自己画一个ActivityIndicatorView－b

苹果的UI控件中有一个UIActivityIndicatorView，俗称菊花。→_→
现在我们仿照它来制作一个其它样式的指示器，如下：

ActivityView.png

自定义指示器

首先画一个白色的扇形。
创建一个MyLayer类继承自CALayer，重写它的绘图方法- (void)drawInContext:(CGContextRef)ctx：

- (void)drawInContext:(CGContextRef)ctx {    
    CGContextSetRGBFillColor(ctx, 1, 1, 1, 1);    
    CGContextSetRGBStrokeColor(ctx, 1, 1, 1, 1);    
    CGContextMoveToPoint(ctx, CGRectGetMaxX(self.bounds)/2, CGRectGetMaxY(self.bounds));    // 顺时针从-70度画到-110度 (0度是3点钟方向)    
    CGContextAddArc(ctx, CGRectGetMaxX(self.bounds)/2, CGRectGetMaxY(self.bounds), 20,  -70 * M_PI / 180, -110 * M_PI / 180, 1);    CGContextClosePath(ctx);    CGContextDrawPath(ctx, kCGPathFillStroke);
}

之后创建一个MyActiveView类继承自UIView，把上面创建的layer添加到MyActiveView上。

@implementation MyActiveView{    
    MyLayer *layer;    
    CABasicAnimation *opacityAnim;
}
- (instancetype)initWithFrame:(CGRect)frame {    
    if (self = [super initWithFrame:frame]) {        
        self.backgroundColor = [UIColor clearColor];        
        CAReplicatorLayer *repLayer = [CAReplicatorLayer layer];        
        repLayer.frame = self.bounds;        
        [self.layer addSublayer:repLayer];        // 画一个扇形的layer        
        layer = [MyLayer layer];        
        layer.frame = CGRectMake(0, 0, 22, 22);        // 调用layer的drawInContext:进行绘图        
        [layer setNeedsDisplay];        // 设置2倍比率，防止边缘出现锯齿        
        layer.contentsScale = 2;        // 透明        
        layer.opacity = 0;        // 设置锚点        
        layer.anchorPoint = CGPointMake(0.5, 0);        // 设置第一个扇形layer的位置        
        layer.position = CGPointMake(self.bounds.size.width/2, 0);        
        [repLayer addSublayer:layer];        // 设置透明度渐变的动画        
        opacityAnim = [CABasicAnimation animationWithKeyPath:@"opacity"];        // 透明度从1变为0        
        opacityAnim.fromValue = [NSNumber numberWithFloat:1.0];        
        opacityAnim.toValue = [NSNumber numberWithFloat:0];        
        opacityAnim.removedOnCompletion = YES;        
        opacityAnim.repeatCount = MAXFLOAT;        
        CGFloat duration = 0.7;        
        opacityAnim.duration = duration;        
        [layer addAnimation:opacityAnim forKey:nil];        
        int count = 8;        
        CGFloat angle = M_PI * 2 / count;        // 复制8个        
        repLayer.instanceCount = count;        // 绕z轴每隔angle角度复制一个        
        repLayer.instanceTransform = CATransform3DMakeRotation(angle, 0, 0, 1);        // 复制子层动画延迟时长        
        repLayer.instanceDelay = duration / count;        // 此视图绕z轴旋转22度        
        CATransform3D transform = CATransform3DRotate(self.layer.transform, 22*M_PI/180, 0, 0, 1);        self.layer.transform = transform;        // 监听App进入前后台        
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(stop) name:UIApplicationWillResignActiveNotification object:nil];        
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(start) name:UIApplicationDidBecomeActiveNotification object:nil];    
    }    
    return self;
}
// 停止动画
- (void)stop {    
    [layer removeAllAnimations];
}
// 开始动画
- (void)start {    
    [layer addAnimation:opacityAnim forKey:nil];
}

接下来就可以创建使用了。记得把视图控制器view的白色改为其它颜色，否则你是看不到这个白色指示器的。

MyActiveView *activityView = [[MyActiveView alloc] initWithFrame:CGRectMake(self.view.bounds.size.width/2-25, self.view.bounds.size.height-200, 50, 50)];
[self.view addSubview:activityView];

