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I've been reading about Clean Architecture from Robert Martin and more specifically about VIPER.
Then I ran into this article/post Brigade’s Experience Using an MVC Alternative which describes pretty much what I'm currently doing.
After actually trying to implement VIPER on a new iOS project, I've ran into some questions:
Is it ok for the presenter to query information in the view or should the "information passing" always start from the view?
For example, if the view triggered some action in the presenter, but then, depending on the parameters passed through that action, the presenter might need more information.
What I mean is: the user tapped “doneWithState:”, if state == “something”, get information from the view to create an entity, if state == “something else”, animate something in the view. How should I handle this kind of scenario?
Lets say a "module" (group of VIPER components) decide to present another module modally. Who should be responsible for deciding if the second module will be presented modally, the first module's wireframe or the second module's wireframe?
Also, lets say the second module's view is pushed into a navigation controller, how should the "back" action be handled? Should I manually set a "back" button with an action in the second module's view controller, that calls the presenter, that calls the second module's wireframe that dismiss and tells the first module's wireframe that it was dismissed so that the first module's view controller might want to display something?
Should the different modules talk only through the wireframe or also via delegates between presenters? For example if the app navigated to a different module, but after that the user pressed "cancel" or "save" and that choice needs to go back and change something in the first module (maybe display an animation that it was saved or remove something).
Lets say a pin was selected on a map, than the PinEditViewController is displayed. When going back, the selected pin's color might need to change depending on use actions on the PinEditViewController. Who should keep the state of the current selected pin, the MapViewController, the MapPresenter or the MapWireframe in order for me to know, when going back, which pin should change color?
1. May the Presenter query information from the view
To answer this to your satisfaction, we need more details about the particular case. Why can't the view provide more context information directly upon callback?
I suggest you pass the Presenter a Command object so the Presenter doesn't have to know what to do in which case. The Presenter can execute the object's method, passing in some information on its own if needed, without knowing anything about the view's state (and thus introducing high coupling to it).
View is in a state you call x (opposed to y and z). It knows about its state anyway.
User finishes the action. View informs its delegate (Presenter) about being finished. Because it is so involved, it constructs a Data Transfer Object to hold all usual information. One of this DTO's attributes is a id<FollowUpCommand> followUpCommand. View creates a XFollowUpCommand (opposed to YFollowUpCommand and ZFollowUpCommand) and sets its parameters accordingly, then putting it into the DTO.
Presenter receives the method call. It does something with the data no matter what concrete FollowUpCommand is there. Then it executes the protocol's only method, followUpCommand.followUp. The concrete implementation will know what to do.
If you have to do a switch-case/if-else on some property, most of the time it'd help to model the options as objects inheriting from a common protocol and pass the objects instead of the state.
2. Modal Module
Should the presenting module or the presented module decide if it's modal? -- The presented module (the second one) should decide as long as it's designed to be used modally only. Put knowledge about a thing in the thing itself. If its presentation mode depends on the context, well, then the module itself can't decide.
The second module's wireframe will receive message like this:
[secondWireframe presentYourStuffIn:self.viewController]
The parameter is the object for which presentation should take place. You may pass along a asModal parameter, too, if the module is designed to be used in both ways. If there's only one way to do it, put this information into the affected module (the one presented) itself.
It will then do something like:
- (void)presentYourStuffIn:(UIViewController)viewController {
// set up module2ViewController
[self.presenter configureUserInterfaceForPresentation:module2ViewController];
// Assuming the modal transition is set up in your Storyboard
[viewController presentViewController:module2ViewController animated:YES completion:nil];
self.presentingViewController = viewController;
}
If you use Storyboard Segues, you'll have to do things a bit differently.
3. Navigation hierarchy
Also, lets say the second module's view is pushed into a navigation controller, how should the "back" action be handled?
If you go "all VIPER", yes, you have to get from the view to its wireframe and route to another wireframe.
