Starting a Cocoa document-based application shows selection window first.

Question

This seems like it should be easy yet I must be missing something. I have a document-based application. I have also built a new XIB that has a NSTableView and three buttons on it that I intend to display a list of previous files. I wish this XIB to be displayed instead of the document window when the application first starts. Once the user selects an old file or hits the "New" button I wish to then go to the document window. This is very common and I've seen used quite often.

In my attempts to get this working I have modified the project-info.plist file and changed the Main NIB File Base Name from MyDocument to my Selection XIB name. This causes the application to display the Selection window instead of the MyDocument window. There seems to be no problem up to this point.

In my Selection window I have set up my table view and an array controller and a custom window controller just for this XIB. I have set the File's Owner to the new window controller and bound the window controller's window property to the window and the Window's delegate property to the File's Owner as well as the "Select", "Cancel", and "New" buttons. Nothing is bound to NSApplication. But the strange thing is when I run this application it seems to want to connect these controllers to NSApplication with the error (same for the other two buttons):

Could not connect the action selectButton: to target of class NSApplication

It also displays an error that NSApplication is not Key-Value compliant for the outlet that holds reference to my array. The Array Controller, Window, and buttons are not bound to NSApplication but to the new Window Controller. I would have expected that if there was any problem is would NOT mention NSApplication but rather the window controller to which the controllers are bound.

Anyone know what is happening here? Is this a Target-Action problem because I changed the "Main NIB File Base Name" from "Main Menu" to "Selection"? If I am not supposed to change this, then how can I get Cocoa allow me to display a selection screen before showing the document window?

Any help is greatly appreciated. Rob

Answer 1

The setting in IB for the class of the File's Owner of the nib is only advisory; it lets IB show only the outlets and actions that are provided by instances of that class. It does not enforce that the File's Owner will be an instance of that class, because the File's Owner is not part of the nib.

The File's Owner is the object that loads the nib. This necessarily means that it is outside of the nib, and nothing in the nib determines anything about it. In the case of the MainMenu nib, its File's Owner—the object that loads the MainMenu nib—is the NSApplication instance. So, everything you hooked up to the File's Owner in your MainMenu nib, you hooked up to the application object, even though you told IB that it wouldn't be the application.

That the application is the owner of the MainMenu nib—regardless of what you tell IB—is not the bug. The application is always the owner of the MainMenu nib. That is normal and correct; you cannot change it, should not attempt to change it, and don't need to change it.

The bug, in a nutshell, is that you are using one nib for two very different purposes.

You should let the MainMenu nib be that alone—containing only the MainMenu, your custom document controller (I'll get to that in a moment), and your app delegate—and move the previous-documents window into a separate nib, owned by the previous-documents window controller. In order to have a window controller be the owner of this nib, you need to have the window controller load it. You must do that in code—you cannot set that up in IB or in a plist.

In your application's delegate, instantiate and own the window controller. It sounds like you made a custom NSWindowController subclass, so you can override its init to have it send itself the initWithWindowNibName: message to load and own the nib. Then, just use alloc and init to create the window controller from the app delegate.

That will get rid of the console message, and ensure that the buttons are actually hooked up to the window controller (because they're hooked up to the File's Owner, which, with this change, will be the window controller).

Have your app delegate respond to applicationOpenUntitledFile: by sending the window controller the showWindow: message. This will make the previous-documents window appear any time the user ordinarily would have created a new document.

If you want to support the usual methods of creating documents (i.e., allow New Document to work), then implement applicationDidFinishLaunching: and applicationShouldHandleReopen:hasVisibleWindows:, not applicationOpenUntitledFile:. Make sure no documents are open, and show your window if that's the case.

You should also make a custom subclass of NSDocumentController and make your document controller an instance of that, and in that class, implement addDocument: and removeDocument: to re-show the previous-documents window when the last open document is closed, and hide it when a document is opened.