Swift中的Objective-C块问题

Question

I'm struggling to access a block from an Objective C file I found on Github and imported into my Swift project.

Here is the Objective C block declaration in the .m file I imported:

-(void)capture:(void (^)(LLSimpleCamera *camera, UIImage *image, NSDictionary *metadata, NSError *error))onCapture exactSeenImage:(BOOL)exactSeenImage;

Here is the block being called in the original Objective C Github sample project:

[self.camera capture:^(LLSimpleCamera *camera, UIImage *image, NSDictionary *metadata, NSError *error) {
        if(!error) {

            [camera stop];

            ImageViewController *imageVC = [[ImageViewController alloc] initWithImage:image];
            [self presentViewController:imageVC animated:NO completion:nil];
        }
    } exactSeenImage:YES];

My Swift translation (done with autocomplete):

self.camera?.capture({ (camera:LLSimpleCamera!, image:UIImage!, metadata:NSDictionary!, error:NSError!) -> Void in
        if error == nil {

            camera.stop()

            let imageVC = ImageCapturedViewController()
            self.presentViewController(imageVC, animated: NO, completion: nil)
        }
    }, exactSeenImage: true)

Xcode shows these two errors:

'_??' is not convertible to 'Void'

'error type?' is not convertible to 'Void'

Answer 1

It is because if the block does not have a return statement, the compiler uses the result of the last statement as the return value

Adding a return () as the last expression to the block fixes the problem

Answer 2

this should do the trick :)

var aa:LLSimpleCamera = LLSimpleCamera()

swift have some converted NSDictionary to [NSObject:AnyObject], so the follow code can do the trick:

aa.capture({ (camera:LLSimpleCamera!, image:UIImage!, obj:[NSObject:AnyObject]!, error:NSError!) -> Void in

}, exactSeenImage: true)

also, in swift, you can also omit the type of variable as follow:

aa.capture({ (camera, image, dict, error) -> Void in

}, exactSeenImage: true)