To pass data back from the presented module ("Second") to the presenting module ("First"), add SecondDelegate and implement it in FirstPresenter. Before the presented module pops, it sends a message to SecondDelegate to notify about the outcome.
"Don't fight the framework", though. Maybe you can leverage some of the navigation controller niceties by sacrificing VIPER pure-ness. Segues are a step into the direction of a routing mechanism already. Look at VTDAddWireframe for UIViewControllerTransitioningDelegate methods in a wireframe which introduce custom animations. Maybe this is of help:
- (id<UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed
{
return [[VTDAddDismissalTransition alloc] init];
}
- (id<UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented
presentingController:(UIViewController *)presenting
sourceController:(UIViewController *)source
{
return [[VTDAddPresentationTransition alloc] init];
}
I first thought that you'd need to keep a stack of wireframes similar to the navigation stack, and that all "active" module's wireframes are linked to one another. But this isn't the case. The wireframes manage the module's contents, but the navigation stack is the only stack in place representing which view controller is visible.
4. Message flows
Should the different modules talk only through the wireframe or also via delegates between presenters?
If you directly send another module B's object a message from Presenter A, what should happen then?
Since the receiver's view is not visible, an animation cannot start, for example. The Presenter still has to wait for the Wireframe/Router. So it has to enqueue the animation until it becomes active again. This makes the Presenter more stateful, which makes it harder to work with.
Architecture-wise, think about the role the modules play. In Ports/Adapters architecture, from which Clean Architecture burrows some concepts, the problem is more evident. As an analogy: a computer has many ports. The USB port cannot communicate with the LAN port. Every flow of information has to be routed through the core.
What's at the core of your app?
Do you have a Domain Model? Do you have a set of services which are queried from various modules? VIPER modules center around the view. The stuff modules share, like data access mechanisms, don't belong to a particular module. That's what you may call the core. There, you should perform data changes. If another module becomes visible, it pulls in the changed data.
For mere animation purposes, though, let the router know what to do and issue a command to the Presenter depending on the module change.
In VIPER Todo sample code:
The "List" is the root view.
An "Add" view is presented on top of the list view.
ListPresenter implements AddModuleDelegate. If the "Add" module is finished, ListPresenter will know, not its wireframe because the view is already in the navigation stack.
5. Keeping state
Who should keep the state of the current selected pin, the MapViewController, the MapPresenter or the MapWireframe in order for me to know, when going back, which pin should change color?
None. Avoid statefulness in your view module services to reduce cost of maintaining your code. Instead, try to figure out whether you could pass a representation of the pin changes around during changes.
Try to reach for the Entities to obtain state (through Presenter and Interactor and whatnot).
This doesn't mean that you create a Pin object in your view layer, pass it from view controller to view controller, change its properties, and then send it back to reflect changes. Would a NSDictionary with serialized changes do? You can put the new color in there and send it from the PinEditViewController back to its Presenter which issues a change in the MapViewController.
Now I cheated: MapViewController needs to have state. It needs to know all pins. Then I suggested you pass a change dictionary around so MapViewController knows what to do.
But how do you identify the affected pin?
Every pin might have its own ID. Maybe this ID is just its location on the map. Maybe it's its index in a pin array. You need some kind of identifier in any case. Or you create an identifiable wrapper object which holds on to a pin itself for the duration of the operation. (That sounds too ridiculous for the purpose of changing the color, though.)
Sending Events to Change State
VIPER is very Service-based. There are lots of mostly stateless objects tied together to pass messages along and transform data. In the post by Brigade Engineering, a data-centric approach is shown, too.
Entities are in a rather thin layer. On the opposite of the spectrum I have in mind lies a Domain Model. This pattern isn't necessary for every app. Modeling the core of your app in a similar fashion may be beneficial to answer some of your questions, though.
