I am new to iOS development and I am currently reading the book : iOS Programming (Objective C) by Big Nerd Ranch.
I am confused as in where to initialize subviews such as UIButtons, UIImageView while creating views programtically:
Should the intialization be done in the Main UIView i.e in the
initWithFrame method and maintain a additional weak reference to the subview in the UIView.
or
should I do it in the UIViewControllers loadView method and maintain a weak reference to the subview in the uiviewcontroller (Same approach used while creating UIVew using the interface builder).
I have seen both the approaches being used in various stackoverflow posts but no post that explains which approach is the right one.
you can initialize as per your app's requirement. If any view or button or anything is part of initial setup of your app then you should initialize it in viewDidload.
Now, for example there is requirement like user press button and then new view will be created then you can initialize view in button's click method etc.
So, it's depends on your requirement.
Static views which will live from start to and of app should be initialize in viewdidload, because this is the first method getting called of viewcontroller.
hope this will help :)
It dependes on which architecture you are using. Apple raises the flag of Model-View-Controller, but in fact, UIViewControllers are the View.
For Example:
Let's say that you have a pretty LoginViewController. When you instantiate it, you will be doing something like
LoginViewController *loginVC = [[LoginViewController alloc] init];
At this point, no view is loaded. Your ViewController has just executed the init method, nothing else. When the system calls
loginVC.view
the first method to be executed will be
- (void)loadView;
there you should do exactly that, load your view. So, the approach i like is to have an additional LoginView.
- (void)loadView
{
// you should have a property #property (nonatomic, strong) LoginView *loginView;
self.loginView = [[LoginView alloc] init];
self.view = self.loginView;
}
and in the LoginView init method, you should put your code to build up the view.
However, you could eliminate LoginView, and instantiate all your subviews like this:
- (void)loadView
{
self.view = [[UIView alloc] init];
UIButton *button = [[UIButton alloc] initWithTargetBlaBlaBla...];
[self.view addSubview:button];
// add more fancy subviews
}
In my experience, the first approach is much cleaner than the second one. It also makes version control a lot easier (try to merge a xib, I dare you). I always use MyView.m to build the view (a.k.a setup constriants, style) and use MyViewController.m things like animations, lifeCycle. I like to think that MyView.m is the programatic xib, so anything that you can do with xibs, you should me able to do it inside your view.
Hope it helps!!
Related
I am completely stumped and have been researching for days. Probably something really simple that I am missing.
I have a ViewController which contains a custom UIView called GameView, and a UIView called buttonBox which contains a "next level" button. What I am trying to achieve is when the level is completed in GameView, it fires a function in my ViewController which shows the buttonBox so the user can click the "next level" button. It simply will not work.
I have attempted this in 3 ways, neither have worked:
Creating an IBOutlet in the ViewController, connecting it to the hidden UIView (and it was definitely connected) and calling setHidden:NO.
Calling the [self.view viewWithTag:xxx] and then calling setHidden:NO.
Using hidden=NO instead of setHidden:NO.
Relevant code for ViewController as follows:
#interface PlayViewController : UIViewController
#property GameView *gv;
#property (strong, nonatomic) IBOutlet UIView *buttonBox;
-(void) showButtonBox;
#end
#implementation PlayViewController
#synthesize buttonBox;
...
- (IBAction)showButtonBox {
UIView *uiv = (UIView*) [self.view viewWithTag:999];
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(#"Showing box function");
NSLog(#"%#", uiv);
uiv.hidden = NO;
});
}
#end
And my custom view:
#implementation GameView
...
dispatch_async(bgQueue, ^{
_loopRunning = true;
//NSLog(#"Calling main loop...");
while ([self loopRunning])
{
...
PlayViewController * pvc = [[PlayViewController alloc]init];
[pvc showButtonBox];
...
}
#end
The thing is, the variable uiv is returning null in NSLog, which is obviously why hidden is not working, but I have no idea why. It also didn't work when I was using IBOutlet.
