I've got a custom UIViewController that loads a xib. The first time it's instantiated, it takes some time before it appears. Is there an elegant way to preload it, so it won't do this? I tried just creating it and immediately after release it. That didn't seem to work. I suppose if I wanna do it that way, I'd have to add it to the main window (for example), and then remove it. But in any case, that solution seems a bit ugly. Any other way?
Try creating it and calling [controller view]. This will load its xib and create and hook up its view outlet, etc.
Related
I'm fairly new to Cocoa Touch. Right now I'm trying to subclass UIViewController to provide my custom view. Since I intend to save the content of a UITextField (passcodeField) using NSUserDefaults, I want to be notified whenever the UITextField changes its value.
I've read somewhere that in order to do that I should add the view controller to be an observer of the UITextFieldTextDidChangeNotification notification. However I'm just not sure when to do that. I've considered several options.
In the -loadView method. However, since I'm loading my view using a XIB, I think i shouldn't mess with this method and should instead leave it as-is. (Am I correct on this point, BTW? )
In the -viewWillAppear method. But this method may be called multiple times because the view may be moved out and into the screen without being destroyed and recreated. (Am I correct? ) This will not do any harm to the program but sure doesn't seem like the correct way.
In the initializer of the UIViewController. If I want to add the notification there I must reference the UITextField. By doing this I essentially cause the view to created before it is really needed. Also I think I read somewhere that if the system runs low on memory the offscreen views may be destroyed. Thus I may lose the notification observing if such thing happens, right?
So I'm totally confused right now. Could you guys give me some advice of where to put it? Thanks so much!
Put it in the - (void)viewDidLoad method of your ViewController remember to call [super viewDidLoad]; at the start of your implementation.
Most of the iOS apps I use are very responsive, when I tap on an element it goes to the next view right away. In my app, some of my view controllers take 0.5-1.0 second to load.
My code is all in the viewDidLoad method and I'm pretty sure that's the problem but I can't move anything out since I need every single element that I instantiate.
A solution I thought is to move all the work I do in viewDidLoad in a thread then call the main thread when I'm ready to call addSubview, would that work even if UIKit is not thread safe? Or is there something else I'm missing?
Try to move some code you might have in viewDidLoad to viewdidAppear. viewDidAppear is being called once the view is presented. If you have to make some hard work, do it there and maybe show aa spinner somewhere while you do that.
What are you exactly doing in viewDidLoad? Btw remember that a view is only loaded when you need it, if you want to switch between views faster I can suggest you to create an initializion phase where you call -view on all the view controller you want to show, maybe helped with a spinner or a progress bar. but pay attention this would work only with intensive loading task and not memory consuming tasks. It sounds very strange your request, so is better the you try to explain better why your viewDidLoad is so slow, maybe there is something wrong.
Define your UI elements in Xcode as part of designing the interface. That way, Xcode can compile your storeyboard or xib files into the rapidly loading binary form.
Ok hopefully this is an easy question:
I have a main viewcontroller that is loaded by the app delegate at application startup.
This viewcontroller has some code in 'viewDidLoad' to create some non view type based objects (some sound/data objects). Aside from that it also loads a UIView.
The sound/data objects take a while to create, but the app is quite functional without them for a start - so I want to load these objects after the UIView has loaded, but can't seem to figure out how.
I have tried moving the appropriate code to viewDidAppear, but this is still called before the UIView actually appears on screen. Is there a function that is called after the viewcontroller actually starts displaying UIViews, or any other way to achieve what I want?
Any help would be much appreciated - thanks!
In case anyone else has a similar problem, I found a way to solve it: use NSThread to load things in the background without pausing everything else.
There's a good simple example here: http://www.iphoneexamples.com/.
For instance:
Create a new UIVC using initWithNibName, using "nib-v1"
Display it, e.g. using [(UINavigationController) nav pushViewController: myVC]
Change the NIB that myVC is using to "nib-v2"
So far as I can see, this is the "correct" approach to app-design for a lot of apps, when paging through information where you need two slightly different UI screens for the info being displayed.
For instance, most of your pages are text, but some of them have an image too (think of an RSS reader, where some RSS entries have text + image, some are text only).
I've dealt with this previously by having one NIB file with a second, invisible, named UIView instance that I layered over the top of the first one, and switched on/off depending on on context, using the "hidden" flag.
But this is clearly wrong, and wastes memory.
