This Xcode project demonstrates the implementation of a custom SwiftUI alert which includes a text field.
While Apple does provide built in alert functionality within SwiftUI, it is insufficient in many cases as it explicitly disallows the inclusion of anything beyond static text. This is clearly a problem if you are trying to present an alert with a text field within your SwiftUI app.
Fortuantely we can work around this problem by creating a custom struct which conforms to the UIViewControllerRepresentable protocol. This struct will implement the makeUIViewController(context:) function to return a custom UIViewController that manages the presentation of a UIAlertController.
This extra level of indirection may seem unnecessary on the surface, however it is required as a UIViewController can only be presented by another UIViewController. Now the UIViewControllerRepresentable protocol handles the presentation of the managed UIViewController within our SwiftUI app, however UIAlertController does not allow for subclassing, and as a result we need a custom UIViewController to sit between the UIViewControllerRepresentable and the UIAlertController.
Please note that in this project I am not making use of the updateUIViewController(_:context:) function, as the user is prevented from interacting with any other part of the app while the alert is presented, and therefor no updates will be forthcoming.
Our custom UIViewController configures and presents a UIAlertController, which has the advantage over SwiftUI alerts in that it can handle the inclusion of any number of UITextField instances. Additionally, as we are now working with UIKit, we can make use of the UITextFieldDelegate protocol, to handle validation of the contents of the text field, and updating the SwiftUI binding for the managed text.
Finally we make our UIViewControllerRepresentable struct accessible in our SwiftUI app by extending View with an instance function which presents a ZStack, within which we conditionally render our custom alert, and unconditionally render the view to which the function is applied.