Also, current output from NSLog is as follows:
2015-11-24 00:18:38.612 ib[12579:1264539] Showing box function
2015-11-24 00:18:38.612 ib[12579:1264539] (null)
Thanks in advance.
Correct Answer:
The problem was that I was using StoryBuilder to build my UI, but by using the alloc init method was creating a new view controller (which is never shown) instead of correctly referencing the view controller which was being displayed. This is achieved by passing the view controller being displayed to the view in the viewDidLoad function, see below:
#implementation PlayViewController
#synthesize buttonBox;
#synthesize gv;
- (void)viewDidLoad
{
[super viewDidLoad];
gv = [self.view viewWithTag:777];
[gv setPlayViewController:self];
}
...
Man, it's simple. Let's take a look at:
#implementation GameView
...
dispatch_async(bgQueue, ^{
_loopRunning = true;
//NSLog(#"Calling main loop...");
while ([self loopRunning])
{
...
PlayViewController * pvc = [[PlayViewController alloc]init];
[pvc showButtonBox];
...
}
#end
Here we have the issue:
dispatch_async(bgQueue, ^{
I assume, bgQueue stands for "background queue", which means this is not served by the main thread (the UI thread).
Having that said, it's quite naive to expect
[pvc showButtonBox];
to work properly. Just move this code into the main thread. For instance, you can just wrap the aforementioned line of code into a dispatch_async on the main queue. That should solve your probem, if your outlets and/or tags are OK. Cheers.
[[PlayViewController alloc]init];
This creates a new instance of PlayViewController. Where have you defined your outlets and views?
In a storyboard? You can't use this initialiser - nothing from the storyboard will be picked up, you have to use a segue or initializeViewControllerWithIdentifier:.
In a xib file? Is it called PlayViewController.xib? If not, it won't be picked up by the initialiser. Plain alloc/init of a view controller will only find a nib file as described in the documentation of the nibName property.
Do you really want alloc / init at all? Do you actually want to make a new view controller, or is one already on the screen?
From your comments it seems option 3 is the right answer. The PlayViewController is already on the screen, alloc/init is creating a new instance of it, which is never being put on screen, which never loads any views regardless of storyboards or nibs.
You need to get a reference to the existing instance of PlayViewController. Without knowing the structure of your app it's not too easy to say how that's done - is it presenting the game view? Is the game view a subview of the view controller's view? You may need to pass in a reference (weak) to the game view when it is created, at viewDidLoad, or set up an outlet in the storyboard.
I was working in a client project. I have written lot many view customisation code inside ViewDidLoad. I have models for data store and access.
The project was working fine. They hired a new iOS developer he said the code is not compliant with MVC architecture. The asked the reason why? He said the views are created inside viewDidLoad which is a controller of the Class hence it is not acceptable code. What should we do when its really dynamic views and can not be created using storyboard.
My answer is No
From apple doc
Controller Objects
A controller object acts as an intermediary between one or more of an application’s view objects and one or more of its model objects. Controller objects are thus a conduit through which view objects learn about changes in model objects and vice versa. Controller objects can also perform setup and coordinating tasks for an application and manage the life cycles of other objects.
I think that the controller has the responsibility to manage what the view look like.
In viewDidLoad,it is good to write one-time view customisation code here.
But if you write a lot configuration code to a view. I think it is better to use a subclass of UIView. This makes your code clear and easy to debug and maintain.
You can make differentiate between Controller and View in this way -
Use - (void)loadView {} delegate method to load your view from viewcontroller.
Suppose you have a view class -
CustomView.h
CustomView.m -
- (id)init {
return [self initWithFrame:CGRectZero];
}
- (id)initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
if (self) {
// Initialization code
self.backgroundColor = [UIColor greenColor];
[self addSubview:self.centerView];
}
return self;
}
Now in your ViewController -
- (void)loadView
{
self.view = [[CustomView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
}
Please refer below url for more details -
http://matthewmorey.com/creating-uiviews-programmatically-with-auto-layout/
Hope this can be help you.