As opposed to Entities as data containers into which everyone might reach through "data managers", a Domain protects its Entities. A Domain will inform about changes proactively, too. (Through NSNotificationCenter, for starters. Less so through command-like direct message calls.)
Now this might be suitable for your Pin case, too:
PinEditViewController changes the pin color. This is a change in a UI component.
The UI component change corresponds to a change in your underlying model. You perform the changes through the VIPER module stack. (Do you persist the colors? If not, the Pin Entity is always short-lived, but it's still an Entity because its identity matters, not just its values.)
The corresponding Pin has changed color and publishes a notification through NSNotificationCenter.
By happenstance (that is, Pin doesn't know), some Interactor subscribes to these notifications and changes its view's appearance.
Although this might work for your case, too, I think tying the edit
This answer may be a bit unrelated, but I'm putting it here for reference. The site Clean Swift is an excellent implementation of Uncle Bob's "Clean Architecture" in swift. The owner calls it VIP (it still contains the "Entities" and the Router/wireframe though).
The site gives you XCode templates. So let's say you want to create a new scene (he calls a VIPER modules, "scenes"), All you do is File->new->sceneTemplate.
This template creates a batch of 7 files containing all the headache of the boilerplate code for your project. It also configures them so that they work out of the box. The site gives a pretty thorough explanation of how every thing fits together.
With all the boiler plate code out of the way, finding solutions the questions you asked above is a bit easier. Also, the templates allow for consistency across the board.
EDIT -> In regards to the comments below, here's an explanation as to why I support this approach -> http://stringerstheory.net/the-clean-er-architecture-for-ios-apps/
Also this one -> The Good, the bad, and the Ugly about VIPER in iOS
Most of your questions are answered on this post: https://www.ckl.io/blog/best-practices-viper-architecture (sample project included). I suggest you pay special attention to the tips for Modules initialization/presentation: it's up to the source Router to do it.
Regarding back buttons, you can use delegates to trigger this message to the desired module. This is how I do it and it works great (even after you insert push notifications).
And yes, modules can definitely talk to each other by using delegates as well. It's a must for more complex projects.
I have created a custom class for my UIBarButtonItem (refreshIndicator.m). This button will be on many different view controllers, all push-segued from my MainViewController/NavigationController.
Instead of dragging an outlet onto every single ViewController.m file for iPhone storyboard THEN iPad storyboard (ugh, still targeting iOS7), I want to know if there is a way to complete my task simply within my UIBarButtonItem custom class. I've looked around everywhere but I haven't quite found an answer to this,
All I need to do is check which UIViewController is present, check the last time the page was refreshed, and then based on that time, set an image for the UIBarButtonItem. (I've got this part figured out though, unless someone has a better suggestion). How can I check for the current UIViewController within a custom button class? Is this possible?
Does it need to know which view controller its on so it can tell that vc it was pressed? If that's the case, then use your button's inherited target and action properties. On every vc that contains an instance of the button, in view did load:
self.myRefreshIndicator.target = self;
self.myRefreshIndicator.action = #selector(myRefreshIndicatorTapped:);
- (void)myRefreshIndicatorTapped:(id)sender {
// do whatever
}
More generally, its better to have knowledge about the model flow to the views from the vc, and knowledge of user actions flow from the views. Under that principal, your custom button could have a method like:
- (void)timeIntervalSinceLastRefresh:(NSTimeInterval)seconds {
// change how I look based on how many seconds are passed
}
And your vcs:
NSTimeInterval interval = [[NSDate date] timeIntervalSinceDate:self.lastRefreshDate];
[self.myRefreshIndicator timeIntervalSinceLastRefresh:interval];
If you really must go from a subview to a view controller, you could follow the responder chain as suggested in a few of the answers here (but I would go to great lengths to avoid this sort of thing).
It is possible to achieve this, but the solution is everything but elegant. It is one way of getting around the basic principles of iOS and is strongly discouraged.
One of the ways is to walk through the responder chain, posted by Phil M.
