I have a UIViewController — let's call it "FormController" — which is simply a form that edits an object. I want to use it in 2 different situations:
Creating a new object — using using UINavigationController's presentModalViewController: method.
Editing an existing object — push the view controller onto the UINavigationController stack, not using a dialog method.
There is a slight difference in that in the modal situation I would like to have a toolbar with "Cancel" and "Done" buttons, whereas in the stack situation I would like to just have the navigation bar provided by the UINavigationController.
This would be similar to the Contacts application where the "New Contact" and the "Edit Contact" screens seem to use the same view controller, but the New Contact form is presented modally while the Edit screen is pushed onto the navigation stack.
My question is: What is the best way to handle both situations without having to write 2 separate, but mostly identical view controllers?
I thought about creating a "ModalFormController" which encapsulates the bare "FormController" through composition and adds a toolbar, but I read somewhere in the docs that Apple doesn't recommend nesting view controllers.
Why not use subclassing? Make ModalCreateFormController a subclass of EditFormController and handle the modal-specific stuff in the subclass.
What I do (sometimes) is set up an enum that specifies the type of the view controller.
For example, you might have two types: an Edit type, and an Add ("new") type.
The Add type is implemented via a modal view controller, while the Edit type is pushed onto an existing navigation stack.
In the view controller's -viewDidLoad: method, I simply do a switch/case tree that sets up the title and other appearance characteristics depending on the type enumeration specified above.
The nice thing about this is that it is easy to add a new type. The downside is that the conditional tree for handing this enumeration can get complicated quickly, depending on how different the types are.
But the switch/case tree makes it a lot easier to manage.
So, it depends on what you're trying to do with the two types. But it's definitely doable.
In addition to having an explicit property on the view controller (as Alex Reynolds suggests), two other approaches that occur to me are:
If you have some kind of model object that you're editing, ask it for its current state. If it's ever been saved, then you're in edit mode. Otherwise, you're in create mode.
Look at the value of the controller's parentViewController property. If it's an instance of UINavigationController, then you're in the navigation stack. If you're being displayed modally, it'll be an instance of your list controller.
Ug, I hate extra ivars…
I use this instead:
if([[self.navigationController viewControllers] objectAtIndex:0] == self){
//Modal
}else{
//Pushed
}
It is a bit of a hack, but we are using the logic that if the offending view controller is the first in the stack, you can't go back. Actually we are ignoring the fact of whether it is modally displayed at all.
I had to do this a bunch of times in my app and after trying a couple different ways of doing it, including modal subclasses & a re-usable modal helper classes that used forwardInvocation. I found the best pattern was to make a containingModalViewController method each view controllers that (usually) creates and returns a UINavigationController for the caller to use with presentModalViewController.
In most cases this method builds and returns a UINavigationController with self as the root view controller (with repeated calls to the method checking self.navigationController and returning that instead if it's not nil). Other cases I made a dummy root controller first and pushed self on second in order to get a back button. Then a trick can be used to catch the back button press: http://smallduck.wordpress.com/2010/10/05/intercepting-uinavigationcontroller/
In some cases the view doesn't need a navigation bar and so this method just adjusts some flags and returns self. I even found in some cases that did need a navigation bar it was simpler to make that method invoke self.view, then tweak the view hierarchy to add a UINavigationBar and again return self. But in any case, the setup often isolated to that one method, and the caller handles it the same in each case.
Apple explains how the contacts application works under the hood:
To allow a custom view controller class to be used to both display and edit content, override the setEditing:animated: method.
You get some functionality for free, e.g. Edit/Done button.
Related
I have created a seperate class to handle loading data from a SqlServer. Right now I pass a search term to the object and it searches for the items in a database.
If it finds more than one item it needs to present a modalviewcontroller. The problem is that this is a NSObject and doesn't know about presenting modal views.
How can I present a modalviewcontroller from a NSObject?
Try to delegate presenting the modal to a view controller - either by posting notifications on duplicates (gives you flexibility in which view controller presents) or defining a delegate protocol. This will keep your model separate from your view, preserving the MVC architecture of your app.