You would ideally have a dedicated class for your main view (the one that's accessed by self.view inside viewcontroller) - derived from UIView.
Inside this view class (say Myview.m) - you will create its subviews inside various view methods - such as init (for instantiation of subviews), layoutsubviews (for frame setting of subviews) and drawrect (any graphics drawing etc.) If the view has NIB, some processing will go inside awakeFromNib too.
I have a UIViewController which creates a custom sub view. The sub view is a UIView object which has been subclassed a few times.
Within the subview class I create a custom init method:
-(id)init {
self = [super init];
if (self) {
// Init code
[self spm_correctGuessViewCustomInit];
}
return self;
}
And within this I create a button and a label. The question relates directly to the button and its target action.
What I would like is for the UIViewController to have the buttons action, not the subclasses UIView (which actually creates and holds the button).
[continueButton addTarget:self.superview action:#selector(correctGuessContinueButtonPressed) forControlEvents:UIControlEventTouchUpInside];
I pass in the target of self.superview, this appears to work correctly and the correct method is run. However, I am shown a warning in the subclass 'Undeclared selector 'correctGuessContinueButtonPressed''
So am I implementing this approach correctly? Please let me know if more information is required.
One solution would be to update your custom view's init method so it takes target and action parameters (much like the addTarget: method of the button). You could then pass these values to the button via the addTarget: call.
- (instancetype)initWithTarget:(id)target action:(SEL)action {
// your normal init code here
// use target and action to setup your button
}
Your view.superview approach will not bring you to the view controller, but to a view.
You can import the header of your implementing class to fix the warning, but I think your design should be improved. Views should work pretty much on their own and not depend on their superviews, or even worse the whole architecture of views and controllers.
I'd pass a delegate down the line that gets called when the user pressed the button, or set some blocks on the views that get called when buttons fire.
Avoid communication over several layers of abstraction.
Reference previous similar question: Calling a method in a UIViewController from a UIButton in a subview
I had to add an import to the View Controller that the method was on, within the custom UIView subclass.
With the controller property set I could set the button target as controller
Ensure that the method that was being called from the button was in the controller header file, so could be seen by the subview implementation file. Previously this was not so the subview was not to know this existed.
Suppose you implement a custom table view and a custom view controller (which mostly mimics UITableViewControllers behaviour, but when initialized programmatically, ...
#interface Foo : MyCustomTableViewController ...
Foo *foo = [[Foo alloc] init];
... foo.view is kind of class MyCustomTableView instead of UITableView:
// MyCustomTableView.h
#protocol MyTableViewDelegate <NSObject, UITableViewDelegate>
// ...
#end
#protocol MyTableViewDataSource <NSObject, UITableViewDataSource>
// ...
#end
#interface MyCustomTableView : UITableView
// ...
#end
// MyCustomTableViewController.h
#interface MyCustomTableViewController : UIViewController
// ...
#end
How should you implement/override init methods in correct order/ways so that you could create and use an instance of MyCustomTableView both by subclassing MyCustomTableViewController programmatically or from any custom nib file by setting custom class type to MyCustomTableView in Interface Builder?
It important to note that this is exactly how UITableView (mostly UIKit for that matter) works right now: a developer could create and use either programmatically or by creating from nib, whether be it File owner's main view or some subview in a more complex hierarchy, just assign data source or delegate and you're good to go...
So far I managed to get this working if you subclass MyCustomTableViewController, where I will create an instance of MyCustomTableView and assign it to self.view in loadView method; but couldn't figure out how initWithNibName:bundle:, initWithCoder:, awakeFromNib, awakeAfterUsingCoder:, or whatever else operates. I am lost in life cycle chain and end up with a black view/screen each time.
Thanks.
It is a real mystery how the UITableViewController loads its table regardless of if one is hooked up in interface builder, however I have came up with a pretty good way to simulate that behavior.
