//
//  ViewController.m
//  TestQuartz 2D
//
//  Created by taobaichi on 2017/3/23.
//  Copyright © 2017年 MaChao. All rights reserved.
//
#import "ViewController.h"
#import <QuartzCore/QuartzCore.h>
#import "newView.h"
@interface ViewController ()
@property (weak, nonatomic) IBOutlet newView *circleView;
- (IBAction)valueChange:(UISlider *)sender;
@end
@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
}
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
- (IBAction)valueChange:(UISlider *)sender {
    //当值改变的时候，把值传递给view，改变圆的半径
    NSLog(@"---value---:%lf",sender.value);
    //把sender的值传递给自定义view，设置圆的半径
    self.circleView.radius = sender.value;
}
@end

//
//  newView.h
//  TestQuartz 2D
//
//  Created by taobaichi on 2017/3/23.
//  Copyright © 2017年 MaChao. All rights reserved.
//
#import <UIKit/UIKit.h>
@interface newView : UIView
@property(nonatomic, assign) float radius;
@end

//
//  newView.m
//  TestQuartz 2D
//
//  Created by taobaichi on 2017/3/23.
//  Copyright © 2017年 MaChao. All rights reserved.
//
#import "newView.h"
@interface newView ()
@property (nonatomic, assign)float imageY;
@end
@implementation newView
//自定义view中的圆不显示
//重写set方法，为半径赋值
-(void)setRadius:(float)radius
{
    _radius = radius;
    //通知自定义的view重新绘制
    [self setNeedsDisplay];
}
//如果view是从xib或storyboard中创建出来的会先调用awakeFromNib方法
-(void)awakeFromNib
{
    [super awakeFromNib];
    self.radius = 20;
}
-(void)drawRect:(CGRect)rect
{
    //获取图形上下文
    CGContextRef context = UIGraphicsGetCurrentContext();
    //绘图
    //在自定义的view中画一个圆
    CGContextAddArc(context, 100, 100, self.radius, 0, 2 * M_PI, 0);
    //设置圆的填充颜色
    [[UIColor grayColor] set];
    //渲染
    CGContextFillPath(context);
}
@end

注意点：
drawRect:方法不能由我们自己手动调用，只能由系统来调用
drawRect:调用的时机：当第一次显示或者一个重绘事件发生时调用
setNeedsDisplay方法:重新绘制，调用这个方法就会通知自定义的view重新绘制画面，调用`drawRect`
提示：当一个view从xib或storyboard创建出来时，会调用awakeFromNib方法

可以通过slider的value属性监听值得改变，当然也可以指定value的取值范围（这里设定为0 ~ 100）

//
//  newView.m
//  TestQuartz 2D
//
//  Created by taobaichi on 2017/3/23.
//  Copyright © 2017年 MaChao. All rights reserved.
//
#import "newView.h"
@interface newView ()
@property (nonatomic, assign)float imageY;
@end
@implementation newView
-(id)initWithCoder:(NSCoder *)aDecoder
{
    //请注意这里一定要先初始化父类的构造方法
    if (self = [super initWithCoder:aDecoder]) {
        NSLog(@"initWithCoder: ");
        //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
        //使用定时器，使用该定时器会出现卡顿现象
        //[NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:@selector(updateImage) userInfo:nil repeats:YES];
        //ACDisplayLink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
        CADisplayLink * display = [CADisplayLink displayLinkWithTarget:self selector:@selector(updateImage)];
        [display addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
    }
    return self;
}
-(void)updateImage
{
    //使用该方法重绘画面
    [self setNeedsDisplay];
}
-(void)awakeFromNib
{
    [super awakeFromNib];
    NSLog(@"awakeFromNib");
}
-(void)drawRect:(CGRect)rect
{
    //把图片绘制到view上
    //每次调用该方法对画面进行重绘，imageY的值就+5
    self.imageY += 5;
    //当雪花超出屏幕的时候，让图片从头开始降落
    if (self.imageY > rect.size.height) {
        self.imageY = 0;
    }
    UIImage * image = [UIImage imageNamed:@"snow"];
    [image drawAtPoint:CGPointMake(0, self.imageY)];
    UIImage * image2 = [UIImage imageNamed:@"me"];
    [image2 drawAtPoint:CGPointMake(80, self.imageY + 20)];
}
@end

-(void)awakeFromNib
-(id)initWithCoder:(NSCoder *)aDecoder

NS_CLASS_AVAILABLE_IOS(2_0) @interface UIView : UIResponder <NSCoding, UIAppearance, UIAppearanceContainer, UIDynamicItem, UITraitEnvironment, UICoordinateSpace, UIFocusItem, CALayerDelegate>

2017-03-23 18:24:28.560 TestQuartz 2D[9196:314708] initWithCoder: 
2017-03-23 18:24:28.561 TestQuartz 2D[9196:314708] awakeFromNib

[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，

CADisplayLink * display = [CADisplayLink displayLinkWithTarget:self selector:@selector(updateImage)];
        [display addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];