控制台的报错百度无果，应该是控件的上下文错误

Jul  1 10:47:47  zuoye[735] <Error>: CGContextSetLineWidth: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

Jul  1 10:47:47  zuoye[735] <Error>: CGContextSetStrokeColorWithColor: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

Jul  1 10:47:47  zuoye[735] <Error>: CGContextMoveToPoint: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

Jul  1 10:47:47  zuoye[735] <Error>: CGContextAddLineToPoint: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

Jul  1 10:47:47  zuoye[735] <Error>: CGContextDrawPath: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

代码如下：

//

//  ChartViewController.m

//  zuoye

//

//  Created by 刘悦 on 2017/6/29.

//  Copyright © 2017年 BNR. All rights reserved.

//

#import "ChartViewController.h"

#import "Quartz2d.h"

@interface ChartViewController ()

@end

@implementation ChartViewController

- (void)viewDidLoad {

    [super viewDidLoad];

    // Do any additional setup after loading the view.

    self.view.backgroundColor = [UIColor whiteColor];

    UIButton *buttonReturn = [[UIButton alloc]initWithFrame:CGRectMake(self.view.frame.size.width/2-50, self.view.frame.size.height-60, 100, 50)];

    buttonReturn.backgroundColor = [UIColor redColor];

    [buttonReturn setTitle:@"返回" forState:UIControlStateNormal];

    [buttonReturn addTarget:self action:@selector(jumpFirst) forControlEvents:UIControlEventTouchDown];

    [self.view addSubview:buttonReturn];

    //绘图的区域

    UIView *viewblue = [[UIView alloc]initWithFrame:CGRectMake(0, 0, 414, 600)];

    viewblue.backgroundColor = [UIColor blueColor];

    [self.view addSubview:viewblue];

    Quartz2d *quartzView = [[Quartz2d alloc]initWithFrame:viewblue.frame];

    [self.view addSubview:quartzView];

    [quartzView drawXY];

    [quartzView setNeedsDisplay];

}

- (void)jumpFirst{

    [self dismissViewControllerAnimated:YES completion:nil];

}

- (void)didReceiveMemoryWarning {

    [super didReceiveMemoryWarning];

    // Dispose of any resources that can be recreated.

}

/*

#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {

    // Get the new view controller using [segue destinationViewController].

    // Pass the selected object to the new view controller.

}

*/

@end

quartz2d的代码如下

//

//  Quartz2d.m

//  zuoye

//

//  Created by 刘悦 on 2017/6/29.

//  Copyright © 2017年 BNR. All rights reserved.

//

#import "Quartz2d.h"

@implementation Quartz2d

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

// An empty implementation adversely affects performance during animation.

- (void)drawRect:(CGRect)rect {

    // Drawing code

    [self drawXY];

}

- (void)drawXY{

    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextSetLineWidth(context, 1.0);

    [[UIColor greenColor]setStroke];

    CGContextMoveToPoint(context, 50, 400);

    CGContextAddLineToPoint(context, 414, 400);

    CGContextStrokePath(context);

}

@end