Sheets implement window modal (as opposed to application modal) dialogs that are attached to the window. Thus, when a dialog pops up asking for attention, it blocks interaction only with that particular window, not the entire application. When a sheet is opened or closed, it appears to slide out of the title bar. Because the sheet is attached to another window, such as a document window, the user never loses track of what dialog belongs with which window. Figure 3-8 shows an example of a sheet.

A TextEdit sheet asking if you want to save changes
Figure 3-8. A TextEdit sheet asking if you want to save changes

The Application Kit defines a number of convenient functions for displaying standard alert and message sheets, including NSBeginAlertSheet, NSBegin-InformationalAlertSheet, and NSBeginCriticalAlertSheet. Each function takes the same parameters; they differ only in the icon displayed on the left of the sheet. The function prototype for NSBeginAlertSheet is the following:

void NSBeginAlertSheet(NSString *title, 
                       NSString *defaultButton, 
                       NSString *alternateButton, 
                       NSString *otherButton,
                       NSWindow *docWindow, 
                       id modalDelegate, 
                       SEL didEndSelector, 
                       SEL didDismissSelector, 
                       void *contextInfo, 
                       NSString *msg, ...)

Table 3-2 describes each parameter.

Table 3-2. Parameters for alert sheet functions




The title of the sheet, displayed at the top of the sheet in bold-faced font.


The title of the ...

Get Cocoa in a Nutshell now with the O’Reilly learning platform.

O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.