However, I cannot see an obvious way to "reload" the view from the NIB file. I'm guessing I want to somehow reproduce the magic that initWithNibName does?
I suspect this is possible, but I'm sure that if you do it "the wrong way" then the app will simply crash horribly.
You can always perform
[[NSBundle mainBundle] loadNibNamed:#"FileName" owner:viewController options:nil]];
but this will undoubtedly really mess things up, if you're not sure what you're doing, especially if view is connected in both of those nibs
You should redesign your view controller hierarchy to swap between two different controllers that load from two different nib files.
Alternately, you can have the controller manage swapping views that it loads from different files that are unrelated to it's nibName. In that case, you can load them in the above manner. And you will want to have their outlets (to, for example, subviewOne and subviewTwo) connected in different nibs.
You should check out the UINib class to see if it does what you want. It will allow you to load a nib file and keep it in memory.
But just to clarify: Do you want to modify the nib file itself? Or do you want to modify the contents of the nib file when it has been loaded into memory?
Off the top of my head, the first would be quite difficult (you can't modify the original file, since it is part of application bundle...maybe you copy it to Documents folder and write your own coder/decoder?) The second is easier, but I am not sure what the reason would be? Why not just modify the viewController/view after it has been loaded (in awakeFromNib, for example) and, if you want those changes to persist, save those changes to file afterwards.
In short, I don't know exactly what you would like to do, but the chances seem high to me there might be a better way to do it.
I agree with Rob, but if you really want to mess with swapping nib's (which is bad as it can easily lead to dangling pointers and the like), you could maybe load the view from the new nib with NSBundle's - (NSArray *)loadNibNamed:(NSString *)name owner:(id)owner options:(NSDictionary *)options method and do the view swapping yourself.
You should rather use different view controllers for different types of content. If they only differ slightly, you can still consider creating one base class and subclassing the different variations.
You shouldn't change what NIB file a UIViewController uses. Attaching the NIB to the UIViewController should be a one-time event. The hidden views are fine; they're certainly not clearly wrong. You can also programmatically add view elements after loading. If you're doing a lot of that, you can skip the NIB entirely and programmatically build the view in -loadView. Any of these are fine, but don't switch the NIB after initialization. I don't even recommend having multiple NIBs that you choose between for a given UIViewController class; it's just too confusing. Generally each NIB should map to a dedicated UIViewController class with a very similar (or identical) name.
In a related note, I recommend moving the name of the NIB into the UIViewController, as described in an earlier posting.
I came looking for an answer to the same problem, and ended up solving it like this:
UIViewController* ctrler = [[UIViewController alloc] initWithNibName:#"NewControllerNIB" bundle:nil];
// Replace previous controller with the new one
UINavigationController* nav = self.navigationController;
[nav popViewControllerAnimated:NO];
[nav pushViewController:ctrler animated:NO];
I'm not sure if it's possible the current controller gets deallocated before the call to push the new controller is executed, but so far it seems to work (until I just redesign the app with a better approach)
I found out this:
applicationDidFinishLaunching (an delegate method of the UIApplicationDelegate Protocol) seems to be called BEFORE my views from the nib file are loaded completely. So I tried all the day to change an image of an UIImageView right after my app launched in the iPhone simulator, but nothing happened.
Then I wrote a little action method that I call with the press of a button. And then it happened: WORKS!
So the applicationDidFinishLaunching delegate method isn't really the right place for stuff that has to be done after the app is really "ready". I gues there's something better that waits for the nib to be loaded completely. but where? and what?
I gues there's something better that waits for the nib to be loaded completely. but where? and what?
For application specific things like global settings, preferences, etc., -appDidFinishLaunching is the right place.
For UIView specific things, you typically use the -viewDidLoad method in a UIVIewController subclass. It is pretty much the only place you are guaranteed that the nib file is loaded, the IBOutlets are initialized and the IBActions are attached.
This is difference from the Mac OS X world, where -awakeFromNib was the place to do it.
Hey until your views and their view controllers instantiated you can't modify their ui. However just for the sake of your problem you can always declare the uiimageview as a property of your app delegate class and initialize it in the appDidFinishLaunching event. But that's the worst practise. As on the iPhone which has limited memory always lazy load ie: only initialize objects when and just before they are actually required by your UI. So ideally you should be doing this in the viewDidLoad event of the view where you want to use this UIImageView.
applicationDidFinishLaunching is usually used for stuff like database file checks, opening database connection, populating global variables, any other application wide logic, checking for an available Internet connection etc