I recently watched this video tutorial on how to create a custom UIPickerView, and I successfully implemented the UIPickerView in my project. However, I would like to make some changes to the UIPickerView that appears within my app.
For starters, is the custom UIPickerView outlined in the video an example of subclassing?
Second, is it possible to modify an instace of the custom UIPickerView to have a different text label other than Done? And if so, would I have to modify the KCModalPicker.h/m files?
Thus bringing me to my third question, if I modify the KCModalPicker.h/m files then every other instance of the class in my project will inheret the changes, so what is a way to keep the base class as is, but be able to add customization to the class, so things like how many columns the UIPickerView has is dependant upon the instance that is obstantiated, and not dependant upon the KCModalPicker.h/m files?
UPDATE
The source for the ModalPicker class I am referring to, can be found here,
https://github.com/subdigital/nsscreencast/tree/master/025-custom-picker-component-part-1
I don't want to watch a video in order to answer your question, and suspect others feel the same way. (I hate watching development videos because they are long and tedious. I don't need somebody explaining in great and painful detail how to do something. Let me skip to the parts I'm interested in.) You should describe the scheme that is used so that we can answer your questions about it.
If that video describes a class KCModalPicker, it might subclass UIPickerView, or it might contain a picker view (that would be a "has-a" relationship, not an "is-a" relationship. The KCModalPicker is probably a modal view controller that has a picker view inside it.)
If you want to modify a class, like KCModalPicker, but don't want to change all instances, then yes, subclassing would probably be a good way to go. Create a subclass called something like MyModalPicker that inherits from KCModalPicker and changes the behavior however you need it to.
EDIT:
After looking at the files on Github, it looks like the project has a class BSModalPickerView which is a subclass of UIView, and contains a UIPickerView. As described above, this is a "has-a" relationship. The BSModalPickerView class has a picker view inside it that it manages. So no, this project does not appear to use subclassing.
The demo program has a view controller that uses the BSModalPickerView method presentInView:withBlock: that displays the picker as a subview of the view controller's main view.
It looks like there is also a method presentInWindowWithBlock: that will display the picker view directly in the window.
If you want to modify the behavior of some BSModalPickerViews and leave others alone, creating your own custom subclass of BSModalPickerView would be a reasonable way to do that. You could also modify the root BSModalPickerView to have more setup options (extra properties or parameters that you pass in the init method).
BTW, your question asks about KCModalPicker.h, but the class I see in the github link you posted is BSModalPickerView. Not sure what the discrepancy is.
Related
Thinking it over, this feels like a bit of a noob MVC question, but I can't come up with or find a definitive answer so I feel I should ask and get some clarity for myself.
I have a custom view that I created using a xib. It is going to be used in, currently, 4 other places in my app. Each usage has identical functionality, so I'm basically just creating a custom control object that I can reuse multiple times.
My "control object" consists of a UITextField, and two UIButtons.
The functionality I'm looking at implementing is, the first button will bring up a UIPicker and the 2nd button is essentially a done button and will just resignFirstResponder on the UITextField. As previously mentioned, this is consistent everywhere this will be used.
What I'm curious about is, is it ok for me to build this functionality directly into the custom UIView subclass since it is consistent behaviour for all instances of my control object? Or, do I need to create a custom UIViewController subclass to go along with it?
Currently, in my main UIViewController for my app I am creating instances of my custom UIView "control object" and treating them the same as any other control object. If I should actually be creating a custom UIViewController class to go along with it, well, I'll have more questions for another thread as to how I should be doing that (unless someone can direct me to a resource on this)
So far, searching the web has yielded nothing for me and from everything I've seen so far with iOS development in general, I've gotten the vibe that UIViewControllers are really only ever for a main, presentable view (that takes up the entire screen.. I might be missing some terminology for this).
My gut feeling is that no view controller is necessary in the scenario I'm describing, but I'd like to try to get some sort of confirmation, if possible.
There is no silver bullet, so no approach is absolutely right or absolutely wrong. What you describe here is just a view that changes its states. So putting everything in your UIView subclass is completely OK. It also conforms to the KISS principle.
However, as far as I understand, and correct me if I'm wrong, the input of your custom view - the text and the picked value from the picker does not really affects the view itself, but the viewController it's attached to. So you need to pass that input to the hosting viewController. This can be achieved by protocol with a default implementation. So the handling of the input data is written only once, but can be attached to whatever viewController you want.
