重绘机制drawRect

AppDelegate.h文件

#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

@end

AppDelegate.m文件

#import "AppDelegate.h"

#import "MainViewDrawRect.h"

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

{

    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

    // Override point for customization after application launch.

    self.window.backgroundColor = [UIColor whiteColor];

    

    

    MainViewDrawRect *mainView = [[MainViewDrawRect alloc] initWithFrame:CGRectMake(0, 20, 320, 320)];

    [self.window addSubview:mainView];

    

    [self.window makeKeyAndVisible];

    return YES;

}

MainViewDrawRect.h文件：

#import <UIKit/UIKit.h>

@interface MainViewDrawRect : UIView

@end

MainViewDrawRect.m文件：

#import "MainViewDrawRect.h"

@implementation MainViewDrawRect

- (id)initWithFrame:(CGRect)frame

{

    self = [super initWithFrame:frame];

    if (self) {

        // Initialization code

        self.backgroundColor = [UIColor cyanColor];

    }

    return self;

}

// Only override drawRect: if you perform custom drawing.

// An empty implementation adversely affects performance during animation.

- (void)drawRect:(CGRect)rect

{

    // Drawing code

    

    //获得处理的上下文

    CGContextRef context = UIGraphicsGetCurrentContext();

    //设置线条样式

    CGContextSetLineCap(context, kCGLineCapSquare);

    //设置线条粗细宽度

    CGContextSetLineWidth(context, 1.0);

    

    //设置颜色

    CGContextSetRGBStrokeColor(context, 1.0, 0.0, 0.0, 1.0);

    //开始一个起始路径

    CGContextBeginPath(context);

    //起始点设置为(0,0):注意这是上下文对应区域中的相对坐标，

    CGContextMoveToPoint(context, 0, 0);

    //设置下一个坐标点

    CGContextAddLineToPoint(context, 100, 100);

    //设置下一个坐标点

    CGContextAddLineToPoint(context, 0, 150);

    //设置下一个坐标点

    CGContextAddLineToPoint(context, 50, 180);

    //连接上面定义的坐标点

    CGContextStrokePath(context);

}

@end

运行结果：