一、运用继承，添加自定义的属性
项目：Homework_MoreCircleMove_Teacher0307
1.1

#import <UIKit/UIKit.h>

@interface CustomImageView : UIImageView
//初始角度
@property float startAngle;
@end

1.2 for…in

    //2.2 使用泛型遍历for in
    for (CustomImageView *earth in earthArray)
    {
        //给变球的角度
        float endAngle = earth.startAngle + speedAngle;
        //计算x,y坐标
        float x = CENTER_X + REDIOUS * cos(HUDU(endAngle));
        float y = CENTER_Y + REDIOUS * sin(HUDU(endAngle));
        earth.center = CGPointMake(x, y);
    }

二、UIView动画设置雪花下落
项目：Homework_FaillingSnow_Teacher0307
1.1 UIView动画

    //1.创建雪花
    _snow = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0, 60, 60)];
    _snow.image = [UIImage imageNamed:@"flake"];
    [self.window addSubview:_snow];
    
    //2.UIView动画
    //a.开启一个动画块儿
    //void * :代表任意指针
    [UIView beginAnimations:nil context:nil];
    //a.1 设置动画时间,秒
    [UIView setAnimationDuration:3];
    //a.2 设置动画要运动的位置坐标
    _snow.frame = CGRectMake(100, 400, 60, 60);
    //a.3 设置动画结束的方法
    //a.3.1 设置代理，让谁来执行动画结束的方法
    [UIView setAnimationDelegate:self];
    //a.3.2 设置动画结束时的方法
    [UIView setAnimationDidStopSelector:@selector(snowChangeAlpha)];
    //b.提交动画
    [UIView commitAnimations];

1.2 结束动画

//改变透明度
- (void)snowChangeAlpha
{
    //a.3 设置透明度变化，取值范围是0~1。
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:1];
//    //RGB:[0,255]
//    [UIColor colorWithRed:180.0/255.0 green:34.0/255.0 blue:120.0/255.0 alpha:1];
    _snow.alpha = 0;
    //方法1：代理
    [UIView setAnimationDelegate:self];
    [UIView setAnimationDidStopSelector:@selector(removeSnow)];
    //方法2：延迟执行方法
    //当代码执行到这一句代码时，会延迟*秒再执行@selector(removeSnow:)方法
    //方法参数类型 与 所传对象（object）类型 保持一致
    [self performSelector:@selector(removeSnow:) withObject:_snow afterDelay:1];
    
    [UIView commitAnimations];
}
//移除雪花
- (void)removeSnow:(UIImageView *)snow
{
    [snow removeFromSuperview];
}