Occasionally, you will want to warn the user about something by presenting an alert. To do this, you use the NSAlert class. NSAlert saves you the work of designing a custom user interface for a simple and common user interaction, while also providing the user with a consistent experience.
Figure 15.1 shows a basic modal alert:
Figure 15.1 A modal alert
Here is the code used to create and present that alert:
let alert = NSAlert() alert.messageText = "Alert message." alert.informativeText = "A more ...