I am at the beginning of developing an iOS app I am having trouble understanding the MVC (Model-View-Controller) design pattern. I thought I had it down but the more I read the more confused I get. I don't know if this should be an iOS specific question or if the same goes for every use of MVC. I am not using storyboards btw, I want to do it all programmatically.
I believe I understand the basic relationship between Controllers and Models, it's the separation of Views and Controllers that I don't get. Let's say I want to create a UIButton and display it on the screen. Should I initiate the button in the Controller or the View? The controller is responsible for what should be displayed, correct? Wouldn't you just call on a View to display that and not worry about creating the button in the Controller? From what I understand, View Controllers are just Controllers and should therefore control the View, not be the View. It seems like most people do just about everything in the View Controllers. I guess my question boils down to what code goes where?
UIViewController is controller part in the MVC pattern of code.
M(Model)
C(ontroller)
V(View)
Controllers handle navigation between different views , etc.
From here you can get more idea : view and viewcontroller
A view is an object that is drawn to the screen. It may also contain other views (subviews) that are inside it and move with it. Views can get touch events and change their visual state in response. Views are dumb, and do not know about the structure of your application, and are simply told to display themselves in some state.
A view controller is not drawable to the screen directly, it manages a group of view objects. View controllers usually have a single view with many subviews. The view controller manages the state of these views. A view controller is smart, and has knowledge of your application's inner workings. It tells the dumb view objects what to do and how to show themselves.
A view controller is the glue between you overall application and the screen. It controls the views that it owns according to the logic of your application
About View Controllers
View controllers are a vital link between an app’s data and its visual appearance. Whenever an iOS app displays a user interface, the displayed content is managed by a view controller or a group of view controllers coordinating with each other. Therefore, view controllers provide the skeletal framework on which you build your apps.
iOS provides many built-in view controller classes to support standard user interface pieces, such as navigation and tab bars. As part of developing an app, you also implement one or more custom controllers to display the content specific to your app.
Not sure about any iOS specifics but from a PHP standpoint controllers are there to get any data that is needed for the view (via models) and then pass that data to the view.
The view is there to render things to the screen only and should have no logic in it.
So from a website point of view if you wanted to display a users name on the screen:
The controller would request the username from the model
The model would get the username and return it to the controller
The controller would then pass the username to the view
And the view would then render the username.
Hope that helps.
To be not specific, but on a upper layer, you can say as following :
You can put controller code in class extending UIViewControllers
You can put view code in class extending UIView
You can put model code in class extending NSObject
Related
I used to consider a CustomUITableViewCell.xib as the view and the corresponding CustomUITableViewCell.swift class as the controller of a table view cell.
Is this correct? A youtube video I stumbled upon considers the class as the view: https://youtu.be/n06RE9A_8Ks?t=177
Edit:
To clarify the question: Which one of the following is the view and controller? Are both considered the view?
CustomUITableViewCell.xib
CustomUITableViewCell.swift
I'd absolutely consider it a "view" (in terms of MVC). It's of the group of logic that (along with the .xib) handles 1 particular view of information, rather than orchestrating some aspect of the general logic of the app.
I also consider a UIViewController as belonging to the "view" part of MVC for the same reason. Of course, if you put far more business logic into your view controllers than that which is necessary to support the single view, then your view controller is some mix of MVC. For example, if your view controller chooses what scene of the app comes next, your view controller then participates in controller logic and it's not really following MVC. Your view controller is forced to do a lot of single view-related work, though, because there's a single view it's responsible for and that the view-work is more practically done in the UIViewController rather than the UIView.
So when you ask about a cell view class's stance in MVC, if it's doing single view work, then it's a "View". If you mix in controller work or model work, then you've muddied up the separation of responsibilities that MVC espouses.
In my personal opinion it is a view. It should be handling only UI components in the class. Think of both files as a complete view. One cannot be without the other. Thus I consider them one.
I am trying to create an app for iOS using Swift but running into problems with the very basics.
