I have an application where small number of objects are defined in the MainWindow. A pair of these objects are a UIViewController and the UIImageView that goes along with this controller. When the application starts up, the entire MainWindow.xib get loaded & I can see that this UIImageView has been loaded into memory. At this point, I have no need for this UIImageView.
When I need the UIViewController, I perform the usual alloc/init setup. At this point, when I look at this controller with the debugger, the controller is setup correctly, but the UIImageView that should have been pre-wired with Interface Builder is always nil.
Any suggegstions on how to make sure this UIImageView is loaded into memory correctly? This is the only case where I've had an issue with objects defined within this single MainWindow.xib file.
Assuming you have connected the view outlet, all you need to do is access the view property. When you look in the debugger, you're seeing the property's corresponding ivar. When you access the property in code, it should load for you. So, it should be as simple as:
[controller view];
Not quite sure I understand the problem, but instead of having the UIImageView in MainWindow.xib, why not have it in the xxxViewController.xib where it's actually going to be needed?
Related
First, I am super-new to Objective-C/iOS development and, in fact, this question is for my first, test project. Also, I come from a C#/WinForms background so I'm coming into iOS development with certain pre-conceived notions of user interface design and application state. Please bear with me and help clear up my confusion.
I just created my first iOS application project which, consists of a Single View. I allowed Xcode to create all the files for me through the Single View project wizard. When it was finished, I opened my new applications, single UIView Nib file in the designer and I dropped three sliders onto the view.
The desired purpose of this application is very simple-- each slider corresponds to either the R, G or B values associated with the background color of my view.
I have figured out how to set the background of my view but I can not figure out how to access the values of each slider objects. Yes, I can hook-up and respond to an IBAction for each slider, but my plan is that each time a slider's value changes, I want the IBAction to call a refactored method that accesses the values of all three sliders and then set's the views Background Color based of the values associated with each one.
How can I access the values of my sliders? Specifically, how can I access the value of the sliders that I created by dragging and dropping them into the Nib designer window? I've seen code explaining how to programatically add a UISlider to your UIView and then access the value, but how do you access the value of a UISlider that's added to the Nib and, I assume, will be automatically "wired" in at compile time?
Hopefully this makes since? If I'm missing an intermediate step or critical concept, please let me know.
You create UISlider ivars/properties and make them IBOutlets:
#property (nonatomic, retain) IBOutlet UISlider* yourSlider;
You synthesize it in your .m file and the connect the IBOutlet in interface builder. The yourSlider pointer is then a reference to the object you connected it to. Note that it will only be loaded with the view of the UIViewController and therefore will be nil until viewDidLoad is called. You also must set it back to nil
self.yourSlider = nil;
in your viewDidUnload method (so that it is released). In Xcode 4 you have a convenient way of doing all the above steps in one action (see the "Interface Builder is Built-in" of What's new in XCode 4)
Similar to CTRL+dragging from the UISlider to the .m file to create the IBAction, you can CTRL+drag the UISlider from your .nib designer to the associated .h file and have it create a property for you. Then, from your .m file, you can access self.mySlider (or whatever you name the property).
There's a video on this page that shows binding to a UISlider specifically.
Another approach is to use the tag property of a view.
#property(nonatomic) NSInteger tag
- (UIView *)viewWithTag:(NSInteger)tag
You can set the tag property of a view in the interface builder and later reference that view in your controller.
UIView *myViewFromTag = [self.view viewWithTag:theNumberYouSetInIB];
In general, it's better to stick with IBOutlets. However, there are certain situations where it makes more sense to use tags.
Good luck!
I have a main window which has the UITabViewController as its root controller. I am using a nib file for this. In Interface Builder, two of the tabs have been wired to Controller_A, Nib_A and Controller_B, Nib_B but the 3rd tab only knows about Controller_C.
I assumed that this would mean that the loadView method of Controller_C would be automatically called since I haven't bothered to specify the NIB file. I want to lay this piece out programmatically. And it DOES indeed get called as I've confirmed by placing a breakpoint inside this method.
BUT when I switched over to Controller_C in the simulator, it comes up empty!
Here's what the loadView of Controller_C looks like:
- (void)loadView
{
[super loadView];
...
[self setTableView:formTableView];
[view addSubview:formTableView];
[self setView:view];
}
Any tips? What am I ignoring?
Looks like you are searching for:
-(void)viewDidLoad {
Here are the main things to check.
Click on your Controller_C in interface builder. In the Identity Inspector, make sure that the Class field is set to Controller_C.
In the Attributes Inspector, make sure the NIB Name field is blank.
If you have an existing Controller_C.xib laying around in your project, remove and delete it. The default implementation of loadView loads this file even if
Remove [super loadView]. Since you're building your view hierarchy in code, you shouldn't invoke the default implementation. You should explicitly allocate the controller's view as a local variable in loadView and set it using setView:.