Based off of everything that you've said, I see no need for another view controller. I can see where the answer could be a little unclear considering that the actions are something that ViewControllers usually handle, but I think you'll be just fine letting your custom view handle this by itself.
If you add more functionality or more complex operations, then perhaps it is time to explore other options but for now I think the single view will be fine.
Maybe this is a silly question, but I've bumped into it a number of times during iOS Development.
Sometimes I'll develop a view component that I want to use on multiple screens, so I'll decide to subclass UIView and make it something I can use in multiple places.
Then, I start adding functionality to it. Maybe it needs to respond to an NSNotification, or it is supposed to respond to user touches.
At a certain point, I start wondering if I should really be making a UIViewController subclass, and add it to my UI as a child ViewController.
Is there any consensus on where to draw the line between adding some behaviors to a UIView, and when to create a full UIViewController?
I can't tell you about the consensus, but here's my opinion:
Subclass UIView only when...
You want to do custom drawing
You need to customize some behaviour of an already existing UIView subclass
You have special needs for layouting subviews. Most layouting can be done by UIViewController, though.
Maybe for special touch handling that you can't be done with gesture recognizers
Subclass UIViewController in all other cases. You almost always need a controller anyway, for writing glue code that ties together views and models, or for handling user interaction. Consequently, Apple has made it easy in UIKit to let controllers do all the work and to keep views as "stupid" as possible. For instance, it is very simple to nest controllers to create complex view hierarchies, without the need to have a single view subclass.
An indicator that subclassing UIView is not the first thing one should do is the section titled "Alternatives to Subclassing" in the UIView class reference. An indicator that subclassing UIViewController is the preferred thing to do is that there is no such section in the UIViewController class reference :-)
You should use a controller anytime that you need to handle or control data. Views are supposed to be as stupid as possible, not knowing what they are displaying but rather where. You can easily subclass and reuse ViewControllers. A good example, say you need to retrieve a string (or text) from the user throughout your app via a popover controller and a modal. Create a generic subclass of UIViewController that has a view with a textfield and a button. You can then use this view and it's controller in any capacity you need. Reusing it in the popover, modal or anywhere else (and generally passing the data back through delegation). Since you are dealing with data you should not being using a sole subclass of UIView.
From my experience I subclass UIViewControllers more often then UIViews. It is a little difficult for me to understand if you are solely talking about Containers or reuse of views in general application workflow. Either way though it should be the same.
I've used the embedded view controllers to load reusable table views from time to time. I've found that it's useful sometimes but not always. Communication between the two can be cumbersome, like if you want the embedded controller to communicate back up to the container. Delegation makes it easier but still cumbersome. It also limits you to iOS 6, if I remember right iOS 5 and lower don't support embedded controllers.
If it's just adding methods you can use a category to store some extra methods. I do that a lot on NSManagedObjects that I don't want to subclass and if I regenerate the NSManagedObject from the datamodel I don't lose the code in my categories. Gives me added functionality like calculated fields or conversion methods without having to subclass. If you don't need those methods for a particular instance just exclude the reference to the category.
Subclassing never is bad though IMO.
If I want to build a generic UI Component (one that will handle its own view and logic, data source,
etc), is it a good practice to subclass UIViewController?
I would say no. But it depends. If your component manages other view controllers or has/will have any kind of logic that's not specific to a view (e.g. navigation logic, business logic etc) , then you should subclass a view controller. Then again that makes it more than an UI component.
Otherwise, you should subclass an UIView, like Apple does with many components, including UITableView (speaking of datasource), GLKView, UICollectionView.
My overly simplistic answer is "no, when building a generic component do not automatically start with a UIViewController subclass". However that alone is not a useful answer and in some cases a UIViewController subclass is exactly the right solution.
Instead let's consider how to decide what your component should be. I think the best way to figure that out is to answer three questions:
What is this component responsible for?
How do you want to interact with it?
What are its dependencies?
In all cases we can try to start as simple as possible and add complexity only when the answers to those questions require it.
Could this component just be a function? No objects, no classes, if all you want to add is some behavior then maybe all we need is a function. If this behavior only applies to specific existing types then maybe we need a category on an existing class.