To keep it simple I just want the app to initially be a single view application with a button and some sort of list view on the page. I believe a TableView is what is recommended here. When I click the button, I just want it to populate the list/table view with some entries, that's it. To start with, I don't care if these entries are hard-coded, I just want to get something working.
I have been looking at different samples but I am getting confused. Some of them seem to suggest using a TableViewController others don't. When I use a tableview controller, the UI I had created seems to get completely replaced with just an empty tableview list and the button is gone.
I previously have developed apps in Windows phone and found it a lot easier. I'd just add a listview object and in the click method of button, add the items programmatically etc. But this is my first time trying to create an iOS app and it seems a lot more confusing. There are delegates, controllers, views all seemingly needed in order to do something very simple.
Can anyone give me some basic step by step instructions about how to add a tableview to an application and load some data into it through a button click?
Make sure you are clear about the difference between a view and a view controller.
iOS uses the MVC design pattern (Model View Controller).
A view object displays contents to the user and responds to user interaction.
A model object stores state data.
A controller object drives the app logic and mediates between the model and the view.
A UITableViewController is a special subclass of a UIViewController who's job is to manage a table view. It has some extra support in it that makes it a good choice for managing a table view, BUT... there is one annoying thing about it. It is designed so the ONLY view it can manage is a table view. You can't use a UITableViewController if you want to add buttons, labels, and other UI elements to your screen outside of the table view.
What I usually do is to create a create a table view controller, create a separate regular view controller, add a container view to the regular view controller, and then use an embed segue to embed the table view controller inside the view controller. (you just control-drag from the container view to the table view controller.) That way you get the best of both worlds. You may want to create a protocol that the table view controller would use to communicate with it's parent view controller.
You should be able to find a tutorial online on setting up a table view controller as a child of another view controller using container views and embed segues. It's quite easy.
I'm currently building a custom view controller container for my iOS project and I nearly understand what I'm doing. The one thing I'm stuck on is how do you (properly - aka not a hack) add a view controller in PART of the Parent controller's frame. See how there are multiple view controllers/views in the email app? How does one build a custom controller container that designates the location of such sub-view controllers? How do you properly add such a controller? I'd like to know the "correct" way as designated by apple (best practice).
EDIT: After looking at this some more I was thinking a possible way would be to create views with custom sizing and then push those to the parent. Is this the correct way?
You sort of answered it yourself. The view you have as an example uses a UISplitViewController to show two separate views (left and right). Each of those views has a view controller that owns it. Note that the left side includes all of the view, like the search, nav bar, and toolbar. So just create two separate view controllers and add them to a UISplitViewController and you should be golden! The views themselves are created however you normally create views. Storyboards, NIBs, or in code works.
The name "View Controller" in iOS programming is a bit confusing as it includes both words "View" and "Controller" in the MVC model. Is "View Controller" actually just another name for Controller (as the view is actually mostly done by the Interface Builder). Why is it called a "View Controller"? Is it because this controller does all the view properties updating and event handling as well?
Yes, a UIViewController lives inside the "Controller" layer of MVC. But it is a special controller that controls and updates a view. View controllers can also handle events because they derive from UIResponder.
You can also create general controllers by subclassing NSObject. For example an accounts controller that manages accounts etc. You actually find other controller classes in the iOS SDK, e.g. UIDocumentInteractionController.
From the iOS View Controller Programming Guide:
For iOS applications, view controllers provide a vital link between an
application’s data and its visual appearance. Understanding when and
how to use view controllers is crucial to the design of iOS
applications. View controllers are traditional controller objects in
the Model-View-Controller design paradigm but they also do much more.
In iOS applications, view controllers provide much of the logic needed
to manage basic application behaviors. For example, view controllers
manage the presentation and removal of content from the screen and
they manage the reorientation of views in response to device
orientation changes.
"Controller" follows the thing being controller. If I were writing a controller for a chair I would call it a ChairController. Since a UIView is being controlled, it makes sense to call it a UIViewController right? The view itself is only responsible for display, but the logic of what to display is up to its controller.
