I´m trying to use Interface Builder (IB) to gain time in my app development. So I´m trying to do new things, for example, connecting objects between File´s Owners and Controllers.
The situation is:
1 - I have a ViewController with a Nib. This view controller have an array set as a IBOutlet.
2 - I put a custom TableViewController inside the Nib. Inside this TableViewController I set another IBOutlet Array, that I want to put as cell values (I will do this inside my TableViewController.m).
3 - The quesntion is, is possible to connect the two IBOutlets Array? Or to create something like a "IBInlet"..? Or in Interface Builder you can just use the IBOutlets as connections to the Library Objects of Cocoa Touch..?
Thanks for everyone..!
First off, I think it's unclear if you're trying to have two pointers to the same Array object or if you actually want to have two Array objects which you keep in sync. The latter makes little sense as it will just double your memory usage with no benefit, so let's assume you just want to have two pointers to the same Array object.
IB will help you link a data structure (your Array object) to a compatible interface widget, but it's still up to you to initialize your data structures in your code. Following that line of thinking, you can use IB to link your Array in the appropriate controller to the widget which you manage in that controller. Independently from that you can have one controller initialize the object and the other controller can get a pointer to that object from the first controller. Just make sure you manage your retains correctly ;)
Related
I want to place multiple pie charts in my application that I create using core plot. I made a wrapper class (lets call it PieChartViewController) that is a view controller and sets up the graph and some buttons and actions to make the graph interactive. To deploy it, I usually just create a property on another view controller that holds the PieChartViewController and when I am initializing this view controller I simply alloc/init thePieChartViewController and add its view to the main view. This usually works fine.
The problem is that on another view, I want to add a variable amount of graphs to the view and this number is decided when the view controller is initialized. I have a method that initializes each PieChartViewController and adds it to an NSMutableDictionary on the parent so that I could keep a reference to them. However, this doesn't seem to keep them alive because I always get BAD_ACCESS 2 crashes and when running instruments I realized that they get deallocated.
So when the PieChartViewControllers are stored on a property it's all good, but when I put them in a dictionary they seem to not be kept alive long enough. I am still not very familiar with memory management in objective-c and I'm not really sure how to go about this, would appreciate any help.
I simply alloc/init the PieChartViewController and add its view to the main view. This usually works fine
It may work fine, but don't do it. This is a misuse of UIViewController. See my answer here: https://stackoverflow.com/a/15962125/341994
I'm new to Objective-C and the iPhone and thought I was getting the hang of it until, after many play apps, I ran into a really basic problem around MVCs, NIBs and IB. Are there any really clear explained examples of how to follow this framework that I could go back to?
#interface test1ViewController : UIViewController {
IBOutlet myView *myview;
IBOutlet myModel *mymodel;
}
Both the views and models are linked in by IBOutlets but instantiating the model object either kills the application or produces an object which does not respond to any messages.
I am also unclear as to where to carry best out initialisations. I currently do this over viewDidLoad in the view controller. Is there a standard way to do this and does the simulator actually always start up in the same way? Should one use awakeFromNib? Does it make any difference if I use plain code or the IB? And if I have use the IB, should it include a model object?
The MVC idea would make good sense for me here because I have potentially several views and view controllers all feeding back into - and sharing - one common central data model. Any references or advance on this newbie problem would be more than welcome!
I wouldn't spend too much time worrying about the 'classic' definition of MVC. iOS follows it, but there's a lot of confusing terminology. ("View Controller")
You say trying to use model kills your app. Are you retaining myModel? You have to retain all IBOutlets.
nibs are collections of "Freeze-Dried" objects. When you load a nib, the objects in it are "rehydrated", if you will. This means they spring back to life with all of their properties set to whatever they were when you froze them. So you talk of "instantiating" and "initializing" but this does not apply to IB. The objects are ALREADY instantiated and initialized. Imagine that compiling the nib 'pauses' the objects. When you load the nib, the objects resume doing whatever they were doing when frozen. They will get an awakeFromNib message, so that's a good place to put some code to check on what the state of the app is, see if you have to do stuff with your object to bring it up to speed.
viewDidLoad seems like an "initialization" method but don't be fooled. It's part of the view controller life cycle and it can be called more than once! (If your controller's view is purged as part of a low memory warning, viewDidLoad might be called again if the view has to be... wait for it... reloaded.) So, it's appropriate to put view setup stuff in viewDidLoad, but not other initialization type things.
For the "common data" thing, I like to create a singleton data model class. Your various views can set properties on the model, or send notifications. You can also use KVO (key value observing) to watch for changes in the model.
IB makes functionality invisible. I don't like it and I don't use IB any more, preferring to have everything in code. Then when you look at code you see what is going on - all the navigation controllers, all the formatters etc. - without switching over to IB. Maybe Xcode4 will make it better with integrated IB but I probably won't go back. Lots of people do like IB so try both methods and see what you like best.
