在视图控制器之间设置变量

var data: String = ""

let sourceViewController = self.navigationController?.viewControllers.first as? SourceViewController
let passedData = sourceViewController?.data

func setData(data: String) {
    // 处理传递的数据
}

let sourceViewController = self.navigationController?.viewControllers.first as? SourceViewController
sourceViewController?.setData(data: "传递的数据")

protocol DataDelegate: class {
    func passData(data: String)
}

weak var delegate: DataDelegate?

class TargetViewController: UIViewController, DataDelegate {
    // ...
    
    func passData(data: String) {
        // 处理传递的数据
    }
}

delegate?.passData(data: "传递的数据")

let data = "传递的数据"
NotificationCenter.default.post(name: NSNotification.Name("DataNotification"), object: data)

NotificationCenter.default.addObserver(forName: NSNotification.Name("DataNotification"), object: nil, queue: nil) { notification in
    if let data = notification.object as? String {
        // 处理传递的数据
    }
}