From Apple docs - http://developer.apple.com/library/ios/#documentation/UIKit/Reference/UIViewController_Class/Reference/Reference.html
The UIViewController class provides the fundamental view-management model for all iOS apps.
Basically it is the container for your views and handles more logic than just the visual display that your view does.
Where necessary, a view controller:
resizes and lays out its views
adjusts the contents of the views
acts on behalf of the views when the user interacts with them
You should see a "View Controller" as a "Class that controles the view".
This is a classic Model View Controller pattern (MVC).
A UIViewController has a view of type UIView and you update this UIView depending on your business objects (Model) for each particular controller.
Also, events that occur on your UIView, are sent back to your UIViewController for handling them properly.
Overview
I am doing an iOS project using the MVC architecture. Pardon my ignorance, I am just confused, I am looking for a good design.
The view I am planning to use will have some buttons on it and some labels and text fields. My view wouldn't need any custom
implementation of drawRect.
All my logic as to what needs to be done when a button is pressed or event occurs is in my view controller
I have a couple of doubts:
for the above scenario, is it still better (good practice) to create a separate view (a view other than view controller's view) ? If so why ?
Other than drawing and displaying the view (in my project, I don't have much of it) what else should a view's implementation code
contain ?
I would like to disable a set of buttons when the user touches on a textfield and the keyboard comes up.
a) So should I place this logic of disabling some buttons in the separate view's implementation (view created in question 1) ?
b) From my parent view (view created in question 1), can I create outlets to the buttons (which are subviews) to disable some of the buttons ? I am not able to do this. Or should I use the method subviews and loop through the button that i am looking for ?
My understanding
Model contains the data
View is responsible for displaying and shouldn't contain business
logic.
View controller is the only one to interact between the model and the view and contains the business logic
There's no need to create a separate view -- the view controller's view (usually just a plain UIView) can certainly contain your buttons and text fields. If you did want to put some of those in a separate container (perhaps so that you could move them as a group), you could use a plain old UIView for that.
Views are responders, so UIView subclasses can override the touch handling methods if you want to do any special touch handling.
a) It's common to put the code that manages views (such as disabling buttons) in the view controller. b) Again, you'd normally put the outlets for your buttons in the view controller.
When people talk about "business logic" they usually mean the logic that's required to maintain and operate on the data that the application deals with. That sort of thing is often best placed in the model. On the other hand, code that manages views, such as enabling or disabling buttons or moving data from the model into views (or vice versa) belongs in the view controller.
Q1. for the above scenario, is it still better (good practice) to create a separate view (a view other than view controller's view) ? If so why ?
If you create your view by Interface Builder, that's a separate view I think. ;) But if you try to create a view hierarchy programmatically without using a n/xib, you can put all your view layouts in loadView method, and populate the data in viewDidLoad, that's what the View-Controller does. And also, you can create a UIView class to implement the layout of the view, just like n/xib, but programmatically.
As the DOC said,
... One can merge the MVC roles played by an object, making an object, for example, fulfill both the controller and view roles—in which case, it would be called a view controller. ...
... A view controller is a controller that concerns itself mostly with the view layer. It “owns” the interface (the views); its primary responsibilities are to manage the interface and communicate with the model. Action methods concerned with data displayed in a view are typically implemented in a view controller. An NSWindowController object (also part of the document architecture) is an example of a view controller. ...
The MVC in Cocoa is a litte different as what you known. You can refer the official doc HERE.
Q2. Other than drawing and displaying the view (in my project, I don't have much of it) what else should a view's implementation code contain ?
You can customize your view, e.g., set text color or font style for your button, etc.
Q3.a. So should I place this logic of disabling some buttons in the separate view's implementation (view created in question 1)
It is better to put logic in controller (or view-controller), just as MVC prefer.
Q3.b. From my parent view (view created in question 1), can I create outlets to the buttons (which are subviews) to disable some of the buttons ? I am not able to do this. Or should I use the method subviews and loop through the button that i am looking for ?
You can set tag (setTag:) for your buttons and get the right one you want. But keep in mind, firstly you need to let the button shown to parent.