根据字符串生成二维码图片

.h

//根据字符串生成指定大小的二维码
+ (UIImage *)createQRCodeImageWithMessage:(NSString *)message size:(CGFloat)size;

.m

#import <CoreImage/CoreImage.h>//用于生成二维码

//根据字符串生成指定大小的二维码
+ (UIImage *)createQRCodeImageWithMessage:(NSString *)message size:(CGFloat)size
{
    // 1.创建过滤器，这里的@"CIQRCodeGenerator"是固定的
    CIFilter *filter = [CIFilter filterWithName:@"CIQRCodeGenerator"];
    // 2.恢复默认设置
    [filter setDefaults];
    // 3. 给过滤器添加数据
    NSString *dataString = message;
    NSData *data = [dataString dataUsingEncoding:NSUTF8StringEncoding];
    // 注意，这里的value必须是NSData类型
    [filter setValue:data forKeyPath:@"inputMessage"];
    // 4. 生成二维码
    CIImage *outputImage = [filter outputImage];
    // 5. 输出二维码
    return [self creatNonInterpolatedUIImageFormCIImage:outputImage withSize:size];
}


/**
 根据CIImage生成指定大小的UIImage
 
 @param image CIImage
 @param size 图片宽度
 @return 生成的高清的UIImage
 */
+ (UIImage *)creatNonInterpolatedUIImageFormCIImage:(CIImage *)image withSize:(CGFloat)size
{
    CGRect extent = CGRectIntegral(image.extent);
    CGFloat scale = MIN(size/CGRectGetWidth(extent), size/CGRectGetHeight(extent));
    //1.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);
    //2.保存bitmap图片
    CGImageRef scaledImage = CGBitmapContextCreateImage(bitmapRef);
    CGContextRelease(bitmapRef);
    CGImageRelease(bitmapImage);
    return [UIImage imageWithCGImage:scaledImage];
}