二維碼和URL的相互轉換

用URL生成二維碼，也可以通過二維碼獲取URL（可用於長按識別二維碼）

#pragma mark - 二維碼轉換
// url生成二維碼
+ (UIImage *)getQRCodeWithUrlString:(NSString *)urlStr size:(CGFloat)size
{
    // 1.創建過濾器
    CIFilter *filter = [CIFilter filterWithName:@"CIQRCodeGenerator"];
    // 2.恢復默認
    [filter setDefaults];
    // 3.給過濾器添加數據(正則表達式/賬號和密碼)
    NSData *data = [urlStr dataUsingEncoding:NSUTF8StringEncoding];
    [filter setValue:data forKeyPath:@"inputMessage"];
    // 4.獲取輸出的二維碼
    CIImage *outputImage = [filter outputImage];
    // 5.將CIImage轉換成UIImage，並放大顯示
    CGRect extent = CGRectIntegral(outputImage.extent);
    CGFloat scale = MIN(size/CGRectGetWidth(extent), size/CGRectGetHeight(extent));
    // 5.1.創建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:outputImage fromRect:extent];
    CGContextSetInterpolationQuality(bitmapRef, kCGInterpolationNone);
    CGContextScaleCTM(bitmapRef, scale, scale);
    CGContextDrawImage(bitmapRef, extent, bitmapImage);
    // 5.2.保存bitmap到圖片
    CGImageRef scaledImage = CGBitmapContextCreateImage(bitmapRef);
    CGContextRelease(bitmapRef);
    CGImageRelease(bitmapImage);
    return [UIImage imageWithCGImage:scaledImage];
}

/**
 *  從照片中直接識別二維碼
 *  @param myQRCode    二維碼包含的內容
 */
- (void)readQRCodeFromImageWithmyQRCode:(void(^)(NSString *qrString,NSError *error))myQRCode
{
    if (!self)
    {
        myQRCode(nil,[NSError errorWithDomain:@"未傳入圖片" code:0 userInfo:nil]);
        return;
    }
    
    CIContext *context = [CIContext contextWithOptions:nil];
    CIDetector *detector = [CIDetector detectorOfType:CIDetectorTypeQRCode context:context options:@{CIDetectorAccuracy:CIDetectorAccuracyHigh}];
    CIImage *image = [CIImage imageWithCGImage:self.CGImage];
    NSArray *features = [detector featuresInImage:image];
    if (features.count)
    {
        CIQRCodeFeature *feature = [features firstObject];
        
        NSString *result = feature.messageString;
        
        myQRCode(result,nil);
    }
    else
    {
        myQRCode(nil,[NSError errorWithDomain:@"未能識別出二維碼" code:0 userInfo:nil]);
        return;
    }
}