Also, your comment on the other answer suggests that you may be confused about when/why loadView and initWithNibName:bundle: get called, so let me clarify:
loadView gets called to lazy load your controller's view the first time its view property gets accessed. This is true whether your view controller was constructed as an object in a NIB, or whether you constructed it yourself in code using initWithNibName:bundle:. The default implementation of loadView loads the NIB that was specified in initWithNibName:bundle: or in the NIB Name property in IB. If a NIB name wasn't specified, the default implementation looks for any NIB in the bundle that has the same name as your class and loads that NIB if one is found. If no appropriate NIB is found, then the default implementation of loadView just creates an empty view and sets that as your controller's view. When we build our own view hierarchy explicitly in loadView, we don't want any of these default behaviors, so we don't call [super loadView].
It seems loadView works as expected, the reason that my view was blank is because the datasource for my tableview was actually NIL. Earlier, I did not consider this scenario as I thought that it would at least present an empty table in such a case but apparently that was an incorrect assumption on my part. All this mistakenly led me to believe that the view wasn't being initialized properly.
#cduhn: Thanks, I had been following steps 1-3 already and it was really good to hear someone else give the same advice. The rest of what you said was educational for me as well.
Thanks Everyone.
I don't really know if what I'm doing is the right way to do it. Right now it seems to be working until it hits a certain point with a EXC_BAD_ACCESS message.
I'll describe what I'm doing as best and with the most relevant details I can tell:
I have a CalendarViewController that inherits UIViewController which is loading from a .xib file (CalendarViewController.xib). The class contains a UIView called contentView which I created and which I initialize with another nib file based on a class which is also inherited from UIViewController:
- (void)viewDidLoad {
[super viewDidLoad];
calendarView = [[CalendarView alloc] initWithNibName:#"CalendarView" bundle:nil];
[contentView addSubview:calendarView.view];
}
(calendarView is the class inheriting UIViewController and viewDidLoad is from CalendarViewController.
CalendarView.xib has a UITableViewController with it's respective UITableView. This Table View Controller is linked to a CalendarTableController to which I also generated a .xib file for it.
Everything is being created just right (apparently) but it is crashing somewhere very unexpected. CalendarTableController also implements a DateLoaderDelegate which loads information from an xml on an external url.
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
// When the data has all finished loading, we set a copy of the
// loaded data for us to access. This will allow us to not worry about
// whether a load is already in progress when accessing the data.
self.lastLoadedMatchXMLData = [self.matchXMLData copy];
// Make sure the _delegate object actually has the xmlDidFinishLoading
// method, and if it does, call it to notify the delegate that the
// data has finished loading.
if ([_delegate respondsToSelector:#selector(xmlDidFinishLoading)])
{
[_delegate xmlDidFinishLoading];
}
}
The application is getting to this point without any problem. _delegate is containing the correct object (a CalendarTableController which implements the DateLoaderDelegate). But when it arrives to the line:
if ([_delegate respondsToSelector:#selector(xmlDidFinishLoading)])
it crashes with the EXC_BAD_ACCESS, I don't really know the reason, if I look at the debugger, the crash is not occurring in any of my classes as any of them are appearing in the execution stack. URLConnectionClient seems to be generating it, but I don't really know why. The loading of the xml had worked earlier before I rearranged the ViewControllers to work as I have described now.
Any ideas?
It's weird. I fixed the problem but I had to dedicate the whole UIViewController to contain the UITableView. What I did was this:
Create an IBOutlet with the custom UITableViewController (CalendarTableViewController) in the custom UIViewController.
In the loaded .xib file I linked the IBOutlet to a created UITableViewController declared as a CalendarTableViewController.
This way I solved the problem of the UITableViewController being deallocated without reason. But now the image views I had placed in the intermediate UIViewController wouldn't appear. I had to set that UIViewController to contain solely the CalendarTableView and place the image views in the initial UIViewController. Weird, isn't it? I don't like much the hierarchy I created... but for now that will do =S
Check that you have defined properties for all of your subviews and that you are retaining everything that you need to be. Bad Access May mean that you're attempting to call respondsToSelector on an object that has been released.
Have you tried calling loadView before adding the nested controller's view to the parent's view?
Maybe viewDidLoad is not executing before you add the view and some variables were never initialized.
I have been having huge issues with this, so I drew a diagram...
alt text http://tomsfil.es/7bdead0a.png
I successfully get to the CLASS A - METHOD B but at that point, IBOutlet Z is Nil? :(
Any ideas?
note
Somebody told me it might be an Overrelease and to use NSZombieEnabled but that confused me
It's all a matter of when you call the class. Right after you create a view controller with initWithNibName, nothing is actually wired up yet - it's only after the view is created that IBOutlets are created and wired in.
One trick is that you can simply ask the view controller for .view, like so:
myViewController.view;
Then the view will be created and the IBOutlet will exist. A better method though, is to create properties on the view controller that you set, and then either in viewDidLoad, or in viewWillAppear you use those properties to set values for your outlets.
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