文件所有者和nsapplication，appdelegate

Question

In the apple docs it states that nsapplication is the file owner of the main nib. Is this just set up by the template or must the first nib to be loaded, be loaded in this way?

Also, I read through the rest of the posts about the file owner and something still confuses me. Can IBoutlets only point to objects, if the Iboutlet is a property of the nibs file owner, and the object is found within that nib? Why does the nib even need to know the class of it's owner In addition to the object? What is enabled or disable by knowing or not knowing this?

One more, where does the appdelegate fit into this picture? Can you even change the app delegate?

Thanks :-)

Answer 1

Xcode's application template sets up MainMenu.xib to be loaded with NSApp as its owner. This is done by the NSApplicationMain function. NSApplicationMain looks up the NSMainNibFile key in the app's Info.plist file. If it finds that key, it uses the corresponding value as the name of the nib file to load. Xcode's app template sets NSMainNibFile to MainMenu .

It doesn't have to be done that way. You can change or delete the NSMainNibFile entry in Info.plist . You could even not use NSApplicationMain . Instead you could initialize NSApp yourself (by calling [NSApplication sharedApplication] ), and then create your user interface programmatically or by loading nibs, and then call [NSApp run] .

The nib loader can only connect outlets to objects in the nib it's loading, or to File's Owner, First Responder, or Application. The outlet itself doesn't have to be on File's Owner; it can be on any object in the nib.

When you set the class of File's owner, Interface Builder scans your source code to find the declaration of that class. That's how it knows which outlets and actions File's Owner should have.

The app delegate is generally the top-level controller for the application. It is notified when a variety of application-level events occur. Look at the NSApplicationDelegate Protocol Reference .

In Xcode's app template, the application delegate is an object in MainMenu.xib (you can have non-user-interface objects in a nib), which is wired to File Owner's delegate outlet. You can modify the class however you want. You can even delete the object from the nib entirely. But any serious app will need an app delegate.