Another way is to look through all subviews of view controllers until you find the button.
Both ways are considered a bad practice and should be avoided.
For your particular case, I would rethink the structure of having a separate instance of the bar button. For example, you could rework it into a single UIButton instance that gets displayed over every view controller and it can also act as a singleton.
Can anyone tell me how I can phrase an if () statement to discover if a segue's destination view controller will appear in the Detail Split or in the Master Split?
I want to put the if() statement inside my prepareForSegue:sender: methods.
EDIT
All my detail views that are relevant to this question (at the moment) conform to a protocol and I am currently performing introspection on the destination controller using:
if ([segue.destinationViewController conformsToProtocol:#protocol(myProtocol)])...
I can see that this would not work if I wanted:
To be able to show the same class in either Master or Detail of the splitView from time to time, and at the same time...
I only want the if() statement to be true when the view is to be presented in the detail split.
Things like segue.destinationViewController.navigationController == ... don't appear to be any use either.
I was hoping that since we need to set "Master Split" or "Detail Split" when we set the segue up... there would be a way to access that information less circuitously.
SECOND EDIT:
The way I have this set up with using introspection does "work". It just doesn't seem very "Object Oriented". I don't think I should be querying the View Controller at all for this information, I can't see why the VC should know anything about which side of the splitView it will be displayed. Surely the object that should hold onto this information is the Segue and, as I say, it appears this is being "set" in the storyboard when we select "Detail" or "Master" split.
Maybe it isn't a property of anything, but I can't see how to get at it.
I suppose I could query the destinationViewController in its viewWillAppear to discover which NavigationController it is in after it appears on screen but, again, it seems a bit "hacky".
There is probably a better more abstract and reusable way to do this that I'm not aware of, but here is a suggestion that could help in your specific project that requires just a bit of special knowledge of your specific project.
If you use introspection in your prepare for segue, you can check to see if methods exist by using the responds to approach.
So for example, in typical implementations of a splitview controller (note - not all) the detail view will implement the methods to handle rotation. So if this is true in your project, you could do something like this:
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([segue.destinationViewController respondsToSelector:#selector(splitViewController:shouldHideViewController:inOrientation:)]) {
//do something
}
}
You could use this same approach based upon something that was unique but constant in your project related to either the master or detail view.
hope that helps,
be well
My experience is a little limited, but most times I've seen prepareForSegue used, the if() block checks segue.identifier to do anything that needs to be done specifically to handle building the new page. If you set the identifier for all your segues, you could just have code to handle each segue from that controller, and change what the code is depending on if that segue goes to a masterViewController or a detailViewController. Not really a well automated way, but it'll get the job done.
EDIT: oh geez, that wording is kinda confusing. If you want me to I can put a code example up, but it'll have to wait until Monday, as I don't have access to a Mac until then.
The talk of classes and protocols gave me another idea, but again, not sure if it will work - I wanted to test it before posting, but I'm not going to have the time to test anytime soon.
I think you should be able to create 2 new classes, UIMasterViewController and UIDetailViewController, that are subclasses of just UIViewController. Then, for each of your actual screens, instead of making them subclasses of UIViewController directly, make them either a UIDetailViewController or UIMasterViewController. Then, in your prepareForSegue,
if ([segue.destinationViewController isKindOfClass:UIMasterViewController])
{
//do master view specific stuff
}
else if ([segue.destinationViewController isKindOfClass:UIDetailViewController])
{
//do detail view stuff here
}
This should be a pretty dependable way to tell where your segue is sending you, as long as you can set up the custom view controller classes right. This still won't solve the first issue noted in the question
"To be able to show the same class in either Master or Detail of the
splitView from time to time, and at the same time..."
This could be overcome by making 2 copies of all of the views you want to be able to show as either or both, then make one a UIMasterViewController and the other a UIDetailViewController - copy-paste should be good for most of the rest.
