Question

What I want to do is a navigation bar with a image on it. I have a tab controller on my main view, and inside each tab I have a UINavigationController. From inside the UIViewController that my tab/navigationController calls, I could set the titleView without much problem, doing this inside the viewDidLoad method:

self.navigationItem.titleView = [[[UIImageView alloc] initWithImage:[UIImage imageNamed:@"mylogo.png"]] autorelease];

But, I want to replace all titles in my navigationBar for this view, and it seems ugly to repeat this everywhere. So I did this on the delegate (after linking all the Outlet stuff)

self.tabOneNavController.navigationBar.topItem.titleView = [[[UIImageView alloc] initWithImage:[UIImage imageNamed:@"mylogo.png"]] autorelease];

Again, it worked! ok, I’m almost getting there.
But the point is, I’ve 5 tabs and all of them have navigationControllers inside. I reduced the code repetition from every internal view to only 5 times, but it still. It requires that I do that for the NavController of each tab.

Then I tried to extend the UINavigationBar to create my own, where I could set this in the initializer, and use it in the interface builder as the object class. But it doesn’t seem to work. Here is what I did:

@implementation MyNavigationBar

- (id)init {
    self = [super self];

    self.tintColor = [UIColor greenColor];
    self.topItem.title = @"testing please work";

    return self;
}

@end

in the interface file MyNavigationBar inherits from UINavigationBar. But this didn’t work. Should I overwrite other method? which one? is this a good practice?
I’m not even sure if I should add one navigationBar for each tab, as I said, I have tabs and I want to have a navigation bar / navigate inside them. By now, after a near death experience trying to figure out how the interface builder / outlets and classes work, the code is working, I just would like to make unglify it.

Thank you!

Answer 1

The problem of repeating code which you describe has an elegant solution. Objective-C supports something called a “category”, which allows you to add methods to a class. A common use for this is to customize navigation and tab bars. In Xcode 4, you would do something like this to add a category on UINavigationBar:

Hit Command+N or open the “New File” dialog. Next, choose “Objective-C category” from the Cocoa Touch menu:

Click Next and you will be prompted to enter the name of the class that you would like to add methods to as a category. It should look something like this:

Then, you should end up with a save file dialog. A quick note about convention here. Convention is to name a category after the original class, the plus sign, and then a description of what you’re adding. Here’s what yours might look like:

Once you save your file, you will need get something like this:

Look at that beauty. You can now override the default drawing/init methods as well as extend the functionality of the navbar.

I’d suggest looking into the init and drawRect methods, although I don’t remember which ones people use. Also, please note that while under NDA, this may change in iOS 5, so just be prepared for that possibility.