Wait for [NSAlert beginSheetModalForWindow:...];

Question

When I display an NSAlert like this, I get the response straight away:

int response;
NSAlert *alert = [NSAlert alertWithMessageText:... ...];
response = [alert runModal];

The problem is that this is application-modal and my application is document based. I display the alert in the current document's window by using sheets, like this:

int response;
NSAlert *alert = [NSAlert alertWithMessageText:... ...];
[alert beginSheetModalForWindow:aWindow
                  modalDelegate:self
                 didEndSelector:@selector(alertDidEnd:returnCode:contextInfo:)
                    contextInfo:&response];

//elsewhere
- (void) alertDidEnd:(NSAlert *) alert returnCode:(int) returnCode contextInfo:(int *) contextInfo
{
    *contextInfo = returnCode;
}

The only issue with this is that beginSheetModalForWindow: returns straight away so I cannot reliably ask the user a question and wait for a response. This wouldn't be a big deal if I could split the task into two areas but I can't.

I have a loop that processes about 40 different objects (that are in a tree). If one object fails, I want the alert to show and ask the user whether to continue or abort (continue processing at the current branch), but since my application is document based, the Apple Human Interface Guidelines dictate to use sheets when the alert is specific to a document.

How can I display the alert sheet and wait for a response?

Answer 1

Unfortunately, there is not much you can do here. You basically have to make a decision: re-architect your application so that it can process the object in an asynchronous manner or use the non-approved, deprecated architecture of presenting application modal alerts.

Without knowing any information about your actual design and how you processes these objects, it's hard to give any further information. Off the top of my head, though, a couple of thoughts might be:

• Process the objects in another thread that communicates with the main thread through some kind of run loop signal or queue. If the window's object tree gets interrupted, it signals the main thread that it was interrupted and waits on a signal from the main thread with information about what to do (continue this branch or abort). The main thread then presents the document-modal window and signals the process thread after the user chooses what to do.

This may be really over-complicated for what you need, however. In that case, my recommendation would be to just go with the deprecated usage, but it really depends on your user requirements.