級別：★★☆☆☆
標籤：「iOS CIDetector」「CIQRCodeFeature」「識別相簿圖片」
作者： Xs·H
審校： QiShare團隊

接上篇 iOS 掃描二維碼/條形碼，本文補充介紹掃描相簿圖片上二維碼的實現方式。先看看QiQRCode中的示例效果：

iOS 8之後，可以結合CIDetector使用CIQRCodeFeature實現掃描相簿圖片上二維碼的功能。具體實現過程如下：

1、遵守協議

@interface QiCodeManager () <UIImagePickerControllerDelegate, UINavigationControllerDelegate>
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2、開啟相簿

- (void)presentPhotoLibraryWithRooter:(UIViewController *)rooter callback:(nonnull void (^)(NSString * _Nonnull))callback {
    _callback = callback;
    
    UIImagePickerController *imagePicker = [[UIImagePickerController alloc] init];
    imagePicker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
    // imagePicker.allowsEditing = YES;
    imagePicker.delegate = self;
    [rooter presentViewController:imagePicker animated:YES completion:nil];
}
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3、實現代理

// UIImagePickerControllerDelegate
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<UIImagePickerControllerInfoKey,id> *)info {
    
    UIImage *pickedImage = info[UIImagePickerControllerEditedImage] ?: info[UIImagePickerControllerOriginalImage];
    CIImage *detectImage = [CIImage imageWithData:UIImagePNGRepresentation(pickedImage)];
    
    CIDetector *detector = [CIDetector detectorOfType:CIDetectorTypeQRCode context:nil options:@{CIDetectorAccuracy: CIDetectorAccuracyLow}];
    CIQRCodeFeature *feature = (CIQRCodeFeature *)[detector featuresInImage:detectImage options:nil].firstObject;
    
    [picker dismissViewControllerAnimated:YES completion:^{
        if (feature.messageString) {
            [self handleCodeString:feature.messageString];
        }
    }];
}
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4、透傳給業務

- (void)handleCodeString:(NSString *)codeString {
    
    if (_autoStop) {
        [self stopScanning];
    }
    if (_callback) {
        _callback(codeString);
    }
}
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5、業務呼叫方式

// 建立“相簿”按鈕
UIBarButtonItem *photoItem = [[UIBarButtonItem alloc] initWithTitle:@"相簿" style:UIBarButtonItemStylePlain target:self action:@selector(photo:)];

self.navigationItem.rightBarButtonItem = photoItem;
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// 實現“相簿”按鈕方法
- (void)photo:(id)sender {
    
    __weak typeof(self) weakSelf = self;
    [_codeManager presentPhotoLibraryWithRooter:self callback:^(NSString * _Nonnull code) {
        [weakSelf performSegueWithIdentifier:@"showCodeGeneration" sender:code];
    }];
}
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上述程式碼中的核心步驟是第3步—實現代理。 我們通過UIImagePickerController拿到image後，使用CIDetector和CIQRCodeFeature讀取image上的資訊，最終得到的feature.messageString就是二維碼的字串資訊。

示例原始碼QiQRCode可從GitHub的QiShare開源庫中獲取。

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