EDIT: using blocks for delegation is a fine approach in my view. I would just adjust your API to take a block to be performed in case of a duplicate, and have your modal take another block to handle the selection from many. That will probably give you maximum flexibility.
EDIT2: Based on understanding of your current API, I'd recommend this:
- (void)searchForItemWithString:(NSString *)searchString completionBlock:(librarianDidSelectItemBlock)block multiSelectBlock:(librarianMultiSelectBlock);
Furthermore I'd design your modal view controller to take a completion block as well.
I'm not going to say this is good design by any means. I'm kind of inheriting something that is existing. Anyway, there is a TabController. One this one tab, there are two views that get loaded on demand based on a UISegmentController. Both of these two ViewControllers are subclasses of another ViewController that has methods I need.
When I'm in the TabController, I want to create a method that uses some of the superclass methods of the two ViewControllers. How do I get access to the tab's current ViewController since it's loaded on demand? Do I need to have a reference of the base controller type, and just have it set to the current view controller when it gets loaded on demand? Thanks.
To get the active tab showing on the screen, you could use [self.tabBarController selectedViewController] which will give you a UIViewController Reference. If you want to use the methods then you can cast it to your ViewController Superclass and then call methods on it like so (where self.tabBarController is your Tab Bar Controller):
MySuperClassViewController *viewC = (MySuperClassViewController *)[self.tabBarController selectedViewController];
[viewC someMethodDeclaredHere];
First, a little bit of terminology to clear up some potential confusion: I assume you mean a UITabBarController which controls various view controllers. Also, it seems you are using a UISegmentedControl which is not a view controller but a subclass of UIView. I hope these are just typos and not conceptional problems.
There is still some ambiguity about what you mean with "when I am in the tab controller". I assume you want to put code into the class representing the UITabBarController. But why? Just put these methods into the appropriate view controller, or if it is something that has to be done before, into your app delegate. However, if these methods are in a view controller superclass, they should have something to do with the logic necessary for this view controller.
If you need the methods elsewhere, i.e. outside your view controllers, consider creating a separate #include file and putting the methods there. Alternatively, you can use your app delegate which is conveniently accessible through [[UIApplication sharedApplication] delegate].
In the app represented by the image below, I'm currently using three UIViewControllers: One master view controller, one for the main menu, and one for a settings screen which is launched by the main menu. As I'm learning more about how UIViewController works and what it's designed for, I'm questioning the wisdom of my architecture.
It seems to me that the main point of subclassing is to be able to override the methods which get called automatically during the life cycle of the controller: viewDidAppear, viewWillAppear, willRotateToInterfaceOrientation, etc. It appears that these methods are only called if the UIViewController (or subclass) is part of the UIViewController hierarchy. Therefore, there's no point in subclassing UIViewController unless I'm going to use one of the standard means of creating a viewcontroller hierarchy i.e. UINavigationController, [UIViewController presentModalViewController] etc.
I'm wary of using the Cocoa-style means of adding view controllers to the hierarchy because they all seem to be very restrictive. For example, I could display my settings screen using [UIViewController presentModalViewController], but but I don't want it to obscure the entire screen. There's background animation which I want the user to be able to interact with even while the settings screen is visible.
Here are my questions:
1) Is it silly to subclass UIViewController unless I'm going to be adding it to the viewController hierarchy via one of Apple's techniques?
2) Am I correct in my assumption that the built-in means of displaying new views are too restrictive for me, and in order to have the flexibility I want, I'm going to need to just load views via [view addSubview]
3) If it's true that subclassing UIViewController makes no sense for my menu and settings views, how should I avoid having all of my code in one monster UIViewController subclass. Should I just subclass NSObject, add the appropriate IBOutlets and IBActions and pass that in as the File's Owner when I load the nib using [NSBundle loadNibNamed]?
Good question. First, a point of clarity: What you refer to as "one of Apple's techniques" is referred to in the UIViewController Programming Guide as "indirect presentation", and includes things like modal presentation, being pushed on a navigation stack, presenting a popover controller, etc. Basically all of these view controller methods are considered "indirect" presentation methods, while the use of -addSubview: (something like [someView addSubview:myViewController.view]) is considered "direct" presentation.
