Loading UIView from a nib file without guesswork

问题:

Ok, here's another question.

I am creating a UIView called ProgressView that is a semi-transparent view with an activity indicator and a progress bar.

I want to be able to use this view throughout different view controllers in my app, when required.

I know of 3 different ways of doing this (but I am only interested in one):

1) Create the entire view programatically, instantiate and configure as required. No worries I get that one.

2) Create the UIView in interface builder, add the required objects and load it using a method like the below. Problem with this is that we are basically guessing that the view is the objectAtIndex:0 because nowhere in the documentation I found a reference to the order of the elements returned from the [[NSBundle mainBundle] loadNibName: function.

NSArray *nibContents = [[NSBundle mainBundle] loadNibNamed:@"yournib" 
                                                 owner:self 
                                               options:nil];
UIView *myView = [nibContents objectAtIndex:0];
myView.frame = CGRectMake(0,0,300,400); //or whatever coordinates you need
[scrollview addSubview:myView];

3) Subclass UIViewController and let it manage the view as per normal. In this case I would never be actually pushing the view controller onto the stack, but only its main view:

ProgressViewController *vc = [[ProgressViewController alloc] initWithNibName:@"ProgressView" bundle:nil];
[vc.view setCenter:CGPointMake(self.view.center.x, self.view.center.y)];
[self.view addSubview:vc.view];
[vc release];

As far as I can tell, #3 is the the correct way of doing this (apart from programatically) but I am not entirely sure if it is safe to release the ProgressView's view controller whilst another controller's view is retaining its main view (gut feel says it is going to leak?)?

What do I do in terms of memory management in this case, where and when should I release the ProgressView's view controller?

Thanks in advance for your thoughts.

Cheers,

Rog

回答1:

I think that your solution #3 adds unnecessary complexity by introducing a UIViewController instance just as a container for your ProgressView so that you can setup nib bindings. While I do think that it is nice to be able to work with an IBOutlet bound property rather than iterating through the nib contents you can do so without introducing a UIViewController whose behavior you neither need nor want. This should avoid your confusion around how and when to release the view controller and what, if any, side effects it might have on the responder chain or other behaviors of the loaded view.

Instead please reconsider using NSBundle and taking advantage of the power of that owner argument.

@interface ProgressViewContainer : NSObject {

}

@property (nonatomic, retain) IBOutlet ProgressView *progressView;

@end

@implementation ProgressViewContainer

@synthesize progressView = progressView;

- (void) dealloc {
    [progressView release];
    [super dealloc];
}

@end

@interface ProgressView : UIView {

}

+ (ProgressView *) newProgressView;

@end

@implementation ProgressView

+ (ProgressView *) newProgressView {
    ProgressViewContainer *container = [[ProgressViewContainer alloc] init];
    [[NSBundle mainBundle] loadNibNamed:@"ProgressView" owner:container options:nil];

    ProgressView *progressView = [container.progressView retain];
    [container release];
    return progressView;
}

@end

Create a nib named "ProgressView" containing a ProgressView and set it's File's Owner class to ProgressViewContainer. Now you can create ProgressViews loaded from your nib.

ProgressView *progressView = [ProgressView newProgressView];
[scrollView addSubview:progressView];
[progressView release];

If you have multiple configurations of your progress view then maybe you'll want to implement a -initWithNibNamed: method on ProgressView instead of +newProgressView so you can specify which nib to use to create each ProgressView instance.

回答2:

I vote for option #2. The return value from -[NSBundle loadNibNamed] is an array of the top-level objects. So as long as you have just one top level object in your nib, then the index 0 will be correct. The other views are subviews and not top level objects.

Another option of course is to do something like create a superclass for all of your view controllers that includes an outlet called something like 'progressView' and then connect your view to that outlet on file's owner in the nib. Seems like overkill for this, though.

回答3:

I also prefer alternative #2. If the "0" is bothering you, you could:

• Create a subclass of UIView called ProgressView
• Create a nib-file called ProgressView.xib describing your progress view.
• Select the topmost view in your nib, and set its Class to ProgressView in interface builder

then do

NSArray *nibContents = [[NSBundle mainBundle] loadNibNamed:@"ProgressView" owner:self options:nil];
ProgressView *progressView = nil;

for (UIView *view in nibContents) {
    if ([view isKindOfClass:[ProgressView class]]) {
        progressView = (ProgressView *) view;
        break;
    }
}

if (progressView != nil) {
    //Use progressView here
}

回答4:

I ended up adding a category to UIView for this:

 #import "UIViewNibLoading.h"

 @implementation UIView (UIViewNibLoading)

 + (id) loadNibNamed:(NSString *) nibName {
    return [UIView loadNibNamed:nibName fromBundle:[NSBundle mainBundle] retainingObjectWithTag:1];
 }

 + (id) loadNibNamed:(NSString *) nibName fromBundle:(NSBundle *) bundle retainingObjectWithTag:(NSUInteger) tag {
    NSArray * nib = [bundle loadNibNamed:nibName owner:nil options:nil];
    if(!nib) return nil;
    UIView * target = nil;
    for(UIView * view in nib) {
        if(view.tag == tag) {
            target = [view retain];
            break;
        }
    }
    if(target && [target respondsToSelector:@selector(viewDidLoad)]) {
        [target performSelector:@selector(viewDidLoad)];
    }
    return [target autorelease];
 }

 @end

explanation here: http://gngrwzrd.com/blog-view-controller-less-view-loading-ios-mac.html