CGPointMake(CGRectGetMidX(self.frame) - radius, CGRectGetMidY(self.frame) - radius)

let fractionOfCircle = 3.0 / 4.0

let twoPi = 2.0 * Double(M_PI)
// The starting angle is given by the fraction of the circle that the point is at, divided by 2 * Pi and less
// We subtract M_PI_2 to rotate the circle 90 degrees to make it more intuitive (i.e. like a clock face with zero at the top, 1/4 at RHS, 1/2 at bottom, etc.)
let startAngle = Double(fractionOfCircle) / Double(twoPi) - Double(M_PI_2)
let endAngle = 0.0 - Double(M_PI_2)
let clockwise: Bool = true

// `clockwise` tells the circle whether to animate in a clockwise or anti clockwise direction
circle.path = UIBezierPath(arcCenter: center, radius: radius, startAngle: CGFloat(startAngle), endAngle: CGFloat(endAngle), clockwise: clockwise).CGPath

// Configure the circle
circle.fillColor = UIColor.blackColor().CGColor
circle.strokeColor = UIColor.redColor().CGColor
circle.lineWidth = 5

// When it gets to the end of its animation, leave it at 0% stroke filled
circle.strokeEnd = 0.0

// Add the circle to the parent layer
self.layer.addSublayer(circle)

// Configure the animation
var drawAnimation = CABasicAnimation(keyPath: "strokeEnd")
drawAnimation.repeatCount = 1.0

// Animate from the full stroke being drawn to none of the stroke being drawn
drawAnimation.fromValue = NSNumber(double: fractionOfCircle)
drawAnimation.toValue = NSNumber(float: 0.0)

drawAnimation.duration = 30.0

drawAnimation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionLinear)

// Add the animation to the circle
circle.addAnimation(drawAnimation, forKey: "drawCircleAnimation")

Answer 3

我找到了解决这个问题的方法，代码如下。我对手头问题的解释似乎搞砸了，所以将其重写为另一个问题，得到了正确的解决方案，请参阅here

感谢大家的建议！

-(void)drawRect:(CGRect)rect
{
    // Drawing code

    CGRect allRect = self.bounds;
    CGContextRef context = UIGraphicsGetCurrentContext();

    // Draw background
    CGContextSetRGBStrokeColor(context, self.strokeValueRed, self.strokeValueGreen, self.strokeValueBlue, self.strokeValueAlpha); // white
    CGContextSetLineWidth(context, 5);

    // Draw progress
    CGPoint center = CGPointMake(allRect.size.width / 2, allRect.size.height / 2);
    CGFloat radius = (allRect.size.width - 4) / 2;
    CGFloat startAngle = - ((float)M_PI / 2); // 90 degrees
    CGFloat endAngle = (self.progress * 2 * (float)M_PI) + startAngle;
    CGContextAddArc(context, center.x, center.y, radius, startAngle, endAngle, 0);
    CGContextStrokePath(context);
}

Answer 4

好的，我有部分修复。我找到了以下绘制圆段的代码。它基本上是一个 UIView 子类，每次更新进度时都会触发它的 drawRect。我现在唯一的问题是如何更改它，而不是绘制部分或切片，而只是绘制圆形笔划？

-(void)drawRect:(CGRect)rect 
{
    // Drawing code

    CGRect allRect = self.bounds;
    CGRect circleRect = CGRectInset(allRect, 2.0f, 2.0f);

    CGContextRef context = UIGraphicsGetCurrentContext();

    // Draw background
    CGContextSetRGBStrokeColor(context, self.strokeValueRed, self.strokeValueGreen, self.strokeValueBlue, self.strokeValueAlpha); // white
    CGContextSetRGBFillColor(context, 1.0f, 1.0f, 1.0f, 0.1f); // translucent white
    CGContextSetLineWidth(context, self.lineWidth);
    CGContextFillEllipseInRect(context, circleRect);
    CGContextStrokeEllipseInRect(context, circleRect);

    // Draw progress
    CGPoint center = CGPointMake(allRect.size.width / 2, allRect.size.height / 2);
    CGFloat radius = (allRect.size.width - 4) / 2;
    CGFloat startAngle = - ((float)M_PI / 2); // 90 degrees
    CGFloat endAngle = (self.progress * 2 * (float)M_PI) + startAngle;
    CGContextSetRGBFillColor(context, 1.0f, 1.0f, 1.0f, 1.0f); // white
    CGContextMoveToPoint(context, center.x, center.y);
    CGContextAddArc(context, center.x, center.y, radius, startAngle, endAngle, 0);
    CGContextClosePath(context);
    CGContextFillPath(context);
}