Not enough to cover what we want to do? Ok, I guess we might be talking about a new type so let's create a class. Can it just be a subclass of NSObject?
Want to display something in a view? Ok, then we at least have a UIView subclass, maybe a UIControl subclass if it is more interactive.
The view needs some data to back it? No problem sounds like we now need two pieces; a view to display data and a data source to provide it. Here the view shouldn't need to know who creates and owns this data source. As long as one was provided to the view we can use it, anything else is outside of the view's area of responsibility. Similarly we might add a delegate to notify some other object of interactions with the view.
If we still haven't covered all of this component's responsibilities then maybe we need yet another piece, something in the controller layer to manage our view. We're still not (yet) talking about a UIViewController though! It's fine to have a "controller" or "service" that is a NSObject subclass. If all this piece needs to do is manage network connections, or map NSFetchedResultController results to our view's data source protocol and update the view, or just provide a convenient implementation of the most common mapping of model objects to the view's data source then a simple "controller" object is still all we need.
Still not enough? Finally we get to the point where we consider providing a UIViewController subclass. Maybe we want to allow users of the component to just present a modal view controller to hand off responsibility for an interaction (send an email, compose a tweet). Maybe there's a common set of default behaviors we want to provide that are tied to view controller life cycle events (UITableViewController flashing scroll bars in -viewDidAppear:).
Build your component from the pieces you need to support the behaviors you want to provide but keep it as small and simple as possible.
Yes, it's good practice in many cases. The iOS SDK contain many examples of UIViewController subclasses. A few of them contain only a small amount of generic behavior and are essentially useless without customization:
GLKViewController
UICollectionViewController
UITableViewController
And some of them provide significant generic behavior but are still mainly containers for your own view controllers:
UINavigationController
UIPageViewController
UISplitViewController
UITabBarController
But most of them are essentially complete packages with little or no need (or ability) to customize their behavior:
ABNewPersonViewController
ABPersonViewController
ABUnknownPersonViewController
EKCalendarChooser
EKEventEditViewController
EKEventViewController
GKAchievementViewController
GKFriendRequestComposeViewController
GKGameCenterViewController
GKLeaderboardViewController
GKMatchmakerViewController
GKTurnBasedMatchmakerViewController
MFMailComposeViewController
MFMessageComposeViewController
MPMediaPickerController
MPMoviePlayerViewController
PKAddPassesViewController
QLPreviewController
SKStoreProductViewController
SLComposeViewController
TWTweetComposeViewController
UIActivityViewController
UIImagePickerController
UIReferenceLibraryViewController
UIVideoEditorController
If you think about what all of these have in common, you may conclude that they all have two things in common:
Each has a specific model (in the MVC sense) that it interacts with, and that model is not specific to your app. The models vary widely (UIVideoEditorController's model is a single video; UIImagePickerController's model is the entire photo library; GKAchievementViewController's model is a database possibly on an Apple server in “the cloud”), in some cases you provide the model (or some properties of the model) up front, and in some cases you receive the model (or a fragment of it) at the end. But in every case, the view controller handles all the interaction between the user and the model with little or no ongoing help from your app.
Each provides its own view hierarchy, with little or no customization required (or even permitted).
In other words, each of these view controllers isn't just the “C” of an MVC pattern. It's the tip of an entire MVC iceberg.
If your component is also an MVC iceberg, then exposing the tip of your iceberg as a UIViewController subclass is quite appropriate.
It depends on the iOS version you used.
A. prior to iOS 5.0, It's not a good practice, and not recommend.
B. start with iOS 5.0, It's just ok.
subclass a view controller for a UI component (UIView), , that means you wanna use the view controller life cycle method, to manage the user interaction and view display procedure, data model etc. So, if the life cycle method can not easily automatic called, the view controller is not that meaningful.
start with iOS 5.0, it's possible to create custom view controller container, so, it's ok to build custom generic ui component with view controller to add as a child view controller.
prior to iOS 5.0. Subclass a UIView with custom delegate protocol is the right way. one other thing is about the code organize. put the all custom delegate method to another custom class, not in the view controller, in the view controller just init a delegate class instance, and set this to the view delegate property.
I'm new to obj-c/iOS and I'm having trouble understanding conceptually at least viewControllers. I've read a lot of the Apple Doc's, I've even used viewControllers to some extent in xCode, but I still don't quite get what they are, or what are the best ways to use them.