I wanted to achieve this with a reusable view controller that contains a MKMapView, and I figured out a trick to make it happen by checking the background color of the view.
The reason this was hard is because any call to self.view caused the storyboard one to load or load a default UIView if didnt exist. There was no way to figure out if inbetween those 2 steps if the user really didn't set a view. So the trick is the one that comes from a storyboard has a color, the default one is nil color.
So now I have a mapViewController that can be used in code or in storyboard and doesn't even care if a map was set or not. Pretty cool.
- (void)viewDidLoad
{
[super viewDidLoad];
//magic to work without a view set in the storboard or in code.
//check if a view has been set in the storyboard, like what UITableViewController does.
//check if don't have a map view
if(![self.view isKindOfClass:[MKMapView class]]){
//check if the default view was loaded. Default view always has no background color.
if([self.view isKindOfClass:[UIView class]] && !self.view.backgroundColor){
//switch it for a map view
self.view = [[MKMapView alloc] initWithFrame:CGRectZero];
self.mapView.delegate = self;
}else{
[NSException raise:#"MapViewController didn't find a map view" format:#"Found a %#", self.view.class];
}
}
The strategy I've used when writing such classes has been to postpone my custom initialization code as late as possible. If I can wait for viewDidLoad or viewWillAppear to do any setup, and not write any custom code in init, initWithNibName:bundle: or similar methods I'll know that my object is initialized just like the parent class no mater what way it was instantiated. Frequently I manage to write my classes without any overrides of these init methods.
If I find that I need to put my initialization code in the init methods my strategy is to write just one version of my initialization code, put that in a separate method, and then override all the init methods. The overridden methods call the superclass version of themselves, check for success, then call my internal initialization method.
If these strategies fail, such that it really makes a difference what way an object of this class is instantiated, I'll write custom methods for each of the various init methods.
This is how I solved my own issue:
- (void)loadView
{
if (self.nibName) {
// although docs states "Your custom implementation of this method should not call super.", I am doing it instead of loading from nib manually, because I am too lazy ;-)
[super loadView];
}
else {
self.view = // ... whatever UIView you'd like to create
}
}
I have a UIViewController called DebugViewController that contains a UITextView, and a public method called debugPrint which is used to write an NSString into the UITextView and display it.
Is it possible to write into the UITextView before I open the UIViewController, so that when I open it, the text previously written into it is displayed?
In my parent view controllers viewDidLoad method, I'm calling initWithNibName on the DebugViewController as follows
debugViewController = [[DebugViewController alloc] initWithNibName:#"DebugView" bundle:nil];
I then call debugPrint as follows
[debugViewController debugPrint:#"viewDidLoad"];
And some time later I call the following to open the debugViewController
debugViewController.delegate = self;
debugViewController.modalTransitionStyle = UIModalTransitionStyleCoverVertical;
[self presentModalViewController:debugViewController animated:YES];
However all the text previously written is missing.
Please let me know how I can use a view controllers methods before the view controller displayed to the user.
Thanks,
JustinP
What you are doing is a little non-standard. The danger with that as always is that if you don't really have an expert grasp on what you're doing, you can quickly find yourself in difficulty.
If you want something set before the view is displayed to the user, then the best way to do that is to do it in the viewWillAppear method. Put it there rather than in viewDidLoad because a view might loaded once but appear many times. Where you place it depends on whether the data changes from appearance to appearance.
So, if your data is pretty static and won't change, use the viewDidLoad method.
Assuming that you'll go for the viewWillAppear option, let's do the first step by having an ivar in the view controller:
NSString *myText;
set that after init:
debugViewController = [[DebugViewController alloc] initWithNibName:#"DebugView" bundle:nil];
debugViewController.myText = #"My text here";
then, in debugViewController's viewWillAppear method:
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
myTextView.text = myText;
}
The view controller life cycle is complex as you can see from the View Controller Programming Guide for iOS. So I'd say best not stray from the path of least resistance unless you have good reason. That said sometimes the best way to learn is by experimentation.