Let me know if this works - I'm not exactly sure how to set up the controllers off the top of my head, but I'm pretty sure it could be done. If it can, I can see this being a very useful thing.
This may be impossible, but I'm trying to save the state of my application between scene transitions, but I can't figure out what to do. Currently I love the way that when you have an application running and hit the home button, you can go back to that application just where you left off, but if you transition between scenes (in a storyboard), once you get back to that scene the application state was not saved.
I only have two different scenes that need to be saved (you transition back and forth from one to the other). How can I go about saving a storyboard scenes state without taking up precise memory?
More Detailed: Here is my entire storyboard. You transition back and forth between scenes using the plus toolbar button. On the second scene the user can tap on the table view cells and a real image will fill the image view (See figure 1.2)
Figure 1.1
In figure 1.2 you see what happens when you tap inside one of the many table view cells (an image view pops up.)
Figure 1.2
THE PROBLEM: When you tap a table view cell, which fills an image view (shown in figure 1.2) it works fine if you stay on that scene or even hit the iPhone home button (if you hit the iPhone home button and then reopen the app the scene's state was saved and the image view filled with a simple image still shows just like we left it), but if I transition (using the plus button) back to the first scene, and then use the plus button on the first scene to get back to the second scene the image view that I created (shown in figure 1.2) disappears and the second scene loads without saving the state and image views we filled.
EDIT: I tried using the same view controller for both scenes, but it didn't solve the problem.
UPDATE: I just found the following code (that I think stores a views state). How could I use this and is this what I've been looking for?
MyViewController *myViewController=[MyViewController alloc] initWithNibName:#"myView" bundle:nil];
[[self navigationController] pushViewController:myViewController animated:YES];
[myViewController release];
I would suggest a combination of two things:
1. Take DBD's advice and make sure that you don't continuously create new views
2. Create a shared class that is the data controller (for the golfers, so that the data is independent of the scene)
The correct way to make the segues would be to have one leading from the view controller on the left to the one on the right. However, to dismiss the one on the right you can use
-(IBAction)buttonPushed:(id)sender
[self dismissModalViewControllerAnimated:YES];
}
This will take you back the the view controller on the left, with the view controller on the left in its original state. The problem now is how to save the data on the right.
To do this, you can create a singleton class. Singleton classes have only one instance, so no matter how many times you go to the view controller on the right, the data will always be the same.
Singleton Class Implementation (Of a class called DataManager) - Header
#interface DataManager : NSObject {
}
+(id)initializeData;
-(id)init;
#end
Singleton Class Implementation (Of a class called DataManager) - Main
static DataManager *sharedDataManager = nil;
#implementation DataManager
+(id)initializeData {
#synchronized(self) {
if (sharedDataManager == nil)
sharedDataManager = [[self alloc] init];
}
return sharedDataManager;
}
-(id)init {
if(self == [super init]) {
}
return self;
}
#end
Then, inside your view controller code you can grab this instance like this
DataManager *sharedDataManager = [DataManager initializeDataManager];
This way you will have the same data no matter how many times you switch views.
Also, you can better adhere to MVC programming by keeping you data and your view controllers separate. (http://en.wikipedia.org/wiki/Model–view–controller)
Figure 1.1 has a fundamental flaw which I believe the basis of your problem.
Segues (the arrows between controllers on the storyboard) create new versions of the UIViewControllers. You have circular segues. So when you go "back" to the original screen through the segue is really taking you forward by creating a new version.
This can create a major problem for memory usage, but it also means you can't maintain state because each newly created item is an empty slate.
Since your are using a UINavigationController and pushViewController:animated: you should "pop" your controller to get rid of it.
On your "second" scene, remove the segue from the + button and create an IBAction on a touchUpInside event. In the IBAction code add the "pop"
- (IBAction)plusButtonTapped {
[self.navigationController popViewControllerAnimated:YES];
}
I see what you mean. This should happen to every application, as when the last view controller in the navigation stack is transitioned away from, it is deallocated and freed. If you need to save values such as text or object positions, a plist may be the way to go. See this related question for how to use a plist.
