IOS调用函数给出错误

Question

我正在使用MTBBarcodeScanner interface实现条形码扫描仪应用程序。
我需要在代码中获取扫描仪的静态图像，因此我尝试调用该函数:

- (void)captureStillImage:(void (^)(UIImage *image, NSError *error))captureBlock {

    if ([self isCapturingStillImage]) {
        if (captureBlock) {
            NSError *error = [NSError errorWithDomain:kErrorDomain
                                                 code:kErrorCodeStillImageCaptureInProgress
                                             userInfo:@{NSLocalizedDescriptionKey : @"Still image capture is already in progress. Check with isCapturingStillImage"}];
            captureBlock(nil, error);
        }
        return;
    }

    AVCaptureConnection *stillConnection = [self.stillImageOutput connectionWithMediaType:AVMediaTypeVideo];

    if (stillConnection == nil) {
        if (captureBlock) {
            NSError *error = [NSError errorWithDomain:kErrorDomain
                                                 code:kErrorCodeSessionIsClosed
                                             userInfo:@{NSLocalizedDescriptionKey : @"AVCaptureConnection is closed"}];
            captureBlock(nil, error);
        }
        return;
    }

    [self.stillImageOutput captureStillImageAsynchronouslyFromConnection:stillConnection
                                                       completionHandler:^(CMSampleBufferRef imageDataSampleBuffer, NSError *error) {
                                                           if (error) {
                                                               captureBlock(nil, error);
                                                               return;
                                                           }

                                                           NSData *jpegData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer];
                                                           UIImage *image = [UIImage imageWithData:jpegData];
                                                           if (captureBlock) {
                                                               captureBlock(image, nil);
                                                           }

                                                       }];

}

从我的 View Controller 中，我调用这个函数，如下所示:

 UIImage *img;
 NSError *e;
 [_scanner captureStillImage:img :e];

但给我错误:

No visible @interface for 'MTBBarcodeScanner' declares the selector 'captureStillImage::

如何将此函数称为我的 UIViewcontroller 子类？

Answer 1

您的 block 的语法不正确。应该是这样的:

[_scanner captureStillImage:^(UIImage *image, NSError *error) {

}];

此外，这是一个回调函数，您不应该向其中提供参数，这些参数是从它返回的。

如果您希望在回调之外使用代表回调函数返回值的变量，则需要声明 __block 变量。

__block UIImage* img;
__block NSError* e;

[_scanner captureStillImage:^(UIImage *image, NSError *error) {
     img = image;
     e = error;
}];