I've been an AS3 dev for many years so my mind works in the context of MovieClips/Sprites and the Display list to get graphics on the screen.
Ok so from my understanding...
A viewController is a kind of class that handles graphics in some
fashion and then allows you to do something with them?? What is it in it's most basic sense?
You seem to add viewControllers to a Window class, which I guess is a bit like
adding a display Object to the Display list?
What is it that a viewController does for you in it's most basic sense?
Are there certain things you definitely can't do with them or shouldn't do
with them?
Do viewControllers need to be connected in some way to the rest of the iOS framework to function (apart from being added to a window).
How exactly do they use data? (I've read up on MVC, I understand that conceptually this is a slightly different question) as I understand it you don't hardcode data into a viewController, so how does a viewController access any static data?
Let's say I just wanted to throw an image up on the screen, exactly what part would the viewController play in that process? is it just something which handles only one small aspect of that process or is it the whole show and handles everything?
Does one viewController handle multiple images? is it like it's term, a "controller" for all the images presented on screen, or does it handle one image at a time?
What is a viewControllers connection to the image(s) it handles? it contains references to them?
I'm using the Sparrow framework which is helping but I would still like to be able to get my head around what viewControllers are so I know how to use them properly.
Ha, I apologise for the above I know it must look like I'm completely confused :) thanks for any advice.
Hope this helps you:
A viewController is a kind of class that handles graphics in some fashion and then allows you to do something with them??
It's the glue between a View (Xib File) and the Data (Could be
CoreData or whatever you're using in the backend). All the UI Elements
you are using in the View you normally define as properties in the
controller to get access to them.
What is it in it's most basic sense?
You seem to add viewControllers to a Window class, which I guess is a bit like adding a display Object to the Display list?
I don't really know AS3 so I cannot compare Display lists with ViewControllers. But basically ViewControllers are there to handle
different types of transitions between the views and accessing
(setting/reading) the data which is displayed in the view.
What is it that a viewController does for you in it's most basic sense?
Like I've written above. Most basic sense they interpret what the user
does on the view and depending on the action of the user changes the
model.
Are there certain things you definitely can't do with them or shouldn't do with them?
It is always hard to keep the border between model and controller.
They are pretty close to each other. So what I normally try is to
delocate all logic stuff (like calculations, database access and so
on) this does more belong into the model part. But of couse you're
using these external classes in the controller.
Do viewControllers need to be connected in some way to the rest of the iOS framework to function (apart from being added to a window).
Well like you already have written the ViewController needs to be
connected to a view. Otherwise it would not make much sense. There are
different subtypes of UIViewController such as UINavigationController
where you probably need to overwrite some other methods to provide the
whole functionality wanted by these special subtypes.
How exactly do they use data? (I've read up on MVC, I understand that conceptually this is a slightly different question) as I understand it you don't hardcode data into a viewController, so how does a viewController access any static data?
There could be different approaches to store the data. Simplest way
would be to have the data directly stored in the UIViewController.
This could be a custom class which is the container of the data. All
changes are directly written into this class and displayed by the
UIViewController. But in most of the cases it makes sense to use
CoreData (Which is responsible for reading/writing the data into a
sqlite database). You could look at CoreData as your model and the
UIViewController gets the data from there and passes the data which
the UIViewController has received from the View back to it.
Let's say I just wanted to throw an image up on the screen, exactly what part would the viewController play in that process? is it just something which handles only one small aspect of that process or is it the whole show and handles everything?
The UIViewController would store an internal Property (UIImageView *)
which is in the Interface Builder connected with the UIImageView you
have created in the Xib file. So over these property you can change
through your Controller the image.
Does one viewController handle multiple images? is it like it's term, a "controller" for all the images presented on screen, or does it handle one image at a time?
Yes, this isn't a big problem. You can have as many images you want.
You just need to have the properties defined in the UIViewController
and linked to the View.
What is a viewControllers connection to the image(s) it handles? it contains references to them?
Yeah, its like a reference to the UIElement. You can then change
whatever property of the UIImageView you want directly from the
UIViewController
Some useful links:
Apple Official ViewController Guide
Apple Official ViewController Basics
You should have a look at Storyboards (U can use them since IOS 5.0)
I recommend you to check:
https://stackoverflow.com/questions/1939/how-to-articles-for-iphone-development-and-objective-c
Here are the answers to your questions:
No, it's doesn't handle graphics. It's the controller of the MVC design pattern. It handles the lifecycle of it's contents (for instance the views) and the data linked with.