OK搞定！旋转吧，小菊花！(ง •̀_•́)ง

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ActiveView.gif

CAReplicatorLayer

使用CAReplicatorLayer可以创建出很多类似的重复动画效果，比如：

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ActiveViews.gif

这些都是常见的指示器效果，它们的代码如下：

条形指示器

创建一个ActiveView1类，继承自UIView。

- (instancetype)initWithFrame:(CGRect)frame {    
    if (self = [super initWithFrame:frame]) {        
        CAReplicatorLayer *repLayer = [CAReplicatorLayer layer];        
        repLayer.frame = self.bounds;        
        [self.layer addSublayer:repLayer];        
        CALayer *layer = [CALayer layer];        // 宽度5等分之后创建3个repLayer        
        CGFloat width = frame.size.width/5;        
        CGFloat height = frame.size.height;        
        layer.bounds = CGRectMake(0, 0, width, height);        // 第一个layer的位置        
        layer.position = CGPointMake(width/2, height/2);        
        layer.backgroundColor = [UIColor greenColor].CGColor;        
        [repLayer addSublayer:layer];        
        CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"transform.scale.y"];        
        animation.fromValue = @1;        
        animation.toValue = @0.3;        
        animation.duration = 0.4;        // 每次重复效果跟上次相反        
        animation.autoreverses = YES;        
        animation.repeatCount = CGFLOAT_MAX;        
        [layer addAnimation:animation forKey:nil];          
        repLayer.instanceCount = 3;        
        repLayer.instanceDelay = 0.2;        // x轴上每隔self.frame.size.width/5*2距离，放置一个repLayer        
        repLayer.instanceTransform = CATransform3DMakeTranslation(frame.size.width/5*2, 0, 0);    
     }    
     return self;
}

在控制器中添加它即可：

ActiveView1 *view1 = [[ActiveView1 alloc] initWithFrame:CGRectMake(20, 200, 70, 50)];
[self.view addSubview:view1];

环形指示器

创建一个ActiveView2类，继承自UIView。

- (instancetype)initWithFrame:(CGRect)frame {    
    if (self = [super initWithFrame:frame]) {        
        CAReplicatorLayer *repLayer = [CAReplicatorLayer layer];        
        repLayer.frame = self.bounds;        
        [self.layer addSublayer:repLayer];        
        CALayer *layer = [CALayer layer];        
        layer.bounds = CGRectMake(0, 0, 10, 10);        
        layer.cornerRadius = 5;        
        layer.masksToBounds = YES;        
        layer.transform = CATransform3DMakeScale(0, 0, 0);        // 第一个layer的位置        
        layer.position = CGPointMake(frame.size.width/2, 5);        
        layer.backgroundColor = [UIColor greenColor].CGColor;        
        [repLayer addSublayer:layer];        
        CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"transform.scale"];        
        animation.fromValue = @1;        
        animation.toValue = @0.2;        
        CGFloat duration = 1.2;        
        animation.duration = duration;        
        animation.repeatCount = CGFLOAT_MAX;        
        [layer addAnimation:animation forKey:nil];        int count = 12;        // 360度分成12份        
        CGFloat angle = M_PI * 2 / count;        // 设置子层总数        
        repLayer.instanceCount = count;        
        repLayer.instanceTransform = CATransform3DMakeRotation(angle, 0, 0, 1);        
        repLayer.instanceDelay = duration / count;    
    }    
    return self;
}

在控制器中添加它：

ActiveView2 *view2 = [[ActiveView2 alloc] initWithFrame:CGRectMake(150, 200, 70, 70)];
[self.view addSubview:view2];

另外一种指示器

除了上面三种指示器，还有一种指示器比较常见，不过它的代码跟上面的不太一样，它不需要使用CAReplicatorLayer来创建，只需要用CAShapeLayer结合贝塞尔曲线画个圆就行。

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Round.gif

代码如下：

- (instancetype)initWithFrame:(CGRect)frame {    
    if (self = [super initWithFrame:frame]) {        // 设置直径为self宽/高的最小值        
        CGFloat diameter = MIN(frame.size.width, frame.size.height);        CAShapeLayer *sLayer = [CAShapeLayer layer];        
        sLayer.anchorPoint = CGPointMake(0.5, 0.5);        
        sLayer.frame = CGRectMake(0, 0, diameter, diameter);        
        sLayer.strokeColor = [UIColor greenColor].CGColor;        
        sLayer.fillColor = [UIColor clearColor].CGColor;        
        sLayer.lineWidth = 2;        
        CGFloat raduis = diameter/2;        
        UIBezierPath *roundPath = [UIBezierPath bezierPathWithArcCenter:CGPointMake(raduis, raduis)                                                                  radius:raduis                                                              startAngle:0                                                                endAngle:(2*M_PI-M_PI_4)                                                               clockwise:YES];        
        sLayer.path = roundPath.CGPath;        
        [self.layer addSublayer:sLayer];        
        CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"transform.rotation"];        
        animation.fromValue = @0;        
        animation.toValue = @(2*M_PI);        
        animation.duration = 1.f;        
        animation.repeatCount = CGFLOAT_MAX;        
        [sLayer addAnimation:animation forKey:nil];    
   }    
    return self;
}