Xamarin WatchOS: Error updating Xcode Project

Xamarin Support team says they don’t support “WatchOS storyboards in the VS Designer, with XCode 11 installed”, the only option to open storyboard is with Xcode Interface Builder from VS.

Now the problem I faced was while opening the storyboard for WatchOS with Xcode Interface Builder, I get the error “Error updating Xcode Project”.

Further looking into the log from VS->Help->Open Log Directory, I found the log as below:

ERROR [2019–12–17 13:32:01Z]: Error updating Xcode project
MonoDevelop.MacDev.ObjCIntegration.ObjectiveCGenerationException: Could not generate Objective-C code for action ‘DidChange’ in class ‘WatchTest.WatchKitExtension.CustomDatePicker’ as the type ‘System.nint’of its parameter ‘sender’ could not be resolved to Objective-C

The problem was with System.nint sender parameter in DidChange method.

[Action (“DidChange:”)]
[GeneratedCode (“iOS Designer”, “1.0”)]
partial void DidChange (System.nint sender);

So, I changed it to

[Action (“DidChange:”)]
[GeneratedCode (“iOS Designer”, “1.0”)]
partial void DidChange (NSObject sender);

Now the problem was solved and I was able to open storyboard in Xcode Interface Builder from VS.

As mentioned above, storyboard for WatchOS are not supported in VS designer, we can use Xcode to manually add Outlets and Actions as described in this link.