iOS加载动画代码实现

```Objective-C

@interface LoadingAnimationView : UIView

@end

@implementation LoadingAnimationView

- (instancetype)init {

    if (self = [super init]) {

        // 设置动画效果时间

        self.alpha = 0.5;

        self.animationDuration = 3.0f;

    }

    return self;

}

- (void)drawRect:(CGRect)rect {

    // 绘制对应的加载动画

    // 例如：一个圆形、一个直线等

    UIBezierPath *path = [UIBezierPath bezierPath];

    [path moveToPoint:CGPointMake(rect.size.width/2, 10)];

    [path addLineToPoint:CGPointMake(rect.size.width/2, rect.size.height - 10)];

    [path addArcWithCenter:CGPointMake(rect.size.width/2, 0) radius:rect.size.height/2 startAngle:M_PI endAngle:3*M_PI clockwise:YES];

    [UIColor.lightGrayColor setStroke];

    [path stroke];

}

- (void)startAnimating {

    // 加载动画，需要实现一个简单的动画组

    // 比如一个圆形，从右边移动到左边，一直重复

    CABasicAnimation *move = [CABasicAnimation animationWithKeyPath:@"position.x"];

    move.fromValue = [NSNumber numberWithFloat:self.frame.size.width/2 + self.frame.size.height/2 - 10];

    move.toValue = [NSNumber numberWithFloat:self.frame.size.width/2 - self.frame.size.height/2 + 10];

    move.duration = self.animationDuration;

   

    CABasicAnimation *rotation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];

    rotation.fromValue = [NSNumber numberWithDouble:0];

    rotation.toValue = [NSNumber numberWithDouble:2*M_PI];

    rotation.duration = self.animationDuration;

    CAAnimationGroup *group = [CAAnimationGroup animation];

    group.animations = @[move, rotation];

    group.duration = self.animationDuration;

    group.repeatCount = 0;

    group.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];

    [self.layer addAnimation:group forKey:nil];

}

@end

```