Apple isn't going to do this for you. You should probably just save the state of each view using NSUserDefaults and each time your application launches re-load your saved data.
If you are storing everything in CoreData you would only need to save the active view and a few object ids, if not you would need to save any data you have.
Don't expect iOS to save anything that you have in memory between launches. Just store it in NSUserDefaults and load it each time.
Store the state of the scene in NSUserDefaults or inside a plist file then when loading up the scene just load it with the settings from there. If the images are loaded from the internet you might also want to save them locally on your iphones hard drive so it runs a bit smoother.
I don't think you should cycle the segues, just use one that connects viewcontroller 1 from viewcontroller 2 should be enough and that way you make sure that no additional viewcontrollers are being made (memory problems maybe?)
However for your particular problem, I believe that you should use core data to save the exact state of your table, view because ios doesn't save the exact state of view at all times. it will require work but you will achieve what you want. You will need to save the exact photo( using a code or enums that will be saved), the location in the table view, the score or well whatever data you need to save that state.
The best of all is that coredata is so efficient that reloading the data when the app is relaucnhed or into foreground it takes no time, and ive used core data to load more than 5k of records until now and works just fine and its not slow at all.
When i get back home ill provide a code you might use to get an idea of what i mean.
The key here is to:
Have some sort of storage for the data that your application needs. This is your application's data model.
Give each view controller access to the model, or at least to the part of the model that it needs to do its job. The view controller can then use the data from the model to configure itself when it's created, or when the view is about to appear.
Have each view controller update the model at appropriate times, such as when the view is about to disappear, or even every time the user makes a change.
There are a lot of ways that you can organize your data in memory, and there are a lot of ways that you can store it on disk (that is, in long term storage). Property lists, Core Data, plain old data files, and keyed archives are all possibilities for writing the data to a file. NSArray, NSDictionary, NSSet, and so on are all classes that you can use to help you organize your data in memory. None of that has anything to do with making your view controllers feel persistent, though. You'll use them, sure, but which one you choose really doesn't matter as far as updating your view controllers goes. The important thing, again, is that you have some sort of model, and that your view controllers have access to it.
Typically, the app delegate sets up the model and then passes it along to the view controllers as necessary.
Something else that may help is that you don't have to let your view controller(s) be deleted when they're popped off the navigation stack. You can set up both view controllers in your app delegate, if you want, so that they stick around. You can then use the ones you've got instead of creating new ones all the time, and in so doing you'll automatically get some degree of persistence.
I've got an app that I've developed for the iPhone, but now want to port to the iPad. The iPhone app is navigation style and based on discrete table view controllers managed by a nav controller. The larger screen real estate of the iPad means that I can comfortably fit a couple of these table view controllers on to the screen at the same time.
The question is how? Should I
a) have the main view load two table view controllers from separate NIBs and then position them on screen (I'm not sure how I set they x and y of subviews loaded from nibs).
b) create sub-views in my main nib and populate these with data from my existing classes (if so how do I hook up the IBOutlets)?
c) do something completely different
One thing I should point out is that I don't want to use the split screen option.
Alert! This QA is now of historic value only.
It is now trivial to do this sort of thing with container views in iOS, which is why Apple edited them:
https://stackoverflow.com/a/25910881/294884
How to add a subview that has its own UIViewController in Objective-C?
Historic answer...
".. how I set they x and y of subviews loaded from nibs?"
I'm not sure if I fully understand your question Phil, but here's an easy and clear way:
Fire up interface builder and in the new larger iPad view, simply add new smaller views (UIViews)... Put them exactly where and how you want them. We are going to call these "basket" views.
Let's say one of your complicated views from the other app is your fatDogs view. Call the new basket view fatDogsBasket. Then in the code, in viewDidLoad, just do the following with all these "baskets"...
