Objective-c – the need of File’s owner in xcode xib files? Can i do the same things without file’s owner

nibobjective cxcodexib

Why should I set File's Owner's Class Identity rather than the Class Identity of my custom object that is shown in the nib and make the connections from it? What happens if I set file's owner to nil?
To me everything works fine with nil file's owner so what is the deference in doing the connection from it?

Best Answer

A NIB represents an archived object graph. You can load it and that object graph will be reconstituted. The thing, you usually want/need the newly-loaded object graph to be hooked into the already-existing object graph of your program. You don't want it to be standing apart, disconnected from everything else.

There are a few ways that the newly-loaded object graph can get connected to the rest of the program's object graph. One way is the set of proxy objects available in a NIB. There's one for the application object. Another such proxy object is File's Owner. A proxy object is a thing which has a representation in the NIB but is not actually contained in the NIB. Unlike the other objects in the NIB, the objects represented by the proxies are not created when the NIB is loaded, they exist before the NIB is loaded. The proxies allow connections between these pre-existing objects and the objects in the NIB. That's how the new object graph from the NIB can be connected to the existing object graph of your program.

The MainMenu NIB is unusual. It is automatically loaded at application startup by Cocoa, which means there isn't (can't be, really) much in the way of pre-existing objects. That NIB also usually contains an instance of the app delegate, which is a kind of coordinating controller. Usually, though, other types of NIBs would not contain coordinating controllers. (They do contain mediating controllers, like NSArrayController, but that's different.) Rather, coordinating controllers are typically created in code and, often, they are responsible for loading NIBs.

For example, you would use an NSWindowController as the coordinating controller for a window. The window would be defined in a NIB. The window controller would be instantiated in code – whichever code decides that a window should be created – and it would load the NIB. It would be the File's Owner of the NIB, too. It would manage the window and the top-level objects of the NIB.

If you are setting the File's Owner to nil, then a) you probably are dealing with very simple NIBs at this point, and b) you may be leaking top-level objects from the NIBs that you load.

Related Solutions

Ios – How to load custom UITableViewCells from Xib files

The right solution is this:

- (void)viewDidLoad
{
    [super viewDidLoad];
    UINib *nib = [UINib nibWithNibName:@"ItemCell" bundle:nil];
    [[self tableView] registerNib:nib forCellReuseIdentifier:@"ItemCell"];
}

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Create an instance of ItemCell
    PointsItemCell *cell = [tableView dequeueReusableCellWithIdentifier:@"ItemCell"];

    return cell;
}

Objective-c – How does loadNibNamed

You have a basic understanding of what is required, though you should also consider memory management (which is slightly different for iPhone versus Mac). To really understand what is going on with this method, you should read the Nib Files section of the Resources Programming Guide. It covers the actual methods used to make the connections (which can be important), and the retain counts that various objects will have when it is done. Again, these are all slightly different between Mac and iPhone. iPhone has generally improved the consistency of how nib objects are handled.

For good measure, I always recommend that people read Memory Management of Nib Objects from the Memory Management Programming Guide. It's critical reading whether you use the lower-level methods or not.

Best Answer

Related Solutions

Ios – How to load custom UITableViewCells from Xib files

Objective-c – How does loadNibNamed

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