1 When choosing Swift for a new class, it will appear whether to choose to generate 
a header file like this, and choose to generate, (used by the class that calls the Oc from the Swift class)
2 Declare the project name in the Oc class plus -Swift.h similar to
3 The method to enter the next interface is the same.
present to the Swift interface:
SwiftViewController *pushSwift = [[SwiftViewController alloc] init];
//[pushSwift leftReturnBtn];
[self presentViewController:pushSwift animated:YES completion:nil];
Swift interface returns to Oc interface
self.dismissViewControllerAnimated(true, completion: nil)
Next, let's talk about how to jump from the Swift interface to the OC interface
1 Declare the OC class to be entered in the project name-Bridging-Header.h class
As shown in the figure:
Next, you can call it in the Swift class
as follows:
let nextVc : ViewController!
nextVc = ViewController.init()
self.presentViewController(nextVc, animated: true, completion: nil)
Methods for declaring properties that can be called by other classes
var trantsStr : String = String()//"The declared attributes cannot be associated, only copy";
I will post the full project link in the comments