From said programming guide: (Giant Block Quote...)
It is recommended that you use only
the suggested techniques for
displaying the views of your view
controllers. In order to present and
manage views properly, the system
makes a note of each view (and its
associated view controller) that you
display directly or indirectly. It
uses this information later to report
view controller-related events to your
application. For example, when the
device orientation changes, a window
uses this information to identify the
frontmost view controller and notify
it of the change. If you incorporate a
view controller’s view into your
hierarchy by other means (by adding it
as a subview to some other view
perhaps), the system assumes you want
to manage the view yourself and does
not send messages to the associated
view controller object. (emphasis mine)
Apart from your setting up your
application’s initial interface, most
other views are presented indirectly
through their view controller objects.
All that is to say that you are correct in thinking that all of those UIViewController messages will be wasted if you if simply add the view to a view hierarchy directly, and take no other further action (key window being the exception). That quote also mentions that it is most common to use indirect presentation.
1) I hesitate to make a blanket statement and say "Yes, in all cases, it is silly to subclass UIViewController unless you're presenting it indirectly." I'm sure there is some good use for it somewhere. I'll settle for saying that I have personally never done so.
2) Absolutely, I would not use a UIViewController subclass here.
3) Allow me to direct your attention to another area of The Programming Guide:
In iPhone applications, the views in a
view hierarchy traditionally cover the
entire screen... If you want to divide
a view hierarchy into multiple
subareas and manage each one
separately, use generic controller
objects (custom objects descending
from NSObject) instead of view
controller objects to manage each
subarea. Then use a single view
controller object to manage the
generic controller objects.
That pretty clearly syncs up with what you're wanting to do here. You're dead on with your self suggested approach. That "Settings Screen launched by main menu" should be managed by a generic controller object descending from NSObject, which is in turn managed by your full-screen UIViewController subclass.
I'm trying to find the best way to refactor this. Right now, each of the view controllers (about 20 of them) have a function that initializes the content of the toolbar / navigation bar like so ie,
-(void)toolbarInit
and on each of the controller's viewDidLoad, you will see that the function is being called ie, [self toolbarInit];
Basically what that toolbarInit does is to put a loginButton on the navigation bar's rightBarButtonItem.
Should I:
a. put the toolbar/nav bar setup in the app delegate ( is it possible to initialize each of the view controller's nav bar no matter how deep down the stack it is already?)
b. create a toolbarController or something and just put all the setup code/login code over there?
Many thanks for any other suggestions.
I'd consider one of these options:
It sounds as though you're repeatedly pushing the same or similar UIViewControllers onto the stack. Is it possible they should all derive from the same UIViewController subclass? If so, the initialization could take place in a superclass shared by all of the 20 or so items in the stack.
If the view controllers have different superclasses, consider defining a category on UIViewController that handles the instantiation and addition of your buttons. Then you need only import the header and call the same [self toolbarInit] in viewDidLoad.
Same as above, except instead of using a category, create a standalone class for handling setup like this. The logic in toolbarInit could be stuck in a class method like setupNavigationItem:.
I have a view that contains a UITableView and a UILabel which works perfectly as far as I can tell. I really don't want to manage the UIView and UITableView with the same controller as the UITableViewController handles a lot of housekeeping and according to the documentation:
If the view to be managed is a
composite view in which a table view
is one of multiple subviews, you must
use a custom subclass of
UIViewController to manage the table
view (and other views). Do not use a
UITableViewController object because
this controller class sizes the table
view to fill the screen between the
navigation bar and the tab bar (if
either are present).
Why does Apple warn against using it and what will happen if I ignore this warning?
Update: Originally I quoted the following from the Apple Documentation:
You should not use view
controllers to manage views that fill
only a part of their window—that is,
only part of the area defined by the
application content rectangle. If you
want to have an interface composed of
several smaller views, embed them all
in a single root view and manage that
view with your view controller.