[fatDogsBasket addSubview:fatDogs.view];
[clientsBasket addSubview:clients.view];
[namesBasket addSubview:names.view];
[flashingLightsBasket addSubview:flashingLights.view];
// etc
You're done! (Obviously, make sure that the relevant view controllers, fatDogs, flashingLights and so on, are all ready to go and instantiated.)
The "basket" system is handy since each one will hold your previous work in one place; usefully you can (say) set overall invisibility or whatever just by touching the baskets. Obviously, if you want to set, or maybe move, the position of a basket in the code, just go
happyBasket.frame = CGRectMake(509,413,
happyBasket.frame.size.width,
happyBasket.frame.size.height);
UIViews in iOS are very lightweight, so it's no problem at all adding another layer of UIViews.
I hope this is what you were getting at!
------Later...
You went on to ask: "Just to make sure I'm clear on the right way to implement this. The main view controller has IBOutlets for each of the 'baskets' and its this IBOutlet connection to the subview that I'm calling. Each of the view controllers that I'm going to show in each basket has it's own nib and associated IBOutlets. Right? –"
So, "The main view controller has IBOutlets for each of the 'baskets'"...
Right, the main view in the new app, would have lines like this in the .h file:
IBOutlet UIView *fatDogsBasket;
Note that you are simply declaring "fastDogsBasket" to be a UIView. You shouldn't worry too much about the "IBOutlet" word. All that means is "I need to be able to look this item up, over in the interface controller." It's important to realise IT DOES NOTHING.
So yes all the "baskets" will be UIViews and hence of course you must delare them as such in the .h file of your main view controller. Personally is would not use the phrase "a view controller has IBOutlets." It sort of confuses things and gives the wrong idea. Just say "don't forget to mark the UIViews as iboutlets in the header file."
So anyway yes that's exactly what you do, declare all the "basket" UIViews in the .h file of the main controller, and indeed mark them all as IBOutlets so that interface builder will work more easily. Next ..
"its this IBOutlet connection to the subview that I'm calling" -- that's wrong.
The basket such as fatDogsBasket IS SIMPLY A UIVIEW and that's that. It's just a UIView.
Now, as you know you can put UIViews inside other UIViews. (Obviously, this is commonplace, every UIView has scores of UIViews inside it and so on and on - it's the most basic part of building up an interface.)
So, what are you going to put inside your fatDogsBasket uiview? You're going to put in ALL YOUR PREVIOUS WORK on fatDogs! Previously (for the iFone) you wrote a wonderful class - a view controller - called fatDogs. (It may well have even had many subclasses and so on.)
We're now going to take the view from fatDogs (of course, that is fatDogs.view) and literally put it inside fatDogsBasket. (Recall that fatDogsBasket is a UIView.)
So firstly you would have to completely include your amazing class fatDogs (from the old project) in your new project. Click "add existing flies/classes" or something like that...you'll figure it out. Yes, add all the class files, xibs, any subclasses and so on.
Then, simply do this .. in your new super-powerful uber-controller, in viewDidLoad, just do the following with all the "baskets"...
[fatDogsBasket addSubview:fatDogs.view];
[clientsBasket addSubview:clients.view];
[namesBasket addSubview:names.view];
[flashingLightsBasket addSubview:flashingLights.view];
// etc
You're done! Note that the view from fatDogs (ie, fatDogs.view) is now displaying inside of the UIView fatDogsBasket. The class fatDogs will now work completely normally, just as it did in the old days! And incredibly, you can easily (here in your new controller) do things like simply move fatDogsBasket, and it will move the fatDogs view easily all at once, without worrying about the details of fatDogs and it's views.
Finally you ask..
"Each of the view controllers that I'm going to show in each basket has it's own nib and associated IBOutlets."
