Next Previous

Presenting a Series of Sheets

Cocoa does not support the notion of cascading, or nested sheets. Per Apple Human Interface Guidelines, “when the user responds to a sheet, and another sheet for that document opens, the first sheet must close before the second one opens.”

Expanding on the sample in Using Alert Sheets, Figure 1 shows a third button added to the alert sheet displayed by deleteSelectedRows:. This button displays additional information to the user in the form of a custom sheet with additional information.

**Figure 1** Alert sheet with three buttons

Listing 1 shows the implementation of the method that creates this alert.

Listing 1 The deleteSelectedRows: method implemented to present a sheet with three buttons

- (BOOL)deleteSelectedRows: (NSWindow *)sender

    NSBeginAlertSheet(

        @"Do you really want to delete the selected information?",

                                // sheet message

        @"Delete",              // default button label

        @"More Info",           // allow user to check on the delete

        @"Cancel",              // other button label

        sender,                 // window sheet is attached to

        self,                   // we’ll be our own delegate

        @selector(sheetDidEndShouldDelete:returnCode:contextInfo:),

                                // did-end selector

        NULL,                   // no need for did-dismiss selector

        sender,                 // context info

        @"There is no undo for this operation.",

                                // additional text in sheet

        nil);                   // no parameters in message

// We don’t know if the rows should be deleted until the user responds,

// so don’t.

    return NO;

The did-end selector is updated to handle the user requesting the additional information. Should the user request the information, the alert sheet is closed prior to presenting the custom sheet:

- (void)sheetDidEndShouldClose: (NSWindow *)sheet

        returnCode: (NSInteger)returnCode

        contextInfo: (void *)contextInfo

    if (returnCode == NSAlertAlternateReturn) {

        [sheet close];

        [self showMoreInfo: (NSWindow *)contextInfo];

    if (returnCode == NSAlertDefaultReturn)

    // delete selected rows here

Creation and display of custom sheets is discussed in Using Custom Sheets.

In a separate nib, a window with the explanatory text and a Close button are defined. The Close button is set to perform the showMoreInfo: method when clicked. Implementation of the showMoreInfo: method would be the same as the showCustomSheet: method shown in Listing 1.

Listing 2 Displaying the custom sheet

- (void)showMoreInfo: (NSWindow *)window

// User has asked for more information about the delete. Display it.

    if (!moreInfoSheet)

        [NSBundle loadNibNamed: @"DeleteExpenseInfo" owner: self];

    [NSApp beginSheet: moreInfoSheet

            modalForWindow: window

            modalDelegate: nil

            didEndSelector: nil

            contextInfo: nil];

    [NSApp runModalForWindow: moreInfoSheet];

    // Sheet is up here.

    [NSApp endSheet: moreInfoSheet];

    [moreInfoSheet orderOut: self];

When the user clicks the Close button, the showMoreInfo: method is executed (this was specified in the nib file when creating the sheet), which stops the application’s modal display of the nested sheet.

Another example of a second sheet that appears as the result of the user clicking a button in a sheet is having a sheet with a progress indicator appear following a Save As dialog.

Next Previous