How to wait for completion of sheet after invoking beginSheet:completionHandler: - xcode

Question

My code results in the sheet appearing and functioning properly but the invoker receives control back (as per Apple definition) before the sheet ends itself with endSheet.
How can I get the invoker to wait for the return from the end of the sheet processing, so the resultValue is updated.
Invoker:
[self.window beginSheet: sheetController.window
completionHandler:^(NSModalResponse returnCode) {
resultValue = returnCode;
}
];
...
Sheet:
...
[self.window.sheetParent endSheet:self.window returnCode:false];

Answer 1

I thought the new beginSheet: was meant to do the whole linkage, but that isn't the case. All it does is put up the sheet window. The passage and return of control remains as it was. So the following code works:
Invoker:
[self.window beginSheet: sheetController.window
completionHandler:nil
];
returnCodeValue = [NSApp runModalForWindow:sheetController.window];
// Sheet is active until stopModalWithCode issued.
[NSApp endSheet: sheetController.window];
[sheetController.window orderOut:self];
Sheet:
[NSApp stopModalWithCode:whatever];

Answer 2

Looks like you're most of the way there. The return code should be type NSModalResponse (ObjC) or NSApplication.ModalResponse (Swift). I've also found that you need to uncheck 'Visible at Launch'. Otherwise it won't launch as modal.

Answer 3

There was an NSAlert category from way back that used the older (deprecated) methods. I’m not all that great with Objective-C (and worse with Swift), but I’ve been using an updated equivalent for a while in one of my RubyMotion projects. Hopefully I’ve come close with reversing the code conversions, but basically it fires up a modal event loop with runModalForWindow: after calling beginSheetModalForWindow;, and the completionHandler exits with stopModalWithCode:
// NSAlert+SynchronousSheet.h
#import <Cocoa/Cocoa.h>
/* A category to allow NSAlerts to be run synchronously as sheets. */
#interface NSAlert (SynchronousSheet)
/* Runs the receiver modally as a sheet attached to the specified window.
Returns a value positionally identifying the button clicked */
-(NSInteger) runModalSheetForWindow:(NSWindow *)aWindow;
/* Same as above, but runs the receiver modally as a sheet attached to the
main window. */
-(NSInteger) runModalSheet;
#end
// NSAlert+SynchronousSheet.m
#import "NSAlert+SynchronousSheet.h"
#implementation NSAlert (SynchronousSheet)
-(NSInteger) runModalSheetForWindow:(NSWindow *)theWindow {
// Bring up the sheet and wait until it completes.
[self beginSheetModalForWindow:theWindow
completionHandler:^(NSModalResponse returnCode) {
// Get the button pressed - see NSAlert's Button Return Values.
[NSApp stopModalWithCode:returnCode];
}];
[NSApp runModalForWindow:self.window] // fire up the event loop
}
-(NSInteger) runModalSheet {
return [self runModalSheetForWindow:[NSApp mainWindow]];
}
#end
The application will wait for the alert to finish before continuing, with the modal response passed in the result. I don’t know about blocking a couple of thousand lines of code, but I found it useful when chaining two or three sheets, such as an alert before an open/save panel.