Exactly correct. When you add your old system "fatDogs" to the new project, you will be adding all of it's xib files and so on. Anyting that happens or doesn't happen inside those classes, to do with perhaps buttons or anything else marked as iboutlets, or anything else, will just still be the same within those classes. I'm pretty sure absolutely NOTHING will change when you use those old classes in your new project.
Just for the record .. "Each of the view controllers that I'm going to show in each basket.." Just to be accurate, you don't really show as such a viewcontroller, you show the view of the viewcontroller (!!). In other words, for fatDogs (a view controller) you will be showing it's view, which is, simply enough, referred to as fatDogs.view. ("view" is, of course, a property of any UIViewController, so you can just say vcName.view and you're done.)
Hope it helps!
And finally you ask .................................
"I've got it compiling OK, but my baskets are showing up empty, i.e. they're not showing the views of the view controllers that I've imported."
Tell is the name of one of your UIViewController classes from the old project, so we can be specific
Let's say you have an old UIViewController called HappyThing. So you will very likely have a file HappyThing.h and a file HappyThing.m and a file HappyThing.xib.
put all those in the new project, you must do so using Add->Existing Files. (Control on one of your current filenames in the list on the left in XCode.)
You will have to do this #import "HappyThing.h" somewhere or other in your new project - either in your Prefix.pch file or at the top of your new UIControllerView
To be clear in HappyThing.h you will have a line of code
#interface HappyThing : UIViewController
In your new UIViewController.h file, you will have to add a new variable, we'll call it xxx,
HappyThing *xxx;
Note that the type of xxx is HappyThing. (Note that as a rule, you would use the naming convention "happyThing" (note the lowercase "h") rather than "xxx", but it's just a variable and I want it to be clear to you that it's just a variable.)
Next! At the moment it's just a variable that is not pointing to anything, it's nothing. (Just as if you said "int x", but then did not actually say "x = 3" or whatever.) So! In your code you have to actually instantiate xxx.
xxx = [[HappyThing alloc] init];
[xxxBasket addSubview:xxx.view];
Note that the first line is what makes an instance of HappyThing come in to existence. And of course, you want to use "xxx" to point to that instance.
The second line puts the view in to the relevant basket! Note that of course what you want is the view associated with xxx (ie, xxx.view) ... remember that xxx is a UIViewController, it is not itself a UIView. The associated UIView is "xxx.view". (The view is literally just a property of xxx.)
Memory management! Note that you used "alloc" to bring xxx in to existence. This means you DO own it, and of course that means YOU DO NOT need to send a retain there. Furthermore, since you do own it, that means You eventually have to RELEASE it. (easy ... [xxx release];)
So simply add the line [xxx release]; to the dealloc routine in your new UIViewController. (Really it won't cause any harm if you forget to do this, but do it anyway.) Conceivably you may want to release it earlier for some reason once you are more comfortable with the process.
(I was just working on a project with a huge number of huge tables, popovers and the like, so I only made them on the fly and got rid of them as soon as possible, to use less memory. But all of that is irrelevant to you at this stage.)
So now you should SEE IT ON THE SCREEN!
Don't forget if you previously had some routine in HappyThing, which you had to call to start it working (perhaps "beginProcessing" or something), you'll have to call that yourself from the new UIViewController. Hence perhaps something like:
xxx = [[HappyThing alloc] init];
[xxxBasket addSubview:xxx.view];
[xxx beginProcessing];
[xxx showAmazingRedFlashingLights]; // or whatever
Finally you asked ...
"When you've use this technique, do you simply include the headers of the imported files in your main view controller, or do you forward class them in some way?"
That was not your problem, your problem was that you were not instantiating it with the line xxx = [[HappyThing alloc] init];. So, good luck!
Regarding the line of code "#class HapyyThing", if you want to simply put it just above the start of the definition of your new UIControllerView. Generally you don't have to if you have your include line in the best place. Anyway it is an unrelated issue. It simply won't compile if your new UIViewController, can't find HappyThing. Enjoy!