When I declare static parameter in extension of class then I have to write @nonobjc before variable like:
@nonobjc static let test = "test"
and sometimes I have to write @objc before method, so what is use of @objc and @nonobjc in Swift.
Can anyone help me for this problem?
This is explained in the Apple's official documentation about Objective-C - Swift interoperability:
When you use the @objc(name) attribute on a Swift class, the class is made available in Objective-C without any namespacing. As a result, this attribute can also be useful when migrating an archivable Objective-C class to Swift. Because archived objects store the name of their class in the archive, you should use the @objc(name) attribute to specify the same name as your Objective-C class so that older archives can be unarchived by your new Swift class.
Conversely, Swift also provides the @nonobjc attribute, which makes a Swift declaration unavailable in Objective-C. You can use it to resolve circularity for bridging methods and to allow overloading of methods for classes imported by Objective-C. If an Objective-C method is overridden by a Swift method that cannot be represented in Objective-C, such as by specifying a parameter to be a variable, that method must be marked @nonobjc.
To summarize, use @objc when you want to expose a Swift attribute to Objective-C without a namespace . Use @nonobjc if you want to keep the attribute available and accessible only in Swift code.