雪花划落

two.gif

#import "SnowView.h"

@interface SnowView()
@property (nonatomic,assign) float imagaeY;

@end

@implementation SnowView

- (instancetype)initWithCoder:(NSCoder *)aDecoder{
    self = [super initWithCoder:aDecoder];
    if (self) {
        //CADisplayLink刷帧定时器，默认是每秒刷新60次
        //该定时器创建后，默认是不会执行的，需要把它加载到消息循环中
        CADisplayLink *display = [CADisplayLink displayLinkWithTarget:self selector:@selector(updateImage)];
        [display addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
    }
    return self;
}

- (void)updateImage{
    //调用此方法重绘画面
    [self setNeedsDisplay];
}

- (void)awakeFromNib{
    [super awakeFromNib];
    NSLog(@"awakeFromNib");
}

- (void)drawRect:(CGRect)rect{
    self.imagaeY += 5;
    if (self.imagaeY > rect.size.height) {
        self.imagaeY = 0;
    }
    UIImage *image = [UIImage imageNamed:@"雪花.png"];
    [image drawAtPoint:CGPointMake(0, self.imagaeY)];
    
}

第一个：

[NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:@selector(updateImage) userInfo:nil repeats:YES];

说明： NSTimer一般用于定时的更新一些非界面上的数据,告诉多久调用一次

第二个：

 CADisplayLink *display= [CADisplayLink displayLinkWithTarget:self selector:@selector(updateImage)];
 [display addToRunLoop:[NSRunLoopmainRunLoop] forMode:NSDefaultRunLoopMode];
 说明： CADisplayLink刷帧，默认每秒刷新60次。该定时器创建之后，默认是不会执行的，需要把它加载到消息循环中

动态改变圆大小

two.gif

#import "CircleView.h"

@implementation CircleView

- (void)setRadius:(CGFloat)radius{
    _radius = radius;
    [self setNeedsDisplay];
}

- (void)drawRect:(CGRect)rect{
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    //将当前View相对于父视图的中心坐标转换为相对于自己坐标系的中心点
    CGPoint center = self.center;
    CGPoint newPoint = [self convertPoint:center fromView:self.superview];
    CGContextAddArc(ctx, newPoint.x, newPoint.y, self.radius, 0, 2*M_PI, 0);
    [[UIColor redColor]setFill];
    CGContextFillPath(ctx);
}

- (void)awakeFromNib{
    [super awakeFromNib];
    self.radius = 20;
}