I am trying use an Objective-C library (MWPhotoBrowser) in my Swift app. My Swift class conforms to MWPhotoBrowserDelegate protocol by implementing required methods. However, I keep getting the following error:
"Type 'PhotoLibrary' does not conform to protocol 'MWPhotoBrowserDelegate'"
Cocoa protocols seem to work fine. Has anyone encountered this issue before?
Here is the sample code:
class PhotoLibrary: UIImageView, MWPhotoBrowserDelegate {
init() {
super.init(frame: CGRectZero)
}
func numberOfPhotosInPhotoBrowser(photoBrowser: MWPhotoBrowser!) -> Int {
return 0
}
func photoBrowser(photoBrowser: MWPhotoBrowser!, photoAtIndex index: Int) -> MWPhoto! {
return nil
}
}
Protocol definition is as follows:
@protocol MWPhotoBrowserDelegate <NSObject>
- (NSInteger)numberOfPhotosInPhotoBrowser:(MWPhotoBrowser *)photoBrowser;
- (id <MWPhoto>)photoBrowser:(MWPhotoBrowser *)photoBrowser photoAtIndex:(NSInteger)index;
@optional
- (id <MWPhoto>)photoBrowser:(MWPhotoBrowser *)photoBrowser thumbPhotoAtIndex:(NSUInteger)index;
- (MWCaptionView *)photoBrowser:(MWPhotoBrowser *)photoBrowser captionViewForPhotoAtIndex:(NSUInteger)index;
- (NSString *)photoBrowser:(MWPhotoBrowser *)photoBrowser titleForPhotoAtIndex:(NSUInteger)index;
- (void)photoBrowser:(MWPhotoBrowser *)photoBrowser didDisplayPhotoAtIndex:(NSUInteger)index;
- (void)photoBrowser:(MWPhotoBrowser *)photoBrowser actionButtonPressedForPhotoAtIndex:(NSUInteger)index;
- (BOOL)photoBrowser:(MWPhotoBrowser *)photoBrowser isPhotoSelectedAtIndex:(NSUInteger)index;
- (void)photoBrowser:(MWPhotoBrowser *)photoBrowser photoAtIndex:(NSUInteger)index selectedChanged:(BOOL)selected;
- (void)photoBrowserDidFinishModalPresentation:(MWPhotoBrowser *)photoBrowser;
@end
In order to use Swift code inside Objective-C one must scrifice some Swift features and write a wrapper around original Swift code that won't use non-compatible features (like structs, generics, enum associated values, protocol extensions etc.). All wrapper classes must inherit NSObject .
Objective-C uses angle brackets to indicate conformance to a protocol. This example declares a weak property for a generic object pointer that conforms to the XYZPieChartViewDataSource protocol.
In Objective-C, protocols are declared with the “@protocol” keyword. Below is an example of declaring a protocol containing one required method. In Swift, the syntax is a little different but the idea is the same. In Objective-C, you add the protocol name in angle brackets beside the class interface declaration.
Unfortunately, it's not possible to subclass a Swift class in Objective-C. Straight from the docs: You cannot subclass a Swift class in Objective-C. See Apple's guide on interoperability for more details on what you can and cannot access with Objective-C.
I got MWPhotoBrowser working in my Swift app with the following code without needing to change the MWPhotoBrowser codebase.
func showFullScreenImage(image:UIImage) {
let photo:MWPhoto = MWPhoto(image:image)
self.photos = [photo]
let browser:MWPhotoBrowser = MWPhotoBrowser(delegate: self)
browser.displayActionButton = true
browser.displayNavArrows = false
browser.displaySelectionButtons = false
browser.zoomPhotosToFill = true
browser.alwaysShowControls = false
browser.enableGrid = false
browser.startOnGrid = false
browser.enableSwipeToDismiss = true
browser.setCurrentPhotoIndex(0)
self.navigationController?.pushViewController(browser, animated: true)
}
func numberOfPhotosInPhotoBrowser(photoBrowser: MWPhotoBrowser!) -> UInt {
return UInt(self.photos.count)
}
func photoBrowser(photoBrowser: MWPhotoBrowser!, photoAtIndex index: UInt) -> MWPhotoProtocol! {
if Int(index) < self.photos.count {
return photos.objectAtIndex(Int(index)) as! MWPhoto
}
return nil
}
func photoBrowserDidFinishModalPresentation(photoBrowser:MWPhotoBrowser) {
self.dismissViewControllerAnimated(true, completion:nil)
}
I set photos as a class var, e.g. private var photos = []
, and added the following imports in my app's Bridging-Header.h file:
#import <MWPhotoBrowser/MWPhoto.h>
#import <MWPhotoBrowser/MWPhotoBrowser.h>
I got most of the above code from https://github.com/mwaterfall/MWPhotoBrowser/issues/325#issuecomment-64781477.
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