IBOutlet/IBAction actually mean nothing to the compiler but they let IB recognise the ivars it can send messages to or that will write to elements in a xib. Your use of it here is a bit simplistic unless you really do have a model that only communicates one way with the xib. What you more usually have is a range of controls in the xib linked to the view object, the view communicating directly with the controller. The controller communicates with the model. Very loosely speaking, model is your internal representation of data and logic, view is what you see, controller is the glue between them.
The MVC line can be fuzzy and you just have to get comfortable with it. If you have a slider control with a value representing some value in your model then it can be hard to think of it as part of the interface especially when you persist the value and use it as a central part of your model. I like the Stanford iPhone class introduction of it. They don't spend a heap of time on it because it can be difficult to follow exactly and there are situations where it isn't best.
Notes from that class - you can find the video on iTunes to follow along.
Your use of viewDidLoad is correct, that's your chance to perform initialization on views and their objects. If using IB you will probably not have much to do there because you can set most properties in the xib. If not using IB you will use it a lot more.
A lot of times something like your model would be wired at runtime by your application delegate or by the view controller itself.
IB is generally used more to link views and controllers together, with the application handing around model(s).
That said, you should be able to have IB create an instance of your model and assign it in an IBOutlet. Was your model OK with just being created without the classic init method being called? Did it implement NSCoding properly?
In my iPhone app, the user will be making multiple NSStrings. Once these are made, I need to pass them to another view completely in the app. How can i do this? All I know at the moment os I can't access objects or variables declared in one view, in another. Thanks.
One way would be to follow the MVC (model view controller) design pattern. Whichever controllers are responsible for your respective views can then store and retrieve the NSStrings from/to a common data model object.
As to how you can make the strings stored in an object visible to the outside, the easiest way is to use Objective-C properties to save you from writing the accessor methods yourself.
I hope this helps with your problem or at least gets you started in the right direction.
Place the strings in a data model object (the M of the MVC pattern), with accessor methods (getter and setters, which can be automagicly created by properties). Then create and place that model object in some central location, a controller common to all views requiring that data, or the appDelegate, a reference for which can be found from any view.
Josh,
I would add to the MVC thing, that still you can do this in several ways.
What I would do for example, is to make your other "View Controller" (MVC), to "observe" when does the user create a new string, and to fetch it accordingly. In that way you would reduce coupling and it will be a cleaner implementation.
Another way would be to create a "delegate" so that the First View controller, "notifies" or calls the delegate method that you created, each time the user creates a new string ( again reducing coupling )
I think I have a basic question that is sort of hard to look up, I think.
Objective-C for Iphone.
I want to create two view controller instances that message and update an instance of a Model Class. How do you do this? I would prefer no using singletons. It's basically an "I really want to learn from you guys because this is awesome and I want to be awesome too!" question.
I would prefer we keep app delegate, singletons, nsnotification center out of the picture. App delegate specifically in that I dont think I wnat to have my data object created by app delegate, but I may have to.
The way, as I understand it, this works is sort of like this. Navigation Controller creates instance of FirstLevelViewController. My FirstLevelViewController creates instances of my SecondLevelViewControllers and then when told to pushes them onto the navcontroller stack.
I have my Model Instance being created by my firstlevelviewcontroller instance. Is that wrong? I think I need a reference to the instance passed to my secondlevelviewcontroller, but I'm having trouble because I can't figure out what the instance name of the firstlevelviewcontroller is (I think NavController instantiated it).
Help is so very much appreciated.
Assuming the model stays the same object (it can be mutable but not deallocated within the lifetime of BOTH view controllers), one might use a separate variable in each view controller to point to the same model class, with each view controller not knowing about the other. This is of course dependent on your application specific logic -- if one view controller 'knows about' the other than of course it makes sense to have the model be 'owned' but the independent one, and accessible to the dependent one via properties. However this considered bad because it promotes code coupling and dependency, which is looked at as poor coding. As to how both view controllers get the same model instance, typically it would be set (preferably in initialization) by whatever knows about them both, such as a higher level view controller, or if they are root view controllers, the app delegate.
i am new to this objective-c
i want to load a view using nib file i created when i press a button .without using any view controller..
This is generally considered a bad idea if you don't know what you're doing, but if you really want to do this then there's 2 places to look, depending on what version of the OS you're developing for.
iOS 4
Look at UINib in the documentation. You can use this to load a nib fairly easily.
iOS 3.2 and earlier
Use NSBundle. There is a category, documented under the name "NSBundle UIKit Additions Reference", that adds a method -loadNibNamed:owner:options:. You can also use this on iOS 4.0 if you so desire.
In both cases, the owner object fills in the role of "File's Owner" in the nib, useful if you have actions or outlets specified on the owner. The method also returns an NSArray of all the top-level objects in the nib. Be careful, if you use this array you need to retain any of the objects that you want to keep, as the array (and all the objects) are returned autoreleased.
Try this. Should show you how to implement your UIView subclass.
http://markuzweb.blogspot.com/2011/05/subclassing-uiview-with-nib-file.html