生成二维码的两种方式：一种是利用第三方生成，一种是自己自定义生成。
1.用的第三方是：QRCode, 使用前先下载第三方。

关于第三方和自定义，直接上代码：

#import "ViewController.h"
#import "WGJViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    UIButton *btn = [UIButton buttonWithType:(UIButtonTypeCustom)];
    [btn addTarget:self action:@selector(clickPush) forControlEvents:(UIControlEventTouchUpInside)];
    [btn setImage:[UIImage imageNamed:@"test01"] forState:(UIControlStateNormal)];
    btn.backgroundColor = [UIColor redColor];
    //    btn.enabled = NO;
    //    btn.userInteractionEnabled = NO;
    btn.frame = CGRectMake(100, 100, 100, 40);
    [self.view addSubview:btn];

}

- (void)clickPush
{
    WGJViewController *tee = [[WGJViewController alloc] init];
    [self.navigationController pushViewController:tee animated:YES];
}
@end

#import "WGJViewController.h"
#import "UIImage+MDQRCode.h"
#import "UIImageView+WProductCode.h"

@interface WGJViewController ()

@property (nonatomic, strong) UIImageView *imgView;
@end

@implementation WGJViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.view.backgroundColor = [UIColor whiteColor];
    
    // Do any additional setup after loading the view.
    UIView *vWhiteView = [[UIView alloc] initWithFrame:CGRectMake(100 , 100,  136 , 250)];
    vWhiteView.layer.cornerRadius = 2;
    vWhiteView.backgroundColor = [UIColor whiteColor];
    [self.view addSubview:vWhiteView];
    
    //二维码---1----
    UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(18 ,18 , CGRectGetWidth(vWhiteView.frame)-36 ,CGRectGetWidth(vWhiteView.frame)-36)];
    
    [vWhiteView addSubview:imageView];
    imageView.backgroundColor = [UIColor whiteColor];
    imageView.image = [UIImage mdQRCodeForString:[NSString stringWithFormat:@"%@",@"12312"] size:imageView.bounds.size.width fillColor:[UIColor blackColor]];
    
    //二维码---2------
    self.imgView=[[UIImageView alloc]initWithFrame:CGRectMake(100, 350, 200, 200)];
    
    [UIImageView productCodeWithImageView:self.imgView codeStr:@"12121"];
    
    [self.view addSubview:_imgView];
    
//    [self erweimaWithSize:_imgView.bounds.size.width codeStr:@"1212"];
    
}
@end

自定义的分类：

\#import <UIKit/UIKit.h>

@interface UIImageView (WProductCode)
//二维码
+ (void)productCodeWithImageView:(UIImageView *)imageV codeStr:(NSString *)codeStr;
@end


\#import "UIImageView+WProductCode.h"

@implementation UIImageView (WProductCode)
//二维码
+ (void)productCodeWithImageView:(UIImageView *)imageV codeStr:(NSString *)codeStr

{
    
    //二维码滤镜
    
    CIFilter *filter=[CIFilter filterWithName:@"CIQRCodeGenerator"];
    
    //恢复滤镜的默认属性
    
    [filter setDefaults];
    
    //将字符串转换成NSData
    
    NSData *data=[codeStr dataUsingEncoding:NSUTF8StringEncoding];
    
    //通过KVO设置滤镜inputmessage数据
    
    [filter setValue:data forKey:@"inputMessage"];
    
    //获得滤镜输出的图像
    
    CIImage *outputImage=[filter outputImage];
    
    //将CIImage转换成UIImage,并放大显示
    
    imageV.image=[self createNonInterpolatedUIImageFormCIImage:outputImage withSize:imageV.bounds.size.width];
    
    
    //如果还想加上阴影，就在ImageView的Layer上使用下面代码添加阴影
    
    imageV.layer.shadowOffset=CGSizeMake(0, 0.5);//设置阴影的偏移量
    
    imageV.layer.shadowRadius=1;//设置阴影的半径
    
    imageV.layer.shadowColor=[UIColor blackColor].CGColor;//设置阴影的颜色为黑色
    
    imageV.layer.shadowOpacity=0.3;
    
    
    
}

+ (UIImage *)createNonInterpolatedUIImageFormCIImage:(CIImage *)image withSize:(CGFloat) size {
    
    CGRect extent = CGRectIntegral(image.extent);
    
    CGFloat scale = MIN(size/CGRectGetWidth(extent), size/CGRectGetHeight(extent));
    
    // 创建bitmap;
    
    size_t width = CGRectGetWidth(extent) * scale;
    
    size_t height = CGRectGetHeight(extent) * scale;
    
    CGColorSpaceRef cs = CGColorSpaceCreateDeviceGray();
    
    CGContextRef bitmapRef = CGBitmapContextCreate(nil, width, height, 8, 0, cs, (CGBitmapInfo)kCGImageAlphaNone);
    
    CIContext *context = [CIContext contextWithOptions:nil];
    
    CGImageRef bitmapImage = [context createCGImage:image fromRect:extent];
    
    CGContextSetInterpolationQuality(bitmapRef, kCGInterpolationNone);
    
    CGContextScaleCTM(bitmapRef, scale, scale);
    
    CGContextDrawImage(bitmapRef, extent, bitmapImage);
    
    // 保存bitmap到图片
    
    CGImageRef scaledImage = CGBitmapContextCreateImage(bitmapRef);
    
    CGContextRelease(bitmapRef);
    
    CGImageRelease(bitmapImage);
    
    return [UIImage imageWithCGImage:scaledImage];
    
}

@end