A UIViewController is set as a root of an UIWindow. For instance, a UINavigationController is a subclass of UIViewController that stacks UIViewController in order to deal with the navigation.
Response in (1)
Try to be more specific with this question please.
As already commented, it's useful if you use the already built-in components like UINavigationController or UITabBarController.
For instance, you can have the data in instance variables and the display them in the contained UIView.
The UIView attached to your UIViewController will contain an UIImageView. Your UIViewController would have a connection with it in order to whatever changes you need, for instance, changing the image when the user press a button.
It can contain multiple UIViewsand therefore multiple UIImageViews (it's a subclass of UIView)
As commented, they would be contained on an UIImageView and would be linked programmatically or with an IBOutlet.
In a nutshell, a view controller is the controller in the MVC pattern. Please check this link before reading further so you're up to date with this pattern:
http://developer.apple.com/library/mac/#documentation/General/Conceptual/DevPedia-CocoaCore/MVC.html
OK, basically a controller manages a collection of views. It also fetches data from your model and sets the state of the views. It's important to note that the views know nothing of your model (your data), and the model knows nothing about your views. A controller also receives events from the views and decides how to change your model accordingly. It is essentially managing the synchronisation between your views and model.
There are technologies that help automate this such as KVO and key value binding. A google search will help you there.
One more thing. No other part of your application should access your views except for the controller. So generally in an application controllers tend to communicate with each other, for example via transitions or the delegate patterns between controllers under a navigation controller. So your application backbone tends to be controllers talking to each other.
I have a UIView subclass which contains some labels, a tableview, and a few other bits an pieces. It is currently the delegate and datasource for the tableview, and also manages many UI actions, none of which rely on data. For example, when an 'edit' button is pressed, it knows how to update its controls, but it won't do anything when 'save' is pressed besides switch the controls back to the previous state. All of this is done in code, I'm not using IB at all in this application.
I now want to plumb in all the data model changes that it can provoke. But I would like to put these in a new controller class, which I guess is the MVC compliant way to do things. I'm not sure how to get there.
First, I need to create a custom controller class. Should I be exposing from the UIView subclass a few of the controls so that the view controller can access them? For example, I will need to read and write to a textfield in the view, so should I provide a getter/setter for this?
Secondly, the tableview - instead of the UIView being the delegate, should I expose this also, and make the view controller the delegate? I.e. view.tableView.delegate = self from the UIViewController?
And finally, how do I launch the view from another view? Specifically, this is a paged scrollview application similar to the weather app, so I have a mainView UIView that specifies the single paged scrollview and then adds multiple custom UIViews, one for each page. How do I replace [scrollView addSubview:myCustomView] and instead add the viewController? And how do I connect the view to it's controller and vice versa?
I've not tried all of this without IB before so thanks for helping.
Your question is very broad, and part of the answer would depend on how you code your solution. I will try replying with a few hints of what works for me:
View: As a general rule of thumb, keep in mind that a view object should be something very generic, that knows nothing about other views outside of its own hierarchy. As such, a view should not rely on any specific interaction with other views, but rather communicate back to its delegate / owner / creator through callbacks, protocols, blocks, etc, when needed.
View Controller: Any time you need to make two views in different hierarchies interact with one another, my suggestion is that you stick to handling that interaction through the view controller. By doing so, you'd be making sure your view is not contaminated by code that would be useless in a different screen.
Also please keep in mind that UIViewController for iOS is intended to be a class that you use for handling the complete visible view hierarchy, as opposed to acting as the controller for a single view. As such, I recommend that you don't attempt have a controller for each view, but rather a single one to handle them all.
Publishing view elements: How much a UIView exposes as public in its header file is up to your implementation. Any method that handles the way the view looks, that looks to be generic and reusable, and that doesn't need anything from outside the scope of the view's tree, is surely something you want to include in it's implementation and publish in the header file.
The same goes for any property that you feel is highly probable that someone from the outside will need to access.
Suggestion: publish only what's really needed. Usually publishing new methods and properties is easier than removing them later on.