While this issue is probably related to why UITableViewController was designed to be fullscreen, it isn't exactly the same issue.
The major practical reason to use only one view controller per screen is because that is the only way to manage navigation.
For example, suppose you have screen that has two separate view controllers and you load it with the navigation controller. Which of the two view controllers do you push and how do you load and reference the second one? (Not to mention the overhead of coordinating the two separate controllers simultaneously.)
I don't think using a single custom controller is a big of a hassle as you think.
Remember, there is no need for the TableviewDataSource and the TableViewDelegate to be in the actual controller. The Apple templates just do that for convenience. You can put the methods implementing both protocol in one class or separate them each into there own class. Then you simply link them up with the table in your custom controller. That way, all the custom controller has to do is manage the frame of tableview itself. All the configuration and data management will be in separate and self-contained objects. The custom control can easily message them if you need data from the other UI elements.
This kind of flexibility, customization and encapsulation is why the delegate design pattern is used in the first place. You can customize the heck out of anything without having to create one monster class that does everything. Instead, you just pop in a delegate module and go.
Edit01: Response to comment
If I understand your layout correctly, your problem is that the UITableViewController is hardwired to set the table to fill the available view. Most of the time the tableview is the top view itself and that works. The main function of the UITableViewController is to position the table so if you're using a non-standard layout, you don't need it. You can just use a generic view controller and let the nib set the table's frame (or do it programmatically). Like I said, its easy to think that the delegate and datasource methods have to be in the controller but they don't. You should just get rid of the tableViewController all together because it serves no purpose in your particular design.
To me, the important detail in Apple's documentation is that they advise you not to use "view controllers [i.e., instances of UIViewController or its subclasses] to manage views that fill only a part of their window". There is nothing wrong with using several (custom) controllers for non-fullscreen views, they just should not be UIViewController objects.
UIViewController expects that its view takes up the entire screen and if it doesn't, you might get strange results. The view controller resizes the view to fit the window (minus navigation bars and toolbars) when it appears, it manages device orientation (which is hard to apply correctly if its view does not take up the entire screen) etc. So given how UIViewController works, I think there is merit to Apple's advice.
However, that doesn't mean that you can't write your own controller classes to manage your subviews. Besides the things I mentioned above, interacting with tab bar and navigation controllers, and receiving memory warnings, there isn't really much that UIViewController does. You could just write your custom controller class (subclassed from NSObject), instantiate it in your "normal" fullscreen view controller and let it handle the interaction with your view.
The only problem I see is the responder chain. A view controller is part of the responder chain so that touch events that your views don't handle get forwarded to the view controller. As I see it, there is no easy way to place your custom controller in the responder chain. I don't know if this is relevant for you. If you can manage interaction with your view with the target-action mechanism, it wouldn't matter.
I have an application where I did use 2 separate UIViewController subclasses below another view controller to manage a table view and a toolbar. It 'kind of' works, but I got myself into a massive pickle as a result and now realize that I should not be using UIViewController subclasses for the sub controllers because they contain behavior that I don't need and that gets in the way.
The sort of things that went wrong, tended to be:
Strange resizing of the views when coming back from sub navigation and geometry calculations being different between viewWillLoad and viewDidLoad etc.
Difficulty in handling low memory warnings when I freed the subview controllers when I shouldn't have done.
Its the expectation that UIViewController subclasses won't be used like this, and the way they handle events, using the navigation controller etc that made trying to use more than one UIViewController subclass for the same page tricky because you end up spending more time circumventing their behaviour in this context.
In my opinion, The Apple Way is to provide you the "one" solution. This served the end-users very well. No choice, no headache.
We are programmers and we want to and need to customize. However, in some cases, Apple still doesn't want us to do too many changes. For example, the height of tab bar, tool bar and nav bar, some default sizes of the UI components(table view), some default behaviors, etc.. And when designing a framework and a suite of APIs, they need to nail down some decisions. Even if it's a very good and flexible design, there is always one programmer in the world wants to do something different and find it difficult to achieve against the design.
In short, you want a table view and a